新疆下三疊統(tǒng)韭菜園組一新小型獸頭類

A new small baurioid therocephalian from the Lower Triassic Jiucaiyuan Formation， Xinjiang， China

Abstract Several therocephalian species， mainly represented by cranial material from the latePermian， have been reported from China in recent years. Here we describe a tiny new baurioidtherocephalian， Jiucaiyuangnathus confusus gen. et sp. nov.， from the Jiucaiyuan Formation，Xinjiang， China. The new taxon is represented by a partial snout with occluded partial lower jawand two postcranial skeletons. Although juvenile in stage， the new species is diagnosed by thefollowing features： round pit in middle of lateral surface of maxilla; lacrimal contact nasal; fossafor dentary tooth on the posterior end of the premaxilla， lateral to the anterior choana; two smallvertical triangular ridges extending dorsally and ventrally on the vomerine anterior portion， andbordering a thin vomerine foramen laterally; anterior projection of the lateral part of the frontalon the nasal; symphyseal region of the dentary projected anteriorly; 5 upper premaxillary teeth，upper and lower canines absent， diastema between the last premaxillary upper incisor and firstmaxillary tooth present， no diastema separating anterior from posterior dentition in the mandible，10 maxillary teeth and 12 dentary teeth， posterior postcanine expands mesiodistally， having amain large cusps and tiny anterior and posterior accessory cusps in line; neural arches of the atlasfused by the neural spine， neural spine of the axis projected posteriorly， procoracoid foramen liesbetween procoracoid and scapula. Features of the dentition resembles those of the small baurioidEriciolacerta parva from South Africa and Silphedosuchus orenburgensis from Russia. Thespecimens provide the rare opportunity to know in detail the postcranial skeleton of baurioids.

Key words Jimsar， Xinjiang; Early Triassic; Jiucaiyuan Formation; Therocephalia， Baurioidea

Citation Liu J， Abdala F， 2024. A new small baurioid therocephalian from the Lower Triassic Jiucaiyuan Formation， Xinjiang， China. Vertebrata PalAsiatica， 62（3）： 201–224

1 Introduction

A well-preserved terrestrial Permo-Triassic transition sequence is exposed along thenorthern and southern flanks of the Bogda Mountains in Xinjiang， northwest China （Yanget al.， 2021）. This sequence is known to have produced a diverse and abundant number of tetrapod fossils （e.g.， Yuan and Young， 1934a， b; Young， 1936， 1939， 1952， 1963， 1973a， b;Koh， 1940; Sun， 1963， 1991; Liu et al.， 2002; Liu and Abdala， 2017a; Liu， 2020; Angielczyket al.， 2022; Liu and Yang， 2022）. Non-mammalian therapsids recorded from this Permo-Triassic transition sequence include dicynodonts （Yuan and Young， 1934a， b; Sun， 1963;Liu et al.， 2002）， gorgonopsians （Liu and Yang， 2022）， and therocephalians （Young， 1952;Sun， 1991; Liu and Abdala， 2017a）. Besides the Early Triassic therocephalian Urumchialii （Young， 1952） from the Jiucaiyuan Formation， Dalongkoua fuae from the GuodikengFormation cropping out in the Dalongkou section， is the only other therocephalian recordedfrom Xinjiang （Liu and Abdala， 2017a） which is possibly Early Triassic （Angielczyk etal.， 2022）. Further therocephalians have also been reported from the Naobaogou， Sunan，Heshanggou， and Ermaying formations of North China， including members of the familiesAkidnognathidae （Shiguignathus， Jiufengia， Euchambersia）， Whaitsiidae （Moschowhaitsia），Baurioidea （Hazhenia， Ordosiodon， Traversodontoides， Nothogomphodon）， and taxa membersof other unnamed lineages （Caodeyao and Yikezhaogia） （Young， 1974; Hou， 1979; Li， 1984;Sun， 1991; Liu and Abdala， 2017b， 2019， 2020， 2022， 2023）. Chinese therocephalians areprimarily known after skulls， associated （articulated） to mandibles and， less frequently， to somepostcranial bones （e.g.， Young， 1952， 1974; Hou， 1979; Li， 1984; Sun， 1991; Liu and Abdala，2017a， b， 2019， 2020， 2022， 2023）. The finding of several associated semi-articulated-toarticulatedpostcranial elements in Chinese therocephalian is rare： Traversodontoides of whichthe preserved bones were only mentioned but remain undescribed （Young， 1974）， Hazheniawith brief description of postcranial bones （Sun and Hou， 1981）， and Ordosia presenting amore thorough study of postcranial elements （Hou， 1979）.

During 2018， a partial tiny snout together with a small slab with several postcranial boneswas collected from the base of the Jiucaiyuan Formation of Jimsar， Xinjiang. X-ray microcomputedtomography （μCT） unveiled two postcranial skeletons preserved in the slab， bothskeletons represented by several bones， some of them articulated. These specimens representa new， small therocephalian taxon that can be identified as a member of Baurioidea （sensuHopson and Barghusen， 1986）.

Postcranial material was described for many early members of Baurioidea， suchas Ictidosuchus primaevus （Broom， 1901）， Ictidosuchoides intermedius （Broom， 1938），Silpholestes jackae （Broom， 1948a）， Regisaurus jacobi （Kemp， 1978）， Tetracynodon darti（Sigogneau， 1963; Sigurdsen et al.， 2012）， Ericiolacerta parva （Watson， 1931; Colbertand Kitching， 1981） and Karenites ornamentatus （Tatarinov， 2004）. However， in most ofthese contributions， the postcranium was only briefly described， other than in an unnamedbaurioid tentatively identified as a regisaurid （Kemp， 1986）. By using computed tomographicdata derived from the known material， we provide detailed information on the cranial andpostcranial anatomy of this new baurioid therocephalian.

2 Computed tomographic setting

The specimens were first mechanically prepared， then X-ray μCT scanned at the Instituteof Vertebrate Paleontology and Paleoanthropology， Chinese Academy of Sciences （IVPP）using the 225 kV micro-computerized tomography （developed by the Institute of High EnergyPhysics， Chinese Academy of Sciences）. The μCT scanning of IVPP V32945 was performedwith a beam energy of 100 kV and a flux of 120 μA at a resolution of 11 μm voxel size usinga 360° rotation with a step size of 0.5°. The μCT scanning of both skeletons of IVPP V32946was performed with a beam energy of 130 kV and a flux of 120 μA at a resolution of 63μm voxel size using a 360° rotation with a step size of 0.5°. A total of 720 projections werereconstructed in a 2048*2048 matrix of 1536 slices using a two-dimensional reconstructionsoftware based on the GPU-accelerated FDK algorithm. The resulting 3D models werereconstructed using the software Mimics@.

Institution abbreviations CUMZ， Cambridge University Museum of Zoology，Cambridge， United Kingdom; IVPP， Institute of Vertebrate Paleontology and Paleoanthropology，Chinese Academy of Sciences， Beijing， China.

3 Systematic paleontology

Therapsida Broom， 1905

Therocephalia Broom， 1903

Baurioidea Hopson amp; Barghusen， 1986

Jiucaiyuangnathus confusus gen. et sp. nov.

Etymology ‘Jiucaiyuan’， refers to the stratigraphic unit which produced the specimens，‘gnathus’ is the Greek word for jaw; ‘confusus’， refers to the confusion on codings on manyimportant characters and its resultant phylogenetic position.

Holotype IVPP V32945， a partial snout with occluded partial lower jaw.

Referred specimens IVPP V32946-1， -2， are used for the two postcranial skeletonspreserved on the same slab. The partial skull is indeed associated with one of the skeletonsbut considering the similarity in size of the skeletons it is not possible to assign the skull withconfidence to any of them.

Locality and horizon 18J4 （N43°58′29″， E88°58′29″）， Jimsar， Xinjiang， China，less than 10 km away from the locality of finding of Dalongkoua fuae; base of JiucaiyuanFormation， Lower Triassic.

Diagnosis A small baurioid with the following combination of characters： a roundpit in the middle of the lateral surface of maxilla; an external nasal-lacrimal contact （as inTetracynodon）; a separated fossa on the posterior end of the premaxilla and lateral to theanterior choana， receiving dentary tooth; two small vertical triangular ridges extending dorsallyand ventrally on the vomerine anterior portion that border a thin vomerine foramen laterally;an anterior projection of the lateral part of the frontal onto the nasal; an anteriorly projectedsymphyseal region of the dentary （resembling the condition in the cynodont Dvinia）; fiveincisors; absence of upper and lower canines （as in Ericiolacerta）; a diastema between lastupper incisor and first upper maxillary tooth; no separation between the anterior and posteriordentition in the mandible; 10 maxillary teeth and 12 dentary teeth; mesiodistally expandedposterior dentary teeth， featuring a main large cusp and tiny anterior and posterior accessorycusps in line （as in Blattoidealestes， Scaloposaurus， Silphedosuchus， Muchia and Malasaurus）;axial neural spine projected posteriorly （anteriorly in Ericiolacerta）; procoracoid with aconcave anterior margin; procoracoid foramen lying between the procoracoid and scapula.

Comments The above diagnosis is comparative with basal baurioid therocephalians（Ictidosuchops， Ictidosuchus， Ictidosuchoides， Regisaurus， Urumchia， Muphasi， Karenites，Lycideops， Choerosaurus， Tetracynodon， Scaloposuchus， Silphedosuchus， Ericiolacerta）. Inaddition， features such as multicusped postcanines should be considered with caution as theyare usually represented in different species of tiny therocephalians and may prove to be anontogenetic feature represented in small， more likely juvenile specimens （see in discussionbelow）.

Description In the description， the ‘in life’ position of the skeleton is assumed to definethe views of the bones.

3.1 Partial skull and anterior mandible （IVPP V32945）

General preservation： IVPP V32945 preserves only parts of the anterior portion of thesnout with occluded anterior portion of the lower jaw. The snout is relatively complete on theleft side， with the septomaxilla， part of the premaxilla， maxilla lacking the posterior process，and part of the lacrimal. Only part of the maxilla is preserved on the right side. The pairednasals and frontals are crushed ventrally close to the palate， and only the left nasal is nearlycomplete. The left palatine is well preserved except for the missing posterior portion. Thesingle vomer is nearly complete. In the lower jaw， the dentaries and splenials are partiallypreserved， the left more complete than the right ones. Most sutures can be traced on the 3Dmodel.

Premaxilla The premaxilla is a narrow strip-like bone in lateral view， forming theanterior and ventral borders of the external naris， which faces anterolaterally （Fig. 1A， B）. Theascending process is broken， but its distal margin， inserting between the nasals， appears tobe short based on what can be inferred from the left nasal bone （Fig. 2A， B）. The premaxillaextends posteriorly and sutures to the maxilla below the septomaxillary foramen. The vomerineprocess is rather long， and almost forms the entire medial margin of the anterior part of thechoana （Fig. 2D， E）.

There are five empty alveoli for the incisors present in the preserved left premaxilla （Fig. 2D）.A small premaxillary fossa lies posterior to the alveolus of the missing first incisor， which hasan anterior opening. An oval fossa lies medial to the choana and posterior to the alveolus of the missing fifth incisor accomodating the crown of an anterior lower tooth （Fig. 2D）.

Septomaxilla The septomaxilla forms the ventral border of the external naris extendingposteriorly beyond the posterior edge of the naris （Fig. 1A， B）. The maxillo-septomaxillaryforamen， for the nasolacrimal duct （Hillenius， 2000） looks large because of the broken anteriormargin of the maxilla， but it was likely smaller. Anteriorly， the foramen connects to theposterior opening of the septomaxillary canal. There is a gap between the septomaxilla andpremaxilla which is possibly due to the immature condition of the specimen.

Maxilla The lateral side of the left maxilla is poorly preserved， leaving suture-like marginsexposed （Fig. 1A， B）. The maxilla is an elongate sheet of bone with a high dorsal lamina.Anteriorly， it contacts the premaxilla below the maxillo-septomaxillary foramen （Fig. 1B） atthe level of the last upper incisor. On the palate， the suture between the premaxilla andmaxilla extends posteriorly and medially to the margin of the anterior choana （Fig. 2D）. Aconcave ventral step in front of the first maxillary tooth is located posteriorly to the suture.Anterodorsally， the maxilla meets the dorsal （facial） process of the septomaxilla and dorsally， itshares a curved suture along with the nasal. Posterodorsally， it contacts the lacrimal （Fig. 1B）.

The maxilla is pitted laterally. On the central portion of the lateral maxillary plate aroundhalf of its height， there is a round pit （Fig. 1B）; this region corresponds to a convex surfaceon the medial side （Fig. 1C）. Some large foramina and small pits distribute slightly above thealveolus. The anteriormost foramen is remarkably larger than the others and has a posterioropening （Fig. 1A， B）， whereas the second largest foramen， which lies above the third maxillarytooth， has an anterior opening. These foramina are for the cutaneous branches of the maxillarybranch of the trigeminal nerve （CNV2） inside the maxillary canal.

In medial view， the dorsal lamina of the maxilla is a thin wall， lacking a canine boss. Themedial surface has a large concave area， and there is no distinct anterior antrum Highmore. Themaxilla sends a medial plate， forming the anterior portion of the crista choanalis. Posteriorly，the medial plate sends a slant dorsal portion， and they wraps a cavity， maxillary antrum （Benoitet al.， 2016）. Above the cavity， lies the naso-lacrimal canal （Fig. 1D）. On the ventral surface ofthe palate， posterior to the small maxilla-palatine foramen， the maxilla has an oblique suturewith the palatine （Fig. 2D）.

Nine out of ten teeth are preserved in the left maxilla， with the first maxillary tooth fallenout of its socket. There is no distinct canine present （Figs. 1B， C， 2D）. The diameter of thealveolus for the first maxillary tooth is similar to those of the following teeth. The alveoli ofthe second and third tooth are internally bubble-like （Fig. 2E）. The third tooth of the seriesis slightly bigger than the others. The teeth have a rounded root， with conical or spatulatedcrowns. Among the latter， some are nearly vertical and seem to have more than one cusp，whereas others have an oblique facet on the labial side more likely due to abrasion.

Lacrimal On the lateral surface， the left lacrimal has a small exposure posterodorsally tothe maxilla， and its anterior limit lies at the level of the eighth maxillary tooth position （Fig. 1A， B）.Considered the quite dorsally extension of the lacrimal in relation to the posterodorsal marginof the maxilla （Fig. 1B）， the lacrimal probably contacted the nasal， and its anterior extension is probably located anterior to that of the prefrontal （Fig. 2B）.

On its medial surface， the lacrimal has a broad exposure ventrally and its anterodorsal margin（lamina infralacrimalis） extends to the level of the seventh maxillary tooth （Fig. 1C）. If this isits natural shape， the lamina infralacrimalis is short， similar to Lycosuchus， Alopecognathus，Oliverosuchus and Theriognathus （Gigliotti et al.， 2023; Pusch et al.， 2024）， but differs fromthat described for other baurioids such as Karenites and Nothogomphodon （Ivakhnenko，2011）， and the whaitsiid Moschowhaitsia （Ivakhnenko， 2011）， in which this structure extendsanteriorly close to the premaxilla.

Palatine The palatine can be divided as three layers and one ridge （Figs. 1C， D， 2D， E）. Theventral layer lies medial to maxilla and the posterior tooth rows， its medial margin forming theposterior portion of the sharp crista choanalis （Fig. 2D）. Dorsolaterally， the medial （internal）layer forms a slant plate which sutures to the maxilla anteriorly and continues as the dorsalcap of the maxillary sinus or antrum of Highmore （Fig. 1C， D）. A large foramen lies betweenmaxilla and palatine， on dorsal or medial view， which is connected to the maxillary sinus. Thepalatine then curves medially as a dorsal layer， with its anterior margin contributing to theposterior margin of the choana （Fig. 3A， C）. The dorsal layer is partially covered by the vomerfrom ventral side （Fig. 3A， C）. A ridge is raised from the lateral junction of the middle anddorsal portions， to connect the lacrimal （Fig. 2E）.

Nasal The nasal is a long and flat bone in dorsal view， which is slightly constrictedin the middle and expands posteriorly （Fig. 2A–C）. The anteromedial process shouldcontact the dorsal process of the premaxilla， and its long anterior margin forms the dorsalmargin of the external naris. Anteroventrally， it features a lateral slot， with ventral anddorsal margins， which is interpreted for the reception of the septomaxilla. Considering this，the septomaxillary posterodorsal process may not touch the maxilla ventrally as in otherspecies. Posteroventrally， the bone has a short contact with the lacrimal， as in Tetracynodon，Lycideops， Choerosaurus （Sigurdsen et al.， 2012）， Ericiolacerta， and Silphedosuchus （personalobservations）. Posterolaterally， its convex margin seems partially covered by the prefrontal.The nasal has a long and irregular suture with the frontal posteriorly. Its lateral portion extendsmore posteriorly than the medial portion. On its ventral surface， the nasal is concave andsmooth except a well differentiated posteriorly longitudinal ridge presumably for support ofcartilaginous turbinals （Gigliotti and Pusch， 2023; Kemp， 1979） and some small foraminapossible for blood vessel （Fig. 2C）.

Frontal Both frontals seem to be partially preserved， but only the anterior portion ofthe left frontal can be recognized （Fig. 2A–C）. Its anterior border is serrated and irregular：the medial portion is nearly straight， the lateral portion is ‘U’-shaped and a sharp roughlytriangular process lies in the middle. The frontal is slightly overlapped by the nasal dorsally，therefore in the dorsal view the naso-frontal suture is showing the posterior margin of thenasal.

Vomer The single vomer is a broad and elongated element， with a long interchoanalprocess （Fig. 3A–C）. The vomer extends anteriorly well behind the anterior margin of thechoana. Its anterior end forms a triangular process in ventral view， similar to those describedfor baurioids such as Ictidosuchoides （Mendrez， 1975） and Scaloposaurus constrictus（Mendrez-Carroll， 1979）， as well as other non-baurioid eutherocephalians such as the whaitsiidIctidostoma hemburyi （Broom， 1911）， Theriognathus （Huttenlocker and Abdala， 2015; Puschet al.， 2024）. Based on its width， the anterior portion of the vomer does not meet the maxillalaterally， and the choana is a continuous fossa in palatal view （Fig. 3B， C）. The interchoanalprocess slightly narrows in width posteriorly， and its ventral portion bears a vertical ridgefor the posterior third of the bone. This ridge extends anteriorly from the middle of theinterchoanal process， to the posterior end of the vomer where it constricts in transverse widthand would have contacted the anterior process of the pterygoid （Fig. 3B， C）. In the posteriormargin of the choana， the vomer becomes a broad plate-like element， which is flanked laterallyby the palatine （Fig. 3C）.

Two small vertical triangular ridges extend dorsally and ventrally and border the thinvomerine foramen laterally. On the dorsal surface of the vomer， there is a distinct medianridge， which extends posteriorly along the entire length of the vomer. The ridge bears a grooveon the dorsal margin， which widens posteriorly. The median groove might have supported acartilaginous nasal septum （van den Heever， 1994）. The trough formed in the junction of themedian ridge with the horizontal （choanal） portion of the vomer （Fig. 3B）， would have beenthe putative location for the vomeronasal organ （sensu Hillenius， 2000： fig. 9）.

Mandible The dentary is elongated， slender and relatively straight with a smooth ventraledge （Fig. 3D–F）. The anterior margin of the symphyseal region is projected anteriorly （Fig. 3C），but the dorsal margin of the anterior tip turns slightly downwards. The symphyseal region is only moderately expanded mediolaterally， with a low mentum angulation in ventral view （Fig. 3F）.The dentary lateral surface is relatively smooth. The two dentaries are unfused and greatlydiverge posteriorly （Fig. 3E）.

Only a few of the preserved lower teeth are in place， whereas the majority have beenfallen out of their sockets. Some of the preserved lower teeth have open roots （e.g.， a toothdistal to left d8 in Fig. 3E）， indicating that they were in process of eruption. The dentaryhouses three incisors， with the third one fallen out on each side. The first incisor in the leftand right dentary is much larger， and shows an eroded surface on the labial side of the crown.The left first incisor shows a remarkable procumbency and a rounded open root. The crown ofthis tooth is lanceolate with the labial side more convex than the lingual side. The second leftincisor is ‘floating’ above its alveolus （Fig. 3D–F）. No canine is identified， but the fourth andfifth alveoli on the left and right side is slightly bigger than the posterior ones. Comparable tothe upper dentition， all preserved more anterior teeth in the left dentary are nearly vertical， andhave a simple conical shape. The left fourth tooth is slightly displaced from its natural positionand has almost fallen out. The fifth and sixth tooth in the left dentary are in place. The sixthtooth has an eroded root lingually and has a small replacement cone at its base. The posteriorlower teeth increase in mesiodistal length and bear three cups at the level of the eighth locus.

Splenial The splenial is detached from the dentary， especially on the right side （Fig. 3E， F）.In medial view， it lies near the dentary ventral margin， and extends anteriorly to contribute tothe medial portion of the symphysis. The bone appears to be completely covered by the dentaryin lateral view.

3.2 Post cranial skeleton （IVPP V32946-1， -2）

General preservation Two skeletons are preserved and numbered as IVPP V32946-1（smaller one， Fig. 4C， D grey） and V32946-2 （larger one， Fig. 4C， D， light purple）. Most postcranialbones lie close to their natural positions in the slab， and can be referred to either specimen （Fig. 4）.However， some dislocated bones are hard to be referred， especially on the middle portion of theskeletons. They include vertebrae， ribs， two metatarsals， one phalange and some unidentifiedbones （Fig. 4C， D， light blue）. The two skeletons present separation of neural arches from thecentra for most vertebrae indicating they are juveniles.

Axial skeleton The vertebral elements of IVPP V32946-1 are preserved from cervicalto caudal， but represented as different independent blocks （Fig. 5A， B）. Ten presacral vertebraeare identified， including the atlas and axis， five thoracics， and three lumbars. Three sacralvertebrae are followed by a caudal series that rapidly attenuate in size. The vertebrae ofV32946-2 are bigger， at least including 10 continuous vertebrae and a separate one in whichthe lengths of the centra are slightly longer than 4 mm （Fig. 6）.

The atlas comprises a separated intercentrum， centrum， and neural arch （Fig. 5D–F）. Thecentrum is deeply amphicoelous， of similar size of the axis centrum. Its left lateral surfacebears a longitudinal groove but the right one only has a pit and a short fissure. The centrum has nearly vertical anterior and posterior surfaces. The intercentrum is separated by a long spacefrom the centrum， and the dorsal surface of the narrower anterior portion bears the facet for articulation with the lower part of the occipital condyle. This intercentrum widens posteriorly，being opposite to the condition of this bone in the regisaurid CUMZ T837 （Kemp， 1986）. Theposterior portion is C-shaped， and its dorsal surface faces posterodorsally， bearing a shallowtrough. The neural arches of the atlas are fused along the midline. They are ossified in differentdegrees. The left side is more complete but do no preserve the transverse process. There is asmall boss on the anterior edge of the left neural arch for articulation with the proatlas. Theright transverse process extends slightly dorsolaterally （Fig. 5D）. The dorsal component of theneural arch extends posteriorly as the postzygapophysis， behind the posterior margin of thecentrum， with their distalmost portion contacting the prezygapophysis of the axis.

The axis comprises the separated centrum and neural arch， and there is no intercentrum（Fig. 5E， F）. The axis centrum has the same size and shape of atlas centrum， except forthe more smoothly concave lateral surfaces. The axis neural arch presents a high ax-likeneural spine. Only a short left transverse process is observed， whose dorsal surface tilts downwards， forming an angle of ～50o with the axial direction in lateral view （Fig. 5E）. Theprezygapophysis is longer and sharper than the postzygapophysis. The anteroposterior lengthof the neural arch is slightly longer than that of the centrum and much more erected.

Three cervical ribs are identified （Fig. 5B）. They are short， slender and slightly curved，with a prominently dichotomous head.

Posterior to the axis， there are four continuous vertebrae （Fig. 5A， B， G）. They areidentified as thoracic vertebrae due to spatial placement and the long-articulated ribs. Thecentra， with a length of around 3.5 mm， are similar to the atlantal and axis centrum. Only theright neural arches are preserved， showing narrow zygapophyses， low posteriorly orientedneural spines， and poorly-developed transverse processes. The postzygapophysis extendsposteriorly beyond the posterior margin of the centrum （Fig. 5G）. The first vertebra of the thirdvertebral segment is the last thoracic. Its neural arch is also separated from the centrum and theneural spines is low.

The preserved vertebrae of IVPP V32946-2 are interpreted as thoracics （Fig. 6A–C）.Their centra are amphicoelous， with slightly concave lateral surfaces. The neural arches andcentra are well-ossified， there are no distinct gap between them， presenting a clear suture（Fig. 6C）. The prezygapophyses are much wider than the postzygapophyses， and theirarticulating surfaces are oriented relatively vertically for dorsal portion. The neural spines aremostly distinct with exception of a few poorly ossified ones and change to a more posteriorlyorientation backwards （Fig. 6C）. The transverse processes are distinctive， slightly expanded inwidth laterally; they are high on the neural arch， a little below the level of the zygapophyses，and their distal ends are slightly upturned. Except for the first preserved vertebra of the group，a ventral buttress connects the middle portion of the transverse process to the neural arch. Thefirst buttress is connected to the ventral margin of the neural arch， and is more vertical （withan angle with the axial direction of 70o）， but on the posterior vertebrae it is more horizontallyoriented and extends to a more anterior place （with an angle with the axial direction of ～45o）.

In IVPP V32946-1， there are five incomplete ribs on the left side and seven nearlycomplete ribs on the right side of the thoracic vertebrae （Fig. 5A， B）. The proximal end is onlywell preserved in two right ribs， having a wide confluent head， with a prominent ridge， startingin the head region， along the dorsal edge of the rib shaft. The proximal portion of the shaft isdistinctly recurved， most of the shaft is only slightly recurved， but the distal end is expandedand curves medially. The last thoracic rib is longer and is more distinctly curved than theanterior ones.

In IVPP V32946-2， 13 complete long left thoracic ribs are preserved; whereas only theproximal side of eight thoracic ribs are preserved on the right side. In the two anterior ribs， thecapitulum and tuberculum are separated by a V-shaped notch. The diaphyses are nearly straightand a prominent dorsal ridge extends on the proximal portion for more than half the length ofthe shaft. The capitulum and tuberculum are fused on other ribs as a long head. The shaft islonger and distinctly recurved on posterior ribs.

The anterior lumbar vertebrae are poorly preserved， but the zygapophyses are widened（Fig. 5A）. The neural spines are low and their lengths are similar to those of the thoracicvertebrae.

In IVPP V32946-1， five continuous vertebrates are present， including sacrals and caudals（Fig. 5H， I）. Based on the length of the ilium and of the vertebral centra， three sacral vertebraeare deduced. The anterior two vertebrae are nearly complete. The neural arches are similar tothe anterior lumbar vertebrae in the widened prezygapophysis， but their neural spines are highand slightly inclined posteriorly. No centrum is preserved for the posterior three vertebrae.Their neural arches decrease in size caudally and their neural spines are more inclinedposteriorly， and decrease in their anteroposterior length.

Two ribs associated with the middle vertebra are identified as sacral ribs for the shortand widened shape. Both the proximal and distal ends are expanded， the distal being widest（Fig. 5I）. An articular facet of the rib extends ventrally， making a thickened proximal end. Athin ridge extends laterally on the dorsal surface. It is identified as the last sacral rib here. Twoincomplete anterior caudal ribs are much smaller.

At least 11 caudal vertebrae are preserved together， five of them being rod-like （Fig. 5J）.In all the caudals， there is synostosis between centrum and arch. There are three relativelycomplete vertebrae whose centra are shorter than the lumbar ones， and whose neural spines arenarrower and generally posteriorly inclined， although one of them is nearly vertical. They havetransverse process or fused ribs. The rod-like vertebrae bear zygapophyses which have more orless vertical articulating surfaces. Because the centra are longer than those of the above caudalones， they possibly belong to the larger individual （IVPP V32946-2）.

A few isolated sacral and caudal ribs of the larger specimen are preserved （Fig. 6D）. Thehead of the first sacral rib is considerably expanded dorsoventrally with a short， stout shaftcurving ventrally and a very expanded distal end to contact the ilium （Fig. 6D， E， F）. The headof the second sacral is also expanded dorsoventrally， but the shaft is less curved ventrally andthe distal end comparatively less expanded than the previous one （Fig. 6G， H）. Other smallerelements located near them are probably the anterior caudal ribs （Fig. 6D）. Isolated two sacralribs are also ventral to the dorsal vertebrae （Fig. 6A）. They are smaller in size （Fig. 6I–L）， andcould belong to the smaller specimen.

Shoulder girdle Elements of this girdle are only preserved in IVPP V32946-2 （Fig. 6）.

Scapula： The nearly complete left scapula and the dorsal portion of the right scapula arepreserved （Figs. 6， 7）. The scapula is slender and concave not very expanded distally （Fig. 7A–D）.Compared to CUMZ T857 and Ericiolacerta parva （Watson， 1931; Kemp， 1986）， the dorsallamina is slenderer. In lateral view， the base of the bone and the dorsal portion of the scapularblade curve forward （Fig. 7B）. The dorsal edge of the left lamina is broken， but complete on theright side （Fig. 7B， D， E）. The dorsal margin is nearly flat （Fig. 7E）， whereas the anterior marginis smooth， without the trace for the cleithrum. The external surface of the lamina is smooth，forming a triangular flat surface. Ventrally， the lamina gradually narrows anteroposteriorly， and a ridge extends from the base of the triangular lamina downwards （Fig. 7A， B）. The middleregion of the scapula is rod-like and nearly triangular in cross section. The medial surface ofthe blade is smooth and convex. The scapula expands ventrally， resulting in a broad， slightlyconcave lateral face （Fig. 7B）. The bone tapers anteriorly to a sharp edge， but retains a robustposterior edge. The scapular glenoid is circular in outline， faces posteromedially and somewhatventrally （Fig. 7C， D）. Ventromedially to the glenoid facet， there is an open groove separatedby a vertical ridge of a triangular fossa located medially.

Procoracoid： Only a separated procoracoid is present， which lies close to the ventralside of the scapula （Fig. 6B）. It is identified as the left one for its position. It is a roughlyquadrilateral plate with a notch. Its dorsal （inner） surface is slightly concave， whereasits ventral （external） surface is nearly flat. The dorsal edge for articulating the scapula isconvex. The procoracoid foramen opens nears the posterior end of this edge， close to wherethe procoracoid meets the scapula and the coracoid （Fig. 7F， G）. The posterior edge for thecoracoid is nearly straight as in Ericiolacerta parva， and it may be directed slightly anteriorlyas reconstructed in regisauridae （Kemp， 1986; Fourie and Rubidge， 2007）， but not in E.parva （Watson， 1931）. The anterior edge is concave while the ventral edge is convex. Theprocoracoid does not contribute to the articulating surface of the glenoid.

Interclavicle and clavicle： An incomplete interclavicle appears as a broad flat bone that gentlycurves ventrally. The ventral surface is smooth， without any trace of keel or ridge （Fig. 6A）. Afragment of the medial end of the right clavicle attaches on the ventral surface. A rod-like boneis identified as part of the shaft of the left clavicle contacting the base of the anterior margin ofthe scapular lamina.

Sternum： The sternum is preserved as a large， thin， longer than wide flat plate （Figs. 4， 6A， B）.The anterior right border is damaged. The anterior portion is slightly wider than the posterior.A median ridge is perceptible from the middle portion of the ventral surface and becomes moredistinct posteriorly. The dorsal surface is smooth.

Pelvic girdles The pelvic girdles are almost complete in both skeletons except for theleft ischium in the smaller specimen （Fig. 5） and the left pubis in the lager one （Fig. 6）. Theelements of the lager skeleton are slightly larger than the corresponding ones of the smallerskeleton， except for the pubis （Fig. 8）.

Ilium： Ilia of the two skeletons are incomplete， but their preserved portions provide arelative complete picture of this bone （Fig. 8A–D， H–K， R）. The iliac blade is well expandedanteroposteriorly， the anteroventral and posteroventral margins form an angle of ～120o， witha dorsal margin length nearly twice of the base length. The blade is high anteriorly and thepoorly preserved posterior portion appears to be much lower. The anterior portion of the bladeis projected far beyond the anterior margin of the base， like in the Chinese therocephalianYikezhaogia megafenestralia （Li， 1984） but markedly differing from the South AfricanEriciolacerta parva （Watson， 1931） and Regisaurus jacobi （Kemp， 1978）.

In lateral view， the anterior margin of the left ilium in the smaller specimen show twoprojections， one directed dorsally and the other anteriorly， separated by a concavity （Fig. 8A， B）.These two projections were also recognized in the ilium of a specimen identified as Regisaurusby Fourie and Rubidge （2007）， which might instead represent an Olivierosuchus （Botha-Brink and Modesto， 2011）. Ilia of other therocephalians shows only one projection orientedanteriorly which is termed anterior process （e.g.， Watson， 1931; Kemp， 1986）. The right iliumof this specimen does not show these projections， probably because of lack of ossification orpreservation （Fig. 8C， D）. The iliac portion of the acetabulum is longer than depth， capped by arudimentary supra-acetabular boss projected laterally. The ilium has a constricted ‘waist’ at thelevel of the supracetabular buttress.

The internal surface of the lower portion of the ilium （at the level of the acetabulum） isconvex from front to back， with a few small foramina near the ventral margin. A thin and sharpridge extends anterodorsally on the blade， roughly parallel with the anteroventral margin ofthe blade. This ridge， better represented in IVPP V32946-2 （Fig. 8I， K）， is the most distinctstructure on the internal surface of the ilium. No clear scars for the sacral ribs can be observed.

Pubis： Both pubes are available in the smaller skeleton but only the proximal portion ofthe right pubis in the larger one （Fig. 8E， F， O–Q）. This bone is ‘L’-shaped， similar to that ofEriciolacerta parva （Watson， 1931）. The pubic component of the acetabulum has a convexsurface smaller than that of the ischium. The articulated surface with the ilium is also smallerfor the pubis （Fig. 8R）. The bone is slightly constrained to form a neck below the acetabularportion， then expands as a roughly rectangular thin blade that curves further medially. Theanterior edge is thickened and extends anteromedially.

The obtuse angle formed by the anterior edges of both pubes is smaller than that reconstructed by Kemp （1986）， but not nearly a straight line as in E. parva （Watson， 1931）.

Ischium： The ischia are relatively well preserved and the left one of IVPP V32946-2 isexposed on the rock （Fig. 4）. The bone is a large， thin plate flaring medially （Fig. 8E， G， L–N）.The ischial part of the acetabulum is flat. It has a small anterolateral facet for articulation withthe pubis. Dorsal to the acetabulum， the articulating surface to the ilium is a slightly convexstrap. The ischium is less constrained in the neck. The plate slightly increases in thicknessdistally on the anterior margin， but become thinner on the rounded distal margin. The lateral/dorsal side of the posterior margin forms a triangular area with a shallow groove in the middle.The anterior edge is shorter and more concave than the posterior one. The anterior portionof the medial （distal） margin is thickened and with rough surface in dorsal view （Fig. 8N）.The anterior end forms a square corner for contacting the pubis. The middle portion contactswith its counterpart in the midline， whereas the posterior portion flares laterally. Based on thereconstruction （Fig. 8R）， the bone is oriented quite close to the horizontal， and the obturatorfenestra between pubis and ischium （Fig. 8E） is slightly larger than in Ericiolacerta parva.

Hindlimb A right femur is exposed on the slab， possibly belonging to IVPP V32946-1（Fig. 4）. Its proximal end is lost and the distal end incomplete （Fig. 5A–C）. The proximal sideof both femurs are preserved in IVPP V32946-2， but the right one is more complete （Fig. 6）.

The more complete femur is more than 3 cm in length， and only moderately expandedin the distal end. The head is slightly recurved from the shaft towards the acetabulum. On theproximal side， there are three trochanters， the distinct internal trochanter posteroventrally， thetrochanter major along the posterior edge and the small trochanter minor along the anterioredge （Fig. 9A–E）. A shallow fossa is formed between the trochanter major and minor on thedorsal surface （Fig. 9C）. The position of internal trochanter is similar to that of CUMZ T857but different from Regisaurus jacobi （Kemp， 1978， 1986）. The overall morphology of the bonealso resembles closely that of Dongusaurus schepetovi （PIN 952/4， 5， personal observation）.

4 Phylogenetic analysis

Jiucaiyuangnathus confusus was scored into a revised version of the original datamatrix of Liu and Abdala （2023）， who performed the most recent phylogenetic analysis oftherocephalians， to assess its relationships. Because a separated fossa for an anterior dentarytooth lies on the premaxilla in Jiucaiyuangnathus， a new state （a fossa for the dentary toothis present on the premaxilla， lateral to the anterior choana） was added to character 37. Theanterior portion of the vomer sends a sharp process inserting the premaxilla in ventral view， asin Theriognathus， Ictidostoma， Ictidosuchoides， Ictidosuchops， and Tetracynodon darti， andtheir coding for character 39 are changed to 0， whereas in Ictidosuchus is ‘？’. The number oflower incisors is coded as unknown.

The data matrix was analyzed in TNT 1.5 （Goloboff and Catalano， 2016）， with allcharacters equally weighted and 18 characters treated as additive as in previous analyses. The modified data matrix and character list are included as Appendices. The routine implementedconsisted of 100 random addition sequences and tree bisection reconnection （TBR）， saving10 trees per replication， and a second search using the trees from RAM as a starting point andimplementing TBR on those trees.

We performed two analyses changing the scoring of canine for Jiucaiyuangnathus.When the upper and lower canines （character 94， 96） were coded as reduced， the analysisresulted in 36 most parsimonious trees （mpt） of 438 steps. It results in a close relationship ofJiucaiyuangnathus with Ericiolacerta and Silphedosuchus （Fig. S1）， which is only supportedby the presence of reduced upper and lower canines. When the canines were coded asunknown， it results in 60 mpts of 437 steps （see Appendix on line）. The new species lies eitheras the sister taxon of clade A or clade B in the cladogram presented in Fig. 10. All analysesrecover Jiucaiyuangnathus as a baurioid （Figs. S1 and S2）.

5 Discussion

5.1 Differences between two skeletons and ontogenetic stages

The neural arches are not fused with the centra in the two specimens， but they are mostlydislocated from the centra in the smaller skeleton， whereas there is no distinct gap betweenthem in the larger one. This perhaps reflect different ontogenetic stages. Shapes of the sacralribs are similar in both specimens （Fig. 6E–L）. Both skeletons preserved the complete pelvicgirdles， but differences between the specimens exists especially in the morphology of the anterior margin of the anterior blade of the ilium （Fig. 8A–D vs Fig. 8H–K）. These differencesmight be due to different ossification between the two skeletons， but it should be mentionedthat differences are even observed between the ilia of the same skeleton. The incomplete pubisof IVPP V32946-2 （Fig. 8O–Q） resembles the proximal portion of the pubis of the smallspecimen. This can be explained as lacking the ossification of distal portion.

This is interpreted as one more example of juveniles of same species preserved together.This phenomenon is common in the fossil amniotes and they are usually interpreted as siblings，e.g.， Psittacosaurus （Meng et al.， 2004）， varanopids （Botha-Brink and Modesto， 2007）， basalcynodonts （Jasinoski and Abdala， 2017）.

5.2 Dentition of Jiucaiyuangnathus and tiny therocephalians

Basal baurioids are represented by a series of taxa that are generally tiny and also presentvariations in the dentition in comparison with the pattern represented in most therocephalians.That is the case with Choerosaurus， Tetracynodon， Scaloposuchus， Silphedosuchus andEriciolacerta and， until recently， Scaloposaurus.

The absence of canines in therocephalians is infrequently represented and we canmention here Ericiolacerta parva， and perhaps， Silphedosuchus orenburgensis， in whichIvakhnenko （2011） tentatively interpreted the second maxillary tooth as the canine. This toothhowever is barely larger than the anterior and following maxillary teeth， and only the last twoupper postcanines are showing a remarkably comparatively large crown. Jiucaiyuangnathusshows a combination of characters of the lower dentition that is unique： the absence of canineand a continuous dental series without any diastema between anterior and posterior dentition，which makes difficult to differentiate an incisor/postcanine number. In Ericiolacerta， the lowerdentition also lacks a canine but a recognizable diastema differentiates the incisors from thepostcanines （Watson， 1931）. A possibility of similitude to Jiucaiyuangnathus could be withthe lower dentition of Dongusaurus schepetovi， where the alveoli are contiguous （there are nopreserved tooth） without diastema （Ivakhnenko， 2011）. However， the dentary is incomplete，and there are strong differences in the morphology of these lower jaws. Considering thepreserved portion in Dongusaurus， it is likely that there were no canine nor diastema separatingthe anterior and posterior teeth. But both features should be considered as a possibility.

Other specimens having contiguous dental series without canine were the tiny skullsdesignated as Homodontosaurus kitchingi （Broom， 1948b; Brink 1950）， which are usuallyinterpreted as juvenile of Tetracynodon （Mendrez， 1973， Colbert and Kitching， 1981）， or of anindeterminated lycideopsid （Huttenlocker and Sidor， 2016）， although Ivakhnenko （2011：1093）recognized it as a valid taxon of the Tetracynodontinae， but recognizing that the group is“somewhat artificial”.

Considering postcanine morphology， several small sized specimens （and species） show acomplexity to the postcanine crown of the last teeth of the series. Typical triconodontid teethwith a large central cusps and tiny mesial and distal ones as observed in Jiucaiyuangnathus are also known in Ericiolacerta， Malasaurus germanus， Muchia microdenta （Watson， 1931;Ivakhnenko， 2011） and in a relatively small specimen （i.e.， holotype） of Scaloposaurusconstrictus （Mendrez-Carroll， 1979）. Also， tricuspid crowns are represented in the last upperpostcanines of Silphedosuchus orenburgensis， but with a remarkable difference： the crown isslightly expanded and in addition to the three cusps also present three tiny cuspules forming alingual cingulum. In addition to all these baurioid-like specimens which are represented in thelate Permian and Early Triassic， tricuspid postcanines is also known in a tiny specimen fromthe middle Permian of South Africa described as Blattoidealestes gracilis （Boonstra， 1954;Abdala et al.， 2008）. This last record， as well as the recent description of a larger specimenof Scaloposaurus constrictus lacking triconodont teeth （Huttenlocker et al.， 2022）， seems tobe a strong indication that this postcanine morphology is more likely to represent a juvenilecharacter.

5.3 Comparison with other therocephalians and phylogenetic position

The skull is definitively distinct from previously reported therocephalians fromChina. The straight maxillary ventral margin is different from the strong concave margin ofDalongkoua fuae （Liu and Abdala， 2017b）. The vomer is only slightly expanded anteriorly，different from the greatly expanded vomer of akidnognathids， which are widely representedin China （Liu and Abdala， 2017a， 2019， 2022）， much wider than that of Caodeyao liuyufengi（Liu and Abdala， 2020）. Different from baurioids from North China and Moschowhaitsia， themaxillary palatal processes do not contact the vomer， and the choana is a continuous fenestra.The dentary tapers anteriorly， with a downward anterodorsal margin， different from theanteriorly deep of Ordosiodon lincheyuensis （Young， 1961） and straight margin in Yikezhaogiamegafenestrala （Li， 1984）.

Although the specimens are juveniles， they show some special features among knowntherocephalian species. Upper and lower canines are absent， and there is no canine boss on themaxillary medial side. In the vomer， there are two small vertical triangular ridges extendingdorsally and ventrally on two sides of the anterior portion， and bordering the thin vomerineforamen laterally; the procoracoid foramen lies between the scapula and procoracoid.

The position of Jiucaiyuangnathus inside Baurioidea is mainly determined by threedental characters： five upper incisor; sectorial mesiodistally long postcanines， and three lowerincisors. This position is inconsistent with the characters related to its palatal morphology.Jiucaiyuangnathus has a primitive secondary palate within Baurioidea： the maxillary palatalprocesses form a well-developed crista choanalis which nearly contact the ventrally extendingvomer， as in Ictidosuchoides and Ictidosuchops （Broom， 1940; Mendrez， 1975）. Premaxillaryvomerine process does not contact maxilla on the border of choana but they are located veryclose （Fig. 3C）. This condition may be typical of young individual and it is likely that themaxilla contacted premaxilla and vomer in a late ontogenetic stage. It is interesting to note thatin Mupashi migrator there was a maxilla-vomerine bridge in one side of the palate but not onthe other （Huttenlocker and Sidor， 2016）.

Because many bones are disarticulated， their relative positions must be deduced from thecurrent state; e.g.， the lacrimal contacts the nasal， the position of procoracoid foramen. Also，we are uncertain on the putative ontogenetic variation of some characters. Therefore， someparticular character codings need to be tested by additional material.

Acknowledgements Thanks to Liu Yudong for discovering and preparing the specimens，Wang Chaoxiong for 3D reconstruction of CT images， and Carmen Fernandez from the UnidadEjecutora Lillo helped with figures 5 and 6. The comments from Luisa Pusch and Julia A.Suchkova significantly improved this paper. This work is supported by the Strategic PriorityResearch Program of Chinese Academy of Sciences （XDB26000000）.

摘要：主要基于晚二疊世的頭部材料，中國近年來報道了多個獸頭類物種。記述了新疆韭菜園組的小型包氏獸超科（Baurioidea）新材料，包括一個頭骨吻端及咬合的下頜以及兩個頭后骨架，并命名為迷惑韭菜園頜獸（Jiucaiyuangnathus confusus）。雖然標本為幼年個體，新種有以下鑒定特征：上頜骨側面中部有小圓坑；淚骨與鼻骨接觸；前頜骨后端在內鼻孔外側有容納下頜齒的窩；犁骨前部側緣有小型三角形脊向背腹兩側延伸，組成細長的犁骨孔的側緣；額骨有尖角延伸到鼻骨后側部；齒骨的聯(lián)合部收窄并指向前方；5枚前頜骨齒，上下犬齒缺失，前頜骨齒與上頜骨齒間有齒缺，下頜前部無齒缺，10枚上頜骨齒，12枚齒骨齒，后部齒加長，有大的主尖及小的前后副尖；寰椎神經(jīng)弓與神經(jīng)棘愈合，樞椎神經(jīng)棘倒向后方，前烏喙骨孔位于前烏喙骨與肩胛骨間。齒系與小型包氏獸超科成員南非的Ericiolacerta parva及俄羅斯的Silphedosuchus orenburgensis類似。新的頭后骨骼材料提供了難得的研究包氏獸超科成員頭后骨骼的機會。

關鍵詞：新疆吉木薩爾；早三疊世；韭菜園組；獸頭類，包氏獸超科

中圖法分類號：Q915.864 文獻標識碼：A 文章編號：2096–9899（2024）03–0201–24

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