''Pinacosuchus'' is an
extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
genus of
crocodylomorph
Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction.
During Mesozoic and early Cenozoic times, cro ...
. Its
fossils were found in the
Late Cretaceous-age
North Horn Formation
The North Horn Formation is a widespread non-marine sedimentary unit with extensive outcrops exposed in central and eastern Utah. The formation locally exceeds in thickness and is characterized by fluvial, lacustrine, and floodplain dominated s ...
of
Utah (
United States). ''Pinacosuchus'' was a diminutive crocodylomorph with spiky armor, and is known only from meagre remains.
History and description
Charles W. Gilmore named ''Pinacosuchus'' in 1942 for
USNM
The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. It has free admission and is open 364 days a year. In 2021, with 7. ...
16592, consisting of a fragment of
upper jaw, seven partial
vertebrae, a partial
coracoid, a partial
thigh bone, numerous pieces of
bony armor, and other fragments. This specimen was discovered at the "Lizard Locality" in the
Manti National Forest,
Emery County, Utah. The
type species is ''P. mantiensis''. Gilmore had difficulty classifying the specimen, due to its fragmentary nature. He ruled out all then-known
orders of reptiles on anatomical ground except for
Crocodilia (which had a more expansive definition at the time) and the nebulous
thecodontia. He considered a
pseudosuchian thecodont identity, but eliminated it because all members were of
Triassic age or older. ''Pinacosuchus'' would have been an archaic crocodilian because it lacked the
procoelous vertebrae (concave articulation surface on the
anterior
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
face of the bone, and convex articulation on the posterior face) of more
derived crocodilians, instead having
amphicoelous vertebrae (concave articulations on both faces).
''Pinacosuchus'' would have been a very small crocodylomorph. The
sacrum
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part ...
(the vertebra supporting the hips) of USNM 16592 was only long. Gilmore regarded the specimen as an adult because the vertebrae lacked sutures for their
neural arches
The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
, a sign of maturity.
[ This assessment was supported by O'Neill and colleagues, comparing ''Pinacosuchus'' to their new spiked crocodilian '']Akanthosuchus
''Akanthosuchus'' (meaning "spine crocodile," in reference to its armor) is an extinct genus of alligatoroid crocodilian, possibly an alligatorine. Its fossils are found in the Paleocene-age Nacimiento Formation of the San Juan Basin, New Mexic ...
''.[ The genus is briefly mentioned in Cifelli ''et al.'' (1999) under the misspelling "''Pinasuchus''". In the text of this publication, it is mentioned that Kenneth Carpenter had observed "some faint resemblances" to the ]Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic, Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandsto ...
goniopholidid
Goniopholididae is an extinct family of moderate-sized semi-aquatic neosuchian crocodyliformes. Their bodyplan and morphology are convergent on living crocodilians. They lived across Laurasia (Asia, Europe and North America) between the Middle Ju ...
genus '' Eutretauranosuchus''. It is incorrectly listed as a possible ankylosaur
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...
in Table 1.
References
{{Taxonbar, from=Q3809429
Late Cretaceous crocodylomorphs of North America
Late Cretaceous reptiles of North America
Prehistoric pseudosuchian genera