A New Basal Salamandroid (Amphibia, Urodela) from the Late Jurassic of Qinglong, Hebei Province, China

Abstract

A new salamandroid salamander, Qinglongtriton gangouensis (gen. et sp. nov.), is named and described based on 46 fossil specimens of juveniles and adults collected from the Upper Jurassic (Oxfordian) Tiaojishan Formation cropping out in Hebei Province, China. The new salamander displays several ontogenetically and taxonomically significant features, most prominently the presence of a toothed palatine, toothed coronoid, and a unique pattern of the hyobranchium in adults. Comparative study of the new salamander with previously known fossil and extant salamandroids sheds new light on the early evolution of the Salamandroidea, the most species-diverse clade in the Urodela. Cladistic analysis places the new salamander as the sister taxon to Beiyanerpeton, and the two taxa together form the basalmost clade within the Salamandroidea. Along with recently reported Beiyanerpeton from the same geological formation in the neighboring Liaoning Province, the discovery of Qinglongtriton indicates that morphological disparity had been underway for the salamandroid clade by early Late Jurassic (Oxfordian) time.

Fig 1. Map showing geographic location of the Nanshimenzi fossil site in relation to other Jurassic salamander fossil localities in Hebei, Liaoning, and Inner Mongolia.

Stratigraphic position of the fossil beds at the Nanshimenzi site is denoted by the salamander figured on the left column.

Fig 2. Type locality outside the Nanshimenzi Village, Qinglong Manchu Autonomous County, Qinhuangdao City, Hebei Province.

Arrow pointing to the fossil beds as cropping out at the type locality.

Fig 3. Holotype of Qinglongtriton gangouensis (PKUP V0226).

Photograph (left) and line drawing (right) of incomplete skeleton in ventral view.

Fig 4. Referred specimen of Qinglongtriton gangouensis (PKUP V0228).

Photograph (left) and line drawing (right) of incomplete skeleton in dorsal view.

Fig 5. Skull of Qinglongtriton gangouensis in dorsal view.

CT images (top) and line drawings (bottom). A, PKUP V0226, holotype skull; B, PKUP V0228, referred specimen; C, PKUP V0254, referred specimen.

Fig 6. Skull of Qinglongtriton gangouensis in palatal view.

CT images (top) and line drawings (bottom). A, PKUP V0226, holotype skull; B, PKUP V0228, referred specimen; C, PKUP V0254, referred specimen.

Fig 7. Dentary groove and angular bone in mandibles of Qinglongtriton gangouensis.

A, lateral view of grooved left dentary in PKUP V0226; B, lateral view of grooved left dentary in PKUP V0229; note arrows in A and B pointing to dentary groove; C, D, medial view of posterior part of mandible in PKUP V0226, showing the angular fused with the prearticular but having a detectable suture on both the right (C) and left (D) mandibles; E, F, medial view of posterior part of mandibles in PKUP V0257, showing the angular remaining separate on the right (E) mandible but completely fused to the prearticular on the left (F) mandible.

Fig 8. Marginal and palatal teeth of Qinglongtriton gangouensis.

A, PKUP V0245, teeth in right premaxilla in lingual view; B, PKUP V0237, teeth in left dentary in labial view; C, PKUP V0257, teeth in right palatine in medial view; D, PKUP V0237, teeth in right coronoid in lingual view. Arrow pointing to dividing zone between basal pedicel and crown.

Fig 9. Preservation of soft-tissue impressions of Qinglongtriton gangouensis.

A, PKUP V0241, preserving mineralized denticles of internal gill, impressions of gill filaments, body outlines of trunk, limbs and tail with skeleton, in dorsal view; B, PKUP V0237, preserving mineralized denticles of internal gill, body outlines of trunk and limbs with skeleton, in dorsal view; C, PKUP V0252, preserving soft-tissue outline of tail with caudal series rotated post-mortem to lie in right lateral view.

Fig 10. Comparison of position of lacrimal in relation to external naris and orbit in different groups of salamanders.

A, Karaurus (Karauridae); B, Salamandrella (Hynobiidae); C, Batrachuperus (Hynobiidae); D, Hynobius (Hynobiidae); E, Ranodon (Hynobiidae); F, Rhyacotriton (Rhyacotritonidae); G, Dicamptodon (Dicamptodontidae); H, Qinglongtriton based on PKUP V0237. A, based on Estes [61]; B–E, based on Fei et al. [82]; F, based on AmphibiaTree [83]; and G, based on Wake [66]. All are depicted in dorsal view, lacrimal is shaded in dark gray and opening of nasolacrimal duct is shaded in dark. Not in scale.

Fig 11. Comparison of basibranchial II of salamanders.

A, Karaurus (Karauridae) based on Estes [61]; B, Chunerpeton (Cryptobranchidae) based on Gao and Shubin [96]; C, Ranodon (Hynobiidae); D, Hynobius (Hynobiidae); E, Salamandrella (Hynobiidae); C–E based on Xiong et al. [112]; F, G, juvenile and adult stage in Qinglongtriton (based on PKUP V0267 and PKUP V0226, respectively); H, Valdotriton (Salamandroidea) based on Evans and Milner [21]; I, Salamandra (Salamandridae); J, Chioglossa (Salamandridae); K, Rhyacotriton (Rhyacotritonidae); L, Dicamptodon (Dicamptodontidae); M, Gyrinophilus (Plethodontidae); I–M based on Wake and Deban [113]; N, Proteus (Proteidae) based on Rose [55]; O, Siren (Sirenidae) based on AmphibiaTree [114]. Not in scale.

Fig 12. Strict consensus tree of three MPTs resulted from analysis of morphological dataset (S1 Appendix) using TNT (Goloboff et al. [124, 125]).