Ankylosaurian dinosaur osteoderms have been discovered in the southeastern part of the State of Coahuila, Mexico, in the township of General Cepeda, in the locality known as El Palmar. The osteoderms were collected from rocks that had been correlated to the Cerro del Pueblo Formation (Late Cretaceous: Campanian) of the Difunta Group. The fossil material includes four dermal scutes and three associated fragments that at present cannot be identified. This is the first description of ostoederms and ankylosaurian material from Coahuila.
Ankylosauridae, dermal scute, Late Cretaceous, Coahuila, Mexico
H.E. & B. (2006).- Ankylosaurid (Dinosauria: Thyreophora) osteoderms from the Upper Cretaceous Cerro del Pueblo Formation of Coahuila, Mexico.- Carnets de Géologie / Notebooks on Geology, Brest, Letter 2006/02 (CG2006_L02)
Découverte de plaques osseuses d'Ankylosauridé (Dinosauria : Thyreophora) du Crétacé supérieur de la Formation Cerro del Pueblo à Coahuila, Mexique.- Des plaques osseuses d'un ankylosauridé ont été découvertes dans la localité El Palmar, commune de General Cepeda, SE de l'État de Coahuila. Ces fossiles proviennent de couches sédimentaires appartenant à la Formation Cerro del Pueblo (Crétacé supérieur : Campanien) du Groupe Difunta. Le matériel comprend des plaques osseuses identifiées comme appartenant à la famille Ankylosauridae et d'autres fragments associés qui n'ont pas été identifiés. Nous présentons ici la première description détaillée de matériel de ce type provenant de l'État de Coahuila.
Ankylosauridae, plaques osseuses, Crétacé supérieur, Coahuila, Mexique
Osteodermos de un Ankylosaurio (Dinosauria : Thyreophora) del Cretácico
superior de la Formación Cerro del Pueblo provenientes de Coahuila, México.-
Osteodermos de un dinosaurio ankylosáurido fueron descubiertos en la parte sureste del Estado de Coahuila, México, Municipio de General Cepeda, en la localidad El Palmar. Los osteodermos fueron colectados de rocas que han sido relacionadas a la Formación Cerro del Pueblo (Cretácico superior : Campaniano) del Grupo Difunta. El material fósil incluye cuatro placas óseas y tres fragmentos asociados que no pueden ser identificados. Esta es la primer descripción de este tipo de osteodermos y material de ankylosáurido para Coahuila.
Ankylosauridae, placa ósea, Cretácico
superior, Coahuila, México
This short communication reports the finding of ankylosaur osteoderms from the area locally known as El Palmar. The site is located 12 km. northeast of the town of La Rosa, in the township of General Cepeda, Coahuila
(Fig. 1
). The fossils described in this study were collected from strata that have been correlated with the Cerro del Pueblo Formation, from the Late Cretaceous (Campanian) Difunta Group, ( et alii,
1974). Other vertebrate and invertebrate remains were collected along with the ankylosaur material, among them several gastropods, bivalves, turtles of the family Tryonichidae, crocodiles and some unidentified fish vertebrae.
It is thought that the Cerro del Pueblo Formation, which consists of mudstone deposits, shell coquinas, and sandstones, was deposited on a low-gradient and broadly homogeneous coastal plain with transgressive-regressive episodes. This environment was a plant-rich wetland, with channels, lakes, swamps, coastal lagoons, deltaic lakes and bay deposits ( et alii,
1974).
Ankylosaurs are well known from the Upper Cretaceous sediments of Asia (China, Mongolia) and North America (Canada, United States). In North America both major ankylosaur lineages, Ankylosauridae and Nodosauridae, are represented ( et alii,
1998). Perhaps the most characteristic synapomorphy of ankylosaurs is the presence of osteoderms and the development of osseous cranial ornamentation (,
1986, 1999; & ,
1990; et alii,
2001).
The distribution of dermal scutes is extensive, reaching from the neck to the distal end of the tail, and sometimes can include elements across the abdomen ( et alii,
2003); the individual osteoderms resemble oval to rectangular plates that may or may not be keeled or bear a spine. They are arranged bilaterally in transverse rows, with a mosaic of much smaller plates filling the spaces between larger elements (,
1986). Larger osteoderms commonly bear a longitudinal ridge or keel that tends to be higher on plates toward the flanks of the body, although in some species these ridges may be higher near the midline too, in some rows as in Euoplocephalus tutus (,
1982). And in ankylosaurids, the individual plates tend to be widely separated, but retain their oval shape ( & ,
1990).
Material from the El Gallo Formation in Baja California (,
1971, 1973), and from other outcrops of the Cerro del Pueblo Formation in Coahuila had been referred to the genus Euoplocephalus ( et alii,
2003; et alii,
2006), but none of these materials has been described, so this is the first published description of fossils of this type from Mexico.
Material: The specimens are stored at the Museo de Paleontología of the Benemérita Escuela Normal de Coahuila (BENC). The material consists of four osteoderms (BENC-1/4-0001; BENC-1/4-0002; BENC-1/4-0003, and BENC-1/4-0004), that were recovered in association with three other indeterminate fragments (BENC-1/4-0005).
Horizon and Locality: The material was recovered from the Cerro del Pueblo Formation (Difunta Group, Upper Cretaceous, Campanian), 12 km northeast from the town of La Rosa, Township of General Cepeda, Coahuila, Mexico.
Description: When viewed dorsally, osteoderm BENC-1/4-0001 is oval in outline, apparently symmetrical, with a surface marked by a raised blunt keel oriented obliquely; the ventral surface is excavated. Osteoderm BENC-1/4-0002 has a circular shape when view dorsally, with a concave dorsal surface, and a convex ventral surface. Osteoderm BENC-1/4-0003 has a circular dorsal profile and lacks a keel. BENC-1/4-0004 is broken with the preserved portion semicircular in dorsal view; it has a slightly concave dorsal surface and a concave ventral surface.
Measurements:
Measurements (in mm) of armor elements. H, height of osteoderm from base to top of crest; L, length of osteoderm along line of crest; W, width of osteoderm at right angle to length.
|
Armor Scutes |
|
L |
W |
H |
|
BENC - 1/4 - 0001 |
Wide Scute |
81 |
113 |
43 |
|
BENC - 1/4 - 0002 |
Circ. Scute |
66 |
83 |
26 |
|
BENC - 1/4 - 0003 |
Circ. Scute |
48 |
50 |
16 |
|
BENC - 1/4 - 0004 |
Circ. Scute |
34 |
39 |
21 |
The most diagnostic feature of the ankylosaurs is their armour (,
1908; , 1982,
1984, 1990). Although several authors have proposed separate sets of terminology to describe the various shapes and sizes of ankylosaur osteoderms (,
2000; , 2001), the utility of these vocabularies remains untested, and therefore we describe them here using customary terminology. Ankylosaur armour is variable between genera, but is generally composed of small rounded osteoderms that form a fairly continuous shield over the dorsal surface of the body with large oval, flat or keeled elements on the neck and shoulders (,
1997), and small keeled elements on the back and tail. The dermal ossifications of the back had a wide range of shapes according to their positions on the different areas (,
1928). The osteoderms described here are referred to the Family Ankylosauridae based on the morphological features observed in the preserved material, mainly in BENC-1/4-0001
(Fig. 2A-C
), where the plates are relatively thin-walled and deeply excavated ventrally as described by
(1978) and (2004) for the Ankylosauridae. They differ from the osteoderms of the Nodosauridae which have a flat ventral surface. The dorsal surface of our specimen has a sharp crest, low at the front end, but rising at the posterior end as described by
(1928), and it is in accordance with
(1978) observations regarding the Ankylosauridae, for its height does not exceeds that of the maximum basal diameter.
Specimens BENC-1/4-0002, BENC-1/4-0003 and BENC-1/4-0004 may be from the legs, among the large plates there (,
1982) or, according to
(1928) could be from the intercalated rows which consist only of flat dermal osteoderms with a more or less circular outline.
The three fragments catalogued under the number BENC-1/4-0005 cannot be osteoderms for they are comprised of more massive and vascularised bone. They might be elements of the skull (,
1981) or another bone that with these characteristics. Because they are fragmentary we cannot identify them more precisely.
The osteoderms (BENC-1/4-0001 and BENC-1/4-0002) share similarities: the oval outline, a keel and an excavated ventral surface, like those referred to Euoplocephalus by
(1910), (1924),
(1928), and (2001). In addition, Euoplocephalus is the most common Campanian-Early Maastrichtian ankylosaurid of western North America ( & ,
1990). However, while it is plausible that the material from Coahuila may represent this taxon, especially considering that the sediments of the Cerro del Pueblo Formation are dated Campanian, at the present time data are insufficient for provide a conclusive identification.
Acknowledgements
We thank Leonel G. , and Mario for their contribution to this research. We extend our thanks to Anibal G. , Simon M. , Ben G. and Linda E. who kindly reviewed a first draft of this manuscript. Thanks also to the referees (Kenneth , Matthew K. and Attila ) for their useful comments.
P. & , D.A. (1978).- Paleoecology of Dinosaur Provincial Park (Cretaceous), Alberta, interpreted from the distribution of articulated remains.- Canadian Journal of Earth Sciences, vol. 15, p. 1012-1024.
W.T. (2001).- Dermal armor of the polacanthine dinosaurs. In: K. (ed.), The Armored Dinosaurs.- Indiana University Press, Bloomington, p. 130-140.
B. (1908).- The Ankylosauridae, a new family of armored dinosaurs from the Upper Cretaceous.- Bulletin of the American Museum of Natural History, vol. 24, p. 187-201.
K. (1982).- Skeletal and dermal armor reconstruction of Euoplocephalus tutus (Ornithischia: Ankylosauridae) from the Late Cretaceous Oldman Formation of Alberta.- Canadian Journal of Earth Sciences, vol. 19, p. 689-697.
K. (1984).- Skeletal reconstruction and life restoration of Sauropelta (Ankylosauria: Nodosauridae) from the Cretaceous of North America.- Canadian Journal of Earth Sciences, vol. 21, p. 1491-1498.
K. (1990).- Ankylosaur systematics: Example using Panoplosaurus and Edmontonia. In: K. & P.J. (eds.), Dinosaur Systematics: Approaches and Presepectives.- Cambridge University Press, Cambridge, p. 281-298.
K. (1997).- Ankylosaurs. In: J.O., & M.K. (eds.), The Complete Dinosaur.- Indiana University Press, Bloomington, p. 307-316.
K. (2001).- Phylogenetic Analysis of the Ankylosauria. In: K. (ed.), The Armored Dinosaurs.- Indiana University Press, Bloomington, p. 455-482.
K. (2004).- Redescription of Ankylosaurus magniventris 1908 (Ankylosauridae) from the Upper Cretaceous of the Western Interior of North America.- Canadian Journal of Earth Sciences, vol. 41, p. 961-986.
K., C. & K. (1998).- Skull of a Jurassic Ankylosaur (Dinosauria).- Nature, vol. 393, p. 782-783.
W.P. Jr. (1978).- The Families of the Ornithischian Dinosaur Order Ankylosauria.- Palaeontology, vol. 21, p. 143-170.
W.P. Jr. & T. (1990).- Ankylosauria. In: D.B., P. & H. (eds.), The Dinosauria, 1st Edition.- University of California Press, Berkeley, p. 456-483.
T.L. (2000).- A review of ankylosaur osteoderms from New Mexico and a preliminary review of ankylosaur armor. In: S.G. & A.B. (eds.), Dinosaurs of New Mexico.- New Mexico Museum of Natural History Science Bulletin, vol. 17, p. 157-176.
L.M. (1910).- Note on the parietal crest of Centrosaurus apertus, and a proposed new generic name for Stereocephalus tutus.- The Ottawa Naturalist, vol. 14, p. 149-151.
E.F., A.E., J.A. & R.C. (1974).- Stratigraphy and Structure of the Parras and La Popa Basins, Northeastern Mexico.- Geological Society of America Bulletin, vol. 84, p. 1603-1622.
W.J. (1971).- Mesozoic and Tertiary Vertebrates in Baja California.- National Geographic Society Research Report, 1966 Projects, p. 195-198.
W.J. (1973).- Mesozoic and Tertiary Vertebrates in Baja California.- National Geographic Society Research Report, 1966 Projects, National Geographic Society, Washington, D.C., p. 197-209.
F. (1928).- Palaeontological notes on reptiles.- Geologica Hungarica, Series Palaeontologica, vol. 1, n° 1, p. 1-84.
H.F. (1923).- Two Lower Cretaceous dinosaurs of Mongolia.- American Museum Novitates, n° 95, p. 1-10.
R. (1842).- Report on British fossil reptiles.- Pt. II.: Report British Association for the Advancement of Science, vol. 11, p. 60-204.
W.A. (1924).- Dyoplosaurus acutosquameus, a new genus and species of armoured dinosaurs; and notes on a skeleton of Prosaurolophus maximus.- University of Toronto Studies, Geological Series, vol. 18, p. 1-35.
P. (2001).- Variation in Specimens Referred to Euoplocephalus tutus. In: K. and K.I. (eds.), The Armored Dinosaurs.- Indiana University Press, Bloomington, p. 261-297.
H.E., R.A. & J.A. (2006).- Review of the dinosaurian record from Mexico. In: F., T.G., M.C., M., S. & S.A. (eds.), Studies on Mexican Paleontology.- Springer, Netherlands, p. 233-248.
P. (1986).- Phylogeny of the bird-hipped dinosaurs (order Ornithischia).- National Geographic Research, n° 2, p. 234-256.
P.C. (1999).- The evolution of dinosaurs.- Science, vol. 284, n° 5423, p. 2137-2147.
T.A. (1981).- The Morphological Uniqueness of Ankylosauria (in Russian).- Paleologicheskii Zhurnal, Paleontological Institute of the Academy of Sciences of the USSR, p. 124-128.
M.K., A.P. & P.J. (2001).- Cranial ornamentation of ankylosaurs (Dinosauria: Thyreophora): Reapraisal of developmental hypotheses. In: K., & K.I. (eds.), The Armored Dinosaurs.- Bloomington, Indiana University Press, p. 318-340.
M.K., T. & D.B. (2003).- Ankylosauria. In: D.B., P. & H. (eds.), The Dinosauria, 2nd Edition.- Berkeley, University of California Press, Berkeley, p. 363-392.
D.B., P.M., R.A., J., X., Z., A., E.M.P. & C.R. (2003).- Dinosaur Distribution. In: D.B., P. & H. (eds.), The Dinosauria 2nd Edition.- University of California Press, Berkeley, p. 517-606.
Click on thumbnail to enlarge the image.
Figure 1: Map showing the location of the area of study, in the southeastern region of the State of Cohauila, Mexico.
Click on thumbnail to enlarge the image.
Figure 2: Ankylosaur osteoderms from Coahuila. a, dorsal view; b, ventral view, and c, caudal view of BENC-1/4-0001. d, Dorsal view of BENC-1/4-0004; e, dorsal view of BENC-1/4-0002, and f, dorsal view of BENC-1/4-0003. (Scale bar = 10 cm).