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Sullivan, R.M. and Lucas, S.G., eds., 2015, Fossil Record 4. New Mexico Museum of Natural History and Science Bulletin 67.
BIOSTRATIGRAPHY OF ANKYLOSAUR (DINOSAURIA: ORNITHISCHIA)
OSTEODERMS FROM NEW MEXICO
MICHAEL E. BURNS1 and SPENCER G. LUCAS2
1Department of Biological Sciences, University of Alberta, 11455 Saskatchewan Drive Edmonton, Alberta, Canada T6G 2E9;
2New Mexico Museum of Natural History, 1801 Mountain Road NW, Albuquerque, NM, 87104
Abstract—Several previously undescribed specimens of ankylosaur osteoderms from New Mexico, allow for a
revision of the biostratigraphic distribution of New Mexican ankylosaur taxa. An osteoderm from the Upper Jurassic
Peterson Quarry (Morrison Formation, Brushy Basin Member) referable to Gargoyleosaurus or Mymoorapelta
represents the rst reported occurrence of Jurassic ankylosaur material in New Mexico. An ankylosaurid osteoderm
from the De-na-zin Member of the Kirtland Formation is consistent with other ankylosaurid material previously
collected from the unit. Several osteoderm specimens collected from the Fruitland Formation (Fossil Forest
Member) are referable to the nodosaurid Glyptodontopelta mimus. Previously known only from the Maastrichtian
Naashoibito Member of the Ojo Alamo Formation, these specimens extend the stratigraphic range of the taxon
back at least 5 My.
INTRODUCTION
The terrestrial Mesozoic sediments of New Mexico have produced
signicant specimens of dinosaurs, representing most of the major
groups currently recognized (Sullivan and Lucas, 2006). Ankylosaur
osteoderm remains have long been known to occur, predominantly in
the Upper Cretaceous Fruitland and Kirtland formations of the San Juan
Basin (Fig. 1). Historically, this material was referred to well-known
ankylosaur taxa from northern Laramidia (Gilmore, 1919; Lehman,
1981). In 1999, Sullivan named Nodocephalosaurus kirtlandensis from
the De-na-zin Member of the Kirtland Formation as the rst ankylosaur
taxon unique to New Mexico. Ford (2000) named Glyptodontopelta
mimus based on a fragment of the pelvic shield and other isolated
osteoderms from the lower Maastrichtian Naashoibito Member of the
Ojo Alamo Formation. Burns (2008) conrmed the validity of the taxon
and reassigned it to the Nodosauridae, synonymizing Edmontonia
australis with G. mimus. Glyptodontopelta is the only recognized
representative of the Nodosauridae from New Mexico and is known
only from osteoderms. Ahshislepelta minor, a small ankylosaurid,
was named from the Hunter Wash Member of the Kirtland Formation
by Burns and Sullivan (2011b). The holotype includes complete and
fragmentary thoracic osteoderms. Most recently, Arbour et al. (2014)
named Ziapelta sanjuanensis for a complete skull and rst cervical
half ring from 6–10.5 meters below, and 525 meters laterally from, the
type locality of N. kirtlandensis. The osteoderms of Ahshislepelta are
characterized by a smoother surface texture than Nodocephalosaurus or
Ziapelta, a texture which is also distinct from all other ankylosaurines
except Euoplocephalus (Burns and Sullivan, 2011b; Arbour et al., 2014).
Based on current material, the osteoderms of Nodocephalosaurus and
Ziapelta cannot be distinguished from one another.
This contribution reviews the occurences of ankylosaur osteoderms
from New Mexico and presents previously undescribed specimens
that add to our understanding of their geographic and stratigraphic
distribution.
Institutional Abbreviations: AMNH = American Museum of
Natural History, New York; DMNH = Denver Museum of Nature and
Science, Denver, CO; MWC = Museum of Western Colorado, Grand
Junction, CO; NMMNH = New Mexico Museum of Natural History,
Albuquerque, NM; SMP = State Museum of Pennsylvania, Harrisburg,
PA; USNM = National Museum of Natural History, Smithsonian
Institution, Washington, D.C.
MATERIALS AND METHODS
Ankylosaur osteoderm specimens from New Mexico were
examined in the collections of the NMMNH, SMP, and USNM. The
rst author has also examined comparative material from numerous
institutions worldwide. Variation in morphology and surface textures
among ankylosaur osteoderms was noted through observations and
photographs. The stratigraphic nomenclature for the Upper Cretaceous
of the San Juan Basin is from Sullivan and Lucas (2006). Anatomical
terminology follows Penkalski (2001), Vickaryous and Russell (2003),
Scheyer and Sander (2004), Burns (2008), and Burns and Currie
(2014). Surface textural descriptions follow Hieronymus et al. (2009)
and Burns and Currie (2014).
OCCURRENCE AND GEOLOGICAL SETTING
The most extensive Upper Jurassic vertebrate-fossil assemblage in
New Mexico is the Peterson Quarry (Bernalillo County), representing a
stratigraphic interval from the lower part of the Brushy Basin Member
of the Morrison Formation, from which most Morrison dinosaur-bearing
localities are found (Turner and Peterson, 1999; Foster, 2003; Heckert
et al., 2003). Vertebrate fossils occur as fragmentary to articulated
elements within a 1.1-m-thick sequence of trough-crossbedded,
subarkosic sandstone. To date, the Peterson quarry has been considered
to yield only fossils of saurischians, namely sauropods (diplodocoid
and camarasaurid) and allosaurids (Hunt and Lucas, 1993; Foster,
2003; Heckert et al., 2003). It also produced an incomplete shell of the
FIGURE 1. Map of New Mexico showing distribution of Cretaceous
outcrops and ankylosaur localities. 1 = Late Cretaceous ankylosaur
records from the west-central San Juan Basin; and 2 = Upper Jurassic
ankylosaur record at the Peterson quarry.
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FIGURE 2. Late Cretaceous ankylosaur osteoderms from the San Juan Basin of New Mexico. NMMNH P-20880, cervical/pectoral half-ring
osteoderms from Glyptodontopelta mimus: right medial, keeled osteoderm in external (A) and basal (B) views, anterior is up; partial osteoderm in
external (C) and basal (D) views, sagittal is up/down, orientation uncertain; oval osteoderm with a sagittally-oriented keel in external (E) and basal
(F) views, sagittal is up/down, orientation uncertain. Partial circular, keeled ?thoracic osteoderm (NMMNH P-22753) of Glyptodontopelta mimus
in external (G) and basal (H) views, sagittal is up/down, orientation uncertain. Keeled ?thoracic osteoderm (NMMNH P-27404) of Ankylosauridae
indet. in external (I) and basal (J) views, sagittal is up/down, orientation uncertain. All from Fossil Forest Member of Fruitland Formation, except
I-J, which is from De-na-zin Member of Kirtland Formation.
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characteristic Morrison turtle genus Glyptops (Lucas et al., 2006).
The Upper Cretaceous vertebrate fossil record of New Mexico is
best known from the Fruitland, Kirtland, and Ojo Alamo formations.
The oldest of these, the Fruitland Formation, is temporally equivalent
to the Judith River (Montana) and Oldman (Alberta) formations of late
Campanian (Judithian) age (Lucas et al., 1987). The Kirtland Formation
overlies the Fruitland Formation and consists of interbedded sandstone,
siltstone, mudstone, coal and shale that is up to 594 m thick (Fassett
and Hinds, 1971). It is roughly contemporaneous with the Bearpaw
Formation (Alberta, Canada) according to ammonite occurrences and
radioisotopes (Obradovich, 1993; Eberth et al., 2001; Lerbekmo and
Braman, 2002; Sullivan and Lucas, 2003; Sullivan and Lucas, 2006).
Sullivan and Lucas (2003) recognized three members within the
formation: Hunter Wash, Farmington, and De-na-zin. The uppermost
of the three members, the De-na-zin Member, lacks the coal layers
characteristic of the older Hunter Wash Member (Sullivan and Lucas,
2003). The lower boundary of the lower conglomerate of the Ojo
Alamo Formation, found above the De-na-zin Member, is demarcated
by an unconformity (Sullivan and Lucas, 2006). Ages from40Ar/39Ar
dating from the De-na-zin Member include Ash H (72.98 ± 0.18 Ma;
originally 73.37 Ma) and Ash J (72.66 ± 0.25 Ma, originally 73.04 Ma)
(Fassett and Steiner, 1997; Lucas and Sullivan, 2000; Sullivan et al.,
2005; Sullivan and Lucas, 2006) These numbers have been recalculated
using Roberts et al. (2013), but the recalibration may be problematic
(see Sullivan and Robinson, this volume).
The base of the Ojo Alamo Formation has been correlated to ~ 69
Ma, based on the index taxon Alamosaurus (Sullivan and Lucas, 2006;
Sullivan et al., 2005; Jasinski et al., 2011). This correlation puts the
formation within the Maastrichtian.
DESCRIPTIVE RESULTS
Glyptodontopelta mimus
Several specimens in the NMMNH collection were collected
from the Fruitland Formation and are referable to Glyptodontopelta
mimus based on their diagnostic surface texture (Burns, 2008; Burns
and Currie, 2014). All of the osteoderms of G. mimus have the same
external surface texture characterized by their lack of surface rugosity
and the presence of a dense pattern of reticular neurovascular grooves.
Neurovascular foramina are sparse and oriented normal to the external
surface. The basal surfaces are at relative to the external surfaces and
preserve sparse neurovascular foramina.
Several partial osteoderms (NMMNH P-20880) likely represent
elements of the cervical/pectoral half-rings. One of these (Fig. 2A-
B) is a right medial, keeled osteoderm similar to the corresponding
elements known for Panoplosaurus mirus (Carpenter, 1990). The
medial side is parallel to the median sagittal plane, whereas the lateral
side diverges posteriorly from it by 10°. The keel is parallel to the
medial side anteriorly and diverges posteriorly, becoming parallel to
the lateral side. The median posterior corner is broken in this specimen.
An osteodermal fragment (Fig. 2C-D) may also represent a cervical
or pectoral element. Although incomplete, it does have a keel oriented
sagittally for at least the preserved portion of its length. Two relatively
large foramina perforate the basal surface. A third osteoderm (Fig.
2E-F) is oval with a sagittal-oriented keel. It is similar in morphology
to the lateral osteoderms from the second cervical half rings seen in
Edmontonia rugosidens (e.g., AMNH 5665). Broken sections for all
three osteoderms show that their cores were composed of trabecular
bone. A weathered and fragmentary specimen (NMMNH P-22753; Fig.
2G-H) likely represents a circular, keeled posterior thoracic osteoderm.
Ankylosauridae indet.
One isolated osteoderm (NMMNH P-27404; Fig. 2I-J) is referable
to Ankylosauridae based on its excavated basal surface. It has a
posteriorly-divergent keel and is likely from the thoracic region. It
was collected from the De-na-zin Member of the Kirtland Formation,
from which other ankylosaurid material has been collected (Sullivan,
1999; Sullivan and Fowler, 2006; Burns and Sullivan 2011a; Arbour
et al., 2014). However, the two ankylosaurid taxa currently recognized
from the formation, Nodocephalosaurus kirtlandensis and Ziapelta
sanjuanensis, cannot be distinguished on the basis of their postcranial
osteoderms given the material currently associated with their holotypes
(Arbour et al., 2014). Therefore, they may only be condently assigned
at present to Ankylosauridae indet.
Ankylosauria indet.
NMMNH P-58749 (Fig. 3A-B) was collected from the Peterson
Quarry, Brushy Basin Member, Morrison Formation. It is an oval
(wider than long), keeled osteoderm with a at basal surface.
Although the external surface is somewhat weathered, there are no
neurovascular grooves or pits present, and the surface texture is
rugose. The overall morphology is most similar to osteoderms of the
roughly contemporaneous Mymoorapelta Kirkland and Carpenter,
1994 (Fig. 3C) and Gargoyleosaurus Carpenter et al., 1998 (Fig. 3D).
In general, osteoderms from Mymoorapelta tend to be less basally
excavated than those from similar body positions in Gargoyleosaurus
(J. Kirkland, pers. comm., 2015), although this has not been tested
statistically. For this reason, NMMNH P-58749 may have more afnity
to Mymoorapelta. This newly reported Jurassic ankylosaur osteoderm
is the oldest ankylosaur record from New Mexico and the rst record of
an ornithischian dinosaur from the Peterson quarry.
NEW MEXICAN ANKYLOSAUR STRATIGRAPHY AND
DIVERSITY
Based on material reported here, New Mexico has both Late
Jurassic and Late Cretaceous records of ankylosaurs (Fig. 4). Late
Jurassic ankylosaur taxa from North America include Mymoorapelta
maysi and Gargoyleosaurus parkpinorum. Mymoorapelta was
originally described based on material from the Mygatt-Moore quarry
in Mesa County westernmost Colorado, from the middle of the Brushy
Basin Member of the Morrison Formation, probably a bit higher in
section than the Peterson Quarry. Gargoyleosaurus is known from
the lower part of the middle Morrison Formation near Bone Cabin
Quarry, Albany County, Wyoming. The preservation of NMMNH
P-58749 is more similar to that of Mymoorapelta material from the
Mygatt-Moore quarry (Fig. 3C), although it is stratigraphically closer
to Gargoyleosaurus.
Since 1999, Nodocephalosaurus kirtlandensis had been considered
the only ankylosaurid from the De-na-zin Member of the Kirtland
Formation until Ziapelta sanjuanensis was named from the same
FIGURE 3. Oval, keeled thoracic ankylosaur osteoderm (NMMNH
P-58749) from the Jurassic Brushy Basin Member, Morrison Formation,
New Mexico, in external (A) and basal (B) views. Its morphology
is most similar to thoracic osteoderms of the contemporaneous
Gargoyleosaurus (DMNH 27726, holotype, C, external view) and
Mymoorapelta (MWC 210, D, external view). Schematic hypothetical
cross sections through thoracic osteoderms of similar body placement
from Gargoyleosaurus (E) and Mymoorapelta (F). Anterior is up in
A–D and external is up in E–F.
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FIGURE 4. Revised lithostratigraphic section and biostratigraphic
distribution of currently valid ankylosaur taxa from the Upper
Cretaceous San Juan Basin of New Mexico. Modied from Fowler
(2006) and Sullivan and Lucas (2006) with information from Jasinski
et al. (2011), Roberts et al. (2013) and Sullivan and Lucas (2014).
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kirtlandensis (Dinosauria: Ankylosauridae), with a review of ankylosaurid
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and paleontology of the Upper Jurassic (Morrison Formation: Brushy
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Formation (Naashoibito Member), San Juan Basin, New Mexico: New
Mexico Museum of Natural History and Science, Bulletin 53, p. 216–265.
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and continental strata from the Red Deer Valley to the Cypress Hills,
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Lucas, S.G., and Sullivan, R.M., 2000, The sauropod dinosaur Alamosaurus
from the Cretaceous of the San Juan Basin, New Mexico: New Mexico
Museum of Natural History and Science, Bulletin 17, p. 147–156.
Lucas, S.G., Rinehart, L. F. and Heckert, A. B., 2006, Glyptops (Testudines,
Pleurosternidae) from the Upper Jurassic Morrison Formation, New
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member (Arbour et al., 2014). The small Ahshislepelta minor is known
only from the holotype from the older Hunter Wash Member (Burns
and Sullivan, 2011b; Fig. 4). Nodocephalosaurus may be characteristic
of the Willow Wash local fauna, and Ahshislepelta is characteristic
of the older Hunter Wash local fauna. The diversity of ankylosaurids
in the San Juan Basin is higher than that of nodosaurids based on the
specimens currently known, and all of the named ankylosaurid taxa
are characteristic of the Kirtlandian land-vertebrate age (Sullivan and
Lucas, 2003, 2006). Because little osteodermal material that can be
condently referred to a taxon has been collected from the De-na-zin
Member (Sullivan and Fowler, 2006; MEB, pers observ.), NMMNH
P-27404 is here conservatively referred to Ankylosauridae indet.
Glyptodontopelta had been considered restricted to the early
Maastrichtian Naashobito Member of the Ojo Alamo Formation and a
taxon characteristic of the Alamo Wash local fauna (Ford, 2000; Burns,
2008; Jasinski et al., 2011). However, the osteodermal specimens
described here demonstrate the taxon’s occurrence in the Fruitland
Formation, which underlies the Kirtland Formation, extending the
stratigraphic range of Glyptodontopelta up to 5.5 My (Fig. 4), although
this is difcult to assess due to the uncertainty surrounding the age
of the Naashoibito Member (Sullivan and Lucas, 2003; Sullivan et
al., 2005; Jasinski et al., 2011). Additional specimens may further
extend the stratigraphic and geographic ranges of this taxon or present
justication for taxonomic revision. At present, it remains the only
nodosaurid taxon known from New Mexico.
ACKNOWLEDGMENTS
Phil Currie read over an early draft of this manuscript. Funding to
MEB was provided by the Alberta Historical Resources Foundation,
Alberta Lottery Fund, Dinosaur Research Institute, and the University
of Alberta, Department of Biological Sciences. J. Kirkland, M. Loewen
and R. M. Sullivan provided helpful reviews of the manuscript. New
Mexican specimens were collected under BLM Paleontological
Resources Use Permits on le at the New Mexico Museum of Natural
History and Science.
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