Eutretauranosuchus is an extinct genus of goniopholidid crocodyliform. E. delfsi is the only known species within the genus.
Discovery and history
The holotype, Eutretauranosuchus delfsi, was discovered by Edwin Delfs in 1957 among remains recovered from the Morrison Formation in Canon City, Colorado. It was first described in detail by Charles Mook in 1967. The fossil remains consisted of an almost-complete skull as well as some limb bones.
The name Eutretauranosuchus was given by Delfs upon its discovery in reference to its "doubly pierced palate". The holotype specimen was named E. delfsi by Mook in tribute to Delfs.
Mook found E. delfsi differs significantly from previously described Mesosuchian crocodiles. This specimen was deemed part of a new species because of its extremely elongated internal narial aperture, which was notably longer than those of previously described specimens of similar size. Mook also described an additional, smaller opening located anterior to the internal nares, divided by the palatine processes, which was hypothesized to have entered the narial passage. According to Mook, these features were an indication of a wide-ranged specialization among Goniopholididae and indicated the described specimen is a holotype for a new genus.
Recent findings suggest that Mook's original description of an additional nasal opening was incorrect and that this opening was part of an elongated choana that is extremely constricted medially by the expansion of the palatines, giving the illusion of a separate anteriorly located opening due to its hourglass-shape—as is commonly described in other E. delfsi, Amphicotylus lucasii and A. gilmorei specimens.
Description and osteology
Skull
Characteristics of E. delfi skulls include an elongated and platyrostral skull, posterolateral depressions on the alveolar maxillary process, minimal lateral undulation of the tooth row (maxillary), broadened nasals located anteriorly to the prefrontals, a lack of contact between the nasals and external nares, a flattened and broad innerfenestral bar with rims that are raised along the supratemporal fenestra, and a nasopharyngeal septum formed by the anterior divergence of the vomeral processes. The lacrimal bone is rectangular and in dorsal view has an anteroposterior length that is two times its width. The lacrimal is contacted by the prefrontal laterally along its length, which separates the prefrontal from the nasal. A large postorbital bar with a triangular cross-section creates a separation between the orbit and the infratemporal fenestra. The quadratojugal has two regions: a smaller dorsal part that lacks dermal pitting, and a larger ventral region that is pitted and forms the bottom half of the infratemporal process, creating a significant indentation that is considered characteristic of this genus.
Palate
While the majority of Goniopholididae have historically been categorized by flattened snouts and posterolaterally located maxillary depressions, there remains great variation within their palatal anatomy. Most Morrison Formation goniopholidids display an ‘incomplete’ secondary palate, in which there is no ventral floor in the nasopharyngeal passage. Differences among palatal anatomy have been observed between Goniopholididae taxa found from the Cretaceous in Europe and species found in North America. European specimens such as G. simus and G.siplingi have a secondary bony palate formed from the palatines and maxillary processes. North American goniopholidids have maxillae and palatines that do not contact, resulting in a more open palate and a ventrally exposed bony nasopharyngeal passage.
Post-cranial skeleton
The postcranial skeleton of Goniopholididae is characterized by amphicoelous vertebrae, two rows of paravertebral osteoderms with "peg and groove" articulation and polygonal ventrally located osteoderms. Goniopholididae commonly have a closed paravertebral armor bracing system. The anteroposteriorly located crest on the ventral surfaces of Goniopholididae dorsal osteoderms has been hypothesized to be evidence that the epaxial musculature attached medially to a single paravertebral osteoderm, which is different from the three groups of epaxial musculature that attach to separate osteoderms in extant crocodylians.