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Ant-nest ichnofossils in honeycomb calcretes, Neogene Ogallala Formation, High
Plains region of western Kansas, U.S.A.
Jon J. Smith
a,
⁎, Brian F. Platt
b
, Greg A. Ludvigson
a
, Joseph R. Thomasson
c
a
Kansas Geological Survey, 1930 Constant Ave., Lawrence, KS 66047, USA
b
Department of Geology, 1475 Jayhawk Boulevard, The University of Kansas, Lawrence, KS 66045, USA
c
Sternberg Museum of Natural History, 3000 Sternberg Drive, Hays, KS 67601, USA
abstractarticle info
Article history:
Received 20 October 2010
Received in revised form 25 May 2011
Accepted 29 May 2011
Available online 2 June 2011
Keywords:
Continental ichnology
Insects
Formicidae
Paleosols
Calcrete
New ichnotaxa
Two new ant-nest trace fossils are described from calcic sandy paleosols of the Neogene Ogallala Formation in
western Kansas. The ichnofossils are preserved within and below calcrete beds weathering in positive relief as
carbonate-filled casts or as cavities in negative relief. Daimoniobarax ichnogenus nov. is established for
burrow systems composed of vertically tiered, horizontally oriented pancake-shaped chambers connected by
predominantly vertical and cylindrical shafts ~0.8 cm in diameter. Ichnospecies of Daimoniobarax are
differentiated based on differences in the plan view outline of chambers, shaft orientation, and junctions
between chambers and shafts.
Daimoniobarax nephroides ichnospecies nov. is composed of an ~24–76 cm long vertical sequence of distinctly
lobed chambers (~2–20 cm wide and ~1 cm high) arranged along sinuous to helical shafts. Chamber shape in
plan view ranges from small teardrops to larger kidney- and U-shaped forms. Shafts intersect at chamber
edges such that chambers appear to bud from the central shafts. Daimoniobarax nephroides is most similar to
the nests of extant seed-harvester ants of the New World genus Pogonomyrmex. Such ants are specialized
granivores and prefer sandy soils in arid to semi-arid grassland and desert regions.
Daimoniobarax tschinkeli ichnospecies nov. is ~ 30–80 cm in vertical extent. Chambers (~ 2–30 cm wide and
~1 cm high) are circular to elongate or pseudopodial in plan view. Vertical shafts are straight to slightly
sinuous and intersect most often toward the center of the chambers. The generalized architecture of
D. tschinkeli is similar to that of the nests or nest portions of several extant ant genera, though it does not
closely resemble any known modern nest.
Ant ichnofossils provide valuable information on hidden biodiversity, paleohydrologic regimes, paleopedo-
genic processes, and paleoclimate during the time of nest occupation. Depth-related changes in chamber size
and vertical spacing may also help interpret paleosurfaces and paleodepths, and serve as geopetal features.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
The Neogene Ogallala Formation underlies much of the North
American High Plains region and is composed chieflyoffluvial and
eolian sediments consisting of interbedded conglomerate, sandstone,
mudrock, loess and their uncemented equivalents (Gustavson and
Winkler, 1988, 1990). In the uppermost Ogallala Formation, pedo-
complexes composed of multiple calcic paleosols with honeycombed
to massive calcretes can be over 10 m thick (Gardner et al., 1992).
Honeycomb calcretes (Stage III of Machette, 1985) were until recently
thought to develop in calcified soils by the partial coalescence of
carbonate nodules and pipy concretions to form a solid lattice-like
framework surrounding less-indurated interstitial soil-material
(Wright, 2007). Recent fieldwork in west-central and southern Kansas
shows, however, that the sizes, basic structural elements, and
architectural morphologies of many of the honeycomb structures in
the Ogallala Formation are nearly identical to the nests of extant
burrowing ants (Insecta: Hymenoptera: Formicidae).
This paper describes the morphology and paleoecological and
paleoenvironmental significance of these newly recognized multi-
chambered trace fossils and their interpreted tracemaking organisms.
Interest in nests of subterranean social insects, particularly those of
hymenopterans and isopterans, has focused largely on how nest
architecture relates to such biological, behavioral, and ecological
research topics as inter- and intraspecific interactions (e.g., Boulton
et al., 2003), social structure and group-level behaviors (e.g.,
Langridge et al., 2008), and biogenic modification of soil properties
(e.g., Cammeraat and Risch, 2008). Detailed information on the three-
dimensional architecture of insect nests and their distinctly identifi-
able characteristics, however, is often lacking in these studies
(Tschinkel, 2004). Our recognition of fossil ant nests in the Ogallala
paleosols is due in large part to recent efforts to document the nest
Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
⁎Corresponding author.
E-mail addresses: jjsmith@ku.edu (J.J. Smith), bfplatt@ku.edu (B.F. Platt),
gludvigson@kgs.ku.edu (G.A. Ludvigson), jthomass@fhsu.edu (J.R. Thomasson).
0031-0182/$ –see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.palaeo.2011.05.046
Contents lists available at ScienceDirect
Palaeogeography, Palaeoclimatology, Palaeoecology
journal homepage: www.elsevier.com/locate/palaeo
architectures of modern ants by casting them in plaster, metal, and
concrete (e.g., Williams and Logfren, 1988; Tschinkel, 2003; Moreira
et al., 2004; Tschinkel, 2004, 2005; Forti et al., 2007; Verza et al., 2007;
Cerquera and Tschinkel, 2010; Halfen and Hasiotis, 2010; Tschinkel,
2010). Such comparisons are possible because the trace fossils of
many soil-dwelling biota do not often differ significantly from the
burrows and nests of extant species (e.g., Genise et al., 2000; Hasiotis,
2003; Duringer et al., 2007; Verde et al., 2007; Smith et al., 2008a;
Hembree, 2009). Ichnofossils provide valuable information on hidden
biodiversity in the absence of body fossils, paleopedogenic modifica-
tion and processes, paleohydrologic regimes, and paleoclimatic
conditions (e.g., Hasiotis, 2007; Smith et al., 2008b).
2. Geologic setting and background
The main study area is located in west-central Kansas where up to
53 m of the Neogene Ogallala Formation is exposed along the bluffs of
Ladder Creek Canyon and in tributary draws in the northwestern
portion of Scott County (Fig. 1). Additional Ogallala localities were
examined in Ellis and Morton counties, Kansas. The formation consists
mostly of gravel, sand, silt and clay of fluvial–alluvial origin,
calcareous paleosols, and eolian silt and clay; local lenses of volcanic
ash and lacustrine limestones are also present (Frye et al., 1956).
Individual beds often grade laterally from one lithology to another and
dramatic changes in thickness and bed continuity over relatively short
distances are not uncommon (Waite, 1947). Calcareous paleosols
occur with high stratigraphic frequency throughout the formation and
are characterized by abundant carbonate nodules, pipy concretions,
root traces, and irregular lenses and beds of ledge-forming calcrete
(Fig. 2;Gutentag, 1988). Fossil mammal and floral assemblages
(Thomasson, 1979, 1990; Zakrzewski, 1990; Martin et al., 2008) and
tephrochronologic analyses of unaltered volcanic ash beds (Perkins,
1998) suggest that Ogallala deposits in Kansas range in age from
middle Miocene to earliest Pliocene (Ludvigson et al., 2009). The
Ogallala Formation is up to several hundred meters thick in western
Kansas, but regional thickness varies greatly because of the uneven
surface upon which sediments were deposited and post-Ogallala
uplift and erosion (Leonard, 2002).
2.1. Devil's Backbone locality
The best-preserved and exposed ichnofossils are located approxi-
mately 1.6 km south of Lake Scott State Park in a road cut through an
east–west trending ridge of Ogallala strata called the Devil's Backbone
(Fig. 1). The road cut exposes ~23 vertical meters of rock composed
chiefly of tan- to reddish brown-colored, moderately sorted, silty, fine-
to very coarse-grained beds of arkosic sandstone (Fig. 3). Calcium
carbonate pervades the section, mostly as fine-grained cement, but also
Fig. 1. Map of study area showing location of Ogallala Formation exposures and Devil's Backbone road cut in Ladder Creek Canyon, Scott County, Kansas. Inset map of Kansas shows
the additional localities in Ellis and Morton Counties.
384 J.J. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
as powdery stringers along cracks; rounded cobble-sized and smaller
nodules; pipy concretions; rhizoliths and burrow casts; and lenses and
discontinuous beds of massive, nodular, and honeycomb calcrete.
These deposits are interpreted as fluvial and floodplain sediments on
which composite soils with thick pedogenic and phreatic calcrete
horizons developed (Gardner et al., 1992). The paleosols probably
formed in overbank deposits during relatively long periods of landscape
stability and low sedimentation rates between major inundations of the
Ogallala floodplain (Gustavson and Winkler, 1988). In general, calcretes
and macro-scale carbonate features develop in modern soils where
Fig. 2. Calcretes and calcareous paleosols in the Ogallala Formation along the rim of Ladder Creek Canyon: A) ledge-forming beds of massive to laminar calcrete not interpreted as
trace fossils; and B) irregular beds of honeycomb calcrete showing carbonate-filled casts of multi-chambered trace fossils. C) Ichnofossils are most obvious weathering from
sandstones below interbedded calcretes. Rock hammer in A is 33 cm; scale in B is 16 cm.
Fig. 3. Measured stratigraphic section and photograph of the lower 13 m of Ogallala Formation exposed on the west side of the Devil's Backbone road cut (N38°38′26″, W100°54′49″).
385J.J. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
there is a net moisture deficit, such thatcarbonate precipitated in a drier
season is not leached from the soil profile during a wetter season
(Wright, 2007). The thick calcrete horizons imply possibly arid to sub-
humid paleoclimatic conditions with low, seasonal rainfall and high
evapotranspiration rates within a few meters of the soil surface.
We examined the structures described as honeycomb calcrete from
the Devil's Backbone locality and other outcrops along the rim of Ladder
Creek Canyon (Figs. 2B–C; 3). After careful inspection, we interpret many,
though not all, of the nodular honeycomb structures as multi-chambered
ichnofossils. The trace fossils are preserved within and below calcrete
beds as carbonate-filled exichnia and endichnia weathering in positive
relief, depending on the hardness of the burrow fill (Fig. 4A–D). Most
burrow systems consist of a mix of hard and soft carbonate, making
collection from the outcrop of more than a small section of the burrow
nearly impossible. Concretionary carbonate growth on or near some of
the trace fossils obscures their true architectural morphologies (Fig. 2B),
though specimens without such growths are also prevalent. In some
cases, the traces are present as cavities in the outcrop face due to nearly
complete weathering of the burrow fill (Fig. 4D).
One of the co-authors of this paper (Thomasson, 2009) often
targets weathered chamber structures in the Ladder Creek Canyon
study area because they contain mass accumulations of the fossilized
reproductive structures (e.g., seeds and fruits) and vegetative
structures (e.g., leaves, stems, and roots) of various angiosperms.
Fossil plant taxa commonly recovered include grasses (Poaceae),
borages (Boraginaceae), sedges (Cyperaceae), and hackberries (Ulma-
ceae) (Thomasson, 2003, 2005). Paleoclimatic conditions inferred
from paleobotanical assemblages suggest subhumid to subtropical
savanna conditions with no extended periods of freezing weather, and
higher annual rainfall than experienced currently in this region
(Thomasson, 1990). Thomasson (1982) was the first to suggest that
mass accumulations of well-preserved plant fossils in sediments of
the Miocene Sheep Creek Formation in western Nebraska were the
food caches of ancient burrowing arthropods.
Fig. 4. Different preservational styles of in-situ, multi-chambered ichnofossils in the Ogallala Formation: fossil burrows at Devil's Backbone locality preserved in A) mostly solid
carbonate and weathering in positive relief, and B) in soft carbonate and weathering in mostly negative relief. C) Silica-filled burrows weathering in positive relief in Elis County
(N39°02′31″, W99°32′09″); and D) burrows in Morton County (N37°06′13″, W101°56′19″) preserved as cavities due to nearly complete weathering of the fill material. All rulers are
in cm increments.
386 J.J. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
2.2. Other localities
Ogallala localities in Ellis County (Fig. 1) correspond to sites 2, 8, 9a,
9b, and 33 of Thomasson (1979). These localities are characterized by a
general coarsening upward sequence of massive ash-dominated beds of
siltstone and claystone overlain by conglomeratic sandstone or
lenticular beds of calcrete and volcanicash. The chambered trace fossils
are present at the bases of calcretes and ash beds and the underlying
mudrock facies in the lower half of the sequence (Fig. 4C). The
ichnofossils are morphologically identical to those at Devil's Backbone,
but are preserved often in fibrous silica instead of carbonate.
Multi-chambered trace fossils were also examined in Ogallala
Formation calcretes at the Point of Rocks landmark in the Cimarron
National Grassland, Morton County, Kansas (Fig. 1). The ichnofossils at
this locality are preserved most commonly as cavities in massive beds
of calcareous, very well-cemented, sandy siltstone, but otherwise are
morphologically identical to casts at Devil's Backbone (Fig. 4D).
3. Systematic ichnology
Figured and cited specimens, except for those represented by field
photographs only, are housed in the Invertebrate Paleontology (IP)
collection at the Sternberg Museum of Natural History, Fort Hays State
University (FHSM), Hays, Kansas. Additional specimens are housed at
the Kansas Geological Survey, Lawrence, Kansas, United States of
America.
3.1. Daimoniobarax ichnogen. nov.
Synonymy:
1896 Daemonelix cakes, Barbour, p. 25, fig. 2
1897a Daemonelix cakes, Barbour, pl. 2, figs. 1–5, 7–9, 11
1897b Daemonelix cakes, Barbour, pl. 32, figs. 5–8
1982 arthropod burrows, Thomasson, p. 1013, fig. 1A–D
?1987 elliptical chambers, Sands, p. 411, pl. II.I: 6
1990 dung cake, Retallack, p. 12, fig. 207F
2002 ant nests, Hasiotis, p. 65, figs. B and C
2007 ant nests, Hamer et al., p. 228, fig. 6F
2010 ant nests, Cuevas Martínez et al., p. 170, fig. 9A–C
Etymology: From the Greek; daimonios,meaning‘of a spirit’,and
barax,atypeofflat cake. The name refers to the type locality, Barbour's
colloquial name for the trace fossil (Barbour, 1896), and the flat,
pancake-like appearance of the chambers.
Type ichnospecies:Daimoniobarax nephroides isp. nov.
Diagnosis: Burrow system composed of a vertically tiered succes-
sion of horizontally oriented, pancake-shaped chambers connected
most commonly by a single vertical to sub-vertical, cylindrical, narrow
shaft (Fig. 4). Chambers are circular or reniform, to multi-lobate and
elongate in plan view (Fig. 5). Chambers and shafts are unlined and
form a ladder-like structure taller than it is wide.
Remarks: Daimoniobarax is distinguished from other trace fossils
composed of multiple chambers by differences in overall orientation,
chamber shape and abundance, and orientation and density of
associated burrows. Parowanichnus formicoides Bown et al., 1997 is a
wider than tall, grid-like lattice of densely spaced oblate to spherical
chambers, shafts, and tunnels that radiate from the central part of
the structure. Parowanichnus perirhizaterion Hembree and Hasiotis,
2008 is similar to P. formicoides, but chambers, shafts, and tunnels are
clustered along a central rhizolith. Socialites tumulus Roberts and
Tapanila, 2006 has a complex network of unlined and branching
tunnels and shafts that connect to larger, ovate J-shaped chambers, all
concentrated within and around conical structures along bedding
planes. Daimoniobarax differs from Attaichnus Laza, 1982,Termitichnus
Bown, 1982, and Vondrichnus Genise and Bown, 1994, in that the
latter are composed of spherical to subspherical chambers. Krausich-
nus Genise and Bown, 1994,Archeoentomichnus Hasiotis and Dubiel,
1995, and Fleaglellius Genise and Bown, 1994, are characterized by
tabular, distinctly lined chambers tiered such that the floor of the
upper chamber is the roof of the one below and the chambers are
supported by pillars and ramps. Daimoniobarax chambers are
distinctly separate and vertically spaced from one another and show
no internal supporting structures. The elongate chambers and burrows
assigned to Syntermesichnus Bown and Laza, 1990 show conspicuous
linings, unlike Daimoniobarax.
Trace fossils nearly identical to Daimoniobarax were first described
by Barbour (1896, 1897a) in association with the helical ichnofossil
Daimonelix circumaxilis from the early Miocene Harrison Formation in
the High Plains of northwestern Nebraska. Barbour called the traces
“Daemonelix [sic] cakes”because they were preserved in the same
white, fibrous, silicified material as the much larger D. circumaxilis and
because they were similar in sizeand thickness to a “camp griddle cake”.
The “cakes”were horizontally-oriented, roughly circular in plan view,
though oftenlobed, and seldom more than10 cm wide and ~1 cm thick;
they occurred as single specimens or as pairs or in stacked clusters
Fig. 5. Plan (top row) and side views (bottom row) of Daimoniobarax isp. chambers and shafts removed from outcrop; note the flat, pancake-like shape of the chambers and the
helical shafts in specimens A and B.
387J.J. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
(Fig. 6A). A periphery of white tubules, or “Daemonelix fibers”,was
described in association with and connecting some of the cakes
vertically (Fig. 6B). Barbour interpreted the cakes, alongwith Daimonelix
circumaxilis, to be members of a phylogenetic continuum showing the
evolution of giant, spiraling aquatic plants from simple root-like fibers
and algal mats (Barbour, 1897b). While D. circumaxilis was eventually
recognized as the fossilized burrow of the Miocene terrestrial beaver
Palaeocastor sp. (Fuchs, 1893; Schultz, 1942; Martinand Bennett, 1977);
the less celebrated “cakes”and smaller traces were still considered likely
to be algal mats, concretions, or the coprolites of large mammals (e.g.,
Kindle, 1923; Lugn, 1941; Schultz, 1942; Retallack, 1990). It is clear,
however, from Barbour's descriptions, illustrations, and photographic
plates that the “Daemonelix cakes”and associated “fibers”are pieces of a
multi-chambered trace fossil identical to Daimoniobarax (Fig. 6).
3.1.1. Daimoniobarax nephroides isp. nov. (Figs. 4A, C, D; 5A–B; 7A–D; 9A)
Etymology: From the Greek; nephros, meaning ‘kidney’, and oides
meaning ‘similar to’.
Holotype: Natural cross section of burrow system in outcrop (Fig. 7A).
Hypodigm: Twelve isolated chambers collected as paratypes: FHSM
IP-1489 andFHSM IP-1490 (Fig. 5A–B; plan and side view respectively);
and all ten specimens (FHSM IP-1491, FHSM IP-1490, FHSM IP-1492,
FHSM IP-1493, FHSM IP-1494, FHSM IP-1495, FHSM IP-1496, FHSM IP-
1497, FHSM IP-1498, and FHSM IP-1499) depicted in Fig. 7D.
Type locality: Lowest red sandstone interval on the west side of
Devil's Backbone road cut (N38°38′26″, W100°54′49″) on Kansas
Highway 95 in Ladder Creek Canyon, approximately 1.6 km south of
Lake Scott State Park, Scott County, Kansas, U.S.A.
Examined material: Nine partial burrow systems were examined
and measured in situ at Devil's Backbone and other Ladder Creek
Canyon localities. Forty-one complete and partial chambers with or
without attached shafts were measured and collected from the
outcrop face and in float. Numerous additional specimens were
examined at the Ellis County and Morton County locations.
Distribution: Neogene deposits of western Kansas and Nebraska.
Numerous specimens were examined in strata of the Ogallala
Formation along the walls of Ladder Creek Canyon and within
Ogallala calcretes and volcanic-ash dominated siltstones approxi-
mately 11 km north of the City of Ellis in Sections 2 and 3, T. 12. S., R.
20 W., Ellis County, Kansas. Trace fossils were also observed in
Ogallala Formation calcretes cropping out at the Point of Rocks
landmark in the Cimarron National Grassland; NE¼ SE¼ section 12, T.
34 S., R. 43 W., Morton County, Kansas. Nearly identical trace fossils
are reported from Neogene deposits of the Harrison and Sheep Rock
Formations in western Nebraska (Barbour, 1897a; Thomasson, 1982).
Diagnosis: Chambers are distinctly lobed and range in plan view
from small teardrop-shaped chambers to larger kidney-shaped and
still larger U-shaped chambers. Shafts are sinuous to helical with a
wide ramp angle (sensu Smith, 1987) and intersect chambers at
chamber edges such that chambers appear to bud outward from shaft
wall, with larger U-shaped chambers appearing to wrap back around
the shaft to which they are attached.
Description:Daimoniobarax nephroides is composed of a 24 to
76 cm long sequence of tiered chambers with flat floors and ceilings
(Fig. 7A). Chambers average 1.2 cm in height and have widths ranging
from 2.0 to 19.7 cm with an average of 6.0 cm. Chambers intersect
shafts at chamber edge and chambers appear to bud outward from the
Fig. 6. Specimen photographs and illustrations of “Daemonelix cakes”collected by Barbour from the early Miocene Harrison Formation, northwestern Nebraska. A) Photographs of
individual and stacked “cakes”in plan and lateral view, modified from Barbour (1897a); B) illustration showing the architectural arrangement in outcrop of the “cakes”and
associated vertical “fibers”, scale unknown; modified from Barbour (1896).
388 J.J. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
shaft. The point of intersection between the chambers and the shaft
rotates with depth around the central shaft forming a vertical
sequence of somewhat offset chambers (Figs. 4D, 7A). Smaller
chambers are teardrop-shaped in plan view and intersect shafts at
the narrow, pointed end of the teardrop (Fig. 7D). Larger chambers
show reniform to U-shaped outlines in plan view that turn back
toward and wrap around the point of intersection with the shaft
(Fig. 7D). Shafts are cylindrical in cross-section with average
diameters of 0.78 cm. Shafts are sinuous to loosely helical with an
average deviation from the vertical of ~ 20–30° (Fig. 5A), though shafts
between closely spaced chambers can be fairly straight. In better
exposed burrow systems, the average vertical distance between the
chambers is ~7 cm and this distance increases with depth. A one-way
analysis of variance (ANOVA) shows that the vertical distance
between D. nephroides chambers measured within calcrete beds is
significantly shorter, F(3, 144)= 6.19, pb0.001, such that chambers
are stacked nearly on top of each other (Fig. 4C). The better exposed
specimens in outcrop likely represent only a portion of the full burrow
system architecture based on observations of multiple in situ
specimens with partial three-dimensional exposures.
3.1.2. Daimoniobarax tschinkeli isp. nov. (Figs. 8A–E; 9B)
Etymology: For Dr. Walter R. Tschinkel, Florida State University
formicologist, and his work inventorying the diversity and develop-
ment of modern social insect nest architectures. Field recognition of
Daimonio barax as a trace fossilwas due in no small part to Dr. Tschinkel's
casts and photographs of extant ant nests.
Holotype: Natural cross section of burrow system in outcrop
(Fig. 8A).
Hypodigm: Six isolated chambers collected as paratypes (FHSM IP-
1500, FHSM IP-1501, FHSM IP-1502, FHSM IP-1503, FHSM IP-1504,
and FHSM IP-1505), and depicted in Fig. 8E.
Type locality: Lowest red sandstone interval on the west side of
Devil's Backbone road cut (N38°38′26″, W100°54′49″) on Kansas
Highway 95 in Ladder Creek Canyon, approximately 1.6 km south of
Lake Scott State Park, Scott County, Kansas, U.S.A.
Examined material: Eight partial burrow systems were examined
and measured in situ at the Devil's Backbone and other Ladder Creek
Canyon localities. Twenty-eight complete and partial chambers with
and without attached shafts were collected from the outcrop face and
in float.
Distribution:Daimoniobarax tschinkeli occurs in deposits of the
Neogene Ogallala Formation in western Kansas. Numerous specimens
were examined in the Ogallala Formation cropping out along the walls
of Ladder Creek Canyon.
Diagnosis: Differs from Daimoniobarax nephroides, its closest
morphological counterpart, in that (1) chamber shapes in plan view
range from circular to elongate and pseudopodial; (2) shafts are
predominantly straight to slightly sinuous; and (3) shafts intersect
chambers toward the center of the chambers; sometimes running
Fig. 7. Architectural morphology and chambers of Daimoniobarax nephroides: A) in-situ holotype at the Devil's Backbone locality; and B) line drawing interpreting architecture of the
holotype (solid and dashed lines), concretions (c) and concretionary outgrowths on the ichnofossils (co) and nearby fossil chambers. C) Chamber diagnostic of D. nephroides showing
helical shaft and intersection between the two at the chamber edge. D) Collected D. nephroides chambers showing a range of sizes and shapes in plan view from small teardrop-
shaped chambers to larger reniform and U-shaped chambers (cf. Tschinkel, 2003, Fig. 10; 2004,Fig. 4). All rulers are in cm increments.
389J.J. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
straight through the chamber and sometime entering from above and
exiting from below at different locations relative to each other.
Description:Daimoniobarax tschinkeli burrow systems exposed in
outcrop range from ~30 to 80 cm in vertical length (Fig. 8A–D).
Chambers average 1.3 cm in height and have widths ranging from
~2.0–30.0 cm with an average width of 9.7 cm. Smaller chambers are
circular in plan view but larger chambers show elongate to irregularly
lobed outlines (Fig. 8E). Unlike D. nephroides, chambers do not appear
to protrude in preferred direction from the shaft. Shafts are cylindrical
in cross-section with an average diameter of 0.85 cm. Shafts are
straight to slightly sinuous and usually intersect with chambers
toward the center of each chamber or at some distance from the
chamber edge. Some shafts descend directly through chambers, that
is, they intersect the chamber from above and below in the same place
on opposite sides. In other specimens, shafts enter and exit chambers
at different locations relative to each other. Both architectures can be
present in the same burrow system (Fig. 8A). Average vertical
distance between the chambers is ~ 6 cm in articulated burrow
systems showing a series of multiple chambers. As with D. nephroides,
vertical distances between chambers increase with depth.
4. Discussion and interpretation
The sizes, basic structural elements, and architectural morphologies
of Daimoniobarax nephroides and D.tschinkeli most resemblethe nests of
extant soil-excavatingants. Ants have a rich fossil record representedby
more than 60 extant and 100 extinct fossil genera (Hölldobler and
Wilson, 1990). The oldest reliably dated ant body fossils are from Early
Cretaceous (Albian–Cenomanian) amber in France and Myanmar:
already with indicators of eusociality, specialized caste members, and
arachnid predators specialized to feed on them (Perrichot et al., 2008).
Recent phylogenetic and molecular clock analyses of ant DNA suggest
that the Formicidae last shared a common ancestor sometime in the
mid-Jurassic to earliest Cretaceous (Moreau et al., 2006;seeBrady et al.,
2006 for an alternative analysis). Though fossil ants from Late
Cretaceous deposits are relatively rare, they began at that time an
explosive taxonomic radiation that appears to have closely tracked the
proliferation of angiosperm-dominated forests and culminated in their
ecological dominance of most terrestrial ecosystems by the end of the
Paleogene (Wilson and Hölldobler, 2005).
Modern ants constitute the largest eusocial insect group, and, with
only half of the estimated 22,000 extant species described, are often
the largest insect components in modern terrestrial environments by
biomass (Ward, 2007). Ants are found in virtually all terrestrial
habitats, though their diversity is highest in the soil and ground litter
of tropical forests where they are the dominant insect predators,
scavengers, and indirect herbivores (Wilson and Hölldobler, 2005).
Ant bioturbation strongly influences soil turnover rates, local porosity,
and infiltration rates by aggregating, moving, or destroying ped
structures and lowering soil bulk density (e.g., Cammeraat and Risch,
2008; Wilkinson et al., 2009). Ant activity and occupation of the soil
may regulate local soil nutrient cycles, the concentration and
decomposition of soil organic material, and the composition of local
soil microbial communities (e.g., Lobry de Bruyn and Conacher, 1990;
Nkem et al., 2000), especially in cold or arid environments where
Fig. 8. Architectural morphology and chambers of Daimoniobarax tschinkeli; A) in-situ
holotype at the Devil's Backbone locality; and B) line drawing interpretation showing
architecture of the holotype (solid lines), concretions (c), concretionary outgrowths on
the ichnofossils (co), and rhizoliths (r). C) Daimoniobarax tschinkeli specimen showing
elongate chambers and relatively vertical shafts; and D) line drawing interpretation
showing ichnofossil and concretionary outgrowths (co). D) Collected D. tschinkeli
chambers displaying generally circular to elongate and pseudopodial shapes in plan
view; arrows indicate point of intersection between chambers and shafts where
discernible. All rulers are in cm increments.
Fig. 9. Computer generated models showing the idealized architecture of Daimonio-
barax nephroides (A; side and oblique view), and D. tschinkeli (B; side and oblique view).
Models were produced using Blender v. 2.54 (Blender Foundation Software, 2010).
390 J.J. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
earthworms are rare (Folgarait, 1998). Ants live in colonies composed
typically of one or more queens and a caste of 10 to 10
6
wingless,
sterile female workers that excavate the nest, tend broods of eggs and
pupae, forage for food, or act as soldiers in defense of the colony
(Wilson and Hölldobler, 2005).
With the exception of a few nomadic species (army or driver ants),
ants live in nests excavated in soil or constructed aboveground for
shelter against temperature and moisture extremes, and for food
storage, reproduction, and fungus cultivation in some species (Sudd,
1967). Nest architecture in some species also seems to organize and
maintain divisions of labor and worker ages within the colony (e.g.,
Sendova-Franks and Franks, 1995; Tschinkel, 1999). Most ants
construct nests in soil by the mechanical removal of sediment to the
surface or to unused portions of the nest. The typical subterranean ant
nest is composed of two basic elements: 1) more or less horizontal
chambers numbering from b10 to 10
3
, and 2) narrow galleries
(tunnels and shafts) that connect chambers to each other and to the
surface (Tschinkel, 2003). The few well-studied modern ant nests are
complex structures that show species-typical differences in their
overall size and orientation, number of chambers and galleries, and
spatial density of individual elements (Tschinkel, 2003).
4.1. Fossil ant nests
Despite the seemingly ubiquitous presence of ants in modern
terrestrial habitats and their extensive body fossil record, surprisingly
few trace fossils have been attributed to ants and these are known
from only a handful of localities (Hasiotis, 2003). Two ichnogenera
have been interpreted confidently as the work of burrowing ants,
Attaichnus and Parowanichnus.
Attaichnus kuenzelii Laza, 1982 was described from the Miocene
Epecuén Formation, Argentina, and consists of large, 140–170 mm
diameter, spherical to globular chambers and smaller diameter
tunnels and shafts within a structure up to 3 m in height and 7 m in
diameter. The chambers are invariably joined from below by shafts,
15–27 mm in diameter, that extend some distance into the chamber
in some specimens. Shafts and tunnels with smaller diameters (5–
9 mm) intersect the tops of chambers and the larger diameter shafts.
Laza (1982) interpreted these and additional chambered ichnofossils
from Pliocene and Pleistocene deposits in Argentina (Laza, 1997)tobe
the nests of fungus gardening (attine) ants based on their overall
morphology, the size and shape of the chambers and burrow system,
and the conical rim within the chambers.
Parowanichnus formicoides was first described from the late
Paleocene–Eocene Claron Formation in southwestern Utah (Bown
et al., 1997). It consists of more than 100 oblate to hemispherical, 10–
50 mm diameter chambers surrounded by a dense network of
primarily horizontal, b12 mm wide tunnels and short shafts. Tunnels,
shafts, and chambers decline in number as they radiate away from the
nest center forming a structure measuring ~ 1.0 m in height and
~3.3 m wide. Parowanichnus formicoides does not closely resemble
any of the handful of well known nests of modern subterranean ants,
though Bown et al. (1997) noted that similar modern nests with
numerous horizontal tunnels are typical of humid soils. Chambered
trace fossils similar to P. formicoides have beendescribed from the Upper
Jurassic Morrison Formation in southeastern Utah (Hasiotis and Demko,
1996). A second ichnospecies of Parowanichnus,P. perirhizaterion
Hembree and Hasiotis, 2008,isverysimilartoP. formicoides, in that it
is composed of a boxwork of interconnected tunnels, shafts, and
chambersthat radiate from the nestcenter, except that nestarchitecture
follows and is confined to the immediate areaaround a central rhizolith.
A third possible ant nest ichnogenus is Socialites Roberts and
Tapanila, 2006. The type and only ichnospecies, S. tumulus, was
described from Upper Cretaceous deposits in southern Utah and is
composed of a complex network of unlined and branching tunnels
and shafts that connect larger ovate chambers within and around
cone-shaped sedimentary structures along bedding planes. While the
conical structures are very well defined, the burrow architecture
within is far more cryptic and defined mainly by differently colored
mottling in the sandstone below the cones. Given the lack of
discernible architectural morphologies with distinguishing character-
istics, an isopteran or other social insect tracemaker for Socialites
cannot be ruled out. Other ichnofossils attributed to ants have been
mentioned (e.g., Tandon and Naug, 1984; Laza, 1995; Hamer et al.,
2007; Buck et al., 2010), however, the fossils themselves were either
not the focus of the study or were not described in enough detail for
ichnotaxonomic evaluation.
4.2. Tracemakers
4.2.1. Daimoniobarax nephroides
Daimoniobarax nephroides is most similar to the nests of modern
seed-harvester ants (Formicidae: Myrmicinae), specifically of the
New World genus Pogonomyrmex (MacKay, 1981; Tschinkel, 2004).
The oldest known representative of Pogonomyrmex is the fossil species
P. fossilis Carpenter from the lacustrine shale of the Eocene Florissant
Formation in Colorado (Carpenter, 1930; Wilson, 1978). Given their
similar nest morphologies, modern harvester ants provide a useful
analog for the D. nephroides tracemaker. Harvester ants are so named
because they collect and store seeds, grains, and other plant materials
in their nests for later consumption by the colony members.
Pogonomyrmex (or “bearded ant”) is represented by more than 70
extant North and South American species (Crist, 2008). The beard is a
tuft of hairs called psammophores that extend from below the heads
of workers and are used in conjunction with the mandibles to carry
fine sediments, small seeds, and eggs. Most harvester ants are highly
specialized granivores, though some will prey on other insects when
such food is readily available (Whitford and Jackson, 2007).
Seed-harvester ants are most abundant in the sandy soils of arid to
semi-arid deserts and grasslands of the North American Southwest;
only the Florida harvester ant, Pogonomyrmex badius, occurs east of
the Mississippi River (Smith, 1979). Some harvester ant nests are
characterized on the ground surface by a barren patch of soil that
surrounds the nest entrance and has a radius of up to several meters
(MacKay, 1981). Entrances in some species are capped by a broad
mound of sediment that may contain internal chambers and can be up
to 20 cm high and over a meter wide (Cole, 1994). A mature
Pogonomyrmex nest may contain 150 chambers clustered directly
below the surface and distributed vertically up to 4 m deep along a
series of 4 to 5 helical shafts (Tschinkel, 2003, 2004). Chambers near
the surface are consistently larger, more complex, and more closely
spaced than those at depth, regardless of colony age and size
(Tschinkel, 2004). In general, colony members are stratified within
the nest by age; more mature workers are near the top of the nest and
callow (immature) ants and the brood reside at depth, possibly due to
a preference by younger workers for higher CO
2
concentrations
(MacKay, 1981; Tschinkel, 1999).
Nest construction and chamber enlargement by the Baraxodaimi-
nios nephroides tracemakers were likely analogous to the excavation
methods of harvester ants based on the strong morphological
similarities between D. nephroides and modern harvester nests
(Tschinkel, 2004). The teardrop shaped chambers of D. nephroides
likely represent the nascent phase of chamber excavation (Fig. 7D).
Chamber enlargement proceeded primarily by the removal of soil
material from the lateral walls of the chamber and back towards and
around the shafts creating horizontally oriented and bilobed, reniform
chambers. Further chamber expansion in this manner resulted in
large, U-shaped chambers that nearly surround central shafts.
4.2.2. Daimoniobarax tschinkeli
The chamber and shaft morphologies of Daimoniobarax tschinkeli
and their relatively simple architectural arrangement appear more
391J.J. Smith et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 308 (2011) 383–394
generalized when compared with D. nephroides. It should be noted
that differentiation between the two Daimoniobarax ichnospecies is
difficult without burrow systems preserved at least partially in
positive relief. Though not diagnostic enough to infer a particular
taxon of ant tracemaker, nest morphologies similar to D. tschinkeli are
known from the subterranean nests or nest portions of such diverse
genera as Myrmecocystus (Conway, 1983), Prenolepis (Tschinkel,
1987), Ectatomma (Antonialli and Giannotti, 2001), Aphaenogaster
(Tschinkel, 2003), and Pheidole (Forti et al., 2007). A better
understanding of the range of modern ant-nest morphologies is
needed to make a more specific interpretation of the tracemaker.
4.3. Paleoenvironmental and paleoecological significance
Although modern ants live in a wide range of terrestrial habitats
and climates, fossil nests can provide some specific information about
paleoecological and paleoenvironmental conditions during nest
construction and occupation. Recognizable ant nests in the fossil
record are important because ant body fossils are relatively rare and
are often preserved in amber or in lacustrine deposits (e.g., Wilson,
1978) and out of their original ecological context (Hasiotis, 2003).
Fossil nests, however, are direct evidence for the presence of ants
within an ancient ecosystem and such ichnofossils are more likely to
be present in depositional and paleopedogenic settings where insect
body fossils are rarely preserved. Although the earliest body fossil of a
given taxon is more commonly used to infer its phylogenetic origin,
diagnostic trace fossils can be used as proxies for the presence of an
organism or group or organisms with similar behavior and anatomies
(e.g., Hasiotis and Mitchell, 1993). Of equal importance is the use of
ant nest ichnofossils for interpreting the evolutionary history of novel
behaviors and the paleoenvironmental conditions under which these
behaviors developed.
An abundance of ant nests suggests relatively low aggradational
rates or a depositional hiatus during which host sediments were
subaerially exposed and pedogenically modified (Hasiotis, 2007;
Smith et al., 2008b). As with most modern ants, fossil tracemakers
likely constructed subterranean nests in the vadose (unsaturated)
zone of generally well-drained or quickly draining soils. The higher
porosity and lower bulk density of the nests themselves create soil
microhabitats that promote rapid drainage after precipitation (e.g.,
Green et al., 1999). In addition, the open burrows extend the
subsurface effects of subaerial exposure and pedogenesis beyond
their normal range (Hole, 1981).
The morphology of fossil ant nests may provide information on
paleosurface position because the size, shape, and vertical spacing of
chambers, and the number and orientation of shafts in the nests of
many extant ant species change with depth (e.g., Tschinkel, 2003). For
example, Pogonomyrmex badius chambers within 15 cm of the soil
surface are consistently larger, more complex, and more closely
spaced than those at depth (Tschinkel, 2004). The vertical distance
between chambers along a descending shaft increases with nest depth
while the size and complexity of the chambers decrease. In some
mature P. badius nests, descending shafts branch at depth, but this
always occurs within 40 cm of the ground surface. Such depth-related
morphological changes could be used as paleosurface and paleodepth
indicators or as geopetal features. If the paleosurface could be
inferred, nest depths as suggested by the vertical height of their
ichnofossils in outcrop may correspond with the depth of the local
water table during the time of construction. Though such morpho-
logical features are suggested or can be quantified in some well-
preserved fossil nests, e.g., the significant decreases in vertical spacing
toward the tops of nests, vagaries in outcrop exposure and specimen
preservation may make it difficult to interpret confidently whether
seemingly connected chambers are portions of the same nest.
Fossil nests, if distinctive enough, may also suggest specific paleocli-
matic interpretations. The architectural morphology of Daimoniobarax
nephroides is very similar to the nests of modern seed-harvester ants in
the genus Pogonomyrmex.IftheD. nephroides tracemaker had climate
and habitat preferences similar to those of modern harvester ant
species, this would imply arid to semi-arid grassland or desert
conditions in the High Plains region during the time of traceformation.
While this interpretation is not inconsistent with the climate conditions
associated with modern settings where thick petrocalcic horizons are
forming (Wright, 2007), an arid to semi-arid paleoclimate is not
necessarily suggested from ongoing paleobotanical studies from these
same localities (Thomasson, 1979, 1990, 2003, 2009).
Although it is beyond the scope of this paper, there is increasing
interest in the role that micro- and macroorganisms play in the
formation and placement of calcic horizons in soils and sediments
(e.g., Wright et al., 1995; Singh et al., 2007; Zhou and Chafetz, 2009).
Fossil ant-nest chambers in the type locality are preserved more
abundantly and stacked more closely together in calcrete beds, and
possibly nearer the paleosurface, compared with less calcified
underlying strata. Modern ant bioturbation lowers soil bulk densities,
enhances infiltration and aeration, enriches organic matter in the nest,
and redistributes soil nutrients and minerals relative to surrounding
soils (e.g., Wagner et al., 1997). Likewise, the Daimoniobarax trace-
maker may have altered physical and chemical soil properties in ways
that promoted the precipitation of thick petrocalcic horizons in the
Ogallala soils after burial. Research on how ancient soil biota
influenced the formation of pedogenic calcretes at Ladder Creek
Canyon and other Ogallala Formation localities is ongoing.
5. Conclusions
Many, though not all, of the honeycomb calcrete structures at the
Devil's Backbone and other localities in the Ogallala Formation are the
fossil casts of ant nests. Daimoniobarax is established to represent multi-
chambered ichnofossils of this type composed of vertically tiered,
horizontally oriented, pancake-shaped chambers connected by sub-
vertical to vertical, small-diameter shafts. Two ichnospecies,
D. nephroides and D. tschinkeli, can be discerned based on differences
in the plan view outline of their chambers, shaft orientations, and points
of intersection between chambers and shafts. In comparison with the
known nest architectures of modern subterranean ant species, D.
nephroides is most similarto the nests of New World seed-harvester ants
of the genus Pogonomyrmex,whileD. tschinkeli is more general in form
and doesn't closely resemble any particular known modern ant or insect
nest. Given that there are likely as many different ant-nest morphotypes
as there areant species, there are maybe a diverse array of unrecognized
or undiscovered Daimoniobarax ichnospecies in the geologic record.
Such recognition will provide a more comprehensive understanding of
the ecological diversity of ancient terrestrial environments.
Acknowledgments
The authors thank Walter Tschinkel, Stephen Hasiotis, Daniel
Hembree,Rolfe Mandel, MariosSophocleous and AlanHalfen for helpful
advice and discussions. We thank David Bottjer, Andrew K. Rindsberg,
and Leif Tapanila for their thoughtful and constructive reviews that
greatly improved the clarity of this manuscript. Thanks go also to Leif
Milliken of the University of Nebraska Press for help with establishing
the copyright status of Barbour images in Fig. 6.WethankMartinStein
for his help with the Blender software. Thisresearch was funded in part
by a Kansas Geological Survey Small Grant for Research to G. Ludvigson,
R. Mandel, and A. Macfarlane.
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