Desmatosuchus (/dɛzmætoʊsuːkəs/, from Greek δεσμός desmos 'link' + σοῦχος soûkhos 'crocodile') is an extinct genus of archosaur belonging to the Order Aetosauria. It lived during the Late Triassic.
Desmatosuchus was a large quadrupedal reptile upwards of 4.5 meters in length.[2] Its vertebral column had amphicoelus centra and 3 sacral vertebrae. This archosaur's most distinguishing anatomical characteristics were its scapulae which possessed large acromion processes commonly referred to as "shoulder spikes".[2] The forelimbs were much shorter than the hindlimbs, with humeri less than two-thirds the length of the femurs.[3] The pelvic girdle consisted of a long pubis with a strong symphysis in the middle, a plate-like ischium, a highly recurved ilium, and a deep, imperforate acetabulum.[3] The femurs were relatively long and straight, the ankles crurotarsal, with calcaneal tubers that gave it large heels.[3]
Its skull was relatively small, on average about 37 centimeters long, 18 centimeters wide, and 15 centimeters high. The braincase was very firmly fused with the skull roof and palate. It had slender, forked premaxillae that turned up and expanded in the front, creating a shovel-like structure.[2] Desmatosuchus is unique among aetosaurs in that its species are the only known aetosaurs that lacked teeth on their premaxillae.[2] Their premaxillae fit loosely together with their maxillae, indicating flexibility at that joint.[2] Their maxilla contained 10 to 12 teeth.[2] Desmatosuchus also had very thin vomers, which bounded the medial side of the internal nares.[2] These internal nares were relatively large, roughly half the length of the entire palate.[2] The lower jaw typically carried 5 or 6 teeth, and had a toothless beak on the end.[2] The dentary was about half the length of the lower jaw, with the front portion being toothless and covered by a horny sheath.[2] Behind the dentary was a moderately large mandibular fenestra.
Individuals of Desmatosuchus were heavily armored. The carapace was made up of two rows of median scutes surrounded by two more rows of lateral scutes. The lateral scutes had well-developed spine-like processes which pointed out laterally and dorso-posteriorly.[4] There were typically five rows of spines, increasing in size anteriorly. The front spine was much larger, around 28 centimeters long, and was recurved. The fourth spine varies in length in each specimen, but remains shorter than the fifth in all of them.[2] Desmatosuchus are the only aetosaurs known to have possessed spines like these.[4]
The first Desmatosuchus discovery occurred in the late 19th century when E.D. Cope classified armor from the Dockum Group in Texas, USA, as the new species Episcoposaurus haplocerus.[5] Case later classified a partial skeleton found in the Tecovas Formation as Desmatosuchus spurensis.[6] Since the localities of Cope and Case were only a few kilometers apart, the two taxa were synonymized into Desmatosuchus haplocerus, the initial type species of the genus.[5]
A revision of Desmatosuchus by Parker (2008) found the lectotype of Episcoposaurus haplocerus to be referable to Desmatosuchus but indeterminate at the species level. Therefore, E. haplocerus was considered to be a nomen dubium and D. spurensis was named the type species of the genus. Two species were accepted as valid: D. spurensis and D. smalli, named after Brian J. Small for his contribution to the study of this genus.[7] Desmatosuchus chamaensis is recognized as a distinct genus, but there is some dispute about whether the name Heliocanthus or Rioarribasuchus applies.[5]