Desmatosuchus

{{Short description|Extinct genus of reptiles}} {{Automatic taxobox | fossil_range = [[Late Triassic]] ([[Carnian]] to [[Norian]]), {{fossilrange|228|210}} | image = HMNS Desmatosuchus cropped.jpg | image_caption = A mounted ''Desmatosuchus'' replica skeleton on display at the [[Houston Museum of Natural Science]] | taxon = Desmatosuchus | authority = Case, 1920 | type_species = {{extinct}}''Desmatosuchus spurensis'' | type_species_authority = Case, 1921 | subdivision_ranks = [[Species]] | subdivision = * {{extinct}}''D. spurensis'' Case, 1921 * {{extinct}}''D. smalli'' Parker, 2005<ref name="Parker, 2005">{{cite journal | last = Parker | first = William G. | date = June 2005 | title = A new species of the Late Triassic aetosaur ''Desmatosuchus'' (Archosauria: Pseudosuchia) | journal = [[Comptes Rendus Palevol]] | volume = 4 | issue = 4 | pages = 327–340 | doi = 10.1016/j.crpv.2005.03.002 }}</ref> | synonyms = *''Episcoposaurus haplocerus'' Cope, 1892 }}

'''''Desmatosuchus''''' ({{IPAc-en|d|ɛ|z|m|æ|t|oʊ|s|uː|k|ə|s}}, from [[Greek language|Greek]] δεσμός ''desmos'' 'link' + σοῦχος ''soûkhos'' 'crocodile') is an [[extinct]] [[genus]] of [[archosaur]] belonging to the Order [[Aetosauria]]. It lived in North America and potentially India (cf. ''Desmatosuchus'') during the [[Late Triassic]].<ref>{{Cite journal|last1=Haldar |first1=A. |last2=Ray |first2=S. |last3=Bandyopadhyay |first3=S. |title=First report of desmatosuchin aetosaurs (Diapsida, Archosauria) from the lower part of Dharmaram Formation and a biostratigraphic re-evaluation of the upper Triassic horizons of India |year=2025 |journal=Historical Biology: An International Journal of Paleobiology |pages=1–30 |doi=10.1080/08912963.2025.2569748 }}</ref>

==Description== [[File:Desmatosuchus spurensis.jpg|thumb|left|''D. spurensis'' compared to a human]] ''Desmatosuchus'' was a large quadrupedal reptile measuring {{cvt|4.5|m|ft||}} to over {{cvt|5|m|ft||}} long and weighing about {{convert|280|-|300|kg|lb|abbr=on}}.<ref name="small">{{cite thesis | last = Small | first= Bryan John | date = December 1985 | title = The Triassic thecodontian reptile Desmatosuchus: osteology and relationships | degree = Masters | publisher = [[Texas Tech University]] | hdl = 2346/19710 }}</ref><ref name=Baczko2021>von Baczko, M. B., Desojo, J. B., Gower, D. J., Ridgely, R., Bona, P., & Witmer, L. M. (2021). [https://www.researchgate.net/publication/355407927_New_digital_braincase_endocasts_of_two_species_of_Desmatosuchus_and_neurocranial_diversity_within_Aetosauria_Archosauria_Pseudosuchia New digital braincase endocasts of two species of Desmatosuchus and neurocranial diversity within Aetosauria (Archosauria: Pseudosuchia)]. The Anatomical Record, 1–20. https://doi.org/10.1002/ar.24798</ref><ref name=Desojo2013>{{cite book | isbn = 9781862393615 | url = https://books.google.com/books?id=TN_KBP3vxg4C | title = Anatomy, Phylogeny and Palaeobiology of Early Archosaurs and Their Kin | publisher = Geological Society | date = 2013 | access-date = 14 September 2022 | pages = 224 | author = Julia Brenda Desojo, Randall B. Irmis, Sterling J. Nesbitt }}</ref><ref>{{Cite journal |last=Parker |first=William G. |last2=Reyes |first2=William A. |last3=Marsh |first3=Adam D. |date=2023-11-08 |title=Incongruent ontogenetic maturity indicators in a Late Triassic archosaur (Aetosauria: Typothorax coccinarum ) |url=https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25343 |journal=The Anatomical Record |language=en |doi=10.1002/ar.25343 |issn=1932-8486|url-access=subscription }}</ref> Its [[vertebral column]] had amphicoelous [[Vertebra|centra]] and 3 sacral vertebrae. This archosaur's most distinguishing anatomical characteristics were its [[scapula]]e which possessed large [[acromion|acromion processes]] commonly referred to as "shoulder spikes".<ref name="small" /> The forelimbs were much shorter than the hindlimbs, with [[humerus|humeri]] less than two-thirds the length of the [[femur]]s.<ref name="charig" /> The [[Pelvis|pelvic girdle]] consisted of a long [[Pubis (bone)|pubis]] with a strong [[symphysis]] in the middle, a plate-like [[ischium]], a highly recurved [[Ilium (bone)|ilium]], and a deep, imperforate [[acetabulum]].<ref name="charig">{{cite book | last = Charig | first = Alan J. | author-link = Alan J. Charig | date = 1972 | chapter = The evolution of the archosaur pelvis and hindlimb: an explanation in functional terms | editor1-first = Kenneth A. | editor1-last = Joysey | editor2-first = Thomas S. | editor2-last = Kemp | title = Studies in Vertebrate Evolution | pages = 121–155 | publisher = Oliver and Boyd | location = Edinburgh | isbn = 978-0050021316 | oclc = 844318914 }}</ref> The femurs were relatively long and straight, the ankles [[crurotarsal]], with [[calcaneal]] tubers that gave it large heels.<ref name="charig" /> [[File:Desmatosuchus Exhibit Museum of Natural History 02.JPG|left|thumb|''Desmatosuchus'' skeleton on display at the [[University of Michigan Museum of Natural History]]]] 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 [[premaxilla]]e that turned up and expanded in the front, creating a shovel-like structure.<ref name="small" /> ''Desmatosuchus'' is unique among aetosaurs in that its species are the only known aetosaurs that lacked teeth on their premaxillae.<ref name="small" /> Their premaxillae fit loosely together with their [[maxilla]]e, indicating flexibility at that joint.<ref name="small" /> Their maxilla contained 10 to 12 teeth.<ref name="small" /> ''Desmatosuchus'' also had very thin [[vomer]]s, which bounded the medial side of the [[internal nares]].<ref name="small" /> These internal nares were relatively large, roughly half the length of the entire palate.<ref name="small" /> The lower jaw typically carried 5 or 6 teeth, and had a toothless beak on the end.<ref name="small" /> The [[dentary]] was about half the length of the lower jaw, with the front portion being toothless and covered by a horny sheath.<ref name="small" /> Behind the dentary was a moderately large mandibular [[Fenestra (anatomy)|fenestra]].

Individuals of ''Desmatosuchus'' were heavily armored. The [[carapace]] was made up of two rows of median [[scute]]s surrounded by two more rows of lateral scutes. The lateral scutes had well-developed spine-like [[Process (anatomy)|processes]] which pointed out laterally and dorso-posteriorly.<ref name="palmer" /> 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.<ref name="small" /> ''Desmatosuchus'' are the only aetosaurs known to have possessed spines like these.<ref name="palmer">{{cite encyclopedia | editor-last = Palmer | editor-first = D. | date = 1999 | title = The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals | location = London | publisher = Marshall Editions | page = 96 | isbn = 1-84028-152-9 }}</ref>

==Discovery and classification== The first ''Desmatosuchus'' discovery occurred in the late 19th century when [[Edward Drinker Cope|E.D. Cope]] classified armor from the [[Dockum Group]] in [[Texas]], USA, as the new species ''Episcoposaurus haplocerus''.<ref name="Parker, 2007">{{cite journal | last = Parker | first = William G. | date = March 2007 | title = Reassessment of the aetosaur ''"Desmatosuchus" chamaensis'' with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia) | journal = [[Journal of Systematic Palaeontology]] | volume = 5 | issue = 1 | pages = 41–68 | doi = 10.1017/S1477201906001994 | s2cid = 85826683 }}</ref> Case later classified a partial skeleton found in the [[Tecovas Formation]] as ''Desmatosuchus spurensis''.<ref>{{cite journal | first = Joseph T. | last = Gregory | author-link = Joseph T. Gregory | title = Typothorax and Desmatosuchus | journal = Postilla | volume = 16 | date = 3 June 1953 | pages = 1–27 | publisher = [[Yale Peabody Museum]] | url = http://peabody.yale.edu/sites/default/files/documents/scientific-publications/ypmP016_1953.pdf }}</ref> 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.<ref name="Parker, 2007" />

A revision of ''Desmatosuchus'' by Parker (2008) found the [[Type (biology)#Lectotype|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.<ref name="Parker, 2008">{{cite journal | last = Parker | first = William G. | date = 12 May 2008 | url = http://www.ucmp.berkeley.edu/science/paleobios/abstracts_26to30.php#pb281 | title = Description of new material of the aetosaur ''Desmatosuchus spurensis'' (Archosauria: Suchia) from the Chinle Formation of Arizona and a revision of the genus ''Desmatosuchus'' | journal = [[PaleoBios]] | publisher = [[University of California Museum of Paleontology]] | volume = 28 | issue = 1 | pages = 1–40 }}</ref> ''Desmatosuchus chamaensis'' is recognized as a distinct genus, but there is some dispute about whether the name ''[[Heliocanthus]]'' or ''[[Rioarribasuchus]]'' applies.<ref name="Parker, 2007"/>

The following [[cladogram]] is simplified, after an analysis presented by Julia B. Desojo, Martin D. Ezcurra and Edio E. Kischlat (2012).<ref name="Aetobarbakinoides">{{cite journal |first1=Julia B. | last1=Desojo | first2=Martin D. | last2=Ezcurra | first3=Edio E. | last3=Kischlat |year=2012 |title=A new aetosaur genus (Archosauria: Pseudosuchia) from the early Late Triassic of southern Brazil |journal=[[Zootaxa]] |volume=3166 |pages=1–33 | doi=10.11646/zootaxa.3166.1.1 |issn=1175-5334 |url=https://www.mapress.com/zootaxa/2012/f/z03166p033f.pdf }}</ref> [[File:Desmatosuchus Exhibit Museum of Natural History.JPG|thumb|upright|''Desmatosuchus'' skeleton from the [[University of Michigan Museum of Natural History]]]] {{clade| style=font-size:90%;line-height:85% |label1='''Aetosauria''' |1={{clade |1=''[[Aetosauroides scagliai]]'' |label2=[[Stagonolepididae]] |2={{clade |1=''[[Aetosaurus ferratus]]'' |2=''[[Coahomasuchus kahleorum]]'' |3={{clade |1=''[[Neoaetosauroides engaeus]]'' |2={{clade |1=''[[Calyptosuchus wellesi]]'' |2=''[[Stagonolepis robertsoni]]'' |3={{clade |1=''[[Aetobarbakinoides brasiliensis]]'' |2={{clade |label1=[[Typothoracisinae]] |1={{clade |1={{clade |1=''[[Typothorax]]'' |2=''[[Redondasuchus]]'' }} |label2=[[Paratypothoracisini]] |2={{clade |1=''[[Tecovasuchus chatterjeei]]'' |2={{clade |1=''[[Rioarribasuchus chamaensis]]'' |2=''[[Paratypothorax andressorum]]'' }} }} }} |label2=[[Desmatosuchinae]] |2={{clade |1=''[[Sierritasuchus macalpini]]'' |2={{clade |1=''[[Longosuchus meadei]]'' |2={{clade |1=''[[Lucasuchus hunti]]'' |2={{clade |1=''[[Acaenasuchus geoffreyi]]'' |label2=''Desmatosuchus'' |2={{clade |1='''''Desmatosuchus haplocerus''''' |2='''''Desmatosuchus smalli''''' }} }} }} }} }} }} }} }} }} }} }} }}

== Paleobiology == [[File:Desmatosuchus BW.jpg|thumb|''D. haplocerus'' from the Late Triassic of Texas]] Bones and armor pieces of ''Desmatosuchus'' are abundant in the Dockum formation, [[Chinle Formation|Chinle]] formation, and Post quarry, indicating that they were widespread and abundant during the Late Triassic.<ref name="small" /> It is possible that ''Desmatosuchus'' traveled in herds or family units. This is evidenced by several findings of multiple ''Desmatosuchus'' skeletons in relatively small areas.<ref name="small" />

''Desmatosuchus'' had blunt, bulbous, slightly recurved teeth. Furthermore, they are believed to have had [[homodont]] dentition.<ref name="small" /> This, combined with its shovel like snout, indicate that ''Desmatosuchus'' fed by digging up soft vegetation.<ref name="palmer" /> This method of feeding is further evidenced by its toothless premaxilla and dentary tip, which were covered in horny sheaths. These sheaths protected the bones and could be used for cutting or holding objects.<ref name="walker">{{cite journal | last = Walker | first = A. D. | date = 31 August 1961 | title = Triassic reptiles from the Elgin area: ''Stagonolepis'', ''Dasygnathus'' and their allies | journal = [[Philosophical Transactions of the Royal Society B: Biological Sciences]] | volume = 244 | issue = 709 | pages = 103–204 | doi = 10.1098/rstb.1961.0007 | jstor = 2992601 | bibcode = 1961RSPTB.244..103W | doi-access = free }}</ref> It is believed that ''Desmatosuchus'' dug for food in the soft mud near bodies of water due to the abundance of lakes and rivers in the Dockum area and the fact that ''Desmatosuchus'' scutes are often found among parts of other reptiles that are known to have fed along waterways.<ref name="small" /> It is unknown whether or not ''Desmatosuchus'' replaced their teeth and, if so, how. The low number of ''Desmatosuchus'' teeth that have been discovered indicates that they were only held in place by soft tissue connections.<ref name="small" /> The jaw articulation point is below the tooth line, holding its upper and lower tooth rows parallel while biting in a way that is reminiscent of [[ornithischian]] dinosaurs.<ref name="walker" /> [[File:HMNS Postosuchus and Desmatosuchus.jpg|alt=|left|thumb|''[[Postosuchus]]'' and ''Desmatosuchus'']] The armor and spikes of ''Desmatosuchus'' were its only ways to defend itself from predators. The lateral spike rows showed variation in size among individuals, especially the second most anterior spike. This spike was always shorter than the one in front of it, but to what extent varied drastically. This variation may indicate [[sexual dimorphism]].<ref name="palmer" /> It has also been hypothesized as a form of sexual display.<ref name="small" /> Aside from this armor, ''Desmatosuchus'' was defenseless from attacks from carnivores. Several ''Desmatosuchus'' bones have been found amongst skeletons of ''[[Postosuchus]]'', indicating predation by ''Postosuchus''.<ref name="small" /> The herd nature of ''Desmatosuchus'' apparently did little to discourage predators, as ''Postosuchus'' along with several other Late Triassic carnivores also traveled in groups.<ref name="small" />

Most thecodonts of the Late Triassic lacked certain pelvic features that aided locomotion, such as a deep acetabulum or a crest over the acetabulum. This, in spite of their upright posture, rendered them only slightly more mobile than sprawling reptiles.<ref name="bakker">{{cite journal | last = Bakker | first = R. T. | author-link = Robert T. Bakker | date = December 1971 | title = Dinosaur physiology and the origin of mammals | journal = Evolution | volume = 25 | issue = 4 | pages = 636–658 | jstor = 2406945 | doi=10.2307/2406945| pmid = 28564788 }}</ref> ''Desmatosuchus'' possessed both of these features, along with its long femur and elongate pubis, making it more mobile than most thecodonts of its time.<ref name="bakker" /> This mobility, along with its size, abundance, and specialized beak made it the chief herbivore in the Dockum area.<ref name="small" />

It has also been suggested that ''Desmatosuchus'' could have been omnivorous or even an insectivore. This is because of several similarities between ''Desmatosuchus'' and [[armadillos]].<ref name="arma">{{cite journal | last = Small | first = Bryan J. | date = September 2002 | title = Cranial anatomy of ''Desmatosuchus haplocerus'' (Reptilia: Archosauria: Stagonolepididae) | journal = [[Zoological Journal of the Linnean Society]] | volume = 136 | issue = 1 | pages = 97–111 | doi = 10.1046/j.1096-3642.2002.00028.x | doi-access = free }}</ref> For instance, both groups are armored. They possess long snouts that lack teeth on the end. Also, there is evidence of bees, wasps, and termites in the Late Triassic, meaning that ''Desmatosuchus'' had access to insects that armadillos prey on.<ref name ="arma" /> Their teeth are somewhat similar in shape, although armadillos have more peg-like teeth.<ref name ="arma" /> Both ''Desmatosuchus'' and armadillos typically carry around 6 teeth on their dentaries. Both armadillos and ''Desmatosuchus'' have hypertrophied processes present on their limb bones, which indicates large limb muscles.<ref name ="arma" /> This connection is more tenuous, however, since ''Desmatosuchus'' have a crest over their hind limbs but lack one on their forelimbs, meaning that they likely didn't have the musculature for digging with their forelimbs the way armadillos do. In spite of these parallels, the general consensus is still that ''Desmatosuchus'' was most likely herbivorous.<ref name="small" /> <ref name="bakker" />

==References== {{Reflist|30em}}

[[Category:Aetosaurs of North America]] [[Category:Chinle fauna]] [[Category:Late Triassic pseudosuchians]] [[Category:Prehistoric pseudosuchian genera]]