''Eopneumatosuchus'' is an extinct

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 basal

crocodyliform Crocodyliformes is a clade of Crurotarsi, crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the ...

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 have been found from two localities within the

Kayenta Formation The Kayenta Formation is a geological formation in the Glen Canyon Group that is spread across the Colorado Plateau area of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. Originally suggested as being Sinemur ...

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

. Both localities are around 20 miles southeast of the

Grand Canyon The Grand Canyon is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is long, up to wide and attains a depth of over a mile (). The canyon and adjacent rim are contained within Grand Canyon Nati ...

and in close proximity to one another. The localities probably date back to the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

, most likely during the

Sinemurian In the geologic timescale, the Sinemurian is an age (geology), age and stage (stratigraphy), stage in the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series. It spans the time between 199.5 ±0.3 annu ...

stage.

Classification

''Eopneumatosuchus'' was initially considered to be a

protosuchia Protosuchia is a group of extinct Mesozoic crocodyliforms. They were small in size (~1 meter in length) and Terrestrial animal, terrestrial. In phylogenetic terms, Protosuchia is considered an informal group because it is a evolutionary grade, gr ...

n, first proposed when the genus was named in 1980. However, this classification was later questioned on the basis of several features of the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

material, and as a result it is no longer considered to be within Protosuchia. Particular features of the posterior part of the cranium, the only material associated with the genus, suggest that ''Eopneumatosuchus'' may have close relations with

teleosaurs. The large supratemporal fenestrae of ''Eopneumatosuchus'' are characteristic of longirostrine

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 ...

ns. Despite the similar cranial morphology with crocodilians, the genus is currently regarded as a basal crocodyliform. Nonetheless, it is considered to be more derived than protosuchians such as ''Protosuchus'', found from the

Moenave Formation The Moenave Formation is a Mesozoic geologic formation, in the Glen Canyon Group. It is found in Utah and Arizona. The Moenave was deposited on an erosion surface on the Chinle Formation following an early Jurassic uplift and unconformity t ...

, whose deposition preceded that of the Kayenta Formation. The basicranium had many cavities that made up a complex tympanic

pneumatic Pneumatics (from Greek 'wind, breath') is the use of gas or pressurized air in mechanical systems. Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A centrally located a ...

system for which the genus has been named. These types of cavities can also be seen in some protosuchians such as ''

Protosuchus ''Protosuchus'' (from , "first" and , "crocodile") is an extinct genus of carnivorous crocodyliform from the Early Jurassic. It is among the earliest animals that resemble crocodilians. ''Protosuchus'' was about in length and about in weight. ...

'' and ''

Hemiprotosuchus ''Hemiprotosuchus'' is an extinct genus of protosuchid crocodyliform from the Late Triassic (Norian stage) Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina, South America. It was named in 1969 by paleontol ...

'', although they are less elongated than in ''Eopneumatosuchus''.

References

{{Taxonbar, from=Q5381848 Crocodyliformes Terrestrial crocodylomorphs Early Jurassic crocodylomorphs Early Jurassic reptiles of North America Prehistoric pseudosuchian genera Kayenta Formation