Late Cretaceous non-avian dinosaurs from the James Ross Basin, Antarctica: description of new material, updated synthesis, biostratigraphy, and paleobiogeography

Abstract

Although the fossil record of non-avian dinosaurs from the Cretaceous of Antarctica is the poorest of any continent, fossils representing at least five major taxonomic groups (Ankylosauria, early-diverging Ornithopoda, Hadrosauridae, Titanosauria, and Theropoda) have been recovered. All come from Upper Cretaceous (Coniacian–Maastrichtian) marine and nearshore deposits belonging to the Gustav and Marambio groups of the James Ross Basin at the northern tip of the Antarctic Peninsula. The majority of these finds have come from the Campanian–Maastrichtian Snow Hill Island and López de Bertodano formations of James Ross and Vega islands. Given the rarity of Antarctic Cretaceous non-avian dinosaurs, discoveries of any fossils of these archosaurs, no matter how meager, are of significance. Here we describe fragmentary new ornithischian (ankylosaur and ornithopod) material from the upper Campanian–lower Maastrichtian Cape Lamb Member of the Snow Hill Island Formation and the Maastrichtian Sandwich Bluff Member of the López de Bertodano Formation. One of these specimens is considered to probably pertain to the holotypic individual of the early-diverging ornithopod Morrosaurus antarcticus. We also provide an up-to-date synthesis of the Late Cretaceous non-avian dinosaur record of the James Ross Basin and analyze the biostratigraphic occurrences of the various finds, demonstrating that most (including all named taxa and all reasonably complete skeletons discovered to date) occur within a relatively condensed temporal interval of the late Campanian to early Maastrichtian. Most or all James Ross Basin dinosaurs share close affinities with penecontemporaneous taxa from Patagonia, indicating that at least some continental vertebrates could disperse between southern South America and Antarctica during the final stages of the Mesozoic.

Full text

• Review • Advances in Polar Science
doi: 10.13679/j.advps.2019.0007 September 2019 Vol. 30 No. 3: 228-250
www.aps-polar.org
Late Cretaceous non-avian dinosaurs from the James Ross
Basin, Antarctica: description of new material, updated
synthesis, biostratigraphy, and paleobiogeography
Matthew C. LAMANNA1, Judd A. CASE2, Eric M. ROBERTS3, Victoria M.
ARBOUR4, Ricardo C. ELY5, Steven W. SALISBURY6, Julia A. CLARKE7,
D. Edward MALINZAK8, Abagael R. WEST9 & Patrick M. O’CONNOR10,11
1 Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh,
Pennsylvania 15213, USA;
2 Department of Biology, Eastern Washington University, Science Building 258, Cheney, Washington 99004, USA;
3 College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia;
4 Royal British Columbia Museum, 675 Belleville Street, Victoria, British Columbia V8W 9W2, Canada;
5 Department of Earth and Atmospheric Sciences, Indiana University, Geological Sciences Building, 1001 East 10th Street,
Bloomington, Indiana 47401, USA;
6 School of Biological Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia;
7 Department of Geological Sciences, The University of Texas at Austin, 2275 Speedway Stop C9000, Austin, Texas
78712, USA;
8 School of Natural Sciences, Black Hills State University, 1200 University Street, Spearfish, South Dakota 57799, USA;
9 Department of Biological Sciences, University of Pittsburgh, 4249 Fifth Avenue, Pittsburgh, Pennsylvania 15260, USA;
10 Department of Biomedical Sciences, Ohio University Heritage College of Osteopathic Medicine, 119 Life Sciences
Building, Athens, Ohio 45701, USA;
11 Ohio Center for Ecology and Evolutionary Studies, Ohio University, Irvine Hall, Athens, Ohio 45701, USA
Received 8 March 2019; accepted 22 May 2019; published online 13 August 2019
Abstract Although the fossil record of non-avian dinosaurs from the Cretaceous of Antarctica is the poorest of any continent,
fossils representing at least five major taxonomic groups (Ankylosauria, early-diverging Ornithopoda, Hadrosauridae,
Titanosauria, and Theropoda) have been recovered. All come from Upper Cretaceous (Coniacian–Maastrichtian) marine and
nearshore deposits belonging to the Gustav and Marambio groups of the James Ross Basin at the northern tip of the Antarctic
Peninsula. The majority of these finds have come from the Campanian–Maastrichtian Snow Hill Island and López de Bertodano
formations of James Ross and Vega islands. Given the rarity of Antarctic Cretaceous non-avian dinosaurs, discoveries of any
fossils of these archosaurs, no matter how meager, are of significance. Here we describe fragmentary new ornithischian
(ankylosaur and ornithopod) material from the upper Campanian–lower Maastrichtian Cape Lamb Member of the Snow Hill
Island Formation and the Maastrichtian Sandwich Bluff Member of the López de Bertodano Formation. One of these specimens
is considered to probably pertain to the holotypic individual of the early-diverging ornithopod Morrosaurus antarcticus. We also
provide an up-to-date synthesis of the Late Cretaceous non-avian dinosaur record of the James Ross Basin and analyze the
biostratigraphic occurrences of the various finds, demonstrating that most (including all named taxa and all reasonably complete
skeletons discovered to date) occur within a relatively condensed temporal interval of the late Campanian to early Maastrichtian.
Most or all James Ross Basin dinosaurs share close affinities with penecontemporaneous taxa from Patagonia, indicating that at
least some continental vertebrates could disperse between southern South America and Antarctica during the final stages of the
Mesozoic.
*Corresponding author, ORCID: 0000-0001-9845-0728, E-mail: lamannam@carnegiemnh.org

Antarctic Cretaceous dinosaurs 229
Keywords Dinosauria, Antarctica, Cretaceous, James Ross Basin, biostratigraphy, paleobiogeography
Citation: Lamanna M C, Case J A, Roberts E M, et al. Late Cretaceous non-avian dinosaurs from the James Ross Basin, Antarctica:
description of new material, updated synthesis, biostratigraphy, and paleobiogeography. Adv Polar Sci, 2019, 30(3): 228-250,
doi: 10.13679/j.advps.2019.0007
1 Introduction
Over the past half-century, research groups from multiple
nations (e.g., Argentina, Brazil, Chile, Poland, the United
Kingdom, the United States) have explored for Cretaceous
fossil vertebrates in the James Ross Basin (JRB), on a series
of islands adjacent to the northeastern tip of the Antarctic
Peninsula (Figure 1). Although abundant material of fishes,
marine reptiles, and birds has been recovered, fossils of
non-avian dinosaurs remain much rarer, a circumstance that
is almost certainly due to the fact that most or all
fossiliferous strata in the JRB were deposited in marine to
shallow marine settings rather than continental depositional
systems in which these archosaurs would be expected to
have been more common (Reguero et al., 2013a, 2013b;
Roberts et al., 2014).
Nevertheless, the non-avian dinosaur fossils that have
been discovered in the JRB—all of which pertain to the
Upper Cretaceous—collectively indicate the presence of a
diversity of taxa that hold significant biostratigraphic and
paleobiogeographic implications (Figure 1 ，Table 1;
Reguero and Gasparini, 2007; Reguero et al., 2013a, 2013b).
Among the most important discoveries are five associated
partial skeletons: (1) the holotype of the ankylosaur
Antarctopelta oliveroi (Olivero et al., 1986, 1991; Gasparini
et al., 1987, 1996; de Ricqlès et al., 2001; Salgado and
Gasparini, 2004, 2006; Coria et al., 2011; Rozadilla et al.,
2016a); (2) three specimens representing at least two taxa of
small to medium-sized, early-diverging ornithopods: the
holotypes of Morrosaurus antarcticus (Cambiaso et al.,
2002; Novas et al., 2002a; Rozadilla et al., 2016b) and
Trinisaura santamartaensis (Coria et al., 2008, 2013) and a
third, still-undescribed skeleton that may represent one of
these species or potentially a third (Hooker et al., 1991;
Thomson and Hooker, 1991; Milner et al., 1992; Hooker,
2000; Barrett et al., 2014); and (3) a partial skeleton of a
medium-sized non-avian theropod that was recently
designated the holotype of the possible deinonychosaur
Imperobator antarcticus (Case et al., 2007; Ely and Case,
2016, 2019). Two other associated specimens, each
consisting of a handful of fragmentary ornithopod hind limb
elements from the latest Cretaceous of Vega Island, have
also recently been identified (Coria et al., 2015a, 2015b;
MCL pers. obs.).
Beginning in the 1990s, and supported by the United
States (US) National Science Foundation (NSF) and the US
Antarctic Program, paleontological expeditions led or
co-led by one of us (Judd A. Case; hereafter JAC1) have
explored the JRB for fossil vertebrate remains, often in
collaboration with scientists from the Museo de La Plata
and the Instituto Antártico Argentino (IAA). Subsequent
field efforts were organized and completed by the
NSF-funded Antarctic Peninsula Paleontology Project (AP3)
during the austral summers of 2009, 2011, and 2016.
Several of these expeditions recovered fragmentary non-
avian dinosaur skeletal elements that remain undescribed.
Among the most notable of these are the distal end of a
pedal phalanx and multiple unidentified fragments collected
by AP3 researchers in 2011 from an outcrop of the upper
Campanian–lower Maastrichtian Cape Lamb Member of the
Snow Hill Island Formation on the Naze Peninsula of James
Ross Island, at or extremely close to the locality that
yielded the holotypic partial right hind limb of the
ornithopod Morrosaurus (Rozadilla et al., 2016b).
The present contribution has three primary aims: to (1)
fully describe previously undescribed and in some cases
recently recovered ornithischian dinosaur fossils from the
Upper Cretaceous of the JRB, including the probable new
material of Morrosaurus; (2) provide an up-to-date synthesis of
the Upper Cretaceous non-avian dinosaur record of the JRB
and its paleobiogeographic significance; and (3) clarify the
stratigraphic positions of previously described JRB dinosaurs,
with attendant paleoecological implications.
2 Description of new material
2.1 Systematic paleontology
DINOSAURIA Owen, 1842
ORNITHISCHIA Seeley, 1887
THYREOPHORA Nopcsa, 1915
ANKYLOSAURIA Osborn, 1923
?NODOSAURIDAE Marsh, 1890
Referred specimen—SDSM 142814 (field number
S061-9927), an isolated osteoderm (Figure 2).
Locality—Sandwich Bluff (63°51'31" S, 57°34'14"
W), western Vega Island, JRB, Antarctic Peninsula. This
osteoderm was collected during the austral summer of 1999,
from within 2 m laterally of where the hadrosaurid tooth
described by Case et al. (2000a) (MLP 98-I-10-1) was
recovered the year prior (JAC1 pers. obs.).
Horizon and age—‘Reptile Horizon’ (≈ Unit SBM12
of Roberts et al., 2014; JAC1 pers. obs.), Sandwich Bluff
Member, López de Bertodano Formation, Marambio Group.

230 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3
Figure 1 Geographic and stratigraphic context of non-avian dinosaur discoveries from the Cretaceous of Antarctica. a, Map of southern
South America, Drake Passage, and Antarctic Peninsula, with study area (the JRB) indicated by box. b, Map of JRB showing localities that
have produced described non-avian dinosaur material (indicated by silhouettes). Exposures of Cretaceous sediments shown in green
(modified from Riding and Crame, 2002: Figure 1 and Olivero, 2012a: Figure 1). See key for details. c, Paleogeographic reconstruction
(south polar view) at 70 Ma showing approximate position of JRB (indicated by arrow). d, Upper Cretaceous stratigraphy of the JRB
showing units that have produced non-avian dinosaur material (indicated by silhouettes, see key for details). e, Aerial photograph of the
Naze Peninsula from the ~west showing the type localities of the early-diverging ornithopod Morrosaurus antarcticus and the non-avian
theropod Imperobator antarcticus. Silhouettes of Ankylosauria, early-diverging Ornithopoda, Hadrosauridae, and non-avian Theropoda in b
and d courtesy Scott Hartman via PhyloPic.org. Paleogeographic reconstruction in c ©2016 Ronald Blakey, Colorado Plateau Geosystems,
Inc. Geologic time scale in d after Walker et al. (2018). Photograph in e courtesy Philip Currie. Scale equals 50 km in b.

Antarctic Cretaceous dinosaurs 231

232 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3

Antarctic Cretaceous dinosaurs 233
Upper Cretaceous: Maastrichtian (Roberts et al., 2014)
(Note that although Roberts et al. [2014] tentatively equated
the ‘Reptile Horizon’ to their Unit SBM11, it probably
corresponds more closely to their Unit SBM12; JAC1 pers.
obs.).
Description—SDSM 142814 (= S061-9927) is a small
element measuring 3.7 cm long by 2.0 cm wide by 2.8 cm
tall, with an oval base and a pointed keel that overhangs
(i.e., projects beyond) the remainder of what we regard as
the posterior surface. The keel is offset from the midline of
the long axis of the bone and has a rounded rather than a
sharp edge. Moving basally from the apex of the keel, the
surfaces on either side of the keel are flat rather than
concave. The basal surface of the element is generally
convex, except for a large, irregularly-shaped excavation
towards the end opposite the overhanging keel. The bone
surface is weathered but appears to initially have been
lightly pitted with a somewhat reticular surface texture.
The surface texture and shape of this bone suggest that
it is best interpreted as an ankylosaur osteoderm.
Osteoderms of this size in other ankylosaurs often have
fewer distinctive features compared to larger osteoderms
(e.g., Ford, 2000; Kilbourne and Carpenter, 2005; Ősi, 2005;
Kirkland et al., 2013; Kinneer et al., 2016). Ankylosaurine
osteoderms are typically deeply excavated on the basal
surface, and as such even very large osteoderms tend to be
quite thin; nodosaurid osteoderms can be excavated basally,
but osteoderms with unexcavated and even convex bases are
not uncommon (Burns and Currie, 2014). The relatively tall
keel relative to basal width is less common for osteoderms of
this size, which are often flat or with low but sharply defined
keels. A few osteoderms associated with the holotype of
Antarctopelta oliveroi (MLP 86-X-28-1) are close to the
morphology of SDSM 142814, but typically have sharper
keel edges or lack overhanging keels (VMA pers. obs.).
Several of the osteoderms of an as-yet unnamed Argentinean
nodosaurid (MPCA-Pv 41–43, 75–76) share with SDSM
142814 the presence of tall, relatively blunt keels, but none
are backswept or overhang the base (Coria and Salgado, 2001;
Arbour and Currie, 2016; VMA pers. obs.). In Antarctopelta
and the Argentinean taxon, as in SDSM 142814, the
osteoderms are lightly pitted with reticulate surface textures,
and the basal surfaces can possess large, deep, circular pits.
SDSM 142814 cannot be referred to a particular
ankylosaurian genus, but it is most likely a nodosaurid
osteoderm and its morphology and surface texture are
consistent with those of other Late Cretaceous Gondwanan
nodosaurids. Its small size and keeled morphology suggest
that it may have originated from the anterior thoracic region
or the forelimbs (e.g., Kinneer et al., 2016).
Figure 2 Photos (left) and interpretive line drawings (right) of ankylosaurian osteoderm (SDSM 142814) from the Upper Cretaceous
(Maastrichtian) Sandwich Bluff Member of the López de Bertodano Formation of Vega Island in (a) ?lateral; (b) ?anterior; (c) ?medial;
(d) ?posterior; (e), apical; and (f) basal views. Hatching indicates damaged surface. Abbreviations: be, basal excavation; k, keel; ok,
‘overhang’ of keel.
ORNITHISCHIA Seeley, 1887
NEORNITHISCHIA Cooper, 1985
ORNITHOPODA Marsh, 1881
Referred specimen—MLP 98-I-10-70, an isolated
pedal ungual (perhaps from the right digit IV) (Figure 3).
Locality—Sandwich Bluff (63°51'31" S, 57°34'14"
W), western Vega Island, JRB, Antarctic Peninsula.
Horizon and age—‘Reptile Horizon’ (≈ Unit SBM12

234 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3
of Roberts et al., 2014), Sandwich Bluff Member, López de
Bertodano Formation, Marambio Group. Upper Cretaceous:
Maastrichtian (Roberts et al., 2014).
Description—Specimen MLP 98-I-10-70 is a small
element that was discovered in 1998 by a joint Argentine-
American expedition funded by NSF and the IAA.
Comparison of the bone to the nearly complete pedes of a
specimen of the early-diverging iguanodontian ornithopod
Dryosaurus altus (CM 21786) suggests that this Antarctic
ungual may represent that of right pedal digit IV of a
similarly-sized ornithopod individual (MCL pers. obs.), and
it is herein described as such. MLP 98-I-10-70 is
subtriangular in dorsal and ventral (= plantar) views and
incomplete distally. As seen in proximal view (Figure 3c), it
is dorsally strongly convex and ventrally gently concave,
substantially wider ventrally than dorsally, and
asymmetrical, with its dorsal apex being slightly displaced
toward the presumed medial side and the medial margin
sloping more steeply than the lateral. The proximal articular
surface is divided by a low, rounded ridge into lateral and
medial articular facets, with the latter being marginally
wider than the former. Dorsally, this ridge merges with a
blunt tuberosity that is subtriangular in dorsal view and that
projects further proximally than the remainder of the
proximodorsal region of the bone (Figure 3d).
As observed in dorsal view (Figure 3d), the medial
facet of the proximal articular surface is more concave than
the lateral. The proximal ~one-third of the medial side of
the ungual meets the proximal articular surface at an
approximate right angle, but the remainder of this side is
angled laterally. The lateral side displays a comparable
morphology in dorsal view, but the curvature (in this case,
medially) begins more proximally and is more gradual than
that of the medial side.
When viewed medially (Figure 3b), the ventral margin
of the ungual is flat through roughly its proximal one-third,
but becomes gently angled dorsally more distally. The ventral
margin of the lateral side is mostly flat (Figure 3a). In both
lateral and medial views, the dorsal margin of the ungual is
mildly sinuous in contour, with a flat proximal ~one-third, a
distoventrally angled middle third, and a flatter distal third. The
lateral side of the bone is marked by a shallow vascular groove
(Figure 3a). Ventrally, a wide fossa embays nearly the entire
length of the ungual except for the flatter distal end (Figure 3e).
This fossa is deepest near the proximodistal midline of the
bone and bordered by broad lateral and medial ridges.
Figure 3 Ornithopod pedal ungual (MLP 98-I-10-70) from the Upper Cretaceous (Maastrichtian) Sandwich Bluff Member of the López
de Bertodano Formation of Vega Island in (a) ?lateral; (b) ?medial; (c) proximal; (d) dorsal; and (e) ventral views. Abbreviations: lf?,
lateral facet; mf?, medial facet; vg, vascular groove.

Antarctic Cretaceous dinosaurs 235
If, as it would appear, MLP 98-I-10-70 is a pedal
element of a non-hadrosaurid ornithopod, it would, along
with a partial distal hind limb currently under study (JAC1
pers. obs.), constitute the first record of these animals from
the Maastrichtian Sandwich Bluff Member of the López de
Bertodano Formation, and therefore the stratigraphically
youngest occurrence of these dinosaurs in Antarctica and
among the youngest in the world.
?ELASMARIA Calvo, Porfiri, and Novas, 2007
Morrosaurus antarcticus Rozadilla, Agnolín, Novas,
Aranciaga Rolando, Motta, Lirio, and Isasi, 2016
Referred specimen—AMNH FARB 30897, the distal
end of a ?right pedal phalanx (Figure 4) and seven
associated but unidentified fragments. Because all elements
assigned specimen number AMNH FARB 30897 were
surface-collected (i.e., not recovered in situ), some of these
fragments may potentially pertain to other vertebrates, such
as marine reptiles.
Locality—North of Fortress Hill, central part of the
northwestern shore of the Naze Peninsula, northern James
Ross Island, JRB, Antarctic Peninsula (63°55'41" S,
57°30'18" W). Note that Rozadilla et al. (2016b) reported
the coordinates of the locality that yielded the Morrosaurus
type specimen (MACN Pv 19777; Figure 4a–4g) as
63°55'40" S, 57°30'15" W, approximately 55 m from the
recorded recovery site of AMNH FARB 30897. However, it
remains uncertain whether either set of coordinates was
taken at the precise site(s) from which bones were collected,
either in early 1998 by Argentine researchers (J. M. Lirio of
the IAA and M. Isasi of the MACN) upon the discovery of
MACN Pv 19777 (Novas pers. comm.) or in February 2011
by the AP3 scientists who recovered AMNH FARB 30897
(Julia A. Clarke [hereafter JAC2] and J. Meng). Moreover,
as noted above, elements comprising AMNH FARB 30897
were surface-collected and as such had likely undergone
some degree of transport from their original burial
location(s) by modern weathering processes. As such, we
regard the site that yielded AMNH FARB 30897 as
probably the same as the Morrosaurus type locality.
Horizon and age—Cape Lamb Member, Snow Hill
Island Formation, Marambio Group (Rozadilla et al.,
2016b). Upper Cretaceous: upper Campanian–lower
Maastrichtian.
Description—Bones recovered from the probable
Morrosaurus site in 2011 include the distal end of a ?right
pedal phalanx (Figure 4h–4m) and several weathered
fragments. One side of the phalanx (the lateral, if this bone
is correctly interpreted as being from the right side) exhibits
a collateral ligament pit, and the hemicondyle on this side is
complete, measuring 2.3 cm in dorsoventral (= dorsoplantar)
height. The other hemicondyle (presumably the medial) is
incomplete but appears to have been dorsoventrally larger
than the presumed lateral condyle; also, the smooth surface
that would have articulated with a more distal phalanx
extends further proximally on the medial side. Although
incomplete, the distal end of the phalanx was clearly wider
along the ventral margin than the dorsal margin. The
interior of the bone is filled with sedimentary matrix,
although it is unclear if this reflects its actual anatomy (e.g.,
that the phalanx was hollow in life) rather than a
taphonomic or preservational artifact (Figure 4j).
Non-avian dinosaur fossils are extraordinarily rare in
the Cape Lamb Member; moreover, all known occurrences
have consisted of isolated partial skeletons or skeletal
elements that presumably were transported into this marine
depositional setting (Reguero and Gasparini, 2007; Reguero
et al., 2013a, 2013b). The Morrosaurus holotype (MACN
Pv 19777) includes only a single pedal phalanx (right
phalanx III-1) that is missing its distal end (Rozadilla et al.,
2016b; Figure 4b–4g). Like that of the AMNH FARB 30897
phalanx, the interior of the MACN Pv 19777 phalanx III-1
is filled with matrix, suggesting that it too may have
originally been hollow (MCL pers. obs.; Figure 4e).
Moreover, the two pedal phalanges are virtually identical in
other preservational aspects as well; for instance, both are
bluish-white in color, as is typical of dinosaur bone that has
weathered from the Cape Lamb Member (MCL pers. obs.).
However, although it seems conceivable that the AMNH
FARB 30897 phalanx could be the distal end of the phalanx
preserved in the Morrosaurus holotype (i.e., that of right
phalanx III-1), the two pieces seem slightly incompatible in
size, with the new element being marginally smaller than
what might be expected (based on the pedal phalangeal
proportions of other early-diverging ornithopod specimens;
e.g., Dryosaurus altus CM 21786; Galton, 1981; MCL pers.
obs.) for the distal end of phalanx III-1 of MACN Pv 19777.
As such, the AMNH FARB 30897 phalanx may represent a
pedal element that was previously unknown for
Morrosaurus (perhaps right phalanx II-1 based on
comparison with CM 21786; MCL pers. obs.).
In sum, given its closely congruent or identical
geographic and stratigraphic provenance, as well as its
morphological consistency and lack of anatomical overlap
with the type specimen, we hypothesize that the distal pedal
phalanx of AMNH FARB 30897 probably pertains to the
same Morrosaurus individual. As such, the new specimen
may augment the preserved morphology of one of the few
non-avian dinosaur taxa yet discovered from the Upper
Cretaceous of Antarctica.
3 Synthesis of JRB dinosaur record
Although all non-avian dinosaur specimens from the JRB are
fragmentary, they are collectively of extraordinary
significance in constituting the only known record of these
animals from the Cretaceous of Antarctica. Moreover, the
JRB dinosaur record currently indicates the presence of at
least five major taxonomic groups in the Late Cretaceous of
the continent: Ankylosauria, early-diverging Ornithopoda
(Elasmaria?), Hadrosauridae, Titanosauria, and non-avian
Theropoda, with associated partial skeletons being known for
several taxa within these groups (primarily ornithischians)

236 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3
Figure 4 Pedal bones of the early-diverging (elasmarian?) ornithopod Morrosaurus antarcticus from the upper Campanian–lower
Maastrichtian Cape Lamb Member of the Snow Hill Island Formation of James Ross Island. a, Right metatarsus of the holotype (MACN
Pv 19777) in dorsal (= anterior) view. b–g, Right pedal phalanx III-1 of MACN Pv 19777 in (b) dorsal, (c) ventral (= plantar), (d) proximal,
(e) distal, (f) lateral, and (g) medial views. h–m, Distal end of ?right pedal phalanx (AMNH FARB 30897) recovered from the Morrosaurus
type locality or a very nearby site by the 2011 AP3 expedition in (h) dorsal, (i) ventral (= plantar), (j) proximal, (k) distal, (l) ?lateral, and
(m) ?medial views. Given its identical or near-identical provenance and lack of anatomical overlap with MACN Pv 19777, the AMNH
FARB 30897 phalanx probably pertains to the same Morrosaurus individual. Scale equals 5 cm in a, 1 cm in b–m. Abbreviations: clp,
collateral ligament pit; lc?, lateral hemicondyle; m, matrix-filled cavity; mc?, medial hemicondyle?.
(Figures 1, 5; Table 1). The highly incomplete nature of most
specimens hinders definitive assessments of their
phylogenetic affinities; nevertheless, most or all non-avian
dinosaurs thus far recorded from the JRB appear closely
related to penecontemporaneous taxa from southern South
America. It should be noted that the fossil record of avian
dinosaurs (birds) from the basin—both from the Cretaceous
and the overlying Paleogene deposits—is generally much
richer than that of their non-avian cousins (e.g., Chatterjee,
2002; Clarke et al., 2005, 2016; Acosta Hospitaleche and
Gelfo, 2015), but an overview of the avian record is beyond
the scope of the present contribution.
Most non-avian dinosaur occurrences from the JRB
consist of skeletal remains; however, there is one possible
record of dinosaurian trace fossils as well. Olivero et al.
(2007) reported poorly preserved putative non-avian
dinosaur footprints from a lower Maastrichtian exposure of
the López de Bertodano Formation near Tesore Hill on
Snow Hill Island (Figure 5a). If confirmed, these tracks
would constitute the first evidence of dinosaurs from that
island as well as the only known dinosaurian trace fossils
from the Cretaceous of Antarctica. Nevertheless, a 2016
reconnaissance of the Tesore Hill area by an AP3 field team
failed to relocate these ostensible tracks and as such could
not substantiate this record. It is possible that the structures
in question were covered by snow during the AP3 survey
(Olivero pers. comm.). Reguero et al. (2013a, 2013b)
suggested that these footprints, if authentic, could have been
made by sauropods, and this may be the case for some of
these potential ichnofossils. Nevertheless, Olivero et al.
(2007) also described putative tracks that they attributed to
bipedal animals; if this identification is correct, such ichnites
could not have been produced by any known sauropod taxon.

Antarctic Cretaceous dinosaurs 237
Figure 5 Previously reported non-avian dinosaur material from Upper Cretaceous strata of the JRB, Antarctic Peninsula. a, Putative
footprints (adjacent to scale bar) from a lower Maastrichtian horizon of the López de Bertodano Formation of the Tesore Hill region of
Snow Hill Island. b, Left dentary fragment of the holotype of the ankylosaur Antarctopelta oliveroi (MLP 86-X-28-1) from the upper
Campanian Gamma Member of the Snow Hill Island Formation of the Santa Marta Cove area of James Ross Island in medial view. c,
Block of caudal vertebrae (c1), left pelvic elements (c2), and scapulocoracoids (c3) of the holotype of the small-bodied basal ornithopod
(elasmarian?) Trinisaura santamartaensis (MLP 08-III-1-1) from the upper Campanian Gamma Member of the Snow Hill Island Formation
of the Santa Marta Cove area of James Ross Island primarily in lateral view (some caudal vertebrae in other views). d, Distal tarsal and
nearly complete metatarsus of the holotype of the medium-sized basal ornithopod (elasmarian?) Morrosaurus antarcticus (MACN Pv
19777) from the upper Campanian–lower Maastrichtian Cape Lamb Member of the Snow Hill Island Formation of the Naze Peninsula of
James Ross Island in posterior (= ventral, plantar) view. e, Partial right dentary with in situ teeth of an undescribed medium-sized basal
ornithopod (elasmarian?) skeleton (NHMUK PV R 36760 [formerly BMNH BAS R.2450]; the ‘BAS ornithopod’) from a lower
Maastrichtian horizon of the Cape Lamb Member of the Snow Hill Island Formation of Cape Lamb of Vega Island in lateral view. f, Tooth
crown of hadrosaurid ornithopod (MLP 98-I-10-1) from the Maastrichtian ‘Reptile Horizon’ of the Sandwich Bluff Member of the López
de Bertodano Formation of Sandwich Bluff of Vega Island in labial view. g, Partial caudal centrum of titanosaurian sauropod (MLP
11-II-20-1) from the upper Campanian Gamma Member of the Snow Hill Island Formation of the Santa Marta Cove area of James Ross
Island in right lateral view. h, Reconstructed distal left hind limb of the possible deinonychosaurian theropod Imperobator antarcticus
(UCMP 276000) from the upper Campanian–lower Maastrichtian Cape Lamb Member of the Snow Hill Island Formation of the Naze
Peninsula of James Ross Island in anterior (= dorsal) view. Photo in a courtesy Eduardo Olivero; e and h reproduced from Hooker (2000)
and Case et al. (2007), respectively. Scale in cm in a; scale equals 1 cm in b and f; 5 cm in c–e and h.

238 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3
Roberts et al. (2014: Tables 1, 2, Figure 3, and
elsewhere) reported putative new non-avian dinosaur
fragments from several horizons of the Maastrichtian
Sandwich Bluff Member of the López de Bertodano
Formation of Vega Island (their units SBM6–7, 12, and 15)
collected by an AP3 expedition in 2011. Nevertheless,
recent reexamination of these specimens by one of us (MCL)
indicates that none are definitively referable to non-avian
Dinosauria. Several (AMNH FARB 30891 [from Unit
SBM15], 30892 [SBM6–7], and 30896 [SBM12, ≈ the
‘Reptile Horizon’ of, e.g., Case et al., 2000a]) appear to be
fragments of avian limb elements, two of which (AMNH
FARB 30892 and 30896) are suggestive of large-bodied
taxa comparable in size to that represented by the isolated
bird femur SDSM 78247, which is also from the Sandwich
Bluff Member (Case et al., 2006; MCL pers. obs.). Another
bone, a dorsal rib shaft approximately 7–8 cm in
proximodistal length and 1 cm in anteroposterior breadth
from Unit SBM15 (AMNH FARB 30895), is reminiscent of
theropod ribs in having a hollow interior; nevertheless, its
thick outer cortex and subcircular distal cross section seem
more consistent with a marine reptile. Although hollow ribs
would be unusual for a marine reptile, they have been
reported in at least one plesiosaur from elsewhere in the
Upper Cretaceous of southern Gondwana, specifically in an
indeterminate elasmosaurid from the Campanian–
Maastrichtian Takatika Grit of the Chatham Islands, New
Zealand (OU22344; Consoli and Stilwell, 2009). Other
material catalogued as AMNH FARB 30896 (in addition to
the ?avian limb fragment mentioned above) may also
belong to marine reptiles (e.g., one bone bearing this
number appears to be a plesiosaur paddle element).
3.1 Ornithischia
Ornithischians are the most abundantly represented
non-avian dinosaurs in the JRB, both in terms of numbers
of individual specimens as well as in associated skeletons.
One of these skeletons constitutes the holotype of the
taxonomically contentious ankylosaur Antarctopelta
oliveroi (MLP 86-X-28-1; Olivero et al., 1986, 1991;
Gasparini et al., 1987, 1996; de Ricqlès et al., 2001;
Salgado and Gasparini, 2004, 2006; Coria et al., 2011;
Rozadilla et al., 2016a). Recovered from the upper
Campanian Gamma Member (approximately equivalent to
the Herbert Sound Member of Crame et al., 1991) of the
Snow Hill Island Formation (which was formerly assigned
to the Santa Marta Formation; Olivero, 2012a) of the Santa
Marta Cove area of James Ross Island, the Antarctopelta
holotype initially consisted of fragmentary cranial bones, a
partial dentary with an in situ tooth (Figure 5b), three other
teeth, two disarticulated cervical vertebrae and a cast of a
natural mold of three additional, articulated cervicals, two
dorsal vertebral centra, dorsal rib fragments, the partial
sacrum, eight incomplete caudal vertebrae, fragments of the
scapula, coracoid, ilium, and femur, five metapodials, two
phalanges, and a collection of osteoderms comprising six
distinct morphotypes (Salgado and Gasparini, 2006; Otero
and Reguero, 2013; Poropat pers. comm.). Subsequently,
Coria et al. (2011) reported the rediscovery of the type
locality of this ankylosaur and the recovery of additional
material that they regarded as pertaining to the holotypic
individual, including a possible maxilla fragment, maxillary
and dentary teeth, vertebral centra, the proximal end of a
metatarsal, three nonungual phalanges, an incomplete
ungual, and additional osteoderms.
Though the elements reported by Coria et al. (2011)
have yet to be described in detail, they hold some promise
for resolving the taxonomic controversies surrounding
Antarctopelta. First, the validity of this taxon has recently
been questioned. Arbour and Currie (2016) argued that the
holotype is a chimera that also includes vertebrae of
plesiosaurs and mosasaurs, and that the elements that are
definitively ankylosaurian exhibit no diagnostic features; as
such, these authors regarded Antarctopelta as a nomen
dubium. Shortly thereafter, however, in an abstract,
Rozadilla et al. (2016a) contended that the putative marine
reptile elements were in fact ankylosaurian caudal vertebrae,
as had originally been claimed by previous authors (e.g.,
Salgado and Gasparini, 2006). According to Rozadilla et al.
(2016a), the posterior caudals of Antarctopelta possess well
developed, anteroposteriorly expanded transverse processes,
a character that these authors regarded as a possible
autapomorphy of this taxon, thereby potentially supporting
its validity.
Second, regardless of whether Antarctopelta may be
valid, different workers have claimed widely varying
systematic positions for the material within Ankylosauria.
Whereas Salgado and Gasparini (2006) and Rozadilla et al.
(2016a) have argued that the form displays a mosaic of
traits typically associated with Ankylosauridae and
Nodosauridae, respectively, thus suggesting an early-
diverging position within Ankylosauria, the recent
phylogenetic analyses of Thompson et al. (2012) and
Arbour and Currie (2016) have postulated Antarctopelta as
a member of Nodosauridae. In particular, Arbour and
Currie’s (2016) analysis (which only incorporated the
fossils of Antarctopelta that these authors regarded as
definitively ankylosaurian) positioned this ankylosaur as
deeply nested within the latter group, in a clade otherwise
comprised of an unnamed Patagonian nodosaurid and
several North American taxa. If substantiated, this
phylogenetic position would support the hypothesis,
advanced by Coria and Salgado (2001), that the Patagonian
taxon and Antarctopelta were ultimately descended from
Laurasian nodosaurids. Along with the occurrence of a
hadrosaurid tooth in the Maastrichtian Sandwich Bluff
Member of the López de Bertodano Formation of the JRB
(MLP 98-I-10-1; see below), this could support the
existence of a North America–South America–Antarctica
dispersal route for non-avian dinosaurs during the Late
Cretaceous. This, in turn, would reinforce the longstanding

Antarctic Cretaceous dinosaurs 239
hypothesis of a paleobiogeographic connection between
South America and Antarctica at the close of the Mesozoic
(e.g., Case et al., 2000a; Reguero and Gasparini, 2007;
Reguero et al., 2013a, 2013b). Given that Antarctopelta
antedates MLP 98-I-10-1 by a few (roughly four or five?)
million years, this might indicate that the South
America–Antarctica route was operative earlier than is
evidenced by that hadrosaurid fossil. This would be
consistent with paleobotanical data that suggest that
southern South America and the Antarctic Peninsula had a
shared flora by the late Campanian or early Maastrichtian;
indeed, a biotic connection between these land areas is
hypothesized to have been established as early as the
Turonian (Cantrill and Poole, 2012; Leppe et al., 2012).
The only other ankylosaurian material known from the
Antarctic Cretaceous is the possible nodosaurid osteoderm
described above (SDSM 142814; Figure 2). Because this
bone was collected from an upper level (the ‘Reptile
Figure 6 Biostratigraphy of non-avian dinosaurs from the Upper Cretaceous (upper Campanian–Maastrichtian) Snow Hill Island and
López de Bertodano formations in the Herbert Sound region of James Ross and Vega islands, JRB, Antarctic Peninsula. a, Map of the
Herbert Sound region showing selected non-avian dinosaur localities on Vega and northern James Ross islands (the Naze Peninsula and
Santa Marta Cove of James Ross Island and Cape Lamb/Sandwich Bluff of Vega Island). b, Simplified stratigraphic section at the Naze
Peninsula, showing positions of the holotypic specimens of the early-diverging ornithopod Morrosaurus antarcticus and the non-avian
theropod Imperobator antarcticus, respectively (stratigraphic sequence summarized from di Pasquo and Martin [2013], with position of
Imperobator after that work and that of Morrosaurus after Rozadilla et al. [2016b]). c, Simplified stratigraphic section at Santa Marta Cove,
showing positions of the holotypic specimens of the ankylosaur Antarctopelta oliveroi and the early-diverging ornithopod Trinisaura
santamartaensis and the isolated ?ornithopod unguals and titanosaurian sauropod caudal vertebra, respectively (after Coria et al., 2013 and
Reguero et al., 2013b). d, Simplified stratigraphic section at Cape Lamb/Sandwich Bluff, showing positions of the early-diverging ‘BAS
ornithopod’, the possible theropod pedal phalanx from the same site, and the dinosaur assemblage from the Maastrichtian Sandwich Bluff
Member of the López de Bertodano Formation (stratigraphic sequence summarized from Pirrie et al. [1991] with 87Sr/86Sr datum from
Crame et al. [1999]; positions of ‘BAS ornithopod’ from Hooker et al. [1991] and Pirrie et al. [1991], and Sandwich Bluff dinosaurs from
Case et al. [2000a], respectively). Ammonite biostratigraphy after Pirrie et al. (1991) and Olivero (2012a, 2012b). Approximate location of
the Campanian–Maastrichtian boundary (considered to reside in the zone marked with “?”) in the JRB after Crame et al. (1999, 2004).
Silhouettes of Ankylosauria, early-diverging Ornithopoda, Hadrosauridae, and non-avian Theropoda courtesy Scott Hartman via
PhyloPic.org. Abbreviation: HS, Herbert Sound.

240 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3
Horizon’) of the Maastrichtian Sandwich Bluff Member of
the López de Bertodano Formation—the stratigraphically
highest Cretaceous formation in the JRB—it is notable in
constituting the youngest record of Ankylosauria from
Antarctica, suggesting that these armored ornithischians
persisted into the latest Cretaceous on the continent. It is
also worth noting that, according to the recollection of one
of us (JAC1), a second probable ankylosaur osteoderm was
collected from the same locality and horizon (the ‘Reptile
Horizon’ of Sandwich Bluff) in 1998 (field number
S061-9856), but unfortunately this fossil cannot presently
be located and as such it has been omitted from Table 1.
Early-branching ornithopods—some or all of which
may be referable to the Gondwanan clade Elasmaria (e.g.,
Novas et al., 2004; Calvo et al., 2007; Ibiricu et al., 2010,
2019; Coria et al., 2013; Barrett et al., 2014; Rozadilla and
Novas, 2016; Rozadilla et al., 2016b; Madzia et al., 2018;
Cruzado-Caballero et al., 2019)—are the best-represented
non-avian dinosaurs in the JRB, and by extension, the
Cretaceous of Antarctica. Three partial skeletons belonging
to basal ornithopods have been recovered from the basin to
date. The most ancient and possibly the most complete of
these is the holotype of the small-bodied taxon Trinisaura
santamartaensis (MLP 08-III-1-1), collected from the upper
Campanian Gamma Member of the Snow Hill Island
Formation of the Santa Marta Cove region of James Ross
Island, from a stratigraphic horizon nearly equivalent to that
which yielded the Antarctopelta holotype (MLP 86-X-28-1)
more than two decades prior (Coria et al., 2013: Figure 1c;
Figure 6). Most bones of Trinisaura are well-preserved,
with described material including an incomplete dorsal
vertebra, two partial dorsal ribs, three sacral centra, seven
caudal vertebrae, one anterior hemal arch, the incomplete
right scapulocoracoid and humerus, two metacarpals, both
ilia, the right pubis, ischium, femur, and distal tibia, an
incomplete metatarsal III, a pedal phalanx III-1, two pedal
digit IV phalanges, and indeterminate fragments (Coria et
al., 2013; Figure 5c). The holotype is believed to represent a
subadult, as evidenced by the fusion of the dorsal and
caudal neural arches to their respective centra as well as the
coossification of the right scapula and coracoid;
nevertheless, the unfused sacral centra indicate that the
individual in question was not fully skeletally mature at
death, a conclusion that accords with its small size (~1.5 m
in total body length; Coria et al., 2013). MLP 08-III-1-1
also includes multiple still-undescribed, well-preserved
bones, such as most of the left scapula (including the
complete blade), the left coracoid, and additional vertebrae
(MCL pers. obs.; Figure 5c). The detailed analysis of this
undescribed material will undoubtedly yield additional
insight into the morphology and phylogenetic relationships
of this important Antarctic neornithischian taxon.
Another early-diverging ornithopod, Morrosaurus
antarcticus, is represented by an incomplete right hind limb
collected from an exposure of the upper Campanian–lower
Maastrichtian Cape Lamb Member of the Snow Hill Island
Formation near Fortress Hill in the central part of the Naze
Peninsula of northern James Ross Island (Cambiaso et al.,
2002; Novas et al., 2002a; Rozadilla et al., 2016b). The
holotype (MACN Pv 19777) includes the proximal and
distal ends of the femur and tibia, the proximal end of the
fibula, a distal tarsal, the nearly complete metatarsals II–IV,
and the proximal two-thirds of pedal phalanx III-1
(Rozadilla et al., 2016b; Figures 4a–4g, 5d). As noted above,
the distal end of a pedal phalanx and some associated
fragments recovered by an AP3 expedition in 2011 from
what appears to be the same locality (AMNH FARB 30897;
Figure 4h–4m) probably also belong to this individual.
Taking into account their close correspondence in
stratigraphic and geographic provenance, plus their
probably similar phylogenetic positions (see, for example,
Rozadilla et al., 2016b: Figure 7), it is at least conceivable
that Morrosaurus and Trinisaura could represent the same
ornithopod taxon. Nevertheless, the considerable difference
in body size of the holotypes of the two taxa (with MACN
Pv 19777 representing an individual perhaps 4 m in total
body length, much larger than MLP 08-III-1-1; MCL pers.
obs.) coupled with the morphological differences between
them pointed out by Rozadilla et al. (2016b) (e.g.,
distinctions in the morphology of the lesser trochanter and
extensor groove of the femur) cast doubt on this possibility.
As such, Morrosaurus and Trinisaura are herein regarded as
separate taxa.
The third and potentially the most complete skeleton of
an early-diverging ornithopod yet recovered from the JRB
was also the first to be found. In 1989, an expedition from the
British Antarctic Survey (BAS) discovered a significant part
of a skeleton of a medium-sized ornithopod (NHMUK PV R
36760, formerly BMNH BAS R.2450; ‘Biscoveosaurus’ of
Stilwell and Long, 2011: 110) at a high elevation on Cape
Lamb of western Vega Island, from an outcrop of the Cape
Lamb Member (Hooker et al., 1991; Thomson and Hooker,
1991; Milner et al., 1992; Hooker, 2000; Barrett et al.,
2014). Unlike other JRB ornithopod skeletons, the
specimen consists of both craniodental (e.g., partial
maxillae and braincase, nearly complete dentaries, teeth)
and postcranial elements (e.g., cervical and dorsal vertebrae,
pectoral girdle and forelimb bones) (Hooker et al., 1991;
Hooker, 2000; Barrett et al., 2014) and indicates an
individual estimated at 4–5 m in length (Hooker et al., 1991;
Thomson and Hooker, 1991; Milner et al., 1992). NHMUK
PV R 36760 remains mostly undescribed, and thus far, the
only element to be illustrated in any published work is the
right dentary, shown in a book chapter by Hooker (2000:
190). This dentary (Figure 5e) possesses tooth crowns that
closely resemble those of other Late Cretaceous basal
ornithopods from Southern Hemisphere landmasses (e.g.,
Anabisetia saldiviai, Coria and Calvo, 2002; Kangnasaurus
coetzeei, Cooper, 1985; Talenkauen santacrucensis, Novas
et al., 2004), supporting the hypothesis, advanced by Barrett

Antarctic Cretaceous dinosaurs 241
et al. (2014), that the taxon it represents might be part of an
endemic Gondwanan radiation of early-branching
ornithopods (e.g., Elasmaria).
Interestingly, both the Morrosaurus hind limb (i.e.,
MACN Pv 19777/AMNH FARB 30897) and the skeleton of
the ‘BAS ornithopod’ NHMUK PV R 36760 were collected
from within the same stratigraphic unit, the Cape Lamb
Member of the Snow Hill Island Formation. Indeed, as
discussed below, these two ornithopod specimens come
from a fairly narrow stratigraphic range within the Cape
Lamb Member (Figure 6). Both pertain to basal ornithopods,
possibly elasmarians, and both represent medium-sized
individuals roughly 4 m in total body length. This raises the
possibility that the ‘BAS ornithopod’ could be referable to
Morrosaurus, and if this is indeed the case, it would greatly
augment the hypodigm of that taxon. Regrettably, however,
as NHMUK PV R 36760 does not preserve the hind limb
(Hooker et al., 1991; Barrett et al., 2014), no elements
currently overlap between the two forms, precluding their
direct comparison (but see also below).
Additional ornithopod material from the JRB is mostly
limited to isolated bones. Coria et al. (2007) described two
dissociated ornithischian—possibly ornithopod—pedal
unguals (MLP 07-III-2-1 and MLP 07-III-2-2) from the
Gamma Member of the Santa Marta Cove area of James
Ross Island, while Coria et al. (2015a, 2015b) briefly
reported an associated partial tibia and astragalus from the
Cape Lamb Member on Vega Island (MLP 15-I-7-1). If, as
argued by Coria et al. (2013), the holotype of Trinisaura is
a subadult (i.e., it was nearly skeletally mature at death),
then the comparatively large size of MLP 07-III-2-1 and
MLP 07-III-2-2 indicates that they are not referable to this
taxon, thus suggesting the presence of at least one
additional ornithopod species in the Gamma Member.
Moreover, along with material currently under study (CM
93790; CM 93791; JAC1 pers. obs.), the ungual described
herein (MLP 98-I-10-70) suggests, for the first time, the
presence of early-diverging ornithopods in the
Maastrichtian Sandwich Bluff Member of the López de
Bertodano Formation.
Hadrosaurid ornithopods are represented in the JRB by
a single, isolated tooth from the Maastrichtian ‘Reptile
Horizon’ of the Sandwich Bluff Member of the López de
Bertodano Formation of Sandwich Bluff on Vega Island
(MLP 98-I-10-1; Case et al., 1998, 2000a [identified as
MLP 99-I-10-1 by Otero and Reguero, 2013]; Figure 5f),
and possibly also by the partial distal end of a metatarsal
from a near-coeval horizon (KlB 9) of this same formation
on Seymour (= Marambio) Island (MLP 96-I-6-2; Rich et
al., 1999). Hadrosaurid pedal phalanges were also reported
from the Sandwich Bluff Member by Case et al. (2000b,
2007), though the specimens in question cannot currently be
located. Conversely, although Otero and Reguero (2013)
reported the tooth MLP 98-I-10-1 as missing, it has since
been relocated in the MLP collection and was examined by
two of the present authors (MCL and PMO) during a visit to
that institution in late 2017. Hadrosaurids presumably
emigrated to Antarctica from South America sometime
during the Campanian or Maastrichtian after their arrival in
the latter continent from North America by the late
Campanian (Casamiquela, 1964; Prieto-Marquez and
Salinas, 2010; Cruzado-Caballero and Powell, 2017). Case
et al. (2000a) tentatively assigned the tooth MLP 98-I-10-1
to Hadrosaurinae (= Saurolophinae of many recent works),
which would accord with the known fossil record of South
American hadrosaurids that, at present, is definitively
composed only of hadrosaurines (e.g., Bonapartesaurus
rionegrensis, Cruzado-Caballero and Powell, 2017;
Secernosaurus koerneri, Prieto-Marquez and Salinas, 2010).
The fact that all JRB hadrosaurid/putative hadrosaurid
specimens come from Maastrichtian horizons—but that
material of these dinosaurs is thus far absent from more
ancient strata within the basin—is notable, and suggests that
these ornithopods may not have colonized the Antarctic
Peninsula until the last few million years of the Cretaceous.
Nevertheless, a much more robust Antarctic Cretaceous
non-avian dinosaur fossil record will be required before this
hypothesis may be evaluated. Furthermore, because the
Seymour Island metatarsal is damaged and missing one of
its distal condyles, and also that metatarsals of hadrosaurids
are generally comparable in distal morphology to those of
non-hadrosaurid ornithopods, it is conceivable that this
bone could instead pertain to another ornithopod clade, such
as Elasmaria, some members of which (e.g.,
Macrogryphosaurus gondwanicus, Calvo et al., 2007;
Sektensaurus sanjuanboscoi, Ibiricu et al., 2010, 2019)
attained body sizes consistent with the individual
represented by this metatarsal (MCL pers. obs.).
3.2 Sauropoda
With the possible exception of at least some of the putative
footprints reported by Olivero et al. (2007; see above),
sauropod dinosaurs are currently represented in the JRB
only by an isolated, incomplete bone: MLP 11-II-20-1, a
partial caudal centrum from the upper Campanian Gamma
Member of the Snow Hill Island Formation of the Santa
Marta Cove area of James Ross Island (Cerda et al., 2012;
Figure 5g). The procoelous nature of this centrum led Cerda
et al. (2012) to interpret the specimen as that of a
lithostrotian titanosaur, a clade that is abundant and
widespread throughout the Upper Cretaceous of other
Gondwanan landmasses (Curry Rogers, 2005; Wilson, 2006;
Gorscak and O’Connor, 2016; Sallam et al., 2018; González
Riga et al., 2019). Nevertheless, as noted by Cerda et al.
(2012), the specimen exhibits only moderate development
of the posterior articular condyle (MCL pers. obs.); this,
coupled with the present, highly labile state of titanosaurian
systematics (see, for example, the phylogenetic hypotheses
presented in the references above) leads us to regard this
vertebra as that of a phylogenetically indeterminate member

242 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3
of Titanosauria.
3.3 Non-Avian Theropoda
Though, as noted above, fossils of avian theropods (i.e.,
birds) are reasonably common in Upper Cretaceous
horizons of the JRB (e.g., Clarke et al., 2005, 2016),
material of non-avian theropods is much scarcer. The most
complete, informative non-avian theropod specimen from
the JRB is the holotype of the recently-named, medium-
sized possible deinonychosaur Imperobator antarcticus,
initially discovered and collected in 2003 from an exposure
of the upper Campanian–lower Maastrichtian Cape Lamb
Member of the Snow Hill Island Formation on the Naze
Peninsula of James Ross Island (UCMP 276000; Case et al.,
2007; di Pasquo and Martin, 2013; Ely and Case, 2016,
2019). Described material of Imperobator currently consists
of teeth and distal hind limb elements (Case et al., 2007;
Ely and Case, 2019; Figure 5h). Recently, however, two of
us (JAC1 and DEM) relocated additional material pertaining
to UCMP 276000 at facilities of Eastern Washington
University and the South Dakota School of Mines and
Technology, respectively, including skull fragments
(probably belonging to at least the premaxilla, maxilla,
and/or dentary), a caudal vertebra, and additional teeth and
pedal elements (MCL, JAC1, DEM pers. obs.). Moreover,
the 2011 and 2016 AP3 expeditions returned to the
Imperobator type locality and recovered additional fossils
that almost certainly pertain to the individual represented by
UCMP 276000, including a tooth and several bone
fragments (AMNH FARB 30894), a partial pedal ungual,
and fragmentary putative cranial remains (Lamanna et al.,
2017). Several of the present authors are currently
undertaking a comprehensive reassessment of the
morphology and phylogenetic relationships of Imperobator
that will include a description of all known material of this
taxon.
Other non-avian theropod material from the JRB is
limited to isolated bones. Molnar et al. (1996) described
MLP 89-XII-1-1, a distal tibia from the Coniacian Hidden
Lake Formation of the Cape Lachman region of James Ross
Island that they considered to belong to an early-diverging
tetanuran similar to the Middle Jurassic megalosauroid
Piatnitzkysaurus floresi (Bonaparte, 1986). This fossil is
important in that it constitutes the only known record of a
continental vertebrate from this stratigraphic unit and the
oldest dinosaurian fossil from the Antarctic Cretaceous
(Schweitzer et al., 2012). As such, although such a study
would be beyond the scope of the present paper, we believe
that MLP 89-XII-1-1 requires reanalysis in light of the
numerous Cretaceous non-avian theropod discoveries that
have been made on Gondwanan continents during the past
quarter-century (e.g., Novas et al., 2013; Ezcurra and Novas,
2016). For example, spinosaurids (e.g., Spinosaurus
aegyptiacus, Stromer, 1915) are the only megalosauroids
known to have survived into the Late Cretaceous, and as
such, MLP 89-XII-1-1 should be compared to the distal
tibiae of these distinctive semi-aquatic theropods.
Megaraptoran affinities also seem possible for the Hidden
Lake tibia, as these enigmatic tetanurans are well
represented in mid- and Late Cretaceous sediments
elsewhere in southern Gondwana (e.g., Australia, Bell et al.,
2016; Patagonia, Porfiri et al., 2018).
More recently, Coria et al. (2015a, 2015b) briefly
reported specimen MLP 15-I-7-2, a putative theropod pedal
phalanx (possibly phalanx III-1) from the Cape Lamb
Member on Vega Island, from the same site on Cape Lamb
that yielded the still-undescribed ‘BAS ornithopod’
(NHMUK PV R 36760) discussed above (Hooker et al.,
1991; Barrett et al., 2014). The occurrence of fossils of two
dinosaurian taxa at this single site—which, as is the case for
other JRB dinosaur localities, represents a marine
depositional environment where material of terrestrial
vertebrates such as non-avian dinosaurs would be expected
to be rare—would be surprising, but since the present
authors have not examined this phalanx firsthand, we accept
its identification as presented by Coria et al. (2015a, 2015b).
Nevertheless, should this phalanx eventually prove
referable to the ‘BAS ornithopod’, it would be important in
constituting the only skeletal element that might overlap
between that skeleton and known material of the potentially
closely related (or perhaps even synonymous) ornithopod
Morrosaurus, for which pedal phalanx III-1 is definitively
known (Rozadilla et al., 2016b). Finally, Case et al. (2003)
mentioned non-avian theropod material from the
Maastrichtian Sandwich Bluff Member of the López de
Bertodano Formation of Sandwich Bluff on Vega Island.
This report likely refers to the same theropod material from
the Maastrichtian of this island that was mentioned by
Olivero et al. (2007: 529): “Recently, (an) additional
theropod (fragment was) recovered from the Maastrichtian
of Vega… (Island) (J. E. Martin, pers. comm. to [E. B.
Olivero], 2005).” According to the recollection of one of us
(JAC1), the specimen in question was an ungual (field
number S061-9917) that is currently missing. If this fossil
can be relocated, it might be significant in comprising the
first non-avian theropod record from the López de
Bertodano Formation–the youngest Cretaceous geologic
unit in the JRB.
4 Biostratigraphy
Analysis of the biostratigraphy of Late Cretaceous
non-avian dinosaur discoveries from the Herbert Sound
region of the JRB demonstrates the near-contemporaneous
occurrence of many of the taxa represented by these finds
(Figure 6; Ely and Case, 2016, 2019; Case and Ely, 2017).
On Vega Island, at least the upper half of the Cape Lamb
Member of the Snow Hill Island Formation falls into the
lower part of the Maastrichtian Stage based on an 87Sr/86Sr
isotopic datum of 71.0 ± 0.2 Ma at a stratigraphic level
approximately 135 m above the base of this member and

Antarctic Cretaceous dinosaurs 243
81 m above the base of the range of the Gunnarites
antarcticus faunal assemblage (Pirrie et al., 1991; Crame et
al., 2004; Figure 6d). In the JRB, the Campanian–
Maastrichtian boundary (72.1 Ma) was suggested to be near
the beginning of this faunal assemblage within the 310 m
reference section on Cape Lamb of Vega Island (Crame et
al., 1999). The G. antarcticus assemblage extends through
approximately 210 m of this reference section, with the
ammonites Gunnarites antarcticus and Kitchinites darwini
occurring throughout this range. However, the heteromorph
ammonite Diplomoceras lambi (= D. cylindraceum
according to some authors; e.g., Kennedy and Henderson,
1992; Witts et al., 2015) is restricted to only ~50 m of the
lower half of the G. antarcticus assemblage range (Pirrie et
al., 1991). Although the stratigraphic range of D. lambi is
much more extensive (from the upper Campanian to upper
Maastrichtian) in the eastern portion of the JRB (i.e., the
Admiralty Sound area, which encompasses the east coast of
James Ross Island plus Seymour and Snow Hill islands)
(see Milanese et al., 2018), this species has only a short
stratigraphic range in the Herbert Sound area. Thus, the
short (~50 m) range of D. lambi in the Herbert Sound area
represents a short-term transgression to a deeper water
setting that was followed by shallowing-upward conditions
from the end of the range of this ammonite species to the
top of the Cape Lamb Member (Pirrie et al., 1991). The
71.0 ± 0.2 Ma datum is from near the top of the D. lambi
range in the reference section on Vega Island (Crame et al.,
1999). A partial skeleton belonging to an as-yet unidentified
early-diverging ornithopod dinosaur (the ‘BAS ornithopod’)
was recovered by the BAS from the same part of the section
(i.e., the top of the D. lambi range; ~5 m above the 71.0 ±
0.2 Ma datum) on the eastern slope of Cape Lamb in 1989
(Hooker et al., 1991; Barrett et al., 2014). As such, this
specimen is considered to be early Maastrichtian in age
(Figure 6d).
The western flank of Comb Ridge at the northern end
of the Naze Peninsula of James Ross Island exposes a 90
m-thick section composed of interbedded green-gray
massive and laminated fine-grained quartz sandstones and
greenish-yellow argillaceous mudstones and siltstones of
the Cape Lamb Member (di Pasquo and Martin, 2013;
Figure 6b). The holotype of the non-avian theropod
Imperobator antarcticus was collected in the middle of the
Comb Ridge section, between 41–48 m above the local base
of this member (Case et al., 2007; di Pasquo and Martin,
2013; Ely and Case, 2019; Figure 6b). Also found at this
stratigraphic level were the ammonites G. antarcticus, D.
lambi, and K. darwini, the pelecypod Pinna sp., and the
decapod Hoploparia stokesi, all of which are members of
the G. antarcticus assemblage (Table 2). Consequently, the
stratigraphic location, biostratigraphic associations, and age
assessment of Imperobator indicates that this theropod was
a near-contemporary of the ‘BAS ornithopod’ (albeit lower
in stratigraphic section and therefore slightly more ancient).
Another partial skeleton of an early-diverging
ornithopod, the holotype of Morrosaurus antarcticus, was
also recovered from deposits of the Cape Lamb Member of
the Naze, approximately 30 m downsection from the
stratum from which Imperobator was collected (Rozadilla
et al., 2016b; Figure 6b). The Morrosaurus specimen was
also associated with the G. antarcticus faunal assemblage,
and it definitively occurs within the D. lambi range, given
that material of the latter ammonite was found in
association with this ornithopod. As such, all three non-
avian dinosaur partial skeletons from the Cape Lamb
Member—the ‘BAS ornithopod’ and the type specimens of
Morrosaurus and Imperobator—were recovered from the D.
lambi stratigraphic range and are thus late Campanian or
early Maastrichtian in age.
As is also the case for Morrosaurus, the small-bodied
neornithischian dinosaur Trinisaura santamartaensis is
generally regarded as an early-diverging ornithopod,
possibly a representative of Elasmaria (Coria et al., 2013;
Rozadilla et al., 2016b; Madzia et al., 2018). The holotypic
specimen of Trinisaura was recovered from the upper
Campanian Gamma Member (Olivero, 2012a; ≈ Herbert
Sound Member of Crame et al., 1991) of the Snow Hill
Island Formation from the Santa Marta Cove area of James
Ross Island, only 12 km west of the Naze (Figure 6c). The
Gamma Member underlies the Cape Lamb Member within
the Herbert Sound region (Figure 6d). The ankylosaur
Table 2 Key species of the Gunnarites antarcticus faunal assemblage recovered from the sections of the Upper Cretaceous
(upper Campanian–lower Maastrichtian) Cape Lamb Member of the Snow Hill Island Formation on Cape Lamb of
Vega Island (Pirrie et al., 1991) and the measured section at Comb Ridge of the Naze Peninsula of James Ross
Island (di Pasquo and Martin, 2013)
Higher taxon
Species
Cape Lamb
(Vega Island)
Comb Ridge, the Naze Peninsula
(James Ross Island)
Ammonoidea
Gunnarites antarcticus
✓
✓
Kitchinites darwini
✓
✓
Diplomoceras lambi
✓
✓
Nautiloidea
Eutrephoceras sp.
✓
--
Decapoda
Hoploparia stokesi
✓
✓
Pelecypoda
Pinna sp.
✓
✓

244 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3
Antarctopelta oliveroi was also recovered from the Gamma
Member, only 10 m below the level that yielded Trinisaura
(Figure 6c). An isolated caudal vertebra of a third
dinosaurian taxon, a titanosaurian sauropod, was recovered
from the upper third of Gamma Member deposits at Santa
Marta Cove (Cerda et al., 2012). The titanosaur vertebra
was collected approximately 40 m upsection from the
Trinisaura locality (Figure 6c).
Olivero (2012a, 2012b) placed the first occurrence of G.
antarcticus at the very top of the Gamma Member section at
Santa Marta Cove, overlapping the 70 m total stratigraphic
range of a second ammonite species, Neograhamites cf.
kiliani. This same ammonite biostratigraphic sequence is
repeated in the Gamma Member (≈ Herbert Sound Member)
-equivalent sequence on Cape Lamb (Olivero, 2012a). The
G. antarcticus and N. cf. kiliani ammonite biostratigraphic
zones allow for correlation between the dinosaur-bearing
sequence in the Santa Marta Cove area with those from the
Cape Lamb Member on the Naze and Cape Lamb (Figure 6).
Based on the stratigraphic sections of Olivero (2012a,
2012b) and Coria et al. (2013), and the reference section for
the Cape Lamb Member on Vega Island (Pirrie et al., 1991;
Crame et al., 2004), this places the three dinosaurs from the
Santa Marta Cove area (Antarctopelta, Trinisaura, and the
titanosaur) near the top of the Campanian depositional
succession. Consequently, these three taxa are probably late
Campanian in age. Moreover, the three dinosaur skeletons
from the Cape Lamb Member (the ‘BAS ornithopod’ and
the Morrosaurus and Imperobator holotypes), all of which
are associated with the D. lambi zone, are temporally
clustered around the Campanian–Maastrichtian boundary.
These six dinosaur discoveries collectively represent at least
five species—Antarctopelta oliveroi, Trinisaura
santamartaensis, Morrosaurus antarcticus, Imperobator
antarcticus, and the unnamed titanosaur—and potentially a
sixth if the ‘BAS ornithopod’ is distinct from M. antarcticus.
Given the limited spread of stratigraphic section, and
therefore age, between these discoveries, we consider all as
occurring within a few million-year span in proximity to the
Campanian–Maastrichtian boundary.
Dinosaur fossils from the Sandwich Bluff Member of
the López de Bertodano Formation of Vega Island are
undoubtedly stratigraphically younger than those from the
underlying Snow Hill Island Formation. The Sandwich
Bluff Member dinosaurs reside within the Maorites
invertebrate faunal assemblage zone rather than the G.
antarcticus zone that is typical of the subjacent Cape Lamb
Member of the Snow Hill Island Formation (Figure 6d).
Based on the dinoflagellate cyst biostratigraphy of the
López de Bertodano Formation of Seymour Island
presented by Bowman et al. (2012), the presence of the cyst
Manumiella bertodano (= “M. n. sp. 2” of Pirrie et al., 1991)
throughout most of the Sandwich Bluff Member supports a
Maastrichtian age for this unit and its fossil assemblage
(Roberts et al., 2014). More precise dating of various
horizons of the Sandwich Bluff Member within the
Maastrichtian must await the results of ongoing studies
(EMR pers. obs.).
5 Paleobiogeography
The paleobiogeographic implications of the Upper
Cretaceous non-avian dinosaur assemblage of the JRB have
been interpreted in a variety of ways in the more than three
decades that have elapsed since the discovery of its first-
known member—the ankylosaur now known as
Antarctopelta oliveroi—in the mid-1980s. The assemblage
has frequently been regarded as endemic on a regional scale
(e.g., Molnar, 1989; Novas et al., 2002a); for instance,
Novas et al. (2002a) noted the seemingly unusual
preponderance of ornithischian fossils and argued that the
JRB dinosaurs were part of a polar Gondwanan faunal zone
that also encompassed Australia and New Zealand. In this
sense, the JRB dinosaurs would constitute a terrestrial
manifestation of the Weddellian Biogeographic Province, a
southern high-latitude biotic region characterized by
endemic shallow marine invertebrate and vertebrate faunas
during the Late Cretaceous and Paleogene (Zinsmeister,
1979, 1982; Case, 1988; Novas et al., 2002b; Otero et al.,
2012; Reguero et al., 2012; O’Gorman and Coria, 2017).
Other authors, by contrast, have interpreted the JRB
dinosaur fauna as largely ‘relictual,’ being primarily
composed of representatives of lineages that were
geographically widespread earlier in the Mesozoic but that
vanished from landmasses other than Antarctica prior to the
late stages of the Cretaceous (e.g., Molnar et al., 1996; Case
et al., 2000a, 2003, 2007; Martin and Case, 2005; Stilwell
and Long, 2011; Leppe and Stinnesbeck, 2014). Still others
(e.g., Reguero and Gasparini, 2007) have considered the
assemblage to be too poorly understood to enable an
assessment of its paleobiogeographic relationships.
In recent years, additional JRB dinosaur fossils have
been discovered, illuminating the nature of the animals
themselves as well as their collective paleobiogeographic
significance. Although a definitive paleobiogeographic
analysis is beyond the scope of the present paper, it now
appears likely that the Campanian–Maastrichtian dinosaur
assemblage of the JRB most closely resembled coeval
faunas from southern South America (Lamanna, 2013;
Reguero et al., 2013a). This is because, with the possible
exception of the non-avian theropod Imperobator
antarcticus (Ely and Case, 2019), all known JRB dinosaurs
that are identifiable to reasonably low taxonomic levels
appear closely allied to penecontemporaneous taxa from
Patagonia. In the case of the ankylosaur Antarctopelta,
although alternative hypotheses have been proposed,
Arbour and Currie (2016) considered this form to be closely
related to the unnamed nodosaurid from the Campanian–
Maastrichtian Allen Formation of Río Negro Province in
northern Patagonia (Salgado and Coria, 1996; Coria and
Salgado, 2001). Similarly, the early-branching (elasmarian?)

Antarctic Cretaceous dinosaurs 245
ornithopods Trinisaura santamartaensis and Morrosaurus
antarcticus (and the ‘BAS ornithopod’, if it is distinct from
Morrosaurus) would appear to be closely related to
Patagonian Late Cretaceous taxa such as Anabisetia saldiviai,
Gasparinisaura cincosaltensis, Macrogryphosaurus
gondwanicus, Notohypsilophodon comodorensis, and
Talenkauen santacrucensis (Coria et al., 2013; Rozadilla
and Novas, 2016; Rozadilla et al., 2016b). Hadrosaurs and
titanosaurs, represented by isolated elements from
Campanian–Maastrichtian deposits in the JRB (Case et al.,
2000a, 2000b; Cerda et al., 2012), are both well-known
from the Patagonian Late Cretaceous; indeed, though it
remains mostly undescribed, a hadrosaur/titanosaur-
dominated fauna has recently been recovered from terminal
Cretaceous sediments in southernmost Chile, constituting
the most austral non-avian dinosaur assemblage yet known
from South America (Leppe et al., 2014; Soto-Acuña et al.,
2014; Vogt et al., 2014). Taken together, this evidence
suggests that at least some non-avian dinosaur lineages
were able to disperse between southern South America and
the Antarctic Peninsula at the end of the Mesozoic. Whether
this proposed Patagonian/West Antarctic Campanian–
Maastrichtian dinosaur fauna extended to more easterly
high-latitude Gondwanan land areas such as southernmost
Africa, southern Australia, New Zealand, and/or East
Antarctica—as might be predicted by the distribution of
Weddellian marine and floral assemblages—has yet to be
confirmed, because, although generally consistent with this
hypothesis, latest Cretaceous continental vertebrate faunas
from these latter regions remain exceedingly poorly known
(e.g., Cooper, 1985; Molnar and Wiffen, 1994; Rich, 1996;
Agnolín et al., 2010).
Again, the only possible exception to this
paleobiogeographic pattern—in other words, the only latest
Cretaceous JRB dinosaur that may not have demonstrable
affinities with southern South American forms—is the
theropod Imperobator, recently postulated as a basal (i.e.,
non-dromaeosaurid, non-troodontid) deinonychosaur (Ely
and Case, 2016) or as a paravian of uncertain phylogenetic
position (Ely and Case, 2019). The only deinonychosaurs
currently known from South America, or anywhere in the
latest Cretaceous of the Gondwanan landmasses, are
unenlagiine dromaeosaurids (e.g., Novas and Puerta, 1997;
Forster et al., 1998; Makovicky et al., 2005; Novas et al.,
2008); as such, the presence of an early-diverging
deinonychosaur in the JRB at the same time would be more
consistent with the ‘relictual’ hypothesis than with any
scenario of end-Mesozoic faunal dispersal between
Patagonia and West Antarctica. Nevertheless, and as noted
above, additional fossils of Imperobator that were not
described by Ely and Case (2016, 2019) have recently come
to light. Forthcoming description and analysis of this
material promises to further clarify (and potentially revise)
the phylogenetic position of this important JRB dinosaur,
and will likely also offer new insights into its
paleobiogeographic significance (MCL pers. obs.).
Finally, it is interesting to note that nearly all non-
avian dinosaur fossils from the JRB—with the exception of
a single partial ornithopod metatarsal from Seymour Island
(Rich et al., 1999) and (possibly) the putative footprints
from Snow Hill Island (Olivero et al., 2007; see above)
—have been found in a geographically restricted area that
encompasses northwestern and north-central James Ross
and southwestern Vega islands (i.e., the land areas that
border Herbert Sound; Figures 1a, 6a). Given the abundance
of exposure of contemporaneous or penecontemporaneous
Upper Cretaceous fossil-bearing sediments further to the
southeast (Figure 1a), this does not appear to be purely a
function of outcrop area. Instead, and although we are
hesitant to speculate given the exceedingly small sample
size at present, it seems possible that non-avian dinosaur
material may be legitimately more abundant (if still
vanishingly rare) in the Herbert Sound region versus other
parts of the JRB. If so, this could potentially be due to the
presumably closer proximity of Cretaceous continental
paleoenvironments (where terrestrial animals such as non-
avian dinosaurs would be expected to have lived) on the
Antarctic Peninsula to the Herbert Sound region as opposed
to other JRB areas (Crame pers. comm.). Only continued
paleontological exploration of Cretaceous horizons within
the basin may enable an evaluation of this hypothesis.
6 Conclusions
The fossil record of non-avian dinosaurs from the JRB
mostly consists of fragmentary specimens, yet multiple taxa
are represented that collectively hold significant
paleobiogeographic implications. Material of Ankylosauria,
early-diverging Ornithopoda, Hadrosauridae, Titanosauria,
and non-avian Theropoda demonstrates that, rather than
comprising a ‘relictual’ or endemic fauna, most Late
Cretaceous dinosaurs from West Antarctica had coeval close
relatives in geographically adjacent southern South America.
This, in turn, supports the proposed existence of some form
of terrestrial biotic connection between these two
landmasses at the close of the Mesozoic. Moreover, the
majority of the most important Antarctic Cretaceous
dinosaur finds—including all five reasonably complete
skeletons and all four named taxa—have been recovered
from a stratigraphically narrow interval that encompasses
the late Campanian and early Maastrichtian of northern
James Ross and western Vega islands. Ongoing field efforts
by researchers from various nations (e.g., Argentina, the
United States) and the comprehensive description of
previously discovered specimens (e.g., the holotype of
Imperobator antarcticus, the ‘BAS ornithopod’, the distal
hind limb CM 93790) promise to further improve our
understanding of the non-avian dinosaurs of the JRB,
thereby casting much-needed light on the nature of
Antarctic continental vertebrate assemblages immediately
preceding the end-Cretaceous mass extinction.

246 Lamanna M C, et al. Adv Polar Sci September (2019) Vol. 30 No. 3
Institutional abbreviations
AMNH–American Museum of Natural History, New
York, USA
BMNH–British Museum of Natural History (now, The
Natural History Museum), London, UK
CM–Carnegie Museum of Natural History, Pittsburgh,
USA
MLP–Museo de La Plata, La Plata, Argentina
MPCA–Museo Provincial Carlos Ameghino, Cipolletti,
Argentina
NHMUK–The Natural History Museum, London, UK
OU–Geology Museum, University of Otago, Dunedin,
New Zealand
SDSM–South Dakota School of Mines and Technology,
Rapid City, USA
UCMP–University of California Museum of
Paleontology, Berkeley, California
Acknowledgments For assistance in the field, we thank the remaining
members of the 2011 and 2016 AP3 expeditions. We are also grateful
to the members of the 1999 US-Argentinean JRB expedition that was
jointly sponsored by NSF and the IAA, as well as the members of the
NSF-funded 2003 expedition. We also acknowledge the extensive
logistical assistance that our expeditions received from personnel from
NSF, the US Antarctic Program, the Lockheed Martin Antarctic
Support Contract, Raytheon Polar Services Corporation, and Edison
Chouest Offshore. M. Reguero, A. Scarano, J. Gelfo, and C. Acosta
Hospitaleche provided access to dinosaur specimens housed at the
MLP to MCL, JAC1, RCE, and PMO, and F. Novas, M. Ezcurra, F.
Agnolín, A. M. Aranciaga Rolando, M. Isasi, and M. Cerroni
facilitated access to the Morrosaurus holotype at the MACN for MCL.
R. Coria participated in valuable discussions regarding the Trinisaura
holotype. A. McAfee produced the figures with his usual skill and care,
and K. Gigler assisted with assembling and formatting the
bibliography. We also acknowledge S. Hartman for providing many of
the silhouettes that appear in Figures 1 and 6 via PhyloPic.org, R.
Blakey for permission to reproduce his paleogeographic map as Figure
1c, and P. Currie for permission to reproduce his photograph as Figure
1e. Similarly, we thank E. Olivero for permission to reproduce his
photograph as Figure 5a and Cambridge University Press for
authorization to reproduce the photograph in Figure 5e. The authors
are especially grateful to C. Acosta Hospitaleche, A. Crame, and J.
Gelfo for inviting us to contribute to this volume, and to M. Reguero
for kindly providing the photographs of the pedal ungual MLP
98-I-10-70 that appear in Figure 3. The manuscript was improved by
comments from reviewers R. Coria and S. Poropat and Guest Editor A.
Crame. AP3 research has been supported by NSF grants ANT-1142129
to MCL, ANT-1141820 to JAC2, ANT-1142104 to PMO, ANT-
0636639 and ANT-1142052 to R. MacPhee, and OPP-9615933 and
ANT-0003844 to JAC1.
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