''Eutretauranosuchus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of goniopholidid

crocodyliform Crocodyliformes is a clade of 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 only pseudo ...

. ''E. delfsi'' is the only known species within the genus.

Discovery and history

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

, ''Eutretauranosuchus delfsi'', was discovered by Edwin Delfs in 1957 among remains recovered from the Morrison Formation in

Canon City, Colorado Canon or Canons may refer to: Arts and entertainment * Canon (fiction), the conceptual material accepted as official in a fictional universe by its fan base * Literary canon, an accepted body of works considered as high culture ** Western can ...

. 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 process In human anatomy of the mouth, the palatine process of maxilla (palatal process), is a thick, horizontal process of the maxilla. It forms the anterior three quarters of the hard palate, the horizontal plate of the palatine bone making up the re ...

es, 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 The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilia ...

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 ''Amphicotylus'' is an extinct genus of goniopholidid mesoeucrocodylian from the Tithonian of Colorado, Wyoming, and Oklahoma. It was described in 1878.E. D. Cope. 1878. Descriptions of new extinct Vertebrata from the Upper Tertiary and Dakota Fo ...

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 The lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders. Several bony landmarks of ...

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 The postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch, which runs laterally around the eye socket. It is a trait that only occurs in mammalian taxa, such as most strep ...

with a triangular cross-section creates a separation between the orbit and the infratemporal fenestra. The

quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

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.

Geological and paleoenvironmental information

Morrison Formation Colorado National Monument

''Eutretauranosuchus'' is currently known from specimens found in the Upper Jurassic Dry Mesa Dinosaur Quarry in Canon City, Colorado; the Brushy Basin Member in Western Colorado; and the

Bone Cabin Quarry Bone Cabin Quarry is a dinosaur quarry that lay approximately northwest of Laramie, Wyoming near historic Como Bluff. During the summer of 1897 Walter Granger, a paleontologist from the American Museum of Natural History, came upon a hillside li ...

site in

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the s ...

—all of which are parts of the Morrison Formation. Other ''Gonopholididae'' appear in strata from 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-J ...

to Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

. The family is classed as a

Laurasian Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

group, with specimens located in North America, Europe, and South-East Asia. Specimens from this group are often found in estuarine and freshwater deposits.

Locomotion, paleoenvironment and feeding

Goniopholidid crocodilians, including ''Eutretauranosuchus'', are widely categorized as semi-aquatic forms.Foster, J.R. Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A.: Bulletin 23. United States, New Mexico Museum of Natural History & Science, 2003. pp 28-37. Preserved specimens indicate ''Eutretauranosuchus'' are moderately sized with an average estimated weight of 50–60 kg. The size and length of Goniopholididae specimens found in the Morrison Formation, as well as striated teeth, support the hypothesis that ''Eutretauranosuchus'' were carnivorous, feeding on prey such as insects, fish, small reptiles, mammals and dinosaurs.

Phylogenetic analysis

''E. delfsi'' is the only recognized species of ''Eutretauranosuchus''. Other genera of Goniopholididae include ''

'', '' Goniopholis'', '' Sunosuchus'', and ''

Calsoyasuchus ''Calsoyasuchus'' (meaning " r. KyrilCalsoyas' crocodile") is a genus of crocodylomorph that lived in the Early Jurassic. Its fossilized remains were found in the Sinemurian-Pliensbachian-age Kayenta Formation on Navajo Nation land in Coconino ...

''. The exact

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

placement of Eutretauranosuchus remains ambiguous. Phylogenetic analysis by Smith et al. in 2010 provides evidence that ''Eutretauranosuchus'', ''Calsoyasuchus'' and ''Sunosuchus'' are closely related, and these findings are widely supported. However, while many publications support the phylogenetic placement of ''Eutretauranosuchus'' within the family of Goniopholididae, there is debate over whether it is more closely related to ''Goniopholis'' or ''Sunosuchus''. Alternatively, phylogenetic assessment by J.R. Foster in 2006 considers ''Eutretauranosuchus'' to be most closely related to ''

Pholidosaurus ''Pholidosaurus'' is an extinct genus of neosuchian crocodylomorph. It is the type genus of the family Pholidosauridae. Fossils have been found in northwestern Germany. The genus is known to have existed during the Berriasian-Albian stages of the ...

'' and

dyrosauridae Dyrosauridae is a family of extinct neosuchian crocodyliforms that lived from the Late Cretaceous (Maastrichtian) to the Eocene. Dyrosaurid fossils are globally distributed, having been found in Africa, Asia, Europe, North America and South Ame ...

, and belonging to a larger clade that includes ''Bernissartia'', ''Eusuchians'' and ''Goniopholis''.Foster, J.R. 2006. The mandible of a Juvenile Goniopholidid (Crocodylefomes) From The Morrison Formation (upper Jurassic) of Wyoming. Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36. Pp 101-105 Further research is needed to clarify these disputes. Phylogenetic analysis by (Allen, 2012) claims that North American goniopholidid forms are monophyletic, excluding all other goniopholidids. It is proposed that this North America specific clade can be defined by channel-like, extremely elongated choanae that completely separate the palatines and that within this clade exists a further distinguished clade of the forms found in the Morrison Formation, which are defined by triangular prefrontals that rostrally extend past the lacrimals, preventing lacrimal contact with the nasals. A recent study re-evaluated evolutionary history in relation to the Triassic-Jurassic mass extinction event. It concluded that the basal phylogenetic positioning of the goniopholidid crocodylomorph ''Calsoyasuchus valliceps'' suggests a substantial number of ghost lineages that should exist at the base of the crocodylomorphs. Furthermore, they reported an increase in crocodylomorph disparity across the Triassic-Jurassic boundary, which suggests there was rapid radiation of adaptation among crocodylomorphs. They hypothesize this was a result of the extinction's "decimation" of pseudosuchian and tetrapod lineages. The study concludes that the extinction was important for the evolutionary success of Goniopholididae. A phylogenetic analysis by Brandelise de Andrade et al.Marco Brandalise de Andrade, Richard edmonds, Michael J Benton, Remmert Schouten. (2011). "A new Berriasian species of ''Goniopholis'' (Mesoeucrocodylia, Neosuchia) from England, and a review of the genus." ''Zoological Journal of the Linnean Society.'' 163 (s1): S66-S108. doi:10.1111/j.1096-3642.2011.00709.x is shown in the following cladogram:

References

{{Taxonbar, from=Q4273243 Neosuchians Crocodyliforms Mesoeucrocodylians Late Jurassic crocodylomorphs of North America Fossil taxa described in 1967 Prehistoric pseudosuchian genera