Eopneumatosuchus is an extinct genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of basal

Basal (phylogenetics)

In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...

 crocodyliform

Crocodyliformes

Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians."In 1988, Michael J. Benton and James M. Clark argued that all traditional names for well-known groups of animals should be restricted to their crown clades, that is, used only for...

. Fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s have been found from two localities within the Kayenta Formation

Kayenta Formation

The Kayenta Formation is a geologic layer in the Glen Canyon Group that is spread across the Colorado Plateau province of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. This rock formation is particularly prominent in southeastern Utah, where it is seen in the...

 of Arizona

Arizona

Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

. Both localities are around 20 miles southeast of the Grand Canyon

Grand Canyon

The Grand Canyon is a steep-sided canyon carved by the Colorado River in the United States in the state of Arizona. It is largely contained within the Grand Canyon National Park, the 15th national park in the United States...

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

Early Jurassic

The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...

, most likely during the Sinemurian

Sinemurian

In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 196.5 ± 2 Ma and 189.6 ± 1.5 Ma...

 stage.

Eopneumatosuchus was initially considered to be a protosuchia

Protosuchia

Protosuchia is a group of extinct Mesozoic crocodyliforms. They were small in size and terrestrial. In phylogenetic terms, Protosuchia is considered an informal group because it is a grade of basal crocodyliforms, not a true clade....

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

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

 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 Early Jurassic

Early Jurassic

The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...

 teleosaurs

Teleosauridae

The teleosaurids were marine crocodyliforms similar to the modern gharial that lived from the Early Jurassic to the Early Cretaceous. They had long snouts, indicative of piscivory and were the closest relatives to the Metriorhynchidae, the Mesozoic crocodilians that returned to the sea and evolved...

. The large supratemporal fenestrae of Eopneumatosuchus are characteristic of longirostrine crocodilia

Crocodilia

Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...

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

Derived

In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...

 than protosuchians such as Protosuchus, found from the Moenave Formation

Moenave Formation

The Moenave Formation is a Mesozoic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.-See also:* List of dinosaur-bearing rock formations...

, whose deposition preceded that of the Kayenta Formation.
The basicranium had many cavities that made up a complex tympanic pneumatic system for which the genus has been named. These types of cavities can also be seen in some protosuchians such as Protosuchus

Protosuchus

Protosuchus is an extinct genus of carnivorous crocodylomorph from the Early Jurassic. The name Protosuchus means "first crocodile", and is among the earliest animals that resemble crocodilians...

and Hemiprotosuchus

Hemiprotosuchus

Hemiprotosuchus is an extinct genus of protosuchid from the Norian stage of the Los Colorados Formation of South America. It was named by prolific Argentinian paleontologist José Bonaparte in 1969. The type species is H. leali.-External links:...

, although they are less elongated than in Eopneumatosuchus.