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Late Jurassic salamander from Liaoning, China (free pdf)



From: Ben Creisler
bcreisler@gmail.com


OK--another non-dino. However, it's significant as the oldest known
salamander--plus the pdf is free.


Ke-Qin Gao and Neil H. Shubin (2012)
Late Jurassic salamandroid from western Liaoning, China.
Proceedings of the National Academy of Sciences (advance online publication)
doi: 10.1073/pnas.1009828109
http://www.pnas.org/content/early/2012/03/07/1009828109.abstract
free pdf:
http://www.pnas.org/content/early/2012/03/07/1009828109.full.pdf+html?sid=6985d282-7203-4add-aa17-1a70243cdce6

Abstract
A Jurassic salamander, Beiyanerpeton jianpingensis (gen. et sp. nov.),
from a recently found site in western Liaoning Province, China is the
earliest known record of Salamandroidea. As a Late Jurassic record of
the group, it extends the range of the clade by ~40 Ma. The Late
Jurassic taxon is neotenic and represented by exceptionally preserved
specimens, including fully articulated cranial and postcranial
skeletons and bony gill structures close to the cheek region. The
fossil beds, consisting of dark-brown volcanic ash shales of the Upper
Jurassic Tiaojishan (Lanqi) Formation (Oxfordian), underlie
trachyandesite rocks that have yielded a SHRIMP zircon U-Pb date of
157 ± 3 Ma. The fossiliferous beds are substantially older than the
Jehol Group, including the Yixian Formation (40Ar/39Ar dates of
122–129 Ma), but slightly younger than the Middle Jurassic Daohugou
horizon (40Ar/39Ar date of 164 ± 4 Ma). The early fossil taxon shares
with extant salamandroids derived character states, including:
separated nasals lacking a midline contact, angular fused to the
prearticular in the lower jaw, and double-headed ribs on the presacral
vertebrae. In contrast to extant salamandroids, however, the
salamander shows a discrete and tooth-bearing palatine, and
unequivocally nonpedicellate and monocuspid marginal teeth in large
and presumably mature individuals. The finding provides insights into
the evolution of key characters of salamanders, and also provides
direct evidence supporting the hypothesis that the split between
Cryptobranchoidea and Salamandroidea had taken placed before the Late
Jurassic Oxfordian time. In this aspect, both paleontological and
molecular data now come to agree.