''Pinacosuchus'' is an
extinct
Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
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. Extinct crocodylomorphs were considerably mor ...
. Its
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s were found in the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...
-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 plain, lacustrine, and floo ...
of
Utah
Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...
(
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
). ''Pinacosuchus'' was a diminutive crocodylomorph with spiky armor, and is known only from meagre remains.
History and description
Charles W. Gilmore
Charles Whitney Gilmore (March 11, 1874 – September 27, 1945) was an American paleontologist who gained renown in the early 20th century for his work on vertebrate fossils during his career at the United States National Museum (now the N ...
named ''Pinacosuchus'' in 1942 for
USNM
The National Museum of Natural History (NMNH) 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. With 4.4 ...
16592, consisting of a fragment of
upper jaw
In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxillar ...
, seven partial
vertebra
Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...
e, a partial
coracoid
A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...
, a partial
thigh bone
The femur (; : femurs or femora ), or thigh bone is the only bone in the thigh — the region of the lower limb between the hip and the knee. In many four-legged animals the femur is the upper bone of the hindleg.
The top of the femur fits in ...
, 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
In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
is ''P. mantiensis''. Gilmore had difficulty classifying the specimen, due to its fragmentary nature. He ruled out all then-known
orders
Order, ORDER or Orders may refer to:
* A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* H ...
of reptiles on anatomical ground except for
Crocodilia
Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorph pseudosuchia ...
(which had a more expansive definition at the time) and the nebulous
thecodontia
Thecodontia (meaning 'socket-teeth'), now considered an obsolete taxonomic grouping, was formerly used to describe a diverse "order" of early archosaurian reptiles that first appeared in the latest Permian period and flourished until the end of t ...
. He considered a
pseudosuchia
Pseudosuchia, from Ancient Greek ψεύδος (''pseúdos)'', meaning "false", and σούχος (''soúkhos''), meaning "crocodile" is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely relat ...
n thecodont identity, but eliminated it because all members were of
Triassic
The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
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 describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...
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 (: sacra or sacrums), in human anatomy, is a 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 of the pelvic cavity, ...
(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
Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
, 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
Kenneth Carpenter (born 21 September 1949) is an American paleontologist. He is the former director of the USU Eastern Prehistoric Museum and author or co-author of books on dinosaurs and Mesozoic life. His main research interests are armore ...
had observed "some faint resemblances" to the Morrison Formation
The Morrison Formation is a distinctive sequence of 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, sandstone, siltston ...
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 J ...
genus '' Eutretauranosuchus''. It is incorrectly listed as a possible ankylosaur
Ankylosauria is a group of herbivorous dinosaurs of the clade 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 l ...
in Table 1.
References
{{Taxonbar, from=Q3809429
Late Cretaceous crocodylomorphs of North America
Late Cretaceous reptiles of North America
Prehistoric pseudosuchian genera