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PaleoBios
Title
First Cretaceous teleostean otolith assemblage (Arkadelphia Formation, upper
Maastrichtian) from Arkansas, USA, early Gadiformes, and the Western Interior Seaway
Permalink
https://escholarship.org/uc/item/6zt71586
Journal
PaleoBios, 40(3)
ISSN
0031-0298
Authors
Stringer, Gary L.
Sloan, James Carson
Publication Date
2023
DOI
10.5070/P940361192
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Copyright 2023 by the author(s).This work is made available under the terms of a Creative
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Gary L. STRINGER & James Carson SLOAN (2023). First Cretaceous tele-
ostean otolith assemblage (Arkadelphia Formation, upper Maastrich-
tian) from Arkansas, USA, early Gadiformes, and the Western Interior
Seaway.
Cover: Drilling rig used in the geotechnical investigations at Cabot, Lonoke County, Arkansas, USA, by the Arkansas Department
of Transportation that produced subsurface samples of the Arkadelphia Formation (Upper Cretaceous, upper Maastrichtian) that
contained teleostean otoliths. Inset is the holotype of Palaeogadus? belli-
ect. Scale bar=1mm.
Citation: Stringer, G.L., and J.C. Sloan. 2023. First Cretaceous telostean otolith assemblage (Arkadelphia Formation, upper Maas-
trichtian) from Arkansas, USA, early Gadiformes, and the Western Interior Seaway. PaleoBios 40(3): 1-39.
DOI: https://doi.org/10.5070/P940361192.
Copyright: Published under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC-BY-NC-SA) license.
PaleoBios 40(3): 1–39, May 25, 2023
PaleoBios
OFFICIAL PUBLICATION OF THE UNIVERSITY OF CALIFORNIA MUSEUM OF PALEONTOLOGY
Citation: Stringer, G.L., and J.C. Sloan. 2023. First Cretaceous telostean otolith assemblage (Arkadelphia Formation, upper Maas-
trichtian) from Arkansas, USA, early Gadiformes, and the Western Interior Seaway. PaleoBios 40(3): 1-39.
DOI: https://doi.org/10.5070/P940361192.
LSID: urn:lsid:zoobank.org:pub:3B70D32F-9BF0-4595-AF4B-45ADEE03B204
First Cretaceous teleostean otolith assemblage (Arkadelphia Formation, upper
Maastrichtian) from Arkansas, USA, early Gadiformes,
and the Western Interior Seaway
Gary L. Stringer¹*and James Carson Sloan2
¹Museum of Natural History, 708 University Avenue, University of Louisiana at Monroe,
Monroe, Louisiana 71209, USA, stringer@ulm.edu;
²Geologist, Arkansas Department of Transportation, Little Rock, Arkansas 72209, USA,
James.Sloan@ardot.gov
The fortuitous discovery of Cretaceous (late Maastrichtian) teleostean otoliths in boring samples (17–31
m below ground level) from the Arkadelphia Formation near Cabot, Arkansas, USA, has consequential
-
ceous assemblages from a single USA site. The diversity of the assemblage is fairly large with a richness
of 19 species with three additional taxa in open nomenclature and one unknown lapillus, which more
than doubles the known actinopterygians from the Arkadelphia Formation. The otolith assemblage is
extremely uneven in its diversity with one species, a putative siluriform Vorhisia vulpes Frizzell (1965b),
accounting for approximately 73% of the total. The most unique feature of the otolith assemblage is the
presence of cool-water gadiforms, which represent approximately 7.6% of the total assemblage. The
presence of the gadiforms is related to the effects of the Western Interior Seaway and paleogeography
during the Late Cretaceous in the western Gulf Coastal Plain. The gadiforms may represent relicts of a
greater population and distribution in the early Maastrichtian. Percentage similarity measurements of
the otolith assemblage indicate that the Arkadelphia Formation is more closely related to the Severn
Formation in eastern Maryland (57.86%) and the Kemp Clay Formation in northeast Texas (35.77%)
than to the Ripley Formation in northeastern Mississippi (5.34%). The similarity measurements and
other factors indicate that the Arkadelphia Formation otolith assemblage belongs to the Western Interior
Seaway community (bioprovince). The Arkadelphia Formation otolith assemblage also contains several
taxa that become extinct, such as the ubiquitous V. vulpes, at the K-Pg extinction event. The otoliths point
to a very shallow marine environment (possibly inner shelf; less than 20 m in depth) with estuarine and
of the Western Interior Seaway during the Late Cretaceous.
Keywords:
INTRODUCTION
No assemblages of Mesozoic teleostean otoliths have
ever been described from Arkansas. Furthermore, the
studies of Mesozoic otolith assemblages in the USA Gulf
Coastal Plain have been limited to a few studies from
Texas, Tennessee, Mississippi, and Alabama. This lack
of investigation increases the importance of this study
of Cretaceous otoliths from the upper Maastrichtian
Arkadelphia Formation. Equally important are the
paleogeographical and paleoecological implications of
the Arkadelphia Formation otolith assemblages and the
occurrence of some of the earliest representatives of
Interior Seaway.
Numerous studies, including Huddleston and Savoie
(1983), Nolf (1985, 2003, 2013), Stringer (1992, 1998),
Schwarzhans (1993, 1996, 2003, 2010), Nolf and Brzobo-
haty (1994), Nolf and Stringer (1996), Lin (2016), Lin
*Author for correspondence
2 PaleoBios 40(3) 2023
et al. (2016), Stringer et al. (2016, 2020), Schwarzhans
et al. (2018a, b), Stringer and Bell (2018), and Stringer
and Shannon (2019), as well as many other references
contained in the aforementioned publications, have cor-
roborated the value of otoliths in determining and inter-
study of the upper Eocene Yazoo Clay in Louisiana, Breard
and Stringer (1995) recovered 12 actinopterygians based
on skeletal remains (primarily teeth). Whereas, Nolf and
Stringer (2003) and Stringer and King (2010) reported
-
comprehended when osteological elements and otoliths
are both considered and analyzed. This, of course, is
dependent upon the presence of skeletal remains and
otoliths in the strata, and unfortunately, the aragonitic
otoliths are susceptible to leaching.
The importance of otoliths for identifying and un-
derstanding the diversity of actinopterygians in the
Arkadelphia Formation at the Cabot locality is shown
level [Enchodus ferox Leidy (1855), Hadrodus priscus
Leidy (1857), Xiphactinus audax Leidy (1870), and Lepi-
sosteus sp. Lacépède (1803)] and two to the family level
[Phyllodontidae indeterminate Darteville and Casier,
(1943) and Albulidae indeterminate Bleeker (1859)].
Manning, personal communication, 2020). The otoliths
from the Arkadelphia Formation made it possible to
unrecognized. Since the actinopterygians represented
by otoliths from the Arkadelphia Formation have not
presented. The systematic paleontology for each taxon
-
liest Gadiformes known in the paleontological record is
discussed. Finally, the otoliths are utilized to interpret
paleogeographical and paleoecological conditions dur-
ing the Late Cretaceous in this portion of the Gulf Coastal
Seaway on the teleosts of the Arkadelphia Formation.
MATERIALS AND METHODS
Geologic setting
The Arkadelphia Formation is primarily a dark-gray
to black marl or marly clay. However, there is also some
limy, gray sandstone, gray sandy clay, sandy limestone,
concretionary limestone, and white to light brown im-
pure chalk present in the formation. The sandy marls and
limestones are found mainly at or near the base, while the
impure chalks are found closer to the top of the formation
(McFarland 2004, Larina et al. 2016). The thickness of the
unit in Arkansas ranges from approximately 36.6 to 48.8
m (Dane 1929, Renfroe 1949). There is a slight uncon-
formity that separates the Arkadelphia Formation from
the underlying Cretaceous Nacatoch Sand, while there is
a more conspicuous unconformity that separates it from
the overlying Paleocene Clayton Formation (Midway)
(Fig. 1). The unconformity between the Cretaceous and
the Paleocene is consistent across the Gulf Coastal Plain
(Hart et al. 2012, 2013). However, it should be noted that
based on borings drilled by the Arkansas Department
of Transportation (ADOT), the Arkadelphia Formation
northeast of Arkadelphia, Arkansas, to Cabot, Arkansas
directly overlies Paleozoic rocks.
(1888) for outcrops at Arkadelphia in Clark County,
Arkansas, according to Veatch (1906). A portion of the
are no longer considered part of the formation but now
considered part of the underlying Nacatoch Formation
Figure 1. Stratigraphy of the Arkadelphia Formation and other
formations discussed in the text based primarily on McFarland
(2004). The gray-shaded area represents an unconformity.
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 3
(McFarland 2004). One of the only references to Creta-
ceous strata in the Cabot area is from the Annual Report
of the Geological Survey of Arkansas for 1892 (Harris
1894). The age of the Arkadelphia Formation is Late Cre-
taceous, and outcrops of the formation are recognized in
the Gulf Coastal Plain in Clark, Nevada, and Hempstead
counties in southwestern Arkansas. Studies indicate
that the Arkadelphia Formation is in the Navarro Group
(Renfroe 1949), but this designation is not used in this
area of Arkansas (see discussion in Stephenson et al.
1942 and McFarland 2004). Several lines of evidence
point to the late Maastrichtian age of the Arkadelphia
Formation including paleomagnetic studies (Liddicoat et
al. 1981), ammonite studies (M. Garb of Brooklyn College,
Brooklyn, New York, personal communication, 2020),
Dastas et al. 2014), combined study of
Larina
et al. 2016), and ostracodes (M. Puckett, University of
Southern Mississippi, Hattiesburg, Mississippi).
As noted previously, no Cretaceous teleostean otoliths
have ever been described from Arkansas, and this study
assemblage from the state. A review of the literature also
clearly indicates that studies of Cretaceous teleostean
otoliths are very limited in the entire U.S. Gulf Coastal
Plain (Nolf and Stringer 1996, Schwarzhans et al. 2018b,
Stringer et al. 2020, Schwarzhans and Stringer 2020a).
Although conducted in other states, otolith studies of
the Upper Cretaceous Coon Creek in Tennessee (Stringer
2016b), the Upper Cretaceous Ripley and Owl Creek
formations in Mississippi (Stringer et al. 2020), and the
Upper Cretaceous Kemp Clay in Texas (Schwarzhans
and Stringer 2020a) are the nearest described otolith
assemblages to the Arkadelphia Formation assemblage
at the Cabot site in Arkansas (Fig. 2).
Several studies that concentrated exclusively on verte-
brate skeletal remains have been conducted on the sur-
face exposures of the Arkadelphia Formation along the
Cabot Site
Owl Creek
Type Locality
Blue Springs Site
South Sulfur River Site
Becker et al. (2010) Site
Texas
Arkansas
Mississippi
North Dakota
North Dakota Geological
Site L140
Mississippi Embayment
Made QGIS using Natural Earth Data
Gulf of Mexico
Figure 2. Regional map of otolith-bearing Cretaceous sites mentioned in the text. Dashed line shows approximate shoreline dur-
ing the late Maastrichtian (Roberts and Kirschaum 1995, Dastas et al. 2014, Stringer and Sloan 2018).
4 PaleoBios 40(3) 2023
Ouachita River near Malvern in Hot Spring County, Arkan-
sas. Malvern is located approximately 111 km southwest
of Cabot, Arkansas, and both of the sites are probably
along the strike of the Late Cretaceous shoreline (Roberts
and Kirschaum 1995, Dastas et al. 2014, Stringer and
Sloan 2018, Schwarzhans and Stringer 2020a). Becker
et al. (2006) reported 17 species of chondrichthyans
from the Arkadelphia. Formation near Malvern based
primarily on shark teeth. Becker et al. (2010) described
osteichthyans from a lag deposit between the Arkadel-
phia Formation and the Clayton Formation (same site as
2006
and other skeletal elements. A total of 11 taxa of bony
incertae sedis
Müller (1845). The authors noted that they were unable
to determine whether the lag deposit comprised the up-
permost Arkadelphia Formation or a locally preserved
basal unit of the Midway Group containing reworked Late
Maastrichtian fossils. Therefore, it is not clear whether all
Formation or could have originated in the Midway Group.
Maisch (2020) described a new myliobatid from the area,
but it was from Clayton Formation (Paleocene) rather
than the underlying Cretaceous Arkadelphia Formation.
Methodology
All of the Arkadelphia Formation specimens examined
for this study were from material obtained as a byprod-
uct of sampling for a geotechnical investigation by the
ADOT for a bridge feasibility study along Arkansas
Highway 321 (Bill Foster Memorial Highway West) in
Cabot, Lonoke County, Arkansas, USA. Cabot is located
of the state (Fig. 3). The samples were obtained by one
Detail of Cabot Locality (Core Sites Numbered)
Figure 3. Location of the study area near Cabot, Lonoke County, Arkansas, USA.
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 5
of the authors (JCS), who was present during the drilling
process. Sample recovery was accomplished utilizing two
method was used in the only borehole encountering the
Arkadelphia Formation. Previous borings encountered
Quaternary alluvium directly above Paleozoic rock. Once
it was observed that Cretaceous/Paleogene sediment was
being encountered, subsequent borings were drilled by
rotary wash with sampling accomplished by split spoon
at 1.52 m intervals to conduct a standard penetration
test known as American Association of State Highway
spoon sampling involves using an automatic hammer to
drive the sampler 0.457 m into the boring wall.
Borings 1 and 3 are on the northern side of the high-
way, while borings 2 and 4–11 are on the southern side.
indurated rock (lower Pennsylvanian Atoka Formation)
from 8.5–10.7 m below ground level (bgl). Based on
these results, it was decided to core Boring 5 (B5). Sub-
sequent borings, Borings 6 through 11 (B6–B11) were
split-spooned in 1.5 m intervals. The only borings of
Cretaceous otoliths were B5, B6, B8, B9, and B10. The
otoliths are as follows: B5 (34.941292, -92.044155), B6
(34.941187, -92.043788), B8 (34.940683, -92.042295),
B9 (34.940450, -92.041533), and B10 (34.940027,
-92.040231). The Upper Cretaceous Arkadelphia For-
-
countered at depths ranging from 17–27 m. The drilling
appears to be essentially along the dip of the Arkadelphia
Formation and is probably the reason for the differences
in the top of the formation in the different borings. It was
approximately 381 m along the roadway between borings
B5 and B10. The upper Pennsylvanian Atoka Formation
was encountered in B5 through B9 (depths from approxi-
mately 23–30 m bgl) but was not encountered in B10.
light-colored concentrated layers. One of the authors
(JCS) extracted these layers including some of the clay
directly above and below for processing. Subsequently,
aragonitic fossils, including otoliths, were observed in
the split-spoon samples. Any otoliths observed with the
naked eye in the split-spoon samples were removed to
avoid damage. However, all samples were processed
by water screening to obtain otoliths. Each individual
sample was dried in a calibrated oven at 110 ± 5 C0 and
then rewetted to break down the clay. This process was
repeated for some samples to extricate the otoliths from
the clay. The samples were then wet-sieved with plain
present after washing, then the sample was dried and
washed again. One of the authors (JCS) extracted the
otoliths from the residue, and the other author (GLS)
Fossil and modern comparative otolith collections
of Nelson et al. (2016
the molecular investigations of Near et al. (2012), Near
et al. (2013), and Betancur-R. et al. (2013). Any deviation
follow Wiley and Johnson (2010), while the family-group
et al. (2014, 2017, 2018). Authors for genera and species
depend greatly upon Eschmeyer’s Catalog of Fishes: Gen-
era, Species, References (Fricke et al. 2019) and FishBase
(Froese and Pauly 2019). Extant and fossil genera were
used when possible, and the recommendations of Jans-
sen (2012) were employed when the generic designation
was not evident. This is accomplished by placing the un-
known genus in the type genus of the family followed by
a question mark indicating that the taxon might belong
to any other of the known (or as yet unknown) genera
investigation are deposited in the Perot Museum of Na-
ture and Science (DMNH) located at 2201 North Field
Street, Dallas, Texas 75201, under the catalog numbers
2021-09-01–2021-09-31. Remaining material is in the
comparative collection of one of the authors (GS).
RESULTS
Late Cretaceous otoliths were obtained from 16
samples in the Arkadelphia Formation from the borings
drilled by the ADOT at Cabot, Arkansas. The number of
samples (shown in parentheses) obtained from each of
the borings was as follow: B-5 (7), B-6 (1), B-8 (3), B-9
(2), and B-10 (3). A geologic section with the formations,
approximate depth at which samples with otoliths were
found, and the number of otoliths from each sample are
shown in Figure 4. Analysis of the 2,109 specimens re-
vealed a fairly diverse Late Cretaceous otolith assemblage
from the Arkadelphia Formation at the Cabot locality in
Arkansas with a diversity of 19 taxa (richness), three taxa
in open nomenclature, and one unknown type of lapillus
representing at least 20 families (several of these families
are indeterminate and may represent extinct families).
6 PaleoBios 40(3) 2023
Figure 4. Geologic section of borings B-5, B-6, B-8, B-9, and
B-10 at the Cabot site, Lonoke County, Arkansas, USA. Black
shapes designate the approximate level at which otoliths were
recovered (bgl m=below ground level in meters). The shape
is indicative of the number of otoliths recovered at that level:
circle=less than 10 specimens; triangle=11–100 specimens;
rectangle=101–500 specimens; and star=greater than 500
specimens.
SYSTEMATIC PALEONTOLOGY
The taxa represented by the 2,109 otoliths recovered
from the Arkadelphia Formation are presented in Table
1. Most of the taxa found in the Arkadelphia Forma-
tion, with the exception of a new gadiform, have been
described from various other Upper Cretaceous forma-
tions in Mississippi (Ripley Formation and Owl Creek
Formation), Texas (Kemp Clay), North Dakota (Fox Hills
Formation), and Maryland (Severn Formation). The taxa
from Mississippi are described in detail by Stringer et al.
(2020), from Texas are given in Schwarzhans and Stringer
(2020a), from North Dakota are reported by Hoganson
et al. (2019) and Schwarzhans and Stringer (2020a), and
from Maryland are discussed by Stringer and Schwar-
zhans (2021). The reader is directed to those works for
additional systematic descriptions. Because of the prior
descriptions, only those taxa requiring further discus-
sion, such as the new gadiform species, are presented
-
cussed. The taxonomic assignment of the Arkadelphia
Formation otolith assemblage is extremely relevant as
it allows comparisons to other Late Cretaceous assem-
blages as well as the possible reasons for the uniqueness
of the Arkadelphia Formation otoliths.
OSTEICHTHYES
ACTINOPTERYGII
ELOPIFORMES
ELOPIDAE
ELOPS
ELOPS SP.
Material—one small, broken specimen, DMNH 2021-
09-01.
Description and Remarks—Although the single,
small specimen (2.5 mm) attributed to Elops from the
Arkadelphia Formation is broken (the anterior portion
is missing), there are enough characteristics to assign it
to this genus. The overall shape is oval (sensu Smale et
al. 1995). The dorsal margin is somewhat rounded, while
the ventral margin is more broadly and evenly rounded.
The inner face is convex. Only a very small portion of the
ostium is present, while the cauda is complete. The cauda
is fairly wide and has an arching of its dorsal margin near
the center. However, the posterior portion of the cauda is
slightly downturned. The terminal portion of the cauda
is rounded. There is no dorsal depression. The ventral
furrow is faint and close to the ventral margin. The outer
The Arkadelphia Formation specimen shows charac-
teristics comparable to Elops eutawanus Schwarzhans,
Huddleston, and Takeuki (2018b) from the Cretaceous
(Santonian) of Alabama. Like the Arkadelphia Formation
specimen attributed to Elops, the specimen of Elops eu-
tawanus is broken anteriorly (Schwarzhans et al. 2018b,
Elops otolith,
especially the cauda and features of the inner face, is
similar to the extant Elops from the eastern Atlantic off
the coast of central Africa (Nolf 2013, Froese and Pauly
2019).
ALBULIFORMES
ALBULIDAE
ALBULIDAE INDETERMINATE
Material—four small, eroded specimens, specimen
DMNH 2021-09-02 (Fig. 5B).
Description and Remarks—These specimens were
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 7
Taxa No. of specimens % of total Known N. Am
Cretaceous
Known N. Am
Paleocene
ELOPIFORMES
Elopidae
Elops sp. 1 0.05 C F
ALBULIFORMES
Albulidae
Albuliformes indeterminate 4 0.19 E B
Elopothrissus sp. 1 0.05 A B
ORDER INDETERMINATE
Family indeterminate
Genartina sp. 1 0.05 B B
Osmeroididae
Osmeroides sp. 3 0.14 A G
ANGUILLIFORMES
Anguillidae
Anguilla? chickasawae 6 0.28 A B
Ophichthidae
Echiophis aff. E. semisphaeroides 11 0.52 B B
Family Indeterminate
Muraenanguilla? sp. 2 0.09 A B
OSTEOGLOSSIFORMES
Family indeterminate
Kokenichthys navis 2 0.09 A No
CLUPEIFORMES
Family indeterminate
Clupeiform? indeterminate 1 0.05 — —
SILURIFORMES
Ariidae
Arius? subtilis 1 0.05 A B
Family indeterminate
Vorhisia vulpes 1,537 72.88 A No
AULOPIFORMES
Ichthyotringidae
Apateodus crenellatus? 3 0.14 A No
GADIFORMES
Merlucciidae
Palaeogadus? belli sp. nov. 148 7.02 No No
Palaeogadus cf. P. weltoni 1 0.05 B No
Table 1. Taxa from the Arkadelphia Formation (Cabot locality, Arkansas, USA) with number of specimens, percentage
of total, and occurrences in the Cretaceous and Paleocene of North America. Letters in third and fourth columns refer to
the following references: A=Stringer et al. (2020); B=Schwarzhans and Stringer (2020a); C=Schwarzhans et al. (2018b);
D=Hoganson et al. (2019); E=Stringer et al. (2018); F=Schwarzhans (1985); G=Frizzell (1965a). References are not inclu-
sive but provide evidence of the range of the species in North America. Order=FORMES, Family=idae
8 PaleoBios 40(3) 2023
assigned to Albulidae indeterminate. They are believed
to be closely related to the genus Albula, but this deter-
mination cannot be made with the existing specimens.
The Arkadelphia Formation Albulidae indeterminate are
very similar to the Albulidae indeterminate illustrated
in Stringer et al. (2020-
tion in northeastern Mississippi. The otoliths are oval in
shape (sensu Smale et al. 1995) and somewhat elongate
(H/L ratios of around 50%). The margins are mainly
smooth. The strongly convex inner face has a sulcus that
is located primarily supramedially and opens onto the
its posterior. There is a wide, smooth ventral area with
slightly concave. The Arkadelphia Formation specimens
appear to be different from Albula cf. A. bashiana (Frizzell,
1965a) reported from the Kemp Clay of Texas by Schwar-
zhans and Stringer (2020a) in respect to the outline,
depth of the cauda, and the down-turned portion of the
cauda. The exact taxonomic position and relationship of
this albulid is not known presently.
ELOPOTHRISSUS
ELOPOTHRISSUS SP.
Material—one specimen, DMNH 2021-09-03.
Description and Remarks—The one elongate speci-
men assigned to Elopothrissus has a prominent sulcus
clearly divided into an oval ostium opening anteriorly and
Taxa No. of specimens % of total Known N. Am
Cretaceous
Known N. Am
Paleocene
GADIFORMES
Family indeterminate
Gadiformes indeterminate 11 0.52 — —
HOLOCENTRIFORMES
Family indeterminate
Tippaha mythica 8 0.38 A No
BERYCIFORMES
Family indeterminate
Eutawichthys maastrichtiensis 21 1.00 A No
Eutawichthys zideki 287 13.61 A No
Eutawichthys cf. E. stringeri 48 2.28 C No
OPHIDIIFORMES
Ophidiidae
Ampheristus cf. A. americanus 6 0.28 B B
Bythitidae
Protobythites brzobohatyi 4 0.19 B No
ORDER UNKNOWN
Family unknown
Lapillus type 1 1 0.05 A No
Family unknown
Unknown sagitta 1 0.05 n/a n/a
Total 2,109 ~100
Table 1 (continued). Taxa from the Arkadelphia Formation (Cabot locality, Arkansas, USA) with number of specimens,
percentage of total, and occurrences in the Cretaceous and Paleocene of North America. Letters in third and fourth columns
refer to the following references: A=Stringer et al. (2020); B=Schwarzhans and Stringer (2020a); C=Schwarzhans et al.
(2018b); D=Hoganson et al. (2019); E=Stringer et al. (2018); F=Schwarzhans (1985); G=Frizzell (1965a). References are
not inclusive but provide evidence of the range of the species in North America. Order=FORMES, Family=idae
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 9
anterodorsally, and a narrower, longer more excavated
cauda. However, as noted in Schwarzhans and Stringer
(2020a
with ontogenetic changes in size, which is caused primar-
ily by an increase in the length of the rostrum. There is
a slight postdorsal angle as well as some faint marginal
crenulation. Like with many other pterothrissids, mor-
phological maturity is only reached when specimens are
more than 5 mm long, hence, smaller specimens should
Schwarzhans 2012).
For this reason, DMNH 2021-09-03, which is only 1.83
Elopothrissus carsonsloani Schwarzhans and Stringer
(2020a) was reported from the Danian Clayton Forma-
tion but not the Maastrichtian Kemp Clay (Schwarzhans
and Stringer 2020a Elo-
pothrissus was noted by Schwarzhans et al. (2018b)
from the Santonian of Alabama. The genus represents an
extinct pterothrissid that extends across the K-Pg extinc-
tion event and well into the Paleogene (Schwarzhans and
Stringer 2020a).
ORDER INDETERMINATE
FAMILY INDETERMINATE
GENARTINA
GENARTINA SP. 1 (
2020a)
Material—one specimen, DMNH 2021-09-04.
Description and Remarks—The one specimen at-
tributed to the fossil otolith-based Genartina is similar to
Genartina sp. 1 reported and illustrated by Schwarzhans
and Stringer (2020a). The specimen is high-bodied,
somewhat discoid in shape (sensu Smale et al. 1995),
and a short, pointed rostrum (which is often broken).
The sulcus is slightly dorsal with a much longer, taper-
ing cauda and a somewhat oval ostium. The Arkadelphia
specimen resembles G. abbatiae (Stinton, 1965) from
the European Paleocene and early Eocene (see under
“Harpadontina” abbatiae in Nolf 2013, pl. 58). The
specimen also somewhat resembles G. texana Dante and
Frizzell (1965) described from the Eocene of the USA
Gulf Coastal Plain (Frizzell and Dante 1965). Schwar-
zhans and Stringer (2020) noted that Genartina has a
relatively large stratigraphic range from Late Cretaceous
(Santonian) to middle Eocene (Bartonian). Its taxonomic
assignment has been greatly debated and included the
Osteoglossiformes Regan (1909) (Frizzell and Dante
1965), Osmeridae Forey (1973) (Nolf 1985), Elopiformes
(including Albuliformes) in Schwarzhans (2003, 2012),
Harpodontidae Bleeker (1875) (Nolf 2013), Synodonti-
dae Gill (1861) (Stringer et al. 2016), and Stomiiformes
Fink and Weitzmann (1982) (Schwarzhans et al. 2018b).
Schwarzhans and Stringer (2020a) proposed that Genar-
tina probably belongs to an extinct family and order of
ANGUILLIFORMES
OSMEROIDIDAE
OSMEROIDES
OSMEROIDES SP.
Material—
2021-09-05.
Description and Remarks—The three small speci-
mens assigned to Osmeroides are slightly oval shaped
(sensu Smale et al. 1995) with a somewhat irregular
dorsal margin and mostly smooth ventral margin. The
is a heterosulcoid-type sulcus that is located primarily
supramedially with a very slight downturn at the poste-
rior of the slanted cauda. The inner face is convex, while
the outer face is concave. The Arkadelphia specimens are
similar to the Osmeroides sp. described and illustrated
from the Ripley Formation in northeastern Mississippi
by Stringer et al. (2020). Due to their small size and poor
preservation, the assignment is tenuous, and a species
determination is not possible.
ANGUILLIDAE
ANGUILLA
ANGUILLA? CHICKASAWAE
2020a
Material—
2021-09-6.
Description and Remarks—Distinguishing charac-
teristics of Anguilla? chickasawae include a somewhat
oval to ovate shape in well preserved specimens (sensu
Smale et al. 1995) with a H/L ratio of approximately
66%, a convex inner face, a narrow, almost horizontal
posterior margin is commonly almost vertical. Stringer
et al. (2020, A.? chicka-
sawae from the Ripley Formation (Maastrichtian) of
Mississippi. Anguilla? chickasawae differs from other
Late Cretaceous or Paleogene anguillid otoliths by its
much longer ostium. Schwarzhans and Stringer (2020a)
postulated that A.? chickasawae could represent a fossil
10 PaleoBios 40(3) 2023
genus of the Anguillidae or a closely related fossil family
of which otoliths are not known presently.
OPHICHTHIDAE
ECHIOPHIS
ECHIOPHIS AFF. E. SEMISPHAEROIDES (
2003)
Material—
2021-09-07.
Description and Remarks—These otoliths tend to
be primarily circular in shape (sensu Smale et al. 1995).
The nearly straight to slightly outwardly curved pos-
terodorsal margin produces a discernible angle. The
otolith is thick with mainly smooth margins. The inner
face is strongly convex and smooth with a deep sulcus.
The sulcus has a long, narrow, and deep cauda, while the
ostium is much shorter and shallower. The outer face is
2003) originally
Echiophis semisphaeroides in the family An-
guillidae. However, Schwarzhans (2019) illustrated the
modern Echiophis brunneus Castro-Aguirre and Suárez
de los Cobos (1983), and examination of the specimen
has shown a great similarity in convexity and smooth-
ness of the inner face as well as the shape and depth of
the sulcus. There are three extant species of Echiophis
known from tropical and subtropical America. Modern
to assign fossil otoliths to genera with very much con-
2020a)
to other known anguilliform otoliths and changed the
species to the family Ophichthidae.
FAMILY INDETERMINATE
MURAENANGUILLA
MURAENANGUILLA? SP.
Material—two worn, broken specimens, specimen
Description and Remarks—The Muraenanguilla?
specimens from the Arkadelphia Formation are oval in
shape (sensu Smale et al. 1995) with a H/L ratio of ap-
proximately 66%. The convex inner face has a fairly deep,
the ostium and cauda. The dorsal margin tends to be
irregularly curved, while the ventral margin appears
to be smooth and regularly curved. These specimens
resemble Muraenanguilla unionensis Schwarzhans and
Stringer (2020b), which is known from the Ripley and
Owl Creek formations (Maastrichtian) of Mississippi
(Stringer et al. 2020). Unfortunately, the specimens are
-
Europe (Schwarzhans 2019), the Upper Cretaceous Coon
Creek type locality in Tennessee (Stringer 2016b), and
the upper Maastrichtian Severn Formation in Maryland
(Huddleston and Savoie 1983, Stringer and Schwarzhans
2021).
OSTEOGLOSSIFORMES
FAMILY INDETERMINATE
KOKENICHTHYS
KOKENICHTHYS NAVIS b
Material—two eroded, but diagnostic, specimens,
Description and Remarks—The sagitta of Kokenich-
thys navis has several diagnostic features including its
very unusual sulcus, which is located almost entirely
dorsally. The shape is mainly oval (sensu Smale et al.
1995) with smooth margins. The ventral margins are
fairly sharp, and there is a rostrum. The convex inner
face has a broad sulcus that appears very shallow and
easily eroded. Other specimens of K. navis show simi-
Stringer et al. 2020, on the
specimens from the Ripley and Owl Creek formations of
Mississippi). However, the other specimens in Stringer et
al. (2020
ostial and caudal regions are clearly visible. In addition to
the Arkadelphia Formation in Arkansas, K. navis is known
from the Ripley Formation in Mississippi and possibly
in the Tar Heel Formation in North Carolina (Stringer
et al. 2018). The species is very abundant in the Ripley
Formation at the Blue Springs locality in northeastern
Mississippi with 69 specimens (Stringer et al. 2020).
CLUPEIFORMES
FAMILY INDETERMINATE
CLUPEIFORM? INDETERMINATE
Material—one eroded, broken specimen, DMNH
2021-09-10.
Description and Remarks—Although small and
somewhat eroded, this specimen is tentatively assigned
to the Clupeiformes and is included because of the rarity
of clupeids in the Cretaceous. The outline of the sagitta,
possible clupeid. Schwarzhans et al. (2018b) assigned 13
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 11
Figure 5. Otoliths from the Cretaceous Arkadelphia Formation. All specimens unless otherwise noted are inner views of right
sagittae. Length in mm. A. Elops sp., DMNH 2021-09-01, 1.89 mm. B. Albuliformes indeterminate, DMNH 2021-09-02, 1.42 mm. C.
Elopothrissus sp. DMNH 2021-09-03, 1.83 mm. D. Genartina sp. DMNH 2021-09-04, 0.85 mm. E. Osmeroides sp. DMNH 2021-09-05,
3.85 mm. F. Anguilla? chickasawae Schwarzhans and Stringer (2020b), DMNH 2021-09-6, 1.90 mm. G. Echiophis aff. E. semisphaer-
oides Schwarzhans (2003), DMNH 2021-09-07, 3.25 mm. H. Muraenanguilla? sp. DMNH 2021-09-08, 2.18 mm.
12 PaleoBios 40(3) 2023
specimens to Clupeiform indeterminate from the Eutaw
Formation (upper Santonian) of Alabama.
SILURIFORMES
ARIIDAE
ARIUS
ARIUS? SUBTILIS
Material—one well preserved specimen, DMNH
2021-09-11.
Description and Remarks—Arius? subtilis is repre-
sented by the utricular otolith or lapillus rather than the
sagitta. The lapillus is oval in outline (sensu Smale et al.
1995) and has characteristically smooth margins except
growth lines visible, especially in eroded specimens. In
some specimens, a very lightly impressed sulcal area
may be visible on the convex side. Arius? subtilis
-
zhans and Bratishko (2011) and is fairly common in the
early Paleocene of Europe (Schwarzhans 2012). It is also
known from the Clayton Formation (early Paleocene) of
the USA (Schwarzhans and Stringer 2020a). However, its
range was extended to the Late Cretaceous when it was
reported from the Ripley and Owl Creek formations of
Mississippi (Stringer et al. 2020), where it was abundant
(125 specimens from the two formations). It also occurs
in the Coon Creek Formation in Tennessee (as Ariidae
indeterminate in Stringer 2016b) and in the Kemp
Clay (upper Maastrichtian) of northeast Texas, where it
was very abundant with 195 specimens (Schwarzhans
and Stringer 2020a). The rarity of Arius? subtilis in the
stratigraphically equivalent Arkadelphia Formation is
enigmatic.
FAMILY INDETERMINATE
VORHISIA b
VORHISIA VULPES b
Material—
DMNH 2021-09-12, DMNH 2021-09-13, DMNH 2021-09-
14, DMNH 2021-09-15, DMNH 2021-09-16.
Description and Remarks—Vorhisia vulpes is one of
most ubiquitous Late Cretaceous otoliths known in the
USA and has been reported in the Fox Hills Formation
(North Dakota), the Kemp Clay (Texas), the Ripley Forma-
tion (Mississippi), and the Severn Formation (Maryland)
(Hoganson et al. 2019, Woodward 2003, Schwarzhans
and Stringer 2020a, Stringer et al. 2020, and Huddleston
and Savoie 1983).
an extinct siluriform, or perhaps an ariid, based on the
large lapillus and similarities to extant ariid lapilli. One
Arkadelphia Formation specimen was extremely large
at 19.36 mm in length and 14.02 mm in height (Fig. 6H),
which is rare, considering that it was recovered from a
bore sample. Stringer et al. (2020) stated that Vorhisia
probably represents an extinct family of the Siluriformes
or Ostariophysi, but there is also the possibility that it
could relate to an extinct higher taxonomic group or
large lapilli.
To state that V. vulpes is the most common species
in the upper Maastrichtian Arkadelphia Formation is
an understatement. The total specimens in the Arka-
delphia Formation assemblage is 2,109, and 1,537 of
those (72.88%) are V. vulpes. The species is abundant
in the Severn Formation (Huddleston and Savoie 1983),
but noticeably less at 55%. Vorhisia vulpes is the most
abundant species in the Kemp Clay, but its percentage is
approximately 35% (Schwarzhans and Stringer 2020a).
The percentage of V. vulpes in the Arkadelphia Formation
certainly seems to indicate that the paleoenvironmental
parameters were decidedly conducive for its growth
and proliferation. Vorhisia vulpes has not been found in
Europe although Cretaceous otoliths have been investi-
gated in several areas (Nolf 2003, Schwarzhans 2010,
Schwarzhans and Jagt 2021). Current studies indicate
that the distribution of Vorhisia vulpes is limited to the
USA. As noted by Schwarzhans and Stringer (2020a), V.
vulpes was one of the most prominent and widespread
teleostean species to succumb to the K-Pg extinction
event in North America.
AULOPIFORMES
ICHTHYOTRINGIDAE
APATEODUS
APATEODUS CRENELLATUS?
2020b
Material—
2021-09-9.
Description and Remarks—The three Arkadelphia
Apateodus
crenellatus presented in Stringer et al. (2020) from the
Ripley Formation in northeastern Mississippi. Unfortu-
nately, none of the thin, fragile specimens have a pre-
served rostrum like the holotype shown in Stringer et al.
(2020A. crenellatus appears to
be more oval (sensu Smale et al. 1995), but if the long and
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 13
Figure 6. Otoliths from the Cretaceous Arkadelphia Formation. All specimens unless otherwise noted are inner views of right sag-
ittae. Length in mm. A. Kokenichthys navis Schwarzhans and Stringer (2020b), DMNH 2021-09-9, 4.10 mm. B. Clupeiform? indeter-
minate DMNH 2021-09-10, 1.42 mm. C. Arius subtilis Schwarzhans and Bratishko (2011), DMNH 2021-09-11, 4.61 mm. D. Vorhisia
vulpes Frizzell (1965b), DMNH 2021-09-13, 2.49 mm. E. Vorhisia vulpes Frizzell (1965b), DMNH 2021-09-14, 3.06 mm. F. Vorhisia
vulpes Frizzell (1965b), DMNH 2021-09-15, 3.99 mm. G. Vorhisia vulpes Frizzell (1965b), DMNH 2021-09-16, 7.98 mm. H. Vorhisia
vulpes Frizzell (1965b), DMNH 2021-09-12, 19.36 mm.
14 PaleoBios 40(3) 2023
moderately pointed rostrum is present, it is more ovate
in outline (sensu Smale et al. 1995). The margins are vari-
able, which may be related to erosion. The heterosulcoid
sulcus appears to be more slightly ventral and extends
across essentially the entire inner fac. The outer face is
A. crenellatus has been debated
for several decades since its initial discovery by Nolf and
Dockery (1990) in the Coffee Sand (Campanian) of north-
2016) and Stringer
et al. (2018
otolith was discovered in situ by CT micro-scanning in A.
corneti Forir (1887) by Schwarzhans et al. (2018a). This
discovery and the subsequent revised taxonomy are also
congruent with modern molecular-based phylogenetic
and dating studies such as Near et al. (2012), Betancur-
R. et al. (2013), Near et al. (2013), and Betancur-R et al.
(2017).
GADIFORMES
MERLUCCIIDAE
PALAEOGADUS
PALAEOGADUS? BELLI
Diagnosis—Moderately compressed, approxi-
mately oblong otoliths (sensu Smale et al. 1995) with
a homosulcoid-type sulcus. The H/L ratio ranges from
approximately 47%–62%, which is related to ontoge-
netic changes. Anterodorsal dome (predorsal expansion)
evident on specimens greater than 2.0 mm. Ostium and
cauda nearly equal in length. Narrow collum with ostial
and caudal colliculi very near. Prominent ventral furrow
that curves away from anteroventral and posteroventral
margins.
Holotype—Palaeogadus? belli sp. nov., DMNH 2021-
09-22, 3.13 mm, Arkadelphia Formation (Upper Cre-
taceous, upper Maastrichtian), Cabot, Lonoke County,
Arkansas, USA ; coordinates: 34.941292, -92.044155.
Paratypes—Palaeogadus? belli sp. nov., DMNH 2021-
09-18, 1.25 mm. Palaeogadus? belli sp. nov., DMNH
2021-09-19, 1.78 mm. Palaeogadus? belli sp. nov., DMNH
2021-09-20, 2.21 mm. Palaeogadus? belli sp. nov., DMNH
2021-09-21, 2.34 mm. Same locality as holotype.
Occurrence—Type locality: Cabot, Lonoke County,
Arkansas, USA ; coordinates: 34.941292, -92.044155
(Boring 5; Station 266; 22.86–23.32 m below ground
elevation), Arkadelphia Formation, Upper Cretaceous
(upper Maastrichtian). The coordinates for the four other
borings that yielded Palaeogadus? belli sp. nov. are as
follows: B6 (34.941187, -92.043788), B8 (34.940683,
-92.042295), B9 (34.940450, -92.041533), and B10
(34.940027, -92.040231).
Etymology—Species named for retired Professor
Dennis Bell (Monroe, Louisiana, USA) for his extensive
assistance in paleontological vertebrate and invertebrate
research, especially in the areas of photography of fossils
Description—Sagitta is moderately compressed.
Shape is elongated and is best described as oblong (sensu
Smale et al. 1995). Larger specimens tend to be more
elongated and narrower posteriorly. Margins are crenu-
lated, especially on the dorsal and ventral margins (all
specimens were less than 3.5 mm in length). The dorsal
margin tends to have more and deeper crenulations.
Anterior margin is somewhat compressed but primar-
ily rounded. Dorsal margin is more broadly rounded on
smaller specimens, but a diagnostic anterodorsal (pre-
dorsal) dome becomes evident in specimens greater than
2.0 mm. Posterior margin is similar to anterior margin
but tends to become more compressed and pointed in the
larger specimens. The ventral margin is gently but un-
evenly curved and can be almost horizontal in the center.
The inner face is convex with a long, homosulcoid-type
sulcus. The sulcus extends from almost the anterior to
1995).
There is a fairly narrow collum between the ostium and
the cauda. The ostium and cauda are both elongated,
compressed ovals in shape and are similar in length.
Colliculi are present in the ostium and cauda and ap-
proach very closely to the collum. The dorsal depression
is found primarily above the collum. The dorsal depres-
sion is small, elongated but somewhat irregular, and
present and is very close to the ventral edge in the center.
However, the ventral furrow curves strongly away from
the anteroventral and posteroventral margins toward the
sulcus. The outer face is irregular with a characteristic
hollowing in the central dorsal area, especially in the
larger of the specimens.
Remarks—Palaeogadus? belli sp. nov. has gadiform
features that seem to place it into the family Merluc-
ciidae. The species is similar to Palaeogadus weltoni
Schwarzhans and Stringer (2020a) described from the
Upper Cretaceous (upper Maastrichtian) Kemp Clay in
northeast Texas (Schwarzhans and Stringer 2020a).
Morphological features similar to P. weltoni include the
nearly equal length of the ostium and cauda, no pseu-
docolliculum in the collum, and the similar shape of the
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 15
Figure 7. Otoliths from the Cretaceous Arkadelphia Formation. All specimens unless otherwise noted are inner views of right sag-
ittae. Length in mm. A. Apateodus crenellatus? Schwarzhans and Stringer (2020b), DMNH 2021-09-17, 1.78 mm. B. Palaeogadus?
belli sp. nov., DMNH 2021-09-18, 1.25 mm (paratype). C. Palaeogadus? belli sp. nov., DMNH 2021-09-19, 1.78 mm (paratype). D.
Palaeogadus? belli sp. nov., 2021-09-20, 2.21 mm (paratype). E. Palaeogadus? belli sp. nov., DMNH 2021-09-21, 2.34 mm (para-
type). F. Palaeogadus? belli sp. nov., DMNH 2021-09-22, 3.13 mm (holotype). G. Palaeogadus? belli sp. nov., DMNH 2021-09-22,
3.13 mm (holotype, outer view). H Palaeogadus? belli sp. nov., DMNH 2021-09-22, 3.13 mm (holotype, dorsal view).
16 PaleoBios 40(3) 2023
ventral furrow. However, there are some features that
readily distinguish it from P. weltoni. These include the
development of a fairly prominent anterodorsal dome
by specimens greater than 2.0 mm and a narrow collum
with the ostial and caudal colliculi situated very near the
collum. Palaeogadus? belli also shows similarity to P. ?
bratishkoi Schwarzhans (2012) known from Paleocene
(Thanetian) of Austria and is especially evident in the
and 113) as illustrated in Schwarzhans (2012).
Palaeogadus? belli is one of the most common speci-
mens in the Arkadelphia Formation comprising 7.02%
of the total assemblage. It is only surpassed by the
extremely abundant Vorhisia vulpes and Eutawichthys
zideki. Unfortunately, all of the gadiform specimens from
the Arkadelphia are small (around 3.1 mm in length for
the best-preserved specimens), and some are poorly
preserved. In spite of the size and preservation, there are
features that indicate that the otoliths could belong to the
merlucciid genus Palaeogadus to which it is tentatively
assigned. However, it is important to note that there are
many primitive features present in the Late Cretaceous P. ?
belli, and there is the distinct possibility that it represents
an unknown fossil genus that may also include P. weltoni
of Schwarzhans and Stringer (2020a) and possibly P. ?
bratishkoi of Schwarzhans (2012). The relatively large
percentage of P.? belli, a putative cool-water form, in the
Arkadelphia Formation at the Cabot site in Arkansas is
certainly important in the determination and evaluation
of the paleoenvironment and paleogeography in this por-
tion of the Gulf Coastal Plain during the late Maastrich-
tian. This importance is addressed further and in greater
detail in the “Paleoecology and Paleogeography” section.
PALAEOGADUS
PALAEOGADUS CF. P. WELTONI S
2020a
Material—one small, slightly eroded specimen, DMNH
2021-09-23.
Description and Remarks—The one Arkadelphia
Formation specimen assigned to Palaeogadus weltoni is
very small and eroded. However, it was felt that it pos-
sessed enough gadid features to compare it to Palaeoga-
dus cf. P. weltoni. Similarities include the overall oblong
shape (sensu Smale et al. 1995), the slightly convex inner
face; the tapered and rounded anterior and posterior
margins that are almost alike; the homosulcoid-type
sulcus; a broadly, gently arched dorsal margin; a very
shallow ventral margin that approaches horizontal; and
a prominent ventral furrow extending from under the
anterior of the ostium to near the posterior of the cauda;
the anterior and posterior ends of the ventral furrow ap-
pear to turn upwards. It compares very well to the one
specimen of P. weltoni illustrated by Schwarzhans and
Stringer (2020a) from the Kemp Clay in Texas and to the
specimens shown by Stringer and Schwarzhans (2021)
from the Severn Formation in Maryland. Palaeogadus is
an extinct genus that is known from otoliths and skel-
etons from the early Paleogene of Europe (Schwarzhans
2003
GADIFORMES INDETERMINATE
Material—11 very small or broken specimens, speci-
Description and Remarks—The 11 specimens
designated as Gadiformes indeterminate are included
because of the rarity of the Gadiformes in the Cretaceous.
Their occurrence is certainly worth noting even at this
taxonomic level. Some of the specimens represent non-
-
ers represent badly eroded specimens. The specimens
have typical gadiform characteristics such as a long,
homosulcoid-type sulcus with a collum, a convex inner
extensive crenulations. It is likely that the specimens rep-
resent gadiforms already known from the Arkadelphia
Formation, but this cannot be determined with certainty.
Schwarzhans (2003-
venile gadiforms from the Paleocene of Denmark.
HOLOCENTRIFORMES
FAMILY INDETERMINATE
TIPPAHA a
TIPPAHA MYTHICA a
Material—eight specimens including three complete
2021-09-25.
Description and Remarks—Tippaha mythica is
certainly the most unique and impressive otolith in the
Arkadelphia Formation assemblage based on its distinc-
tive morphological characteristics. The basic outline is
somewhat oblong to elliptic (sensu Smale et al. 1995),
but there are numerous features that modify the shape.
The convex inner face has a distinct and characteristic
pseudobiostial sulcus that is primarily shallow except
for a slightly deeper posterior portion of the cauda. An
exceptional feature of the anterior portion of the cauda
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 17
Figure 8. Otoliths from the Cretaceous Arkadelphia Formation. All specimens unless otherwise noted are inner views of right
sagittae. Lapilli are macular views. Length in mm. A. Palaeogadus cf. P. weltoni Schwarzhans and Stringer (2020a), DMNH 2021-09-
23, 1.46 mm. B. Gadiformes indeterminate, DMNH 2021-09-24, 1.56 mm. C. Tippaha mythica Schwarzhans and Stringer (2020a),
DMNH 2021-09-25, 3.85 mm. D. Eutawichthys maastrichtiensis Nolf and Stringer (1996), DMNH 2021-09-26, 3.93 mm. E. Euta-
wichthys zideki Nolf and Stringer (1996), DMNH 2021-09-27, 1.42 mm. F. Eutawichthys cf. E. stringeri Schwarzhans, Huddleston,
and Takeuchi (2018b), DMNH 2021-09-28, 1.85 mm. G. Ampheristus cf. A. americanus Schwarzhans and Stringer (2020a), DMNH
2021-09-29, 1.58 mm. H. Protobythities brzobohatyi Schwarzhans (2010), DMNH 2021-09-30, 1.68 mm. I. Lapillus type 1, DMNH
2021-09-31, 2.98 mm.
18 PaleoBios 40(3) 2023
is the fading of its dorsal margin toward the moderately
deep, well-marked, oval dorsal depression. There is no
ventral furrow, but a long, obvious ventral depression is
present under the sulcus. The most prominent feature is
leans anteriorly at about 65–750. The length of this con-
spicuous protuberance is often 25–30% of the length of
the otolith. The outer face is usually irregular and nearly
Stringer et al. (2020) noted that T. mythica is probably
the most distinct and remarkable otolith morphology
presently known from the Cretaceous. In addition to
the eight specimens from the Arkadelphia Formation,
T. mythica is known from the Ripley Formation and the
Owl Creek Formation, both Upper Cretaceous sites in
northeastern Mississippi (Stringer et al. 2020) and the
Providence Sand in Alabama, according to J. Ebersole,
Director of Collections at McWane Science Center, Bir-
mingham, Alabama (personal communication, 2020).
BERYCIFORMES
FAMILY INDETERMINATE TYPE 1 (
)
EUTAWICHTHYS -
b
EUTAWICHTHYS MAASTRICHTIENSIS (
1996)
Material—
2021-09-26.
Description and Remarks—Eutawichthys maastrich-
tiensis has a nearly circular to slightly oval outline (sensu
Smale et al. 1995). The dorsal margin is irregular, while
the ventral margin can have crenulations that are often
obliterated by erosion. The thin sagitta is only slightly
convex with a distinctive, long sulcus (heterosulcoid
type) that is wide and continuously curved. The cauda
curves diagnostically dorsally in its posterior section.
There is a depressed area that is fairly distinct above the
center of the sulcus.
Eutawichthys maastrichtiensis was designated as an
apogonid for many years, and there are certainly resem-
blances to the apogonids. Its designation as a berycid is
discussed at length in Stringer et al. (2016) and is more
congruent with molecular studies such as Betancur-R.
et al. (2013) that indicate a much later divergence for
the apogonids (around 45 Ma). The fossil-based genus
Eutawichthys was erected by Schwarzhans et al. (2018b).
Eutawichthys maastrichtiensis is known from several
Cretaceous formations including the Severn Formation
of Maryland (Huddleston and Savoie 1983), the Wood-
bury Formation of New Jersey (Stringer et al. 2016), the
Eutaw Formation of Alabama (Schwarzhans et al. 2018a),
the Tar Heel Formation of North Carolina (Stringer et al.
2018), the Coon Creek Formation of Tennessee (Stringer
2016b), the Ripley Formation of Mississippi (Stringer et
al. 2020), and the Kemp Clay of Texas (Schwarzhans and
Stringer 2020a).
EUTAWICHTHYS ZIDEKI ()
Material—
2021-09-27.
Description and Remarks—Eutawichthys zideki is
the most abundant species of this genus in the Arkadel-
phia Formation. It is characterized by an oval outline
(sensu Smale et al. 1995), but larger specimens can
become somewhat angular. Although the sulcus (het-
erosulcoid type) is not deeply impressed, it is distinct
and extends for approximately 75% of the length of the
inner face. The sulcus is almost horizontal, which is a
distinguishing feature of the species. The ostium and
cauda are approximately the same length, and the ostium
is only slightly wider than the cauda. Eutawichthys zideki
is geographically widespread in its distribution and has
been reported from the Severn Formation of Maryland
(Huddleston and Savoie 1983), the Woodbury Forma-
tion of New Jersey (Stringer et al. 2016), the Tar Heel
Formation of North Carolina (Stringer et al. 2018), the
Coon Creek Formation of Tennessee (Stringer 2016b),
the Eutaw Formation of Alabama (Schwarzhans et al.
2018b), and the Ripley Formation of Mississippi (Stringer
et al. 2020).
EUTAWICHTHYS STRINGERI
b
EUTAWICHTHYS CF. E. STRINGERI
Material— DMNH
2021-09-28.
Description and Remarks—The specimens assigned
to Eutawichthys stringeri are characterized by an anterior
margin with a broad, dorsally shifted rostrum, a broadly
rounded dorsal margin, a broadly rounded posterior
margin, and a moderately deep, gently and regularly
curved convex ventral margin. The inner face is slightly
convex with a shallow, moderately wide sulcus divided
into an ostium and cauda. The ostium is curved upwards
towards the dorsal margin of the rostrum. The cauda
is about the same length as the ostium and is oriented
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 19
upwards. The cauda has a rounded tip that ends well
before the posterior margin.
E. stringeri are
found in Schwarzhans et al. (2018b) and readily illustrate
the differences between it and other species of Euta-
wichthys. The distribution of E. stringeri is not nearly as
widespread as E. maastrichtiensis and E. zideki. It has only
been previously reported from the Woodbury Formation
(early–middle Campanian) of New Jersey (Stringer et al.
2016) and the Eutaw Formation (upper Santonian) of
Alabama (Schwarzhans et al. 2018b), where it represents
the most abundant species.
OPHIDIIFORMES
OPHIDIIDAE
AMPHERISTUS
AMPHERISTUS CF. A. AMERICANUS
a
Material—
2021-09-29.
Description and Remarks—The sagitta of Ampher-
istus cf. A. americanus is basically oval (sensu Smale et
al. 1995) with a long, nearly straight, smooth dorsal
margin, while the ventral margin is regularly curved,
deepest anterior of its middle, and relatively shallow.
The inner face is convex horizontally with a long, slightly
s-shaped sulcus that is medially located. The sulcus al-
most reaches the anterior margin but ends well before
the posterior margin. Ampheristus americanus
named by Schwarzhans and Stringer (2020a) based on
143 specimens from the Kemp Clay (Maastrichtian) of
Texas and the Clayton Formation (Danian) of Arkansas.
According to Schwarzhans (1981) the fossil genus Am-
pheristus is considered to be closely related to the extant
Hoplobrotula Gill (1863).
PROTOBYTHITES
PROTOBYTHITES BRZOBOHATYI
Material—
2021-09-30.
Description and Remarks—The four Arkadelphia
Formation otoliths assigned to Protobythites brzobohatyi
are similar to Ampheristus, but they are distinguished
from Ampheristus in the inner face being distinctly convex
in both the horizontal and vertical directions. Protoby-
thites brzobohatyi also has a relatively smooth inner face
except for the slightly deepened sulcus (especially the
cauda). The sulcus has a wide, long ostium and a short,
-
pression present and a faint ventral furrow on the inner
face. The margins are sharp. Protobythites brzobohatyi
species was based on a single well-preserved otolith from
the Maastrichtian of Bavaria (Schwarzhans 2010). It is
also known from the Maastrichtian Kemp Clay of Texas
(Schwarzhans and Stringer 2020a). Its occurrence is now
extended to the Maastrichtian Arkadelphia Formation
of Arkansas.
FAMILY INDETERMINATE
GENUS INDETERMINATE
LAPILLUS TYPE 1 ()
Material—one small, slightly eroded specimen, DMNH
2021-09-31.
Description and Remarks—The single utricular
-
phia Formation is small (around 3 mm) and rounded on
several sides, which gives it a lobe-like appearance. The
Arkadelphia specimen appears to be identical to speci-
indeterminate) from the Ripley Formation (Cretaceous,
Maastrichtian) in northeast Mississippi by Stringer
(1991), Nolf and Stringer (1996), and Stringer et al.
(2020, as Lapillus type 1). It was also noted from the
Severn Formation by Stringer and Schwarzhans (2021).
Typically, Lapillus type 1 is not numerous, but Stringer
et al. (2016) reported 36 of these utricular otoliths from
the Woodbury Formation (Cretaceous, early-middle
Campanian). Some of the utricular otoliths from Stringer
et al. (2016) are preserved especially well (their pl. 2,
Arkadelphia Formation specimen. If the specimens rep-
resent the same taxon, then the teleost has a fairly long
stratigraphic range from the early-middle Campanian to
the late Maastrichtian.
DISCUSSION
The Arkadelphia Formation otoliths and their
indications of paleoecology and paleogeography
The otolith assemblage of the Arkadelphia Forma-
tion at Cabot, Arkansas, consisted of 19 species, three
taxa in open nomenclature, and one unknown type of
lapillus representing at least 19 families based on 2,109
specimens. The richness or number of species in the
Arkadelphia Formation otolith assemblage is relatively
high, but it is considerably less than the Upper Cretaceous
20 PaleoBios 40(3) 2023
(Maastrichtian) Ripley Formation in Mississippi, which
had a richness of 30 species and two morphological
types of unknown lapilli representing at least 22 families
based on 3,802 specimens (Stringer et al. 2020) and the
Severn Formation with 32 taxa with one unknown lapil-
lus representing 24 families based on 2,296 specimens.
The richness of taxa in the Ripley Formation and the
Severn Formation was approximately 36% and 41%,
respectively, more than the Arkadelphia Formation. The
Arkadelphia Formation otolith assemblage was closer to
the number of taxa in the Upper Cretaceous Kemp Clay
in richness (25 species with two in open nomenclature
based on 1,202 specimens). The Upper Cretaceous
Fox Hills Formation otolith assemblage was extremely
diminutive with only four species from four different
families (Hoganson et al. 2019). It must be taken into con-
sideration that the otolith specimens of the Arkadelphia
Formation were obtained from boring samples (17–31 m
samples collected on the surface and weighed. However,
even with this caveat, the richness and evenness of the
Arkadelphia Formation otolith assemblage provides
relevant information for comparison.
Another aspect of diversity, evenness or the percent-
age of individual species, is meaningful for analyzing the
Arkadelphia Formation otolith assemblage and compar-
ing it to other Late Cretaceous assemblages (Fig. 2). The
Arkadelphia Formation is extremely uneven with one
species, the presumed siluriform Vorhisia vulpes, repre-
senting almost 73% of the total number of specimens.
If the other two most abundant species are included
(Eutawichthys zideki and Palaeogadus? belli), these three
species account for almost 94% of the assemblage and
are indicative of a very uneven distribution. The Kemp
Clay is also uneven in the distribution of species but not
as much as the Arkadelphia Formation. The same spe-
cies that is so abundant in the Arkadelphia Formation,
Vorhisia vulpes, also represents the greatest percentage in
the Kemp Clay (almost 35%). Another siluriform, Arius?
subtilis, represents around 16% of the Kemp Clay. So,
two species account for over 50% of the Kemp Clay. The
Fox Hill Formation is also uneven in its diversity with a
presumed gadid, Dakotaichthys hogansoni Schwarzhans
and Stringer (2020a), comprising approximately 66%
of the total. The ubiquitous Vorhisia vulpes accounts for
around 29%. So, two species make up 95% of the assem-
blage. The Ripley Formation assemblage is somewhat
uneven with the two species Hoplopteryx oscitans (Nolf
and Stringer, 1996) and Paraulopus pseudoperca (Nolf
and Dockery, 1990) making up about 53% of the total.
However, of the other 28 species in the Ripley Formation,
all of them represent less than 6% of the total specimens
with many less than 1%. It should also be noted that the
exceptionally abundant Vorhisia vulpes in the Arkadel-
phia Formation, Kemp Clay, Severn Formation, and the
Fox Hills Formation represents only 0.27% in the Ripley
Formation.
An informative and insightful tool for comparing
otolith assemblages from various sites is the
percentage similarity measurement (Reitz and Wing
1999, Stringer et al. 2018, Stringer and Hulbert 2020,
Stringer and Schwarzhans 2021). The percentage
similarity measurement allows for a comparison of
assemblages from different geographical localities.
The measurement, also known as percent similarity
or proportional similarity, is calculated using the
following equation:
1i, p2i)
where:
P = percentage similarity between assemblages 1 and 2
p1i = percentage of species i in assemblage 1
p2i = percentage of species i in assemblage 2
The otolith assemblages from the Fox Hills Formation
(NDGS 5597 locality), Kemp Clay (South Sulphur River
locality, Texas), Ripley Formation (Blue Springs local-
ity, Mississippi), and Severn Formation (four localities
in Maryland of Stringer and Schwarzhans 2021) were
selected for comparison to the Arkadelphia Formation
assemblage because of their similar age (late Maastrich-
distant states), and relatively large number of specimens.
Data for the percentage similarity calculations were
obtained from Table 1 for the Arkadelphia Formation,
Table 2 for the Fox Hills Formation, the Kemp Clay, and
the Ripley Formation, and table 3 of Stringer and Schwar-
zhans (2021) for the Severn Formation. The results of the
percent similarity measurements are presented in Table
3. It should be noted that the species and percentages for
the Ripley Formation were based on specimens derived
from bulk samples and did not include the specimens
collected by systematic surface collecting conducted at
the Blue Springs locality.
The percentage similarity measurement for the Arka-
delphia Formation (Cabot locality) and Fox Hills Forma-
tion (NDGS 5597 locality, North Dakota) was 30.32%.
This would indicate that the two either shared a number
of species but with low percentages or shared a few spe-
cies with larger percentages. In this case, three of the four
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 21
Taxa in Fox Hill., Kemp Clay, and
Ripley formation sites
Fox Hills Fm.,
North Dakota
Kemp Clay,
Tex a s
Ripley Fm.,
Mississippi
No. of
otoliths
% of
total
No. of
otoliths
% of
total
No. of
otoliths
% of
total
Megalopidae
Megalops? 0 0 0 0 3 0.40
Albulidae
Albula cf. A. bashiana 0 0 7 0.58 0 0
Pollerspoeckia sp. 4 1.50 0 0 0 0
Pterothrissus conchaeformis10 0 113 9.33 6 0.81
Pterothrissus cf. P. foreyi 0 0 2 0.17 0 0
Albula sp. 0 0 0 0 7 0.94
Elopothrissus sp. 0 0 0 0 0 0
ORDER INDETERMINATE
Genartina sp. 0 0 3 0.25 0 0
Osmeroididae
Osmeroides mississippiensis 0 0 0 0 14 1.89
Osmeroides sp. 0 0 0 0 4 0.53
Anguillidae
Anguilla chickasawae 0 0 0 0 2 0.27
Ophichthidae
Echiophis aff. E .semispaeroides 0 0 2 0.17 0 0
Family Ind. (ANGUILLIFORMES)
Muraenanguilla cf. M. unionensis 0 0 0 0 19 2.56
Heterenchelyidae
Pythonichthys arkansasensis 0 0 3 0.25 0 0
Congridae
Rhynchoconger? piger 0 0 38 3.14 0 0
Rhynchoconger brettwoodwardi 0 0 25 2.06 0 0
Congrophichthys transterminus 0 0 3 0.25 0 0
Family ind. (OSTEOGLOSSIFORMES)
Kokenichthys navis 0 0 0 0 7 0.94
Kokenichthys ripleyensis 0 0 0 0 1 0.13
Family Ind. (CLUPEIFORMES)
Clupeiform indeterminate 0 0 0 0 0 0
Ariidae
Arius? danicus 0 0 67 5.53 0 0
Arius? subtilis 0 0 195 16.10 13 1.75
Table 2. Comparison of the otoliths (taxa and percentage of total) of the Fox Hills Formation (NDGS 5597 locality, near Burnstad,
North Dakota, USA), Kemp Clay (South Sulphur River, near Commerce, Texas, USA), and Ripley Formation (near Blue Springs, Mis-
sissippi, USA) based on bulk samples. 1Pterothrissus cf. P. conchaeformis, 2 includes specimens
Ampheristus cf. A. americanus. Order=FORMES, Family=idae
22 PaleoBios 40(3) 2023
Taxa in Fox Hill., Kemp Clay, and
Ripley formation sites
Fox Hills Fm.,
North Dakota
Kemp Clay,
Tex a s
Ripley Fm.,
Mississippi
No. of
otoliths
% of
total
No. of
otoliths
% of
total
No. of
otoliths
% of
total
Family Ind. (SILURIFORMES)
Vorhisia vulpes 78 29.32 423 34.93 2 0.27
Ichthyotringidae
Apateodus crennelatus? 0 0 0 0 42 5.66
Thrax acutus 0 0 0 0 1 0.13
Ichthyotringa? tavernei 0 0 0 0 4 0.53
Paraulopidae
Paraulopus pseudoperca 0 0 4 0.33 190 25.61
Family Ind. (ORDER UNKNOWN)
Choctawichthys ceploides 0 0 0 0 2 0.27
Polymixiidae
Cowetaichtys carnevalei 0 0 0 0 3 0.40
Cowetaichthys alabamae 0 0 0 0 9 1.21
Merlucciidae
Paleogadus weltoni 0 0 2 0.17 0 0
Palaeogadus belli 0 0 0 0 0 0
Gadidae?
Dakotaichthys hogansoni 177 66.29 16 1.32 0 0
Family Ind. (GADIFORMES)
Archaemacruroides bratishkoi 0 0 11 0.91 0 0
GADIFORMES Ind. 0 0 0 0 0 0
Family Ind. (HOLOCENTRIFORMES)
Tippaha mythica 0 0 0 0 1 0.13
Tippaha cavata 0 0 0 0 1 0.13
Trachichthyidae
Hoplopteryx oscitans 0 0 0 0 278 37.47
Hoplopteryx langfordi 0 0 0 0 11 1.48
Hoplostethus stringeri 0 0 52 4.29 0 0
Berycidae
Centroberyx apogoniformis 0 0 42 3.47 0 0
Family Ind. (BERYCIFORMES)
Argyroberyx? dentatus 0 0 1 0.08 0 0
Argyroberyx? dockeryi 0 0 0 0 2 0.27
Table 2 (continued). Comparison of the otoliths (taxa and percentage of total) of the Fox Hills Formation (NDGS 5597 locality,
near Burnstad, North Dakota, USA), Kemp Clay (South Sulphur River, near Commerce, Texas, USA), and Ripley Formation (near
Blue Springs, Mississippi, USA) based on bulk samples. 1Pterothrissus cf. P. conchaeformis, 2 in-
Ampheristus cf. A. americanus. Order=FORMES, Family=idae
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 23
species found in the Fox Hills Formation (very low diver-
sity) were also found in the Arkadelphia Formation, and
one of them, V. vulpes represented a large percentage of
the Fox Hills Formation assemblage and the Arkadelphia
Formation assemblage.
Percentage similarity for the Arkadelphia Formation
(Cabot locality) and the Kemp Clay (South Sulphur River)
was 35.73%. This would indicate that either there were
some of the same species that had somewhat abundant
percentages at both sites or more species in common but
lower percentages. In this case, there were seven species
in common, and six of them were very low percentages.
However, one species, V. vulpes, represented a large per-
centage of the Kemp Clay and the Arkadelphia Formation.
Although the percentage similarity value (35.73%) is not
that large, it would point to a greater similarity between
the Arkadelphia Formation and the Kemp Clay than other
assemblages compared except for the Severn Formation.
The Arkadelphia Formation (Cabot locality) and
Ripley Formation (Blue Springs locality) pointed to a
very small percentage similarity with a value of 5.46%.
However, the Arkadelphia and Ripley formations otolith
assemblages actually had 11 species in common, but ten
of the 11 species were 1% or less similarity except for
Eutawichthys zideki. So, the assemblages shared species,
but they were all low percentages. One of the most telling
of the percentage similarity measurements was the one
comparing the Kemp Clay (South Sulphur River locality)
and Ripley Formation (Blue Springs locality). These two
sites had an extremely low percentage similarity with
Taxa in Fox Hill., Kemp Clay, and
Ripley formation sites
Fox Hills Fm.,
North Dakota
Kemp Clay,
Tex a s
Ripley Fm.,
Mississippi
No. of
otoliths
% of
total
No. of
otoliths
% of
total
No. of
otoliths
% of
total
Family Ind. (BERYCIFORMES)
Eutawichthys cf. E. choctawae 0 0 7 0.58 0 0
Eutawichthys maastrichtiensis 8 3.00 2 0.17 15 2.02
Eutawichthys zideki20 0 0 0 24 3.23
Eutawichthys stringeri 0 0 0 0 0 0
Family Ind. (BERYCIFORMES)
Ossulcus labiatus 0 0 0 0 3 0.40
Ophidiidae
Ampheristus americanus20 0 130 10.73 0 0
Bythitidae
Bidenichthys? crepidatus 0 0 2 0.17 0 0
Protobythites brzobohatyi 0 0 1 0.08 0 0
Pempheridae
Pempheris? huddlestoni 0 0 0 0 29 3.91
Serranidae
Serranus? caribbaeus 0 0 12 0.99 0 0
Serranus? severnensis 0 0 0 0 1 0
Incertae sedis
Otolithopsis cumatilis 0 0 0 0 4 0.54
Percoid sp. 0 0 0 0 3 0.40
ORDER/Family unknown
Lapillus type 1 0 0 0 0 7 0.94
Table 2 (continued). Comparison of the otoliths (taxa and percentage of total) of the Fox Hills Formation (NDGS 5597 locality,
near Burnstad, North Dakota, USA), Kemp Clay (South Sulphur River, near Commerce, Texas, USA), and Ripley Formation (near
Blue Springs, Mississippi, USA) based on bulk samples. 1Pterothrissus cf. P. conchaeformis, 2 in-
Ampheristus cf. A. americanus. Order=FORMES, Family=idae
24 PaleoBios 40(3) 2023
only 3.33% (Table 3). This would be a clear indication
that the two shared few species (5), and the ones that
were shared were not abundant (very low percentages).
The percentage similarity measurement would indicate
that the otolith assemblages of the Kemp Clay and Ripley
Formation were not similar and notably different.
It is important to note that three of these percentage
similarity measurements were calculated between sites
in the Arkadelphia Formation, Kemp Clay, and Ripley
Formation that are essentially the same age (Late Creta-
ceous, late Maastrichtian). Furthermore, these three sites
are located in the Gulf Coastal Province, and their present
latitudinal differences are small (less than 20 difference in
latitude between the three sites), and their geographical
separation is not that large (approximately 70 longitude
between Commerce, Texas, and Blue Springs, Mississippi,
with Cabot, Arkansas, approximately between the two).
So, the two very low percentage similarity measurements
between the Kemp Clay (South Sulphur River locality)/
Ripley Formation (Blue Springs locality) and the Arka-
delphia Formation (Cabot locality)/Ripley Formation
between the otolith assemblages of the sites. Of course,
the question is what factor or factors are causing such
This question is addressed later in the discussion of the
paleoecology and paleogeography.
Although the Fox Hills Formation assemblage in North
Dakota is Maastrichtian in age and has a relatively large
number of otoliths, it is certainly not in geographical
proximity to the other localities. The Fox Hills Formation
locality (NDGS 5597) is located in Logan County, North
Dakota, which is in the south-central portion of the state.
Presently, the Fox Hills Formation locality (46.3855,
-99.6326) is almost 120 latitude further north and over 70
longitude further west than the Cabot locality (34.9745,
-92.0165). In addition, the Fox Hills Formation local-
ity in North Dakota is approximately 1,704 km north-
northwest of the Arkadelphia Formation site in Cabot,
Arkansas. This allowed for comparison to a site that was
latitudinally separated from the other sites. During the
Late Cretaceous, the Fox Hills Formation locality would
have been in the Western Interior Seaway fairly close to
the shore of Laramidia (Stringer and Schwarzhans 2021).
Although separated by a substantial number of degrees of
latitude, the percentage similarity measurement between
the Arkadelphia Formation and the Fox Hills Formation
was 30.32%. While not a large percentage similarity, it
certainly appears unusual that the Arkadelphia Forma-
tion and Fox Hills Formation otolith assemblages have a
much greater percentage similarity than the Arkadelphia
Formation has with the Ripley Formation. The Arkadel-
phia Formation (Cabot site) and the Ripley Formation
(Blue Springs site) are both Maastrichtian, essentially
the same latitude, and only separated by 358 km. Obvi-
ously, some factor or factors are affecting the percentage
similarity differences.
Equally intriguing and compelling is the percentage
similarity analysis of the Arkadelphia Formation and the
Severn Formation (Upper Cretaceous, Maastrichtian)
based on data from four localities in Maryland from
recent studies by Stringer and Schwarzhans (2021). Al-
though the assemblages are widely separated geographi-
cally (central Arkansas and eastern Maryland, which are
approximately 1426 km apart with a latitudinal differ-
ence of about 40), the percentage similarity between the
two is 57.68%. This is much greater similarity than any of
the other assemblages that were compared to the Arka-
delphia Formation. The percentage similarity between
the Severn and Arkadelphia otoliths is unquestionably
-
ther later in this discussion.
The otolith assemblage from the Owl Creek Formation
at its type locality northeast of Ripley, Tippah County,
Mississippi, was also considered for comparison to the
Arkadelphia Formation assemblage. However, the Owl
Creek otolith assemblage from the type locality only
met two of the criteria applied to the other sites. It is
stratigraphically equivalent to the Arkadelphia Forma-
tion as both are uppermost Maastrichtian (Larina et al.
2016
Mississippi. However, the number of otolith specimens
available from the Owl Creek type locality was less than
for comparison. In spite of not meeting all three criteria,
the percentage similarity was calculated with this proviso
noted and was slightly greater than 1.00% (1.08%). The
percentage similarity of the Arkadelphia Formation and
the Owl Creek type locality was even less than the Arka-
delphia Formation and the underlying Ripley Formation
(5.46%). The very small percentage similarity between
the Owl Creek type locality and Arkadelphia Formation
otolith assemblages does serve as ancillary evidence of
the dissimilarity of the Arkadelphia otolith assemblages
with those to the east in Mississippi.
Schwarzhans and Stringer (2020a) proposed four
based on a correlation of Late Cretaceous otoliths at the
genus level (i.e., lineages) including open nomenclature
records. The communities (bioprovinces) were the
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 25
Seaway. Some of the most compelling evidence for this
categorization may be found in the percentage similar-
ity measurements (Table 3). The Arkadelphia Formation
otolith assemblage has a percentage similarity of 30.32%
with the Fox Hills Formation and a percentage similar-
ity of 35.73% with the Kemp Clay. Contrast this with
a similarity percentage of 5.46% and 1.08% between
the Arkadelphia Formation and the Ripley and the Owl
Creek formations, respectively (both formations in the
Appalachian Community). A seemingly unusual result
is the percentage similarity between the Arkadelphia
and the Severn formations otoliths (57.68%), which is
the most similarity of any of the comparisons made in
this study. Schwarzhans and Stringer (2020a) placed the
Severn Formation in the Appalachian Community with
the Ripley and Owl Creek formations.
Figure 9. Maastrichtian otolith localities in North America
and otolith-based faunal communities (bioprovinces) based
on Schwarzhans and Stringer (2020a). The Western Interior
Seaway community is outlined in green, and the localities are
shown in green circles. The Appalachian community is outlined
in red, and the localities are shown in red circles. The number
in the circle is the number of species known from the locali-
ties. The white star is the Arkadelphia Formation site at Cabot,
Arkansas, and the focus of this study. The base paleogeographic
2014) and Scotese (2014).
Localities compared Percent
similarity
Arkadelphia Formation (Cabot locality,
Arkansas) and Fox Hills Formation
(NDGS 5597, North Dakota)
30.32%
Arkadelphia Formation (Cabot locality,
Arkansas) and Kemp Clay (South
Sulphur River locality Texas)
35.73%
Arkadelphia Formation (Cabot locality,
Arkansas) and Ripley Formation (Blue
Springs locality, Mississippi)
5.46%
Arkadelphia Formation (Cabot locality,
Arkansas) and Severn Formation (four
sites in Maryland)
57.68%
Kemp Clay (South Sulphur River
locality, Texas) and Ripley Formation
(Blue Springs locality, Mississippi)
3.33%
Appalachian community, the Western Interior Seaway
community, the Peninnic community, and the Boreal
European community. This investigation is primarily
concerned with the Western Interior Seaway commu-
nity and the Appalachian community (Fig. 9). These
communities (bioprovinces) were based on studies of
Late Cretaceous otoliths from the USA and Europe, the
primary areas in which Cretaceous otoliths have been
reported, although Nolf et al. (2008) did report Creta-
ceous otoliths from India. The Kemp Clay of Texas and
the Fox Hills Formation of North Dakota were placed
in the Western Interior Seaway (WIS) community (bio-
province) based on the occurrence of common ariids,
abundant siluriforms (e.g., Vorhisia vulpes), diverse
anguilliforms, and the occurrence of gadiform otoliths.
Based on the results of this study, the Arkadelphia Forma-
tion otolith assemblage matches the criteria of the WIS
community (bioprovince) with its characteristic taxa,
especially relatively abundant gadiforms, and deposition
near the southeastern portion of the Western Interior
Table 3. Percentage similarity measurements for the otolith as-
semblages from the Arkadelphia Formation (Cabot locality, Ar-
kansas, USA), Fox Hills Formation (NDGS 5597, North Dakota,
USA), Kemp Clay (South Sulphur River locality, Texas, USA),
Ripley Formation (Blue Springs locality, Mississippi, USA, and
-
tions were obtained from this study (Table 1) for the Arkadel-
phia Formation (Cabot locality), from Hoganson et al. (2019)
for the Fox Hills Formation (NDGS 5597 locality), from Schwar-
zhans and Stringer (2020a) for the Kemp Clay (South Sulphur
River locality), from Stringer et al. (2020, table 2) for the Ripley
Formation (Blue Springs locality; bulk samples only), and from
Stringer and Schwarzhans (2021; table 3) for the Severn For-
mation (four sites).
26 PaleoBios 40(3) 2023
However, more detailed study with additional locali-
ties indicated the presence of gadiforms (merluccids)
in the Severn Formation (Stringer and Schwarzhans
2021). This is not typical of otolith assemblages found
in the southern portion of the Appalachian Community.
However, it is not unexpected that the Severn Formation
would be affected by cooler waters from the northern
of the paleoenvironments of the Severn and Arkadelphia
could explain the percentage similarity between the two
otolith assemblages.
In order for otoliths to be used for paleoenvironmental
interpretations, an essential taphonomic consideration
that inhabited the area during a given interval of geo-
logic time. Evidence from multiple strands indicate that
nature, and therefore, represent part of the biocoenosis
which otoliths become part of the sediment are death and
neocranium or skull and the excretion from piscivorous
(Fitch 1967, Schafer 1972, Stringer 1992). Nolf (1985,
2013) contended that predation and subsequent excre-
otoliths become incorporated into sediment. Only a very
small percentage (<1% of the total) of otoliths recov-
ered from the Arkadelphia Formation exhibit evidence
of invertebrate boring, settlement, and encrusting that
indicate that the otoliths were present on the sea bottom
for an extended period. Figure 5L shows the rare occur-
rence of a gastropod boring on a V. vulpes lapillus from
the Arkadelphia Formation. This is very similar to what
was found by Stringer (2016a) in the otolith assemblage
from the Moodys Branch Formation (Eocene, Bartonian).
A very small percentage of otoliths with evidence of in-
vertebrate settlement were reported from the Campan-
ian Woodbury Formation (Stringer et al. 2016) and the
Campanian Tar Heel Formation (Stringer et al. 2018).
The evidence or lack thereof is most likely related to the
amount of time exposed on the sea bottom before being
incorporated into the substrate (i.e., longer exposure
time equates with a greater chance of invertebrate boring
or settlement given a similar number of invertebrates).
-
conclusion includes those of Wigley and Stinton (1973),
Gaemers (1978), Stringer (1992), McBride et al. (2010),
Lowry (2011), Firestine et al. (2012), Schwarzhans
(2013), Lin (2016), Lin et al. (2016, 2017). Taxonomic
otoliths have greatly facilitated investigations of the
otoliths of modern sea bottoms sediments. Taxonomic
Schwarzhans (1993, 1999, 2013, 2019), Smale et al.
(1995), Rivaton and Bourret (1999), Campana (2004),
Veen and Hoedemakers (2005), Florida Fish and Wild-
life Conservation Commission (2007), Furlani et al.
(2007),Tuset et al. (2008), McBride et al. (2010), Lin
and Chang (2012), Nolf (2013), and Schwarzhans and
Aguilera (2013, 2016) . It appears that a strong cor-
relation exists between otolith associations in modern
sea-bottom sediments in particular environments and
2017) demonstrated that
various taphonomic processes, such as time-averaged
and spatial-averaged, may affect otoliths, but otoliths
seem to remain part of the biocoenosis and can be in-
terpreted as such in the fossil record.
Paleoenvironmental analysis using otoliths is based
to obtain data on the preferred habitats of comparable
Cretaceous otoliths are too far removed from modern
counterparts to be utilized for uniformitarian applica-
must be considered. Unquestionably, the Late Cretaceous
otolith assemblages cannot provide the accuracy and
precision that is possible with Plio-Pleistocene otoliths
we maintain that general paleoecological parameters
within limits are still discernable with Late Cretaceous
otoliths. Interpretations based on otoliths are also
compared to data from microfossil groups as well as to
paleogeographical reconstructions. This use of other fos-
sil groups as well as paleogeography provides essential
ancillary data to the use of otoliths in paleoenvironmental
reconstructions.
Examination of the otoliths from the Arkadelphia
Formation samples recovered from the drilling (Table 1)
and comparing them to closely related extant forms when
possible revealed the absence of representatives that are
indicative of deep waters exclusively (greater than outer
shelf or 200 m of the USA) according to Page et al. (2013).
-
semblage (Nolf and Brzobohaty 1992). Therefore as a
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 27
otoliths indicate a marine environment no deeper than
outer shelf and probably much shallower. Most of the oto-
salinity, but some of the forms could tolerate reduced
salinities (brackish) and even fresh water. These salinity
ranges would be expected in shallow marine waters close
to estuaries and freshwater input.
In geologically younger strata in the Atlantic and Gulf
coastal plains, it is possible to compare the families of
of the modern ichthyological fauna from the Gulf of
Mexico and the Atlantic Ocean (Hoese and Moore 1998,
McEachran and Fechhelm 1998, 2005, Nelson et al.
2016
of the families are unknown (i.e., indeterminate). In the
Arkadelphia Formation otolith assemblage, ten of the
-
cause it is not possible to relate them to extant families,
and they may also, and probably do, represent extinct
families. Many of these taxonomic questions could be
in situ oto-
liths could be recovered. In spite of this limitation, the
Arkadelphia Formation otoliths can be related to nine
extant families. Six of these families (Elopidae, Albulidae,
Anguillidae, Ophichthidae, Ariidae, and Bythitidae) are
listed as fresh water, brackish, and marine by Froese and
Pauly (2019). However, this is somewhat misleading
since three of the six families (Elopidae, Albulidae, and
fresh water or brackish. There are three families that
are listed as exclusively marine (Macrouridae, Merluc-
ciidae, and Ophidiidae). The general climate range of
these families extend from tropical only, subtropical,
warm temperate, and temperate. However, there are
families with representatives that occur in cold and even
Arctic waters. It could be contended that gadiforms that
preferred warm waters were present in the Late Creta-
ceous. However, there is no indication of this occurrence
in previous studies of otoliths and related fossil groups,
especially microfossils (Huddleston and Savoie 1983,
Nolf 2003, Schwarzhans et al. 2018b, Stringer et al 2018,
Hoganson et al. 2019, Stringer et al. 2020, Schwarzhans
and Stringer 2020a, Stringer and Schwarzhans 2021).
-
matic ranges is very unusual in otolith assemblages in
the Atlantic and Gulf coastal plains, especially in the Gulf
Coastal Plain (Fitch and Lavenberg 1983, Huddleston and
Savoie 1983, Schwarzhans et al. 2018b, Stringer and Bell
2018; Stringer et al. 2018, Ebersole et al. 2019, Stringer
and Shannon 2019, Stringer et al. 2020). This occurrence
would seem to signify atypical and different parameters
than what normally occurs in the Gulf and Atlantic coastal
plains. A strong consideration for the unusual climatic
conditions is the Late Cretaceous paleogeography and
the Western Interior Seaway. Numerous studies and
the resulting paleogeographic maps have indicated a
substantial Western Interior Seaway that linked the
Arctic Ocean (sometimes referred to as the Boreal Sea)
through central North America with the Gulf of Mexico
during much of Cretaceous times. Studies include, but
certainly not limited to, Williams and Stelck (1975),
Erickson (1978, 1999), Kennedy et al. (1998), Cobban
et al. (2006), Boyd and Lillegraven (2011), Landman et
al. (2012), Blakey (2014), Scotese (2014), Slattery et al.
(2015), and Hoganson et al. (2019). Slattery et al. (2015)
noted that the Western Interior Seaway was one of the
largest post-Paleozoic epeiric seas and covered a large
portion of west-central North America for an estimated
46 Ma. The resulting paleogeography was primarily
controlled by the interaction of sea level with the Late
Cretaceous physiography.
-
terior Seaway provided for a unique set of environmental
conditions related to atmospheric and oceanographic
parameters. Models developed by Kauffman (1975),
Eicher and Diner (1985), and others indicated cold,
the Western Interior Seaway in a portion of the Late
Cretaceous. Wright (1987) conducted a detailed study
Interior Seaway for the early Maastrichtian. Paleotem-
oxygen and carbon isotopic signatures of shell material
(cephalopods, epifaunal bivalves, and infaunal bivalves).
Wright’s results indicated a reduced salinity surface layer,
an intermediate normal salinity layer, and a denser, more
saline, warmer bottom layer. Wright noted that the south-
ern part of the Western Interior Seaway was subtropical
part of the year.
Studies such as Landman et al. (2004), Umhoefer and
Blakey (2006), Dastas et al. (2014), Scotese (2014), Slat-
tery et al. (2015), DePalma et al. (2019), and Hoganson
et al. (2019) indicated a fairly unobstructed interchange
between the northern and southern reaches of the
Western Interior Seaway throughout most of the Late
Cretaceous. Several studies noted the faunal similarity,
especially ammonites, of the Arctic Basin, North Dakota,
and Texas (Slattery et al. 2015, DePalma et al. 2019, Ho-
ganson et al. 2019). This assertion has been challenged
28 PaleoBios 40(3) 2023
by some who believe the seaway was closed by late
Maastrichtian (Roberts and Kirschbaum 1995, Kennedy
et al. 1998, Erickson 1999, Crowell 2011). For example,
Roberts and Kirschbaum (1995) indicated an expansive
Western Interior Seaway westward from the middle of
Wyoming to almost the eastern border of South Dakota
and extending northward from the Gulf Coast to northern
late Maastrichtian, they showed the seaway ending in
2014) in
his paleogeographic map of the Western Interior Seaway
at 69.7 Ma (Late Maastrichtian) depicted the seaway
completely separated from the Gulf of Mexico. In fact, it
indicated that that all of central and eastern Oklahoma
and western Arkansas were terrestrial.
As noted in the aforementioned studies, there are dif-
ferences in the timing and geographical location of the
closure of the Western Interior Seaway. However, it ap-
the seaway remained open until at least the beginning of
the Maastrichtian and perhaps later. No matter the exact
timing of the closure, the effects of the seaway upon the
closure, which was probably gradual and perhaps even
intermittent (due to erosional processes and reopening).
still present in the Arkadelphia Formation during the late
Maastrichtian as evidenced by the numerous gadiform
otoliths. It does appear that the “Fox Hills-Hell Creek
delta” (sensu Hoganson et al. 2019) was instrumental in
the closure of the seaway by the Paleocene (Danian) and
effectively isolating the northern and southern portions
(Slattery et al. 2015Hoganson et al. 2019, text-
Formation are markedly different from the Maastrichtian
otoliths from the Arkadelphia Formation. These differ-
ences are believed to be related not only to the closure
of the Western Interior Seaway but also the effect of the
K-Pg extinction event. An extensive discussion of the ef-
fect of the K-Pg boundary event on the marine teleostean
Stringer (2020a).
In summary, there is considerable debate over the
closure of the Western Interior Seaway, especially in
the exact timing and the precise process of the closure
as noted in the aforementioned references. However, it
should be emphasized that the earlier conditions, i.e.,
those in the early part of the Maastrichtian, were prereq-
uisite for the occurrence of the cool-water gadiforms. It
is postulated that the early Maastrichtian, primarily open
Western Interior Seaway was instrumental in providing
an environment suitable for the cool-water gadiforms.
Regardless of when the Western Interior Seaway closed
still be present. The Fox Hills Formation (North Dakota)
otolith assemblage is older than the Arkadelphia as-
semblage and considerably further north. The Fox Hills
assemblage is dominated by gadiforms (approximately
66.3%), while the Arkadelphia Formation assemblage
is approximately 7.6%. The Arkadelphia Formation also
lies directly under the Paleocene Clayton Formation. It is
postulated that the gadiforms were relicts of the earlier
cooler conditions when there was greater interchange
with the north. This could explain their more limited
abundance in the Arkadelphia Formation and complete
disappearance in the overlying Clayton Formation, along
with the effects of the K/Pg extinction.. Nolf and Stringer
(1992
assemblages and their eventual disappearance. One of
Plotosus Lacépède (1803),
in numerous assemblages in the Caribbean Neogene
but completely absent today in the Gulf of Mexico and
Caribbean. It and other taxa are interpreted as relicts
of the western Tethys fauna prior to the closure of the
Isthmus of Panama. A similar scenario is envisioned for
the closure of the Western Interior Seaway and the cool-
water gadiforms.
In determining the paleoenvironment of the Arkadel-
phia Formation at the Cabot site, emphasis can be given
to the most abundant taxa since the conditions appear to
be most conducive to those groups (i.e., environmental
factors favor the growth and proliferation of those taxa).
Examination of Table 1 indicates that Vorhisia vulpes,
Eutawichthys zideki, and Palaeogadus? belli comprise
93.51% of the total number of otoliths in the Arkadelphia
Formation assemblage. Unfortunately, these taxa are
problematic in that two of the three most abundant taxa
belong to indeterminate families, and their relationship
to extant forms is less certain. However, some useful
paleoecological and paleogeographical data can still be
attained.
Vorhisia vulpes constitutes almost three-fourths
(72.88%) of the total otoliths from the Arkadelphia
Formation. Most studies consider V. vulpes as an extinct
ariid, or at the least, a siluriform of some type based
on the large lapillus and some features found in extant
ariid lapilli (Huddleston and Savoie 1983, Hoganson et
al. 2019, Schwarzhans and Stringer 2020a, Stringer et
al 2020). This premise is followed in this study with the
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 29
concession that it is possible that it could relate to an
extinct higher taxonomic group. However, the taxon is
considered presently as most likely some type of Siluri-
formes in an indeterminate family.
Huddleston and Savoie (1983) noted that Vorhisia
vulpes comprised approximately 55% of the total otolith
assemblage of the early-middle Maastrichtian Severn
Formation in Maryland. They interpreted the paleoen-
vironment as very shallow marine, probably 0–20 m in
depth (inner shelf). Stringer and Schwarzhans (2021)
reported V. vulpes as the most abundant species in the
upper Maastrichtian Kemp Clay in Texas (approximately
35%). Again, this environment was interpreted as very
shallow marine with estuaries and freshwater input
most likely nearby. Hoganson et al. (2019) noted that V.
vulpes comprised almost 30% of the Fox Hills Formation
in North Dakota, which was interpreted primarily as
estuarine and shallow marine. Vorhisia vulpes was also
present in the Ripley Formation, which was interpreted
as 20–100 m (middle shelf) by Stringer et al. (2020).
However, V. vulpes only represented 0.27% of the total
specimens of the bulk sample studies. So, there is evi-
dence that a high percentage of V. vulpes is indicative of
very shallow marine conditions with possible estuarine
1813C analysis of the growth
rings of the lapilli of V. vulpes in the Fox Hills Formation
in North Dakota by Carpenter et al. (2003). Their studies
indicated that V. vulpes most likely spawned in estuarine
The second most abundant species in the Arkadelphia
Formation otolith assemblage was the beryciform and
otolith-based genus and species Eutawichthys zideki
(13.61% of the total specimens). The exact taxonomic
position of Eutawichthys zideki within the Beryciformes
is not known, and the species is assigned to an indeter-
minate, probably extinct family. Perhaps, like the aulopi-
form Apateodus, in situ otoliths in skeletal remains will
possible (Schwarzhans et al. 2018a). The Woodbury
Formation in New Jersey was reported as having a tre-
mendous number of beryciforms, primarily Eutawichthys
maastrichtiensis and Eutawichthys zideki with 3,100
beryciforms of the total 3,555 (Stringer et al. 2016).
Obviously, conditions were optimum for the beryciforms
based upon their abundance. The paleoenvironment was
interpreted based on otoliths, foraminifera, and calcar-
eous nannofossils as 0–100 m. A more exhaustive and
detailed examination of the site by Oman et al. (2016)
indicated a paleoenvironment of slightly deeper than
The paleoenvironment of the Arkadelphia Formation at
The third most abundant species (7.02% of the total
specimens) in the Arkadelphia Formation assemblage
is a gadiform assigned to Palaeogadus? belli in the fam-
ily Merlucciidae. The presence of gadiforms in the Gulf
Coastal Plain is unusual, and 112 specimens are really
unique. Schwarzhans and Stringer (2020a) noted that the
Late Cretaceous and probably since their origin despite
the lack of data from the Arctic Basin. Late Cretaceous and
early Paleogene gadiform evidence in the boreal province
of northern Europe support this premise.
As mentioned previously, ostracodes were also recov-
ered from the samples while extracting otoliths. These
ostracodes were sent to M. Puckett at the University of
Southern Mississippi for stratigraphic and paleoeco-
logic analysis. All but one of the specimens belonged to
Haplocytheridea everetti and included male and female
forms. The other specimen belonged to Brachycythere cf.
B. ovata. Both of these Late Cretaceous ostracod species
are restricted to the North American Coastal Plain and
indicate relatively shallow marine paleoenvironment
(Puckett, personal communication, 2020).
When the parameters of the paleoecology indicated
by the Arkadelphia Formation otoliths at a family level
are evaluated, they generally indicate a marine environ-
ment no deeper than outer shelf (200 m) and probably
much shallower (0–100 m). Many of the families point to
a normal marine salinity, but there are representatives of
families that could tolerate reduced salinities. The fami-
lies present denote a wide range of climatic preferences
including tropical, subtropical, temperate, subtemper-
ate, and even cold waters. This is extremely unusual,
especially in the Gulf Coastal Plain, and it is believed that
the Late Cretaceous paleogeography and the Western
Interior Seaway were agents for the atypical array of
-
liths. Furthermore, the overall cooling trend of the latest
Friedrich et al. 2005, 2012, Thibault et
al. 2011, Linnert et al. 2014, Hassan and Nassif, 2018).
Vorhisia vulpes,
Eutawichthys zideki, and Palaeogadus? belli) that make
up almost 94% of the Arkadelphia Formation otolith as-
semblage point to a very shallow marine environment
(possibly inner shelf; less than 20 m) with estuarine and
freshwater input nearby. The high percentage of Vorhisia
30 PaleoBios 40(3) 2023
vulpes is believed to be highly indicative of very shal-
low marine and accompanying estuaries. The relatively
-
ern Interior Seaway and possible cool-water currents
affecting the Gulf Coast prior to the Late Cretaceous, and
most possibly, during the late Maastrichtian as well as
the overall cooling trend of the Maastrichtian.
The paleoenvironmental interpretation of the Arkadel-
phia Formation based on otoliths agrees generally with
other lines of evidence. Pitakpaivan and Hazel (1994)
interpreted the Upper Cretaceous Arkadelphia Forma-
tion in Arkansas to be inner sublittoral zone based
on ostracodes, while it was noted that the ostracodes
pointed to a relatively shallow marine paleoenvironment
(Pucket, personal communication, 2020). Becker et al.
(2006) agreed with the assessment of Pitakpaivan and
Hazel (1994) and noted that a shallow marine setting
ostracodes, and chondrichthyans. Manning (personal
communication, 2020) noted the occurrence of six bony
Lepisosteus sp.,
Hadrodus priscus Leidy (1858), Albulidae indetermi-
nate, Phyllodontidae indeterminate, Enchodus ferox
Leidy (1855), and Xiphactinus audax Leidy (1870). He
marine with indications of estuarine. Furthermore, the
paleoecological parameters suggested by the teleostean
otoliths for the Arkadelphia Formation are in general
agreement with numerous paleogeographic maps for the
Late Cretaceous in central Arkansas including Smith et
al. (1994, map 10), Roberts and Kirschbaum (1995
22); Sampson et al. (2010 2014, Meso-
zoic: NAM_Key-72 Ma_LateK), Scotese (2014, map 17),
Slattery et al. (20152019
and Hoganson et al. (2019
to note that the paleoenvironment for the Arkadelphia
Formation based on otoliths is in agreement with paleo-
geographic maps regardless of an early or late closure of
the Western Interior Seaway. Thus, numerous and diverse
-
cal parameters as demonstrated by the otoliths.
Evolutionary implications of the otolith
assemblage
-
-
tion on teleostean evolution during the terminal portion
of the Late Cretaceous. Other studies such as Huddleston
and Savoie (1983), Stringer (1991), Nolf and Stringer
(1996), Nolf (2013), Stringer (2016b), Schwarzhans and
Stringer (2020a), Stringer et al. (2020), and Stringer and
Schwarzhans (2021) demonstrate the importance of
otoliths in unraveling and understanding the evolution
of the teleosts during the Late Cretaceous in the USA.
The occurrence of fossil otoliths in a wide variety of
paleoenvironments provides an abundance of data for
investigating the origin and geological distribution of
Nolf 1995
analysis in the paleontological record was emphasized by
Friedman and Sallan (2012:707) in a large-scale diversity
patterns study when they stated, “No other vertebrate
assemblage encompasses as much taxonomic richness
and morphological disparity distributed over such as
long geological interval and represented by such a di-
Certainly,
the Arkadelphia Formation otoliths as well as otoliths
from other North American Late Cretaceous studies,
such as the Severn, Ripley, Owl Creek, Kemp Clay, and
Fox Hill formations (Huddleston and Savoie 1983, Nolf
and Stringer 1996, Hoganson et al. 2019, Schwarzhans
and Stringer 2020a, Stringer et al. 2020
value of otoliths in ascertaining the geological range of
history. The otoliths from the Arkadelphia Formation
present an opportunity to catch a glimpse of the bony
extinction event and a baseline for discerning their plight
subsequently.
The most abundant species in the Arkadelphia Forma-
tion based on otoliths is the putative siluriform Vorhisia
vulpes. The species is incredibly abundant (n=1,537) and
represents 72.88% of the total otolith specimens in the
Arkadelphia Formation assemblage. Yet in the overlying
Paleogene Clayton Formation (Danian) in Arkansas, V.
vulpes is completely absent (Schwarzhans and Stringer
2020a). This scenario is repeated in several other Upper
Cretaceous formations in the USA. Huddleston and Savoie
(1983) reported that V. vulpes was the dominant species
(approximately 55% of the total otolith specimens) of the
Upper Cretaceous Severn Formation (Maastrichtian) in
Maryland. Likewise, V. vulpes is not found in any overly-
ing strata. Similar results were obtained in the analysis
Schwarzhans (2021) with V. vulpes present in four of the
recovered. Schwarzhans and Stringer (2020a) noted that
V. vulpes was the most common species in the Kemp Clay
and represented 423 of 1,160 otoliths (34.93%). How-
ever, the species is not found in any overlying Paleogene
strata in Texas. So, evidence indicates that this very
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 31
successful, highly adapted, abundant species becomes
extinct at the end of the Cretaceous. It is interesting to
note that V. vulpes is not known from the Cretaceous
outside of the U.S. (Koken 1891, Schwarzhans 1996,
Schwarzhans 2010, Schwarzhans and Stringer 2020a).
The center of evolution for V. vulpes surely appears to
Late Cretaceous (Frizzell 1965b, Waage 1968, Frizzell
and Koenig 1973, Huddleston and Savoie 1983; Nolf
and Stringer 1996, Hoganson et al. 2019, Schwarzhans
and Stringer 2020a, Stringer et al. 2020, Stringer and
Schwarzhans, 2021).
The abundant and wide distribution in North America
of V. vulpes, a putative member of the order Siluriformes
Nelson et al. 2016), may appear enigmatic
given that Lundberg (1975
in North America from the late Paleocene. However,
-
ing the Cretaceous (Cione and Prasad 2002, Bogan and
Agnolin 2011, Alves et al. 2019). These Late Cretaceous
occurrences all occur in non-marine environments. The
-
plained by differences in skeletal or osteological remains
versus otoliths. In the classic work of Patterson (1993),
he reported that 224 modern families were known as
fossils, and 54 of those were represented exclusively by
otoliths. Nolf (2013) reported the number had increased
to 78. Nolf also noted that for many families that have a
fossil record of both skeletal material and otoliths that the
Nolf 2013,
Lundberg (1975) in North America is based on osteologi-
cal records, while the Cretaceous record is established
on otoliths.
indications regarding modern teleostean groups from the
Arkadelphia Formation is the presence and abundance of
representatives of the Gadiformes. Schwarzhans (2003)
had noted, “Cretaceous gadiforms are not known from
otoliths or skeletons,” which was true at that time. Like-
wise, Kriwet and Hecht (2008) in their investigation of
the oldest skeletal record of a gadiform was a macrourid
from the Eocene of Antarctica. Like several others, they
mentioned the rich and diverse gadiforms known from
otoliths in the North Sea Basin since the Paleocene. Nolf
(2013) in his extensive survey of fossil otoliths does not
indicate any Cretaceous gadiform otoliths. Nelson et al.
(2016) reiterated that the oldest Gadiformes are skeletal
remains of the Paleocene macrourid from Antarctica.
Schwarzhans and Aguilera (2016)
in the Antarctica early Eocene. However, evidence and
ideas on the evolutionary history of the Gadiformes has
changed drastically and rapidly in the last few years.
Schwarzhans and Stringer (2020a) recorded three
gadiform otolith-based species based on 29 specimens
from the Upper Cretaceous (upper Maastrichtian) Kemp
Clay of northeastern Texas. They noted that a form from
the Upper Cretaceous Fox Hills Formation in North
Dakota reported by Hoganson et al. (2019) as an argen-
tiniform was an undescribed genus of gadiform. These
discoveries led to a re-evaluation of an older study by
Voigt (1926) in the Campanian of northern Germany.
Although the otoliths are poorly preserved (generic iden-
Otolithus. Gadidarum erraticus Voigt (1926) appears to
represent a gadiform otolith. Gadiform otoliths have also
been reported from the Maastrichtian type area (Neth-
erlands, Belgium). Although it is a very small number
-
forms are present with one of them a typical merluccid
(Schwarzhans and Jagt 2021
been reported from the eastern coast of the USA from
the Upper Cretaceous Severn Formation, although only a
small number of specimens (six) were present (Stringer
and Schwarzhans 2021).
The Arkadelphia Formation gadiforms of this study
supply another important piece of evidence in unraveling
the evolution of the Gadiformes. The gadiform otoliths
from the Arkadelphia Formation are the largest number
of specimens (n=160) from any Cretaceous formation
known to date. Two gadiform taxa are present in the
Arkadelphia Formation as well as specimens left in open
nomenclature. Palaeogadus cf. P. weltoni adds to the geo-
graphic distribution of the species, and the presence of a
new species, Palaeogadus? belli provides salient data on
the development of the gadiforms in the Late Cretaceous.
The Arkadelphia Formation gadiforms, along with the
above-mentioned records, provide further evidence of
the presence of this order and clearly indicate speciation
earlier investigations. Equally important and relevant is
the abundance of Palaeogadus? belli in the Arkadelphia
Formation. The 148 specimens of Palaeogadus? belli rep-
resent 7.02% of the total assemblage of 2,109 otoliths.
Thus, it appears that these early gadiforms were not only
prior to the K-Pg extinction.
The gadiforms in the Arkadelphia Formation, the
32 PaleoBios 40(3) 2023
Kemp Clay, and the Severn Formation verify the presence
and geographical distribution of the order in the Late
Cretaceous. However, gadiform otoliths are completely
missing from the Santonian Eutaw Formation (Schwar-
zhans et al. 2018b) of Alabama and from the Campan-
ian Tar Heel Formation of North Carolina (Stringer et
al. 2018) and the Campanian Woodbury Formation
of New Jersey (Stringer et al. 2016). This is especially
evident in the study of the Woodbury Formation in New
Jersey by Stringer et al. (2016). Otolith specimens were
numerous in the investigation of the Woodbury Forma-
tion with 3,555 specimens and were obtained through
bulk sampling. If gadiforms were present during this
interval of the Late Cretaceous, it would seem that they
should have been recovered. Furthermore, New Jersey
was located at a more northern latitude and open to the
Atlantic realm. Both of these factors would have been
conducive to the presence of gadiforms. Yet, no evidence
of gadiforms were found. A paramount consideration
is that the Woodbury Formation is lower to middle
Campanian. Likewise, the Tar Heel Formation is lower
Campanian. If the gadiforms evolved in the late Campan-
ian as proposed by Schwarzhans and Stringer (2020a)
based on two specimens reported by Voight (1926), then
the absence of gadiforms may be related to the timing
of their evolutionary development. This premise is also
supported by time-calibrated molecular analysis using 15
fossil taxa that suggested the evolution of the Gadiformes
at approximately 79.5 Ma (Roa-Varón et al. 2021). This
date would indicate that the Gadiformes evolved in the
middle Campanian (Cohen et al. 2013) and would be very
close to the geological age proposed by Schwarzhans and
Stringer (2020a).
As noted by Stringer et al. (2020), the evolution of the
-
especially notable in the genus Eutawichthys. This taxon
E. compressus Schwar-
zhans, Huddleston, and Takeuchi (2018b), E. stringeri, E.
maastrichthiensis, E. zideki, and E. choctawae Stringer and
Schwarzhans (2020) during the Late Cretaceous in North
America (Stringer et al. 2016, Schwarzhans et al. 2018b,
Stringer et al. 2018, Schwarzhans and Stringer 2020a,
Stringer et al. 2020). Although E. maastrichthiensis and
E. zideki appear to be replacing E. compressus and E.
stringeri during the Late Cretaceous, E. stringeri is pres-
ent in the Arkadelphia Formation, but its abundance is
much less than E. zideki. Otoliths of E. zideki comprised
13.61% (287 specimens) of the total assemblage in the
Arkadelphia Formation and were second only to Vorhisia
vulpes in abundance. The genus Eutawichthys was abun-
dant and well represented starting in the Santonian and
extending through the Campanian and Maastrichtian.
However, this diverse beryciform genus became extinct
at the K-Pg boundary and appears to be replaced by
perciformes in the Paleogene.
One of the most spectacular and striking otolith mor-
phologies to evolve in the Late Cretaceous was Tippaha
mythica, which is present in the Arkadelphia Formation.
The otolith morphology of this species is not comparable
placed in the order Holocentriformes by Stringer et al.
(2020
as an ophidiid by Nolf and Stringer (1996). Some of the
more distinctive morphological features of this species
unusual shape of the sagitta, the pseudobiostial sulcus
-
ventral of the sagitta. As noted by Stringer et al. (2020),
one of the most distinguishing features is the fading of
the dorsal margin of the anterior section of the cauda
towards the dorsal depression, which is also known in
the extant Myripristidae. This feature connects to an
Popper
1977). The extant Myripristis Cuvier (1829) possesses
an enhanced auditory ability for very high sound fre-
quencies (Coombs and Popper 1979). This feature and
a connection of the otic capsule to the swim bladder.
This arrangement has also been noted in the otoliths of
extant morids (Deng et al. 2011). The basis of the tenta-
tive taxonomic assignment of this species by Stringer
et al. (2020) was its resemblance to extant myripristid
skeletons from the Late Cretaceous (Patterson 1964),
and holocentriform otoliths from the Maastrichtian of
Germany (Schwarzhans 2010). This species with its
impressive otolith morphology and possible heighten
auditory capabilities became extinct at the K-Pg event
(Schwarzhans and Stringer 2020a).
Although the Upper Cretaceous Ripley Formation, Owl
Creek Formation, Kemp Clay, and Severn otolith assem-
blages included very limited, possible representatives of
the order Perciformes (Schwarzhans and Stringer 2020a,
Stringer et al. 2020, Stringer and Schwarzhans 2021),
no perciformes were represented in the Arkadelphia
Formation. Possible perciform taxa in the Ripley and
Owl Creek formations were Pempheris? huddlestoni (Nolf
and Stringer, 1996) and Serranus? severnensis (Nolf and
Stringer, 1996) while Serranus? caribbaeus (Nolf and
STRINGER & SLOAN—LATE CRETACEOUS OTOLITHS FROM ARKANSAS, USA PaleoBios 40(3) 2023 33
Dockery, 1990) was present in the Kemp Clay. However,
S.? severnensis was tentatively allocated to the fossil
genus Holocentronotus in the Holocentridae by Stringer
and Schwarzhans (2021). Although perciform otoliths
represented only a very small percentage of the assem-
blages in these formations, they do provide evidence of
the early percomorph lineage development. The lack of
perciforms in the Arkadelphia Formation otolith assem-
blage does not appear to be related to the paleoenviron-
ment since several of the other formations have similar
paleoenvironmental conditions. It also does not seem to
be related to the geologic age of the Arkadelphia Forma-
tion since it is the same age as other formations that have
putative perciforms in their assemblage. For the present,
the complete absence of perciforms in the 2,109 otolith
specimens of the Arkadelphia Formation may attest to
the rarity of the perciforms in the Late Cretaceous.
CONCLUSIONS
Although unexpected, the opportune and propitious
Arkadelphia Formation (Cretaceous, upper Maastrich-
tian) has provided an abundant array of information. The
Mesozoic of Arkansas and represent one of the largest
assemblages from a single site in the Gulf Coastal Plain.
The otolith assemblage diversity is characterized by a
richness of 19 unequivocal taxa and a pronounced un-
evenness with one species (Vorhisia vulpes) accounting
for 72.88% of the total specimens. The number of species
the Arkadelphia Formation from 6 to 28 taxa (a very
-
forms and their percentage (7.59% of the assemblage)
in the Arkadelphia Formation are distinctive and rare
for the Gulf Coastal Plain. The gadiforms are associated
-
ography and the Western Interior Seaway. The otoliths
-
cantly more closely related to the Kemp Clay Formation
(Texas), the Fox Hills Formation (North Dakota), and the
Severn Formation (Maryland) than to Upper Cretaceous
formations in the central Gulf Coastal Plain (Mississippi)
based on percentage similarity measurements. The
Arkadelphia Formation otolith assemblage was placed
in the WIS Community proposed by Schwarzhans and
Stringer (2020a) based on a number of correlative char-
acteristics. A fairly large component of the Arkadelphia
Formation otolith assemblage becomes extinct at the
K-Pg boundary event. An analysis of the otoliths based
on families and species indicates a very shallow marine
environment (possibly inner shelf; less than 20 m) with
estuarine and freshwater input nearby. The interpreted
paleoenvironment of the Arkadelphia Formation agrees
well with other fossil groups, especially microfossils, and
generally with paleogeographic maps. However, the Arka-
delphia Formation paleoenvironment may necessitate
some revisions to the paleogeography for the southern
portions of the Western Interior Seaway.
ACKNOWLEDGEMENTS
Special thanks are extended to the drill crew (D.
Thornton, D. McCollum, T. Frazier, A. Dillman, S. Bates)
DOT for allow-
ing the analysis of the drill core samples. K.A. Johnson
(National Marine Fisheries Service, Southeast Fisheries
Science Center, Pascagoula, MS), R. Taylor (formerly of
the Florida Fish and Wildlife Conservation Commission,
Fish and Wildlife Research Institute, St. Petersburg, FL),
and J.R. Hendon (Center for Fisheries Research and De-
velopment, Gulf Coast Research Laboratory, University
of Southern Mississippi, Ocean Springs, MS) generously
Royal des Sciences Naturelles de Belgique, Brussels, Bel-
gium) also supplied extant and fossil otolith specimens.
W. Schwarzhans (Natural History Museum of Denmark,
Zoological Museum, Copenhagen, Denmark) made valu-
able suggestions regarding the identity and taxonomy of
-
logical remains from the Arkadelphia Formation. Karen
Morton, Collections Manager, and R.S. Tykoski, Director
of Paleontology and Curator of Vertebrate Paleontology,
both of the Perot Museum of Nature and Science, Dallas,
Texas, were especially helpful in the repositing of the
otolith specimens at their institution. D. Bell graciously
provided expertise and assistance in the development of
Appreciation is extended to J. Ebersole (Director of Col-
lections, McWane Science Center, Birmingham, Alabama)
and an anonymous reviewer for their detailed and helpful
review of the manuscript. A special word of thanks to D.M.
Erwin (Senior Museum Scientist, University of California
Berkeley, Museum of Paleontology, Berkeley, California)
for her assistance.
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