Friday, May 6, 2016

[Paleontology • 2016] Qinglongtriton gangouensis • A New Basal Salamandroid (Amphibia, Urodela) from the Late Jurassic of Qinglong, Hebei Province, China


Fig 3. Holotype of Qinglongtriton gangouensis  (PKUP V0226).
Photograph (left) and line drawing (right) of incomplete skeleton in ventral view.

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.


Systematic Paleontology

Class Amphibia Linnaeus, 1758
Subclass Lissamphibia Haeckel, 1866

Superorder Caudata Scopoli, 1777
Order Urodela Duméril, 1806
Suborder Salamandroidea Dunn, 1922

Family Incertae Sedis

Genus Qinglongtriton gen. nov.
urn:lsid:zoobank.org:act:DE89F7C6-1870-4B3E-A4BD-8C2BB208D193

Qinglongtriton gangouensis gen. et sp. nov.
urn:lsid:zoobank.org:act:B8CFC9E4-051C-4DD9-8C9F-0EC6AF0C7C0A


Holotype: PKUP V0226, an incomplete skeleton including articulated cranium and postcranium, with part of the tail missing (Figs 3, 5A, 6A, 7C and 7D; S1 Fig; S1 and S3 Movies).

Diagnosis: A basal salamandroid sharing with Beiyanerpeton derived features including: palatine present as discrete and dentate element; sensory groove present on external surface of premaxilla and maxilla; lateral surface of dentary deeply grooved; presacral vertebrae 15 in number. Differing from closely related Beiyanerpeton in having: lacrimal dorsally grooved for nasolacrimal duct; anterior ramus of pterygoid bearing teeth and directing anteromedially; ossification of orbitosphenoid absent; free operculum lacking; coronoid present as a dentate element; marginal teeth pedicellate; metacarpal II longest in manus; phalangeal formula 2-2-3-3-3 in pes. The new taxon has the basibranchial II ossified with paired anterolateral and posterolateral processes fused with a median rod as a unique feature among salamanders.

Etymology: Qinglong” refers to the Qinglong Manchu Autonomous County; “triton”, suffix commonly used for salamander names; “gangou” refers to Gangou Township, in which the fossil locality occurs.

Referred Specimens: PKUP V0227–V0271, all specimens from the same locality and the 13th layer of the stratigraphic section as the holotype.

Type Locality and Horizon: Fossil locality approximately 300 m northwest of Nanshimenzi village (N40°31'52"/E119°29'11"), Gangou Township, Qinglong Manchu Autonomous County, Qinhuangdao City, Hebei Province, China; the 13th layer of the stratigraphic section measured as outlined in Fig 1; Upper Jurassic (Oxfordian) Tiaojishan Formation.



Conclusions

The following conclusions can be drawn from our study of Qinglongtriton gangouensis from the Nanshimenzi locality:

1. Qinglongtriton gangouensis is a neotenic salamandroid named and described based on multiple specimens from the Upper Jurassic Tiaojishan Formation.
2. The new salamandroid displays several features of ontogenetic or taxonomic significance, including: lacrimal with a dorsally open groove for the nasolacrimal duct; presence of a stapedial foramen; lack of ossification of the orbitosphenoid; pedicellate teeth with monocuspid crowns; presence of a toothed coronoid; ontogenetic fusion of the angular bone to the prearticular; and a unique shape of the basibranchial II.
3. Phylogenetic analysis places Qinglongtriton as the sister taxon to Beiyanerpeton, and the two taxa together form the basalmost clade within the Salamandroidea. Along with the coexisting Beiyanerpeton the new discovery indicates that morphological disparity of the salamandroid clade was already underway by early Late Jurassic (Oxfordian) time.


Jia Jia and Ke-Qin Gao. 2016. A New Basal Salamandroid (Amphibia, Urodela) from the Late Jurassic of Qinglong, Hebei Province, China.  PLoS ONE. 11(5): e0153834. DOI: 10.1371/journal.pone.0153834


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