{{Short description|Extinct genus of reptiles}} {{Automatic taxobox | fossil_range = [[Middle Triassic]] {{fossil range|242|237}} | image = Diandongosuchus fuyuanensis 334.jpg | image_upright = 1.1 | image_caption = Skull in [[Beijing Museum of Natural History]] | image2 = Diandongosuchus skeletal.png | image2_caption = Skeletal reconstruction and size comparison, in dorsal (top) and lateral (bottom) views | taxon = Diandongosuchus | authority = Li ''et al.'', [[2012 in paleontology|2012]] | type_species = {{extinct}}'''''Diandongosuchus fuyuanensis''''' | type_species_authority = Li ''et al.'', 2012 }}
'''''Diandongosuchus''''' is an extinct genus of [[Archosauriformes|archosauriform]] reptile, possibly a member of the [[Phytosaur]]ia, known from the [[Middle Triassic]] of China. The [[type species]] '''''Diandongosuchus fuyuanensis''''' was named in 2012 from the [[Zhuganpo Formation]] of [[Yunnan Province]]. It is a marine species that shows similarities with another Chinese Triassic species called ''[[Qianosuchus mixtus]]'', although it has fewer adaptations toward marine life. It was originally classified as the [[basal (phylogenetics)|basal]]-most member of the [[pseudosuchia]]n clade [[Poposauroidea]].<ref name="Letal12">{{Cite journal |last1=Li |first1=C. |last2=Wu |first2=X. C. |last3=Zhao |first3=L. J. |last4=Sato |first4=T. |last5=Wang |first5=L. T. |year=2012 |title=A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China |url=https://www.researchgate.net/publication/254315203 |journal=Journal of Vertebrate Paleontology |volume=32 |issue=5 |pages=1064 |doi=10.1080/02724634.2012.694383 |s2cid=86797826}}</ref> However, a subsequent study conducted by Stocker ''et al.'' (2016, 2017) indicated it to be the basalmost known phytosaur instead.<ref name=":0">{{cite journal |author1=Michelle R. Stocker |author2=Sterling J. Nesbitt |author3=Li-Jun Zhao |author4=Xiao-Chun Wu |author5=Chun Li |year=2016 |title=Mosaic evolution in Phytosauria: the origin of long-snouted morphologies based on a complete skeleton of a phytosaur from the Middle Triassic of China |journal=Society of Vertebrate Paleontology 76th Annual Meeting Program & Abstracts |pages=232 |url=http://vertpaleo.org/PDFS/2016/SVP-2016-Program-Book-v10-with-covers.aspx |access-date=2016-10-30 |archive-date=2016-10-18 |archive-url=https://web.archive.org/web/20161018211820/http://vertpaleo.org/PDFS/2016/SVP-2016-Program-Book-v10-with-covers.aspx |url-status=dead }}</ref><ref name=":1">{{Cite journal|author1=Michelle R. Stocker |author2=Li-Jun Zhao |author3=Sterling J. Nesbitt |author4=Xiao-Chun Wu |author5=Chun Li |year=2017 |title=A Short-Snouted, Middle Triassic Phytosaur and its Implications for the Morphological Evolution and Biogeography of Phytosauria |journal=Scientific Reports |volume=7 |article-number=46028 |doi=10.1038/srep46028 |pmc=5385495 |pmid=28393843 |bibcode=2017NatSR...746028S }}</ref>
==Description== [[File:Diandongosuchus fuyuanensis.jpg|thumb|left|Restoration]] [[File:Diandongosuchus skull.png|thumb|Reconstruction and retro-deformation of the skull]] ''Diandongosuchus'' is known from a nearly complete articulated skeleton ([[Zhejiang Museum of Natural History|ZMNH]] M8770) missing most of the tail. The total length of the specimen is {{convert|97|cm|ft}} and the estimated body length of the animal in life is around {{convert|155|cm|ft}}. The specimen is preserved on its right side, with the underside of the lower jaws and the trunk showing. It was prepared out of a limestone slab to reveal details on the left side of the skeleton, many of which are better preserved. The skull of ''Diandongosuchus'' is proportionally large for its size; it was long and pointed, with oval-shaped eye sockets, [[antorbital fenestra|antorbital]] and [[temporal fenestra|temporal]] openings. Distinctive features include a long [[premaxilla]] bone bearing 9 teeth at the tip of the snout that extends backward past the nostril openings, a large ridge on the [[jugal bone]] that runs beneath the eye socket, and two supratemporal openings on the [[skull table]] that have prominent ridges surrounding them.<ref name=Letal12/>
ZMNH M8770 preserves all 24 presacral vertebrae (9 in the neck and 15 on the back), three [[sacral vertebra]]e,<ref name=":0" /> and seven of the forward-most tail vertebrae. The neck vertebrae are taller and narrower than they are in ''Qianosuchus''. Most of the back vertebrae are obscured by overlying ribs. At the back of the trunk near the hips are bones belonging to small vertebrates such as fish - likely the stomach contents of the individual. Small overlapping [[osteoderm]]s (bony scutes) overlay many of the vertebrae. Two rows run along the neck, back, and tail with two pairs of osteoderms overlaying each vertebra. Small osteoderms also would have covered the limbs.<ref name=Letal12/>
Some features of the limbs, [[pelvic girdle|pelvic]] and [[pectoral girdle]]s are also diagnostic in ''Diandongosuchus'', including a thick [[ischium]] bone in the hip, a large opening of the [[coracoid]] bone in the pectoral girdle that is much larger than those of other archosaurs and is closed by the end of the [[scapula]], and a fourth [[metatarsal]] bone in the foot that is longer than the other metatarsals. The scapula of ''Diandongosuchus'' is longer and narrower than that of ''Qianosuchus''. The [[iliac crest|iliac blade]] of the hip is unusual in that it is narrow and projects far back from the rest of the hip. As in ''Qianosuchus'', the femur of ''Diandongosuchus'' is slightly twisted, but the fibula is thinner and more curved. The [[Talus bone|astragalus]] and [[calcaneum]] bones of the ankle fit together like a ball-and-socket.<ref name=Letal12/>
==Classification== [[File:Diandongosuchus skeleton.jpg|thumb|Diagram of the holotype specimen with insert photos showing traits shared with [[phytosaurs]]]]
A phylogenetic analysis conducted by Li ''et al.'' (2012) in the original description of ''Diandongosuchus'' concluded that it was the most basal member of a clade called Poposauroidea, which includes mostly terrestrial pseudosuchians such as the bipedal ''[[Poposaurus]]'' and the sail-backed ''[[Arizonasaurus]]''. It was compared, and found to be closely related to ''Qianosuchus'', an aquatic pseudosuchian and basal member of Poposauroidea. The data matrix of Li ''et al.'', a list of characteristics that was used in the analysis, was based on that of Nesbitt (2011), one of the most extensive on archosaurs.
However, more recent studies have found it to actually be a basal [[phytosaur]], as it showcases several anatomical features on its skeleton that are characteristic of derived, late triassic members of the clade ([[Synapomorphies|synamorphies]]).<ref name=":0" /><ref name=":1" /> For example, the overall morphology of the shoulder guirdle is basically identical to that of other phytosaurs, showing this part remained anatomically consistent throughout time. Other certain skull characteristics shared with phytosaurs seem to be associated with strengthening of the skull and its bite, likely an adaptation related to hunting. These include a tight, interdigitating suture between the premaxilla and maxilla (unlike the looser articulation in most other basal archosauriforms), and very similar shapes in the bones of the mandible and jaw joint, which provide a bigger surface area for muscles.<ref name=":1" />
''Diandongosuchus'' is a taxon that provides valuable insight into the evolution of phytosauria, being the earliest known member of the clade, and demonstrating that many anatomical characteristics that define them appeared early in their evolution.<ref name=":1" />
Below is a cladogram resulting from the phylogenetic analysis by Stocker ''et al.'' (2017)
{{clade |{{clade |1=''[[Litorosuchus]]'' |2={{clade |1=[[Proterochampsia]] |2={{clade |1=''[[Euparkeria]]'' |2={{clade |label1=[[Archosauria]] |1={{clade |1=[[Avemetatarsalia]] |label2=[[Pseudosuchia]] |2={{clade |1=[[Ornithosuchidae]] |label2=[[Suchia]] |2={{clade |1=[[Aetosauria]] |label2=[[Paracrocodylomorpha]] |2={{clade |1=[[Loricata]] |2=[[Poposauroidea]] }} }} }} }} |label3=[[Phytosauria]] |3={{clade |1=''Diandongosuchus''<div style="{{MirrorH}}">[[File:Diandongosuchus skeletal lateral transparent.png|80px]]</div> |label2=[[Parasuchidae]] |2={{clade |1=''[[Wannia]]'' |2={{clade |1=''[[Parasuchus]]'' |2={{clade |1=''[[Ebrachosuchus]]'' |2={{clade |1=''[[Angistorhinus]]'' |2={{clade |1=''[[Rutiodon]]'' |2={{clade |1=''[[Smilosuchus]]'' |2=[[Mystriosuchini]] }} }} }} }} }} }} }} }} }} }} }} }}
==Paleoecology== [[File:Diandongosuchus skull.jpg|thumb|Skull features]] ''Diandongosuchus'' was found in a [[Ladinian]]-age marine limestone formation that has preserved many marine reptiles including [[thallatosaur|thalattosaur]]s, [[nothosaur]]s, [[pistosaur]]s, and some [[protorosaur]]s. The pseudosuchian ''Qianosuchus'' was found in a marine deposit about {{convert|50|km|mi}} northwest of the ''Diandongosuchus'' locality that is slightly older ([[Anisian]] in age) and possesses many features consistent with a marine lifestyle. However, ''Diandongosuchus'' shows no features that are clear adaptations to a marine lifestyle. Possible adaptations include nostrils that are positioned slightly farther back on the skull than most terrestrial pseudosuchians and a greater number of premaxillary teeth (a feature seen in possible semiaquatic archosaurs such as ''[[Chanaresuchus]]'' and [[spinosaurid]]s). Fish bones within its stomach contents are additional evidence that it was a marine archosaur. ''Diandongosuchus'' may have had a similar lifestyle to modern marine crocodylians like the [[saltwater crocodile]] that live along coastlines yet are not fully marine.<ref name=Letal12/>
The fossil assemblage in which ''Diandongosuchus'' was found bears many similarities to that of European fossil localities such as [[Monte San Giorgio]]. Both include marine reptiles like thalattosaurs and nothosaurs and probably represented environments along the northern shorelines of the [[Tethys Ocean]]. No marine archosaurs like ''Diandongosuchus'' and ''Qianosuchus'' are known from Europe, although the pseudosuchian ''[[Ticinosuchus]]'' from Monte San Giorgio was probably adapted to life along the shorelines of the Tethys. In the analyses of Li ''et al.'' (2012) and Nesbitt (2011), ''Ticinosuchus'' is either the most basal member of a clade called [[Loricata]] which is the [[sister taxon]] of Poposauroidea, or the sister taxon of [[Paracrocodylomorpha]] which includes both Loricata and Poposauroidea.<ref name=Letal12/>
==References== {{Reflist}}
{{Phytosauria}} {{Taxonbar|from=Q5271376}}
[[Category:Phytosauria]] [[Category:Middle Triassic reptiles of Asia]] [[Category:Triassic archosaurs]] [[Category:Prehistoric reptile genera]]