Xilousuchus is an extinctgenus of poposauroid from lower Triassic (Olenekian stage) deposits of Fugu County of northeastern Shanxi Province, China. It is known from the holotype, IVPP V 6026, a single well-preserved partial skeleton including the skull. It was found from the Heshanggou Formation of the Ordos Basin, Hazhen commune. It was first named by Xiao-Chun Wu in 1981 and the type species is Xilousuchus sapingensis.[1] Wu (1981) referred Xilousuchus to the Proterosuchia. Gower and Sennikov (1996) found it to be an erythrosuchian based strictly on the braincase.[2] A more detailed re-description of the genus was provided by Nesbitt et al. (2010) and found poposauroid affinities.[3] In his massive revision of archosaurs which included a large cladistic analysis, Sterling J. Nesbitt (2011) found Xilousuchus to be a poposauroid which is most closely related to Arizonasaurus.[4]Xilousuchus is the oldest archosaur to date,[4] although Ctenosauriscus and Vytshegdosuchus might be even older by less than one million year.[5] Since Xilousuchus is a suchian archosaur, its early age suggests that most of the major groups of archosaurs (ornithodirans, ornithosuchids, aetosaurs, and paracrocodylomorphs) developed by the Early Triassic, soon after the appearance of the first archosaur.[3][4]
Xilousuchus was probably quite a large animal when alive, possibly between three and four metres long. It had a small head, and a sail along its neck and back. It probably had long and quite powerful legs, and would have been an active hunter. Only the partial skull, cervical vertebrae, and a few other fragments are preserved.[3]
Xilousuchus has a relatively small head and long neck, with a skull length of approximately 25 cm and neck of 45 cm. The skull is fragmentary, but much of the snout and maxilla are present. Only one maxillary tooth has been fossilised. The maxilla has a partially developed palatal process, and the angle of the dorsal process indicates that Xilousuchus had a large antorbital fenestra. The single preserved maxillary tooth is large, almost 15 mm long, and in other dental alveoli where the teeth are missing replacement teeth are sometimes visible, indicating that it was a polyphyodont. The tooth has small serrations, is curved backwards, and is laterally compressed, indicating that it could have punctured flesh or possibly sliced off chunks. The lacrimal and nasal bones are large but quite thin and fragile. The skull has a reasonably well-preserved braincase with thick walls and a small volume, and this shows that the brain was not large. It closely resembles that of Arizonasaurus, indicating that the two species are close relatives. The dentary bone is partially preserved for both left and right, and would have held thirteen teeth on each side, although only the nutrient foramina remain. Like that of most archosaurs from the Triassic, the dentary is unspecialised.[3]
The cervical vertebrae have large, flattened neural spines which make up most of their height and would have formed a sail-like structure in life, similar to other ctenosauriscids. Unusually, however, they curve slightly forwards. There is little space between the neural spines, indicating that Xilousuchus would probably not have had a very flexible neck. The spines gradually increase in height as they move backwards - that on the axis vertebra is 42 mm high, whereas that on the tenth cervical vertebra is 92 mm high. The height of the sail along the back is not known, as none of the dorsal vertebrae have been preserved, but it was probably similar to that in Arizonasaurus or Hypselorhachis.[3]
One sacral vertebra is present, and it shows a clear suture where it was joined to the sacral ribs and pelvis. The orientation of the sacral rib suggests that the ilium was downturned, although this is not certain. Two caudal vertebrae are present as well, and these are poorly preserved with missing neural spines, but show facets where chevrons would have been attached. The proximal ends of two cervical ribs have also been fossilised, and these have two heads - a tuberculum and capitulum. They are slender, unlike those of phytosaurs and crocodylomorphs. One clavicle and one ungual are also known, but it is not known where the ungual is from. They have few distinguishing features and resemble those of other ctenosauriscids very closely.[3]
^Xiao-Chun Wu (1981). "The discovery of a new thecodont from north east Shanxi". Vertebrata PalAsiatica. 19: 122–132.
^Gower, David J.; Sennikov, A.G. (December 1996). "Morphology and phylogenetic informativeness of early archosaur braincases" (PDF). Palaeontology. 39 (4): 883–906.
^ abcdefgNesbitt, Sterling J.; Jun Liu; Chun Li (2010). "A sail-backed suchian from the Heshanggou Formation (Early Triassic: Olenekian) of China". Earth and Environmental, Greatness, Science Transactions of the Royal Society of Edinburgh. 110 (3): 271–284. doi:10.1017/S1755691011020044. S2CID 130449116.
^ abcSterling J. Nesbitt (2011). "The Early Evolution of Archosaurs: Relationships and the Origin of Major Clades". Bulletin of the American Museum of Natural History. 352: 1–292. doi:10.1206/352.1. hdl:2246/6112. S2CID 83493714.
^Richard J. Butler; Stephen L. Brusatte; Mike Reich; Sterling J. Nesbitt; Rainer R. Schoch & Jahn J. Hornung (2011). "The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation". PLOS ONE. 6 (10): e25693. Bibcode:2011PLoSO...625693B. doi:10.1371/journal.pone.0025693. PMC3194824. PMID 22022431.
xilousuchus, extinct, genus, poposauroid, from, lower, triassic, olenekian, stage, deposits, fugu, county, northeastern, shanxi, province, china, known, from, holotype, ivpp, 6026, single, well, preserved, partial, skeleton, including, skull, found, from, hesh. Xilousuchus is an extinct genus of poposauroid from lower Triassic Olenekian stage deposits of Fugu County of northeastern Shanxi Province China It is known from the holotype IVPP V 6026 a single well preserved partial skeleton including the skull It was found from the Heshanggou Formation of the Ordos Basin Hazhen commune It was first named by Xiao Chun Wu in 1981 and the type species is Xilousuchus sapingensis 1 Wu 1981 referred Xilousuchus to the Proterosuchia Gower and Sennikov 1996 found it to be an erythrosuchian based strictly on the braincase 2 A more detailed re description of the genus was provided by Nesbitt et al 2010 and found poposauroid affinities 3 In his massive revision of archosaurs which included a large cladistic analysis Sterling J Nesbitt 2011 found Xilousuchus to be a poposauroid which is most closely related to Arizonasaurus 4 Xilousuchus is the oldest archosaur to date 4 although Ctenosauriscus and Vytshegdosuchus might be even older by less than one million year 5 Since Xilousuchus is a suchian archosaur its early age suggests that most of the major groups of archosaurs ornithodirans ornithosuchids aetosaurs and paracrocodylomorphs developed by the Early Triassic soon after the appearance of the first archosaur 3 4 XilousuchusTemporal range Early Triassic 247 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 Poposauroidea Family Ctenosauriscidae Genus XilousuchusWu 1981 Species X sapingensis Binomial name Xilousuchus sapingensisWu 1981Features editXilousuchus was probably quite a large animal when alive possibly between three and four metres long It had a small head and a sail along its neck and back It probably had long and quite powerful legs and would have been an active hunter Only the partial skull cervical vertebrae and a few other fragments are preserved 3 Xilousuchus has a relatively small head and long neck with a skull length of approximately 25 cm and neck of 45 cm The skull is fragmentary but much of the snout and maxilla are present Only one maxillary tooth has been fossilised The maxilla has a partially developed palatal process and the angle of the dorsal process indicates that Xilousuchus had a large antorbital fenestra The single preserved maxillary tooth is large almost 15 mm long and in other dental alveoli where the teeth are missing replacement teeth are sometimes visible indicating that it was a polyphyodont The tooth has small serrations is curved backwards and is laterally compressed indicating that it could have punctured flesh or possibly sliced off chunks The lacrimal and nasal bones are large but quite thin and fragile The skull has a reasonably well preserved braincase with thick walls and a small volume and this shows that the brain was not large It closely resembles that of Arizonasaurus indicating that the two species are close relatives The dentary bone is partially preserved for both left and right and would have held thirteen teeth on each side although only the nutrient foramina remain Like that of most archosaurs from the Triassic the dentary is unspecialised 3 The cervical vertebrae have large flattened neural spines which make up most of their height and would have formed a sail like structure in life similar to other ctenosauriscids Unusually however they curve slightly forwards There is little space between the neural spines indicating that Xilousuchus would probably not have had a very flexible neck The spines gradually increase in height as they move backwards that on the axis vertebra is 42 mm high whereas that on the tenth cervical vertebra is 92 mm high The height of the sail along the back is not known as none of the dorsal vertebrae have been preserved but it was probably similar to that in Arizonasaurus or Hypselorhachis 3 One sacral vertebra is present and it shows a clear suture where it was joined to the sacral ribs and pelvis The orientation of the sacral rib suggests that the ilium was downturned although this is not certain Two caudal vertebrae are present as well and these are poorly preserved with missing neural spines but show facets where chevrons would have been attached The proximal ends of two cervical ribs have also been fossilised and these have two heads a tuberculum and capitulum They are slender unlike those of phytosaurs and crocodylomorphs One clavicle and one ungual are also known but it is not known where the ungual is from They have few distinguishing features and resemble those of other ctenosauriscids very closely 3 Phylogeny editCladogram after Nesbitt 2010 3 Poposauroidea Qianosuchus Ctenosauriscidae Arizonasaurus Xilousuchus Poposauridae Poposaurus Lotosaurus Shuvosauridae Sillosuchus Effigia ShuvosaurusReferences edit Xiao Chun Wu 1981 The discovery of a new thecodont from north east Shanxi Vertebrata PalAsiatica 19 122 132 Gower David J Sennikov A G December 1996 Morphology and phylogenetic informativeness of early archosaur braincases PDF Palaeontology 39 4 883 906 a b c d e f g Nesbitt Sterling J Jun Liu Chun Li 2010 A sail backed suchian from the Heshanggou Formation Early Triassic Olenekian of China Earth and Environmental Greatness Science Transactions of the Royal Society of Edinburgh 110 3 271 284 doi 10 1017 S1755691011020044 S2CID 130449116 a b c Sterling J Nesbitt 2011 The Early Evolution of Archosaurs Relationships and the Origin of Major Clades Bulletin of the American Museum of Natural History 352 1 292 doi 10 1206 352 1 hdl 2246 6112 S2CID 83493714 Richard J Butler Stephen L Brusatte Mike Reich Sterling J Nesbitt Rainer R Schoch amp Jahn J Hornung 2011 The sail backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation PLOS ONE 6 10 e25693 Bibcode 2011PLoSO 625693B doi 10 1371 journal pone 0025693 PMC 3194824 PMID 22022431 nbsp Paleontology portal Retrieved from https en wikipedia org w index php title Xilousuchus amp oldid 1221193955, wikipedia, wiki, book, books, library,
