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{{Automatic taxobox
| name = ''Yarasuchus''
| fossil_range = [[Middle Triassic]], {{fossilrange|Anisian}}
| image =
|
| image_caption =
| taxon = Yarasuchus
| authority = Sen, [[2005 in paleontology|2005]]
| display_parents = 3
| type_species = '''''Yarasuchus deccanensis'''''
| type_species_authority = Sen, 2005
|subdivision_ranks=|subdivision=}}
'''''Yarasuchus''''' (meaning "red crocodile") is an [[extinct]] [[genus]] of
''Yarasuchus'' has had a complicated taxonomic history, after originally being described as a "[[Prestosuchidae|prestosuchid]] [[rauisuchia]]n", it was later variously recovered as a [[Poposauroidea|poposauroid]] [[pseudosuchia]]n and a non-archosaurian [[Archosauriformes|archosauriform]] of unstable position. In 2017 it was determined to be related to the similarly enigmatic Triassic reptiles ''[[Teleocrater]]'', ''[[Dongusuchus]]'' and ''[[Spondylosoma]].'' Together, they belong to a group called [[Aphanosauria]] and are placed at the base of Avemetatarsalia, sister to Ornithodira, making ''Yarasuchus'' one of the earliest diverging bird-line archosaurs known. The relative completeness of ''Yarasuchus'' and its evolutionary position helps to shed light on the origins of later, well known bird-line archosaurs such as the [[Dinosaur|dinosaurs]] and [[Pterosaur|pterosaurs]].<ref name="Teleo">{{cite journal |last1=Nesbitt |first1=S.J. |last2=Butler |first2=R.J. |last3=Ezcurra |first3=M.D. |last4=Barrett |first4=P.M. |last5=Stocker |first5=M.R. |last6=Angielczyk |first6=K.D. |last7=Smith |first7=R.M H. |last8=Sidor |first8=C.A. |last9=Niedźwiedzki |first9=G. |last10=Sennikov |first10=A.G. |last11=Charig |first11=A.J. |title=The earliest bird-line archosaurs and the assembly of the dinosaur body plan |journal=Nature |date=2017 |doi=10.1038/nature22037 |url=https://www.nature.com/nature/journal/vaop/ncurrent/full/nature22037.html}}</ref>
==Description==
''Yarasuchus'' was a relatively small, gracile, low-slung quadruped with a long neck and a small head, estimated to be around {{convert|2-2.5|m|ft}} long.<ref name="Sen, 2005"/><ref name=":0"/> Despite its appearance, ''Yarasuchus'' has a number of features in common with other avemetatarsalians, such as its elongated neck vertebrae. It has long, slender limb bones, unlike the more robust limbs of most pseudosuchians, but similar to other avemetatarsalians. Unlike later avemetatarsalians though, ''Yarasuchus'' has a "crocodile-normal" ankle configuration, more similar to pseudosuchians and some stem-archosaurs. ''Yarasuchus'' is very similar in appearance to its close relative ''Teleocrater'', and differs in only a few minor anatomical features of the skeleton, such as having a less of a rear facing [[Glenoid cavity|glenoid]] (the bony shoulder socket) than that of ''Teleocrater''.<ref name=Teleo/>
==
The skull of ''Yarasuchus'' is poorly represented, known from only a few isolated pieces. A number of bones were initially identified by Sen (2005), including a [[jugal]], [[quadrate]] and part of the [[quadratojugal]], [[squamosal]], both [[pterygoid]]s and two [[maxilla]] that included a portion of [[premaxilla]] attached to one of them, as well as an associated tooth.<ref name="Sen, 2005"/> However both maxillae differ from the known maxilla in ''Teleocrater'' and instead more closely resemble those of an [[allokotosaur]]. [[Sterling Nesbitt|Nesbitt]] and colleagues also regarded the jugal, quadrate and quadratojugal as indeterminate bones, and re-identified the squamosal as a [[Postorbital bone|postorbital]] belonging to a larger individual than the holotype specimen. As of 2017, the right postorbital and both pterygoids are the only positively identified cranial material belonging to ''Yarasuchus''.<ref name=Teleo/>
===Skeleton===
[[File:Yarasuchus.jpg|thumb|left|Outdated life restoration depicting ''Yarasuchus'' as a "raisuchian" with osteoderms.]]
Almost the whole [[vertebral column]] is represented in ''Yarasuchus'', including at least 8 [[Cervical vertebrae|cervicals]] (including the [[Atlas (anatomy)|atlas]] and [[Axis (anatomy)|axis]]), 17 [[Thoracic vertebrae|dorsals]], 2 [[Sacral vertebra|sacral]], and at least 11 proximal [[Caudal vertebra|caudal]] vertebrae. The long neck of ''Yarasuchus'' is made up of a series of characteristically elongated cervical (neck) vertebrae, in contrast to its proportionately small skull. The articulating surfaces of the [[zygapophyses]] that connect between each vertebra are inclined and the [[Vertebral centrum|centra]] are strongly curved along the bottom margin with offset faces, indicating that the neck was held raised up from the body and arched along its length. The cervicals are uniquely characterised by a prominent midline keel that runs along the front half of the underside of each centrum, followed by two separate keels that continue to the rear edge.<ref name=NJKP07>{{cite journal |last1=Jalil |first1=Nour-Eddine |last2=Peyer |first2=Karin |year=2007 |title=A new rauisuchian (Archosauria, Suchia) from the Upper Triassic of the Argana Basin, Morocco |journal=[[Palaeontology (journal)|Palaeontology]] |volume=50 |issue=2 |pages=417–430 |doi=10.1111/j.1475-4983.2007.00640.x}}</ref> The posterior [[cervical rib]]s have three heads, an unusual condition in archosaurs, and the corresponding cervicals possess an accessory articular facet to accommodate this.<ref name="Sen, 2005"/><ref name=Teleo/><ref name=":0"/><ref name=Teleo2/>
Unlike the cervicals, the dorsal (back) vertebra are short and compact, almost only half the length of the cervicals, as are the two sacral (hip) vertebra. The front-most two or three dorsal vertebra possess similar keels to the cervicals, unlike the condition in ''Teleocrater'' which has no keeled dorsals. The preserved proximal caudal (tail) vertebra are consistently elongate, however the distal caudals are missing and so the end of the tail is unknown. The vertebrae all have tall [[neural spines]] that run down the back, the tallest of which are over the hip where the spines are two times taller than the corresponding centra. The neck has similarly tall neural spines, however they are longer than tall and inclined forward so as to overhang the vertebra before it. The cervical neural spines are also unusually thickened and roughly textured at the top. The caudal neural spines are also tall and narrow, unlike the elongated centra, and are inclined backwards, decreasing in height further down the tail. The tall, broad neural spines were initially believed to be associated with rows of paramedian [[osteoderm|osteoderms]] (although see below).<ref name="Sen, 2005" /><ref name=":0" />
The [[Pectoral girdle|pectoral (shoulder) girdle]] is delicately built, with a tall and slender [[scapula]] that is expanded distally and constricted near the glenoid. The scapula has continuous [[acromion process]], as well as an unusual sharp, thin ridge of bone running down its posterior margin, a feature only found in aphanosaurs and [[Silesauridae|silesaurids]].<ref name="Teleo" /> The [[coracoid]] is small and rounded, and forms a down and rearward facing glenoid fossa with the scapula. The [[Ilium (bone)|ilium]] of the [[Pelvic girdle|pelvic (hip) girdle]] has a prominent posterior process and supraacetabular crest—a ridge of bone over the [[acetabulum]]. The acetabulum itself is relatively large and almost completely closed, unlike the fully open acetabulum of dinosaurs. The [[Pubis (bone)|pubis]] is short and points downwards, with a thickened, flattened end. The [[ischium]] is very similar to that of ''Teleocrater'', and is directed down and back from the hips, with a tapered shaft and slightly expanded distal end.<ref name="Teleo2" /> The pelvic girdle articulates with the spine via the sacral ribs, of which the first is larger and more robust. The nature of the articulation between the ilium and the sacral ribs suggests the hip was held sub-horizontally and faced ventrolaterally, causing the legs to be positioned down and outwards from the body.<ref name="Sen, 2005" /><ref name=":0" />
The limb bones of ''Yarasuchus'' are characteristically slender. The [[humerus]] is long and cylindrical, with a moderately developed elongated deltopectoral crest that occupies roughly 30% of the length of the bone, similar to the condition in dinosaurs. The [[ulna]] is arched somewhat, and is roughly equal in length to the humerus. The [[femur]] is similarly gracile, and has a sigmoidal (s-shaped) curve along its length. The head of the femur is not turned in. A moderately developed fourth trochanter is placed proximally on the femur, unlike the well developed fourth trochanters of dinosaurs. The manus and pes are almost entirely missing, except for the calcanues of the ankle joint. The calcaneus indicates that ''Yarasuchus'' had a "crocodile-normal" ankle, which allowed for more rotation of the foot than the derived hinge-like avemetatarsalian ankle. The forelimb to hindlimb length ratio is roughly 3:5, with much longer back legs than the front. Although the manus is missing, the overall similarity of ''Teleocrater'' suggests it would have had a relatively small hand.<ref name="Sen, 2005" /><ref name="Teleo" /><ref name=":0" />
The osteoderms attributed to ''Yarasuchus'' are greatly sculptured with a ridge running anteroposteriorly along each one.<ref name="Sen, 2005" /> This is unusual in comparison to ''Teleocrater,'' which has been interpreted as lacking any form of similar dermal armour. However, these osteoderms are larger in proportion to the presacral vertebra than would be expected and bear a close similarity to osteoderms of an [[Erythrosuchidae|erythrosuchid]] also found in the same formation. Nesbitt and colleagues considered it probable that the osteoderms do not belong ''Yarasuchus'' and so it may have also lacked osteoderms like other aphanosaurs and avemetatarsalians.<ref name="Teleo" />
==Discovery and naming==
''Yarasuchus'' is known from at least two individuals collected from a single {{convert|1|m2|sqft}} assemblage in the [[Yerrapalli Formation]], located near the Bhimaram village in the [[Adilabad district]] of [[India]], in a layer of fine red mudstone. The material was found disarticulated, however it represents the majority of the skeleton, missing only the distal caudal vertebrae, [[Radius (bone)|radius]], [[fibula]], manus, and most of the pes and skull. The name is derived from 'Yara', meaning red in the local dialect, and the Greek ''suchos'' ("crocodile"), referring to the red mudstones the fossils were discovered in. The specific name refers to the [[Deccan (disambiguation)|Deccan region]] of India, where the Yerrapalli Formation and surrounding [[Pranhita-Godavari Basin]] are situated.<ref name="Sen, 2005"/> The fossils were also found in association with two specimens of the allokotosaur ''[[Pamelaria]].''<ref name="Sen, 2005" /><ref name=":0" /><ref name="SK03" /> It was initially reported on in a 1993 thesis by Dasgupta, who considered it an indeterminate [[Rauisuchidae|rauisuchid]],<ref name=":0">{{Cite journal|last=Kasturi|first=Dasgupta,|date=1993|title=New reptiles diapsida archosauromorpha from the triassic yerrapalli formation Deccan India their importance in geology and palaeontology|url=http://shodhganga.inflibnet.ac.in/handle/10603/159402?mode=simple}}</ref> before being officially described and named as a new taxon by Sen in 2005.<ref name="Sen, 2005" /> All the material is held at the Geology Museum of the [[Indian Statistical Institute]] in [[Kolkata]], India.<ref name="Sen, 2005"/><ref name=Teleo/><ref name=":0"/>
In 2016, the material was re-examined by Nesbitt and colleagues in their description of ''Teleocrater'', which revealed a number of previously unrecognised anatomical characteristics. This re-evaluation prompted the inclusion of ''Yarasuchus'' within the newly recognised avemetatarsalian clade Aphanosauria. In their examination, Nesbitt and colleagues were able to refer a number of previously undescribed [[calcaneus|calcanea]] collected at the site to the hypodigm of ''Yarasuchus'' based on their similarity to ''Teleocrater'', and identified ischia that were originally reported as missing. They also removed a number of erroneously referred skull bones and osteoderms from the hypodigm. The relatively complete skeleton of ''Yarasuchus'' allowed Nesbitt and colleagues to confidently refer a number of isolated bones as all belonging to specimens of ''Teleocrater'' because of their close similarity to those of ''Yarasuchus'', which provided a key reference point for understanding the anatomy of the previously enigmatic taxon.<ref name=Teleo/><ref name=Teleo2>{{cite journal |last1=Nesbitt |first1=S.J. |last2=Butler |first2=R.J. |last3=Ezcurra |first3=M.D. |last4=Charig |first4=A.J. |last5=Barrett |first5=P.M. |year=2018 |title=The anatomy of ''Teleocrater rhadinus'', an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic) |url=https://www.tandfonline.com/doi/abs/10.1080/02724634.2017.1396539 |journal=Journal of Vertebrate Paleontology |volume=37 |issue=Supplement to No. 6 |pages=142–177 |doi=10.1080/02724634.2017.1396539 }}</ref>
== Classification ==
[[File:Qianosuchus_BW.jpg|thumb|Restoration of ''[[Qianosuchus]]'', a basal [[poposauroid]] formerly considered to be a close relative of ''Yarasuchus''.]]
The position of ''Yarasuchus'' in subsequent studies has been similarly unstable,<ref name=Butleretal11>{{Cite journal|last1=Butler |first1=R.J. |last2=Brusatte |first2=S.L. |last3=Reich |first3=M. |last4=Nesbitt |first4=S.J. |last5=Schoch |first5=R.R. |last6=Hornung |first6=J.J. |year=2011 |title=The sail-backed reptile ''Ctenosauriscus'' from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation |url=http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0025693 |journal=PLoS ONE |volume=6 |issue=10 |pages=e25693 |doi=10.1371/journal.pone.0025693 |pmid=22022431 |pmc=3194824}}</ref><ref name=Decuriasuchus>{{Cite journal|author1=Marco Aurélio G. França |author2=Jorge Ferigolo |author3=Max C. Langer |year=2011 |title=Associated skeletons of a new middle Triassic "Rauisuchia" from Brazil |url=http://www.springerlink.com/content/431nmk50220u113q/ |journal=Naturwissenschaften |volume=98 |issue=5 |pages=389–395 |doi=10.1007/s00114-011-0782-3 |pmid=21445632}}</ref><ref name=Nundasuchus>{{cite journal |last1=Nesbitt |first1=Sterling J.|last2=Sidor |first2=Christian A. |last3=Angielczyk |first3=Kenneth D. |last4=Smith |first4=Roger M. H. |last5=Tsuji |first5=Linda A. |year=November 2014 |title=A new archosaur from the Manda beds (Anisian, Middle Triassic) of southern Tanzania and its implications for character state optimizations at Archosauria and Pseudosuchia |url=http://www.bioone.org/doi/full/10.1080/02724634.2014.859622 |journal=Journal of Vertebrate Paleontology |volume=34 |issue=6 |pages=1357–1382 |doi=10.1080/02724634.2014.859622 }}</ref> though it has nonetheless typically been regarded as a pseudosuchian.<ref name=Desojo09>{{cite journal |last1=Desojo |first1=J.B. |last2=Arcucci |first2=A.B. |year=2009 |title=New material of ''Luperosuchus fractus'' (Archosauria: Crurotarsi) from the Middle Triassic of Argentina: the earliest known South American "rauisuchian" |journal=Journal of Vertebrate Paleontology |volume=29 |issue=4 |pages=1311–1315 |doi=10.1671/039.029.0422}}</ref><ref name=Rauisuchus>{{cite journal |last1=Lautenschlager |first1=S. |last2=Rauhut |first2=O.W.M. |title=Osteology of Rauisuchus tiradentes from the Late Triassic (Carnian) Santa Maria Formation of Brazil, and its implications for rauisuchid anatomy and phylogeny |year=2015 |journal=[[Zoological Journal of the Linnean Society]] |volume=173 |issue=1 |pages=55–91 |doi=10.1111/zoj.12196 |url=https://academic.oup.com/zoolinnean/article/173/1/55/2453081}}</ref><ref name="Chatterjee2017">{{Cite book|url=https://books.google.co.uk/books?id=0DI5DwAAQBAJ&lpg=PP1&pg=PA28#v=onepage&q&f=false|title=Indian Plate and Its Epic Voyage from Gondwana to Asia: Its Tectonic, Paleoclimatic, and Paleobiogeographic Evolution|last=Chatterjee|first=Sankar|last2=Scotese|first2=Christopher R.|last3=Bajpai|first3=Sunil|publisher=Geological Society of America|year=2017|isbn=0813725291|edition=Illustrated|volume=529|pages=28-29}}</ref> A study by Ezcurra on archosauromorph phylogeny in 2016 found ''Yarasuchus'' in a position outside of Archosauria, clading together with ''Dongusuchus'' in a [[polytomy]] with ''[[Euparkeria]]'' and a clade made up of [[Proterochampsia]] and archosaurs.<ref name=Ezcurra2016>{{Cite journal|last=Ezcurra |first=M.D. |date=2016 |title=The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms |url=https://peerj.com/articles/1778/ |journal=[[PeerJ]] |language=en |volume=4 |pages=e1778 |doi=10.7717/peerj.1778 |pmid=27162705 |pmc=4860341 |issn=2167-8359}}</ref> The left cladogram depicts the results of Brusatte and colleagues in 2010<ref name=Betal10/>, while the right cladogram depicts that of Ezcurra in 2016:<ref name=Ezcurra2016/>
<div class="NavContent">
{| width="75%"
|- valign="top"
| align="left" width="50%" |
{{clade| style=font-size:85%;line-height:85%;
|label1= [[Poposauroidea]]
|1={{clade
|1='''''Yarasuchus'''''
|2={{clade
|1=''[[Qianosuchus]]''
|2={{clade
|1=''[[Arizonasaurus]]''
|2=''[[Bromsgroveia]]''
|3=''[[Lotosaurus]]''
|4=''[[Poposaurus]]''
|5=''[[Sillosuchus]]''
|label6= [[Shuvosauridae]]
|6={{clade
|1=''[[Effigia]]''
|2=''[[Shuvosaurus]]'' }} }} }} }} }}
| align="left" width="50%"|
{{clade| style=font-size:85%;line-height:85%;
|label1= [[Eucrocopoda]]
|1={{clade
|1=''[[Dorosuchus]]''
|2={{clade
|1=''[[Euparkeria]]''
|2={{clade
|1=''[[Dongusuchus]]''
|2='''''Yarasuchus''''' }}
|3={{clade
|label1=[[Proterochampsia]]
|1={{clade
|1=[[Doswelliidae]]
|2=[[Proterochampsidae]] }}
|label2=[[Archosauria]]
|2={{clade
|1=[[Ornithodira]]
|2=[[Pseudosuchia]] }} }} }} }} }}
| align="left" width="50%" |
|}
</div>
Further complicating the issue were suggestions that the hypodigm of ''Yarasuchus'' was a chimeric assemblage of material from both a "rauisuchian" archosaur and a [[Prolacertiformes|prolacertiform]] archosauromorph, if not including material from yet other archosauromorphs.<ref name=Chimera>{{cite journal |last1=Lautenschlage |first1=S. |last2=Desojo |first2=J.B. |title=Reassessment of the Middle Triassic rauisuchian archosaurs ''Ticinosuchus ferox'' and ''Stagonosuchus nyassicus'' |journal=[[Paläontologische Zeitschrift]] |year=2011 |volume=85 |issue=4 |pages=357–381 |doi=10.1007/s12542-011-0105-1 |url=https://link.springer.com/article/10.1007/s12542-011-0105-1 |issn=1867-6812}}</ref><ref name=Rauisuchia>{{cite journal|last1=Nesbitt |first1=S.J. |last2=Brusatte |first2=S.L. |last3=Desojo |first3=J.B. |last4=Liparini |first4=A. |last5=De França |first5=M.A.G. |last6=Weinbaum |first6=J.C. |last7=Gower |first7=D.J. |title=Rauisuchia |journal=[[Geological Society, London, Special Publications]] |volume=379 |issue=1 |pages=241—274 |year=2013 |doi=10.1144/SP379.1 |url=http://sp.lyellcollection.org/content/379/1/241}}</ref> However, later examination of the material by Ezcurra found that none of it could be assigned to either a "rauisuchian" or prolacertiform, and that they all likely pertained to a single non-[[Suchia|suchian]] archosauriform taxon.<ref name=Ezcurra2016/>
In 2017, ''Yarasuchus'' was included in an updated analysis of Triassic archosauromorphs by Nesbitt and colleagues in their official description of ''Teleocrater'', utilising two modified datasets, those of Nesbitt (2011)<ref name="NSJ11">{{cite journal |last=Nesbitt |first=S.J. |year=2011 |title=The early evolution of archosaurs: relationships and the origin of major clades |url=http://digitallibrary.amnh.org/dspace/bitstream/2246/6112/1/B352.pdf |journal=Bulletin of the American Museum of Natural History |volume=352 |pages=1–292 |doi=10.1206/352.1}}</ref> and Ezcurra (2016)<ref name="Ezcurra2016" />. Both analyses recovered ''Yarasuchus'' in a newly recognised clade they named Aphanosauria, which included ''Yarasuchus'' in a polytomy with ''Teleocrater'' and ''Dongusuchus'', as well as ''Spondylosoma''. Indeed, the clade Aphanosauria was cladistically defined as "the most inclusive clade containing ''Teleocrater rhadinus'' and ''Yarasuchus deccanensis'' but not ''[[House sparrow|Passer domesticus]]'' or ''[[Nile crocodile|Crocodylus niloticus]]"''. Aphanosaurs were found to be the earliest diverging clade of [[Avemetatarsalia]], sister taxon to the clade [[Ornithodira]] that includes the [[Pterosauria]] and [[Dinosauromorpha]].<ref name="Teleo"/> The results of their analyses are reproduced and simplified below, combining the general topology of the Ezcurra dataset with the Nesbitt datset results for Avemetatarsalia.
{{clade| style=font-size:85%; line-height:85%
|label1=[[Archosauriformes]]
|1={{clade
|1=[[Proterosuchidae]]
|2={{clade
|label2=[[Archosauriformes|Eucrocopoda]]
|1=[[Erythrosuchidae]]
|2={{clade
|label2=[[Archosauria]]
|1=[[Proterochampsia]]
|2={{clade
|label2=[[Avemetatarsalia]]
|1=[[Pseudosuchia]]
|2={{clade
|label1=[[Aphanosauria]]
|label2=[[Avemetatarsalia|Ornithodira]]
|1={{clade
|1=''[[Spondylosoma]]''
|2={{clade
|1='''''Yarasuchus'''''
|2=''[[Dongusuchus]]''
|3=''[[Teleocrater]]'' }}}}
|2={{clade
|1=[[Pterosauria]]
|2={{clade
|label2=[[Dinosauriformes]]
|1=[[Lagerpetidae]]
|2={{clade
|1=''[[Marasuchus]]''
|2={{clade
|1=[[Silesauridae]]
|2=[[Dinosauria]]}}}}}}}}}}}}}}}}}}}}
=== Evolutionary significance ===
[[File:Teleocrater v1.png|thumb|Life restoration of the closely related aphanosaur ''[[Teleocrater]]''.]]
The recognition of a close relationship between ''Yarasuchus'', ''Teleocrater'' and other aphanosaurs and their relation to other avemetatarsalians settled a number of the unusual anatomical features of ''Yarasuchus''. Many of the previously unique features of ''Yarasuchus'' unite it with other aphanosaurs, including the elongated neck, high neural spines, three-headed cervical ribs and slender [[appendicular skeleton]]. ''Yarasuchus'' and the other aphanosaurs play a significant role in our understanding of early avemetatarsalian evolution, exemplified in the relatively completely known anatomy of ''Yarasuchus''. The structure of the foot, particularly the bones of the ankle (such as the calcaneus), demonstrate that avemetatarsalians evolved from ancestors with 'crocodile-normal' ankles, unlike the simple hinge-like ankles characteristic of derived ornithodirans. The 'crocodile-normal' ankle was once thought to be unique to pseudosuchians, but its presence in aphanosaurs like ''Yarasuchus'' imply that the evolution of the avemetatarsalian ankle was a more complicated process than initially believed.<ref name="Teleo" /> The anatomy of ''Yarasuchus'' also demonstrates that other typical avemetatarsalian features, such as slender limb girdles, had evolved prior to the eponymous 'advanced mesotarsal' ankles.<ref>{{Cite journal|last=Cau|first=Andrea|date=2018|title=The assembly of the avian body plan: a 160-million-year long process|url=http://paleoitalia.org/media/u/archives/01_Cau_2018_BSPI_571.pdf|journal=Bollettino della Società Paleontologica Italiana|volume=57|issue=1|pages=1-25|doi=10.4435/BSPI.2018.01|via=}}</ref>
Unusually, ''Yarasuchus'' and other aphanosaurs share a number of features convergently evolved with poposauroids. Aphanosaurs and poposauroids share only one unique trait (the presence of an accessory articulation facet just above the parapophysis of the cervicals for the three-headed cervical rib), however they have also convergently acquired a similar set of traits that are found throughout archosaurs. The previous phylogenetic position of ''Yarasuchus'' as a poposauroid by Brusatte and colleagues was likely due to this convergence.<ref name="Teleo2"/> The convergence between ''Yarasuchus'' and poposauroids could be attributed to the broader trend of poposauroids converging on [[coelurosaur]]ian [[theropods]], a derived clade of avemetatarsalians.<ref name="Nesbitt2007">{{Cite journal |last=Nesbitt |first=Sterling J. |date=2007 |title=The anatomy of ''Effigia okeeffeae'' (Archosauria, Suchia), theropod-like convergence, and the distribution of related taxa. |url=http://digitallibrary.amnh.org/dspace/handle/2246/5840 |journal=[[Bulletin of the American Museum of Natural History]] |issue=302 |pages=1—84 |doi=10.1206/0003-0090(2007)302[1:TAOEOA]2.0.CO;2}}</ref> The similarity between poposauroids and aphanosaurs like ''Yarasuchus'' means it is difficult to determine the identity of isolated archosaur material that has features present in both groups, particularly as aphanosaurs are the earliest diverging avemetatarsalians while poposauroids are the oldest known pseudosuchians and so their [[stratigraphic]] ranges broadly overlap with each other.<ref name="Teleo2" />
==Palaeobiology==
''Yarasuchus'' was proposed to be facultatively bipedal by Dasgupta in 1993 on the basis of its gracile body, slender shoulder girdle and proportionately short forelimbs, among other features, and this suggestion was repeated by Sen in its official description in 2005.<ref name="Sen, 2005" /><ref name=":0"/> The closely related ''Teleocrater'' has since been interpreted to have been a quadruped, and as ''Yarasuchus'' has similar limb proportions, it likely was as well.<ref name=Teleo/> The lack of definitive jaw material leaves the diet of ''Yarasuchus'' ambiguous, however the teeth of ''Teleocrater'' imply aphanosaurs were carnivorous, as with other early avemetatarsalians. Furthermore, [[histology|histological]] samples from ''Teleocrater'' show that its growth rates were more similar to those of other avemetatarsalians compared to pseudosuchians and stem-archosaurs, and so ''Yarasuchus'' may have also had a similarly higher growth rate.<ref name=Teleo/>
==Palaeoecology==
[[File:Pamelaria_dolichotrachela.jpg|thumb|Restoration of the contemporary allokotosaur ''[[Pamelaria]]''.]]
Many other vertebrate remains have been found from the Yerrapalli Formation alongside those of ''Yarasuchus'', and would have coexisted with it during the Middle Triassic. Remains of the allokotosaur ''Pamelaria'' in particular have been found in close proximity to those of ''Yarasuchus''.<ref name="SK03">Sen, K. (2003). ''Pamelaria dolichotrachela'', a new prolacertid reptile from the Middle Triassic of India. ''Journal of Asian Earth Sciences'' '''21''': 663–681.</ref> Other vertebrate remains include those of the [[lungfish]] ''[[Ceratodus]]'', the [[Actinopterygii|actinopterygian]] fish ''[[Saurichthys]]'', the [[temnospondyl]] ''[[Parotosuchus]]'', the [[dicynodont]]s ''[[Rechnisaurus]]'' and ''[[Wadiasaurus]]'', the [[rhynchosaur]] ''[[Mesodapedon]]'', and a large undescribed erythrosuchid.<ref name="BS99"/><ref name=":0" /><ref name="Chatterjee2017"/>
[[File:Wadiasaurus1DB.jpg|thumb|left|Restoration of the contemporary dicynodont ''[[Wadiasaurus]]''.]]
The anatomical similarity between ''Yarasuchus'' and ''Teleocrater'' is mirrored by the similarities in fauna and environment shared between the Yerrapalli Formation and the [[Manda Formation]] in [[Tanzania]], and both are estimated to be Anisian in age.<ref name="BS99/><ref name="Sen, 2005" /> At the time, India was still a part of the supercontinent [[Gondwana]] in [[Pangaea]], and was located directly adjacent to East Africa. This demonstrates that early avemetatarsalians like ''Yarasuchus'' were geographically widespread in the Middle Triassic, as with other archosauriforms, in contrast to previous suggestions that pseudosuchians were more diverse''.'' The close similarity between ''Yarasuchus'' and the Russian ''Dongusuchus'' further supports this, indicating [[biogeographical]] affinities between India and Russia despite their widely separated [[Palaeolatitude|palaeolatitudes]].<ref name="Teleo" /><ref name="Teleo2" /><ref name="Ezcurra2016" />
The sediments of the Yerrapalli Formation are interpreted as fluvial deposits, indicative of a broad, interchannel floodplain environment with seasonal ephemeral stream channels. The climate is thought to have been hot and dry with seasonal rainfall. This is consistent with the preservation state of the fossils, as the remains of ''Yarasuchus'' were found dismembered and disarticulated, suggesting the material was left exposed at the surface for a period before being buried by suspended fluvial sediments.<ref name="Taphonomy">{{cite journal |last1=Brandyopadhyay |first1=S. |last2=Roy Chowdhury |first2=T.K. |last3=Sengupta |first3=D.P. |title=Taphonomy of some Gondwana vertebrate assemblages of India. |journal=[[Sedimentary Geology (journal)|Sedimentary Geology]] |year=2002 |volume=147 |issue=1—2 |pages=219—245 |doi=10.1016/S0037-0738(01)00198-1}}</ref> There are few plant fossils known from the Yerrapalli Formation, however this is not believed to be due to it being an arid environment, but rather due to the hot and dry conditions being unsuitable to the fossilisation of plant material.<ref name=":0" />
==References==
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*[http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=148342&is_real_user=1 ''Yarasuchus''] in the [[Paleobiology Database]]
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{{Ornithodira|A.}}
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[[Category:Anisian genus first appearances]]
[[Category:Anisian genus extinctions]]
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