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Pachycheilosuchus Temporal range: Early Cretaceous, 119–112 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauria
Clade:	Pseudosuchia
Clade:	Crocodylomorpha
Clade:	Crocodyliformes
Clade:	Neosuchia
Clade:	Eusuchia
Family:	†Hylaeochampsidae
Genus:	†Pachycheilosuchus Rogers, 2003
Type species
†Pachycheilosuchus trinquei Rogers, 2003

Pachycheilosuchus (meaning "thick lipped crocodile") is an extinct genus of neosuchian from the Early Cretaceous of Texas, United States. Previously known, in part, as the "Glen Rose form", this crocodylomorph is notable for its procoelous vertebrae, otherwise found only in derived eusuchian crocodilians (the vertebrae articulate with a cup on the anterior surface and a rounded posterior surface), a thick margin on the maxillae (the main tooth-bearing bones of the upper jaw; thus "thick lipped crocodile"), and a shield of armor on the neck formed by the fusion of six individual scutes.

Description

Pachycheilosuchus is based on SMU 75278, a right maxilla, with the remains of at minimum 13 other individuals also known, representing most of the skeleton except hands, feet, and part of the skull. The remains were recovered near the top of the Glen Rose Formation of Erath County in central Texas, in rocks dating from the early Albian faunal stage. The fossils were found in a bonebed in a limestone rock unit, with scattered lenses of mudstone, probably deposited in a shallow, protected, nearshore brackish water setting. The type species is P. trinquei, in honor of Lance Trinque, a field assistant who helped discover and excavate the site where this animal's remains were found. This genus was named and described by Jack Rogers in 2003.

It was not a large crocodylomorph; for example, of the collected thigh bones, the longest measured only 91.2 millimeters long (3.59 in). Its body length was initially estimated at 63.5–80 centimetres (2.08–2.62 ft), using two methods. Although the remains are small, it appears that at least some of the individuals were mature, with fusion of parts of individual vertebrae. Additionally, a 49 millimeter-long (1.9 in) crocodyloid egg was recovered with the skeletal fossils, and is of reasonable size to have come from an individual with a length of 63.5 centimeters, suggesting that some of the individuals were sexually mature. A study in 2020 suggests that it may have reached up to 1.15 metres (3.8 ft) in total body length.

The maxillae had overhanging lips along their outer margins, and the tooth row was set away from the margin. One maxilla has an oval puncture mark, 5 millimeters by 6.5 millimeters (0.2 by 0.26 in), probably made by a larger predator. The snout was short and flat. The vertebrae were procoelous in the neck, back, and part of the tail, and the procoelous shape was most strongly developed in the neck vertebrae. Procoely is a type of vertebral articulation, based on the shape of the anterior and posterior faces of the vertebral centrum. In procoelous vertebrae, the vertebrae articulate with a concave leading surface and a convex posterior surface. The vertebrae of Pachycheilosuchus had a slight dimple or concavity on the posterior surface as well, making these bones different from the procoelous vertebrae that are a hallmark of derived eusuchian crocodilians. Because of this difference, and because Pachycheilosuchus did not have many of the other features of eusuchians, it probably evolved procoely independently. The ulna, the major bone of the forearm, is strongly curved. Pachycheilosuchus had among its armor a unique shield of bony scutes for its neck, composed of six individual fused scutes.

Classification

Using a cladistic analysis, Rogers found that Pachycheilosuchus was most likely closest to the Atoposauridae. This clade of small crocodylomorphs is also known from the Early Cretaceous, and includes some members with procoelous vertebrae. However, a subsequent 2011 study found Pachycheilosuchus to be a member of Hylaeochampsidae, a group of basal eusuchians, as shown in the cladogram below.

The "Glen Rose Form"

Previously, Glen Rose crocodylomorph fossils had been known under the informal designation of the "Glen Rose Form". Fossils known under this name include a skull at the National Museum of Natural History and two partial skeletons at the Texas Memorial Museum, along with isolated bones. With the description of Pachycheilosuchus, it appears that the "Glen Rose Form" had been chimeric; the skull and the two skeletons lack the lipped jaw and procoelous vertebrae, and so are not Pachycheilosuchus but an undescribed form, but at least some of the isolated remains are Pachycheilosuchus. Thus, there were at least two crocodylomorphs in the Glen Rose Formation.

References

1. ^ Rogers, Jack V. II (2003). "Pachycheilosuchus trinquei, a new procoelous crocodyliform from the Lower Cretaceous (Albian) Glen Rose Formation of Texas". Journal of Vertebrate Paleontology. 23 (1): 128–145. doi:10.1671/0272-4634(2003)23[128:PTANPC]2.0.CO;2.
2. Iijima, M.; Kubo, T. (2020). "Vertebrae-Based Body Length Estimation in Crocodylians and Its Implication for Sexual Maturity and the Maximum Sizes". Integrative Organismal Biology. 2 (1). obaa042. doi:10.1093/iob/obaa042. PMC 7891683.
3. Buscalioni, A.D.; Piras, P.; Vullo, R.; Signore, M.; Barbera, C. (2011). "Early eusuchia crocodylomorpha from the vertebrate-rich Plattenkalk of Pietraroia (Lower Albian, southern Apennines, Italy)". Zoological Journal of the Linnean Society. 163: S199–S227. doi:10.1111/j.1096-3642.2011.00718.x.

v t e Pseudosuchia
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Clade: Archosauria Sauropsida see Sauropsida Archosauromorpha see Archosauromorpha Pseudosuchia see below↓
Pseudosuchia Pseudosuchia †Dasygnathoides †Nundasuchus †Phytosauria? †Ornithosuchidae Aenigmaspina? Dynamosuchus Ornithosuchus Riojasuchus Venaticosuchus Suchia †Heteropelta? †Koilamasuchus? †Mandasuchus †Nundasuchus? †Ticinosuchus †Erpetosuchidae Archeopelta? Dyoplax? Erpetosuchus Pagosvenator Parringtonia Tarjadia †Aetosauriformes Acaenasuchus Euscolosuchus Revueltosaurus Aetosauria see Aetosauria †Gracilisuchidae Gracilisuchus Maehary? Parvosuchus Turfanosuchus Yonghesuchus Paracrocodylomorpha see below↓
Paracrocodylomorpha Paracrocodylomorpha †Mambawakale †Poposauroidea Benggwigwishingasuchus Lotosaurus Schultzsuchus? Qianosuchus Ctenosauriscidae Arizonasaurus Bromsgroveia Bystrowisuchus Ctenosauriscus Hypselorhachis Tsylmosuchus? Xilousuchus Poposauridae Dolichobrachium Poposaurus Shuvosauridae Effigia Shuvosaurus Sillosuchus Loricata †Apatosuchus †Arganasuchus †Batrachotomus †Dagasuchus †Decuriasuchus †Etjosuchus †Fasolasuchus †Heptasuchus †Heteropelta? †Incertovenator? †Luperosuchus †Mandasuchus? †Prestosuchus †Procerosuchus †Saurosuchus †Stagonosuchus †Youngosuchus †Rauisuchidae Arganasuchus? Energosuchus? Jushatyria? Polonosuchus Postosuchus Procerosuchus? Rauisuchus Scolotosuchus Scythosuchus? Teratosaurus Tikisuchus? Vivaron Vjushkovisaurus? Vytshegdosuchus? Crocodylomorpha see below↓
Crocodylomorpha Crocodylomorpha †Carnufex †Dibothrosuchus †Dromicosuchus †Hesperosuchus †Heteropelta? †Junggarsuchus †Kayentasuchus †Parrishia †Phyllodontosuchus †Pseudhesperosuchus †Redondavenator †Sphenosuchus †Syntomiprosopus? †Trialestes †Saltoposuchidae Litargosuchus Saltoposuchus Terrestrisuchus †Hallopodidae Almadasuchus Hallopus Macelognathus †Thalattosuchia see Thalattosuchia Crocodyliformes †Entradasuchus †Eopneumatosuchus †Kemkemia †Microchampsa †Platyognathus †Stegomosuchus †Tagarosuchus †Protosuchidae Coloradisuchus Dianosuchus Edentosuchus Erythrochampsa Hemiprotosuchus Hoplosuchus Orthosuchus? Pedeticosaurus? Protosuchus †Notochampsidae Notochampsa Orthosuchus? †Gobiosuchidae Cassissuchus Gobiosuchus Lisboasaurus? Zaraasuchus Mesoeucrocodylia †Dianchungosaurus †Hsisosuchus †Induszalim †Lusitanisuchus †Neuquensuchus †Pachycheilosuchus? †Titanochampsa †Thalattosuchia? †Shartegosuchoidea Hadongsuchus Shantungosuchus Sichuanosuchus Zosuchus Shartegosuchidae Adzhosuchus Fruitachampsa Kyasuchus Nominosuchus Shartegosuchus Metasuchia †Ziphosuchia see Ziphosuchia includes notosuchians Neosuchia see Neosuchia includes crocodilians
See also: Rauisuchia Prestosuchidae Bathyotica Sphenosuchia Protosuchia Mesosuchia Category

v t e Neosuchia
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Clade: Pseudosuchia Clade: Metasuchia Pseudosuchia see Pseudosuchia Neosuchia see below↓
Neosuchia Neosuchia †Burkesuchus †Isisfordia †Karatausuchus †Khoratosuchus †Montsecosuchus †Stolokrosuchus? †Susisuchus †Tadzhikosuchus? †Wahasuchus? †Zhyrasuchus? †Thalattosuchia? †Tethysuchia Pholidosauridae Anglosuchus Chalawan Crocodilaemus Dakotasuchus Elosuchus Meridiosaurus Oceanosuchus Pholidosaurus Sarcosuchus Terminonaris Vectisuchus Woodbinesuchus Dyrosauridae Acherontisuchus Anthracosuchus Arambourgisuchus Atlantosuchus Brachiosuchus Cerrejonisuchus Chenanisuchus Congosaurus Dorbignysuchus Dyrosaurus Fortignathus Guarinisuchus Hyposaurus Luciasuchus Phosphatosaurus Rhabdognathus Rodeosuchus Sabinosuchus? Sokotosuchus Tilemsisuchus †Atoposauridae Alligatorellus Alligatorium Aprosuchus Atoposaurus Knoetschkesuchus Sabresuchus Theriosuchus Varanosuchus †Stomatosuchidae Laganosuchus Stomatosuchus †Paluxysuchidae Deltasuchus Paluxysuchus †Goniopholididae Amphicotylus Anteophthalmosuchus Calsoyasuchus Coelosuchus Denazinosuchus Diplosaurus Eutretauranosuchus Goniopholis Hulkepholis Nannosuchus Ophiussasuchus Oweniasuchus Pinacosuchus? Siamosuchus Sunosuchus Symptosuchus? †Bernissartiidae Bernissartia Koumpiodontosuchus †Paralligatoridae Batrachomimus Brillanceausuchus Kansajsuchus Paralligator Rugosuchus Scolomastax Shamosuchus Tarsomordeo Turanosuchus Wannchampsus Yanjisuchus Eusuchia see below↓
Eusuchia Eusuchia †Borealosuchus †Confractosuchus †Dolichochampsa †Gilchristosuchus †Heterosuchus †Isisfordia? †Portugalosuchus †Pristichampsus †Susisuchus? †Titanochampsa? †Atoposauridae? †Bernissartiidae? †Paralligatoridae? †Hylaeochampsidae Acynodon? Hylaeochampsa Iharkutosuchus Pachycheilosuchus? Pietraroiasuchus Turcosuchus Unasuchus †Allodaposuchidae Agaresuchus Allodaposuchus Arenysuchus? Ischyrochampsa Lohuecosuchus Massaliasuchus Musturzabalsuchus? †Aegyptosuchidae Aegyptosuchus Aegisuchus †"Thoracosaurs" Argochampsa Eogavialis Eosuchus Eothoracosaurus Thoracosaurus †Planocraniidae Boverisuchus Duerosuchus Planocrania Crocodilia see Crocodilia for extant taxa, and Extinct Crocodilia for extinct ones
See also: Coelognathosuchia Category

• Early Cretaceous crocodylomorphs of North America
• Early Cretaceous reptiles of North America
• Neosuchians
• Prehistoric pseudosuchian genera