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Xiaochelys, new sinemydid turtle from Jehol Biota of China (free pdf)

Ben Creisler

A new paper:

Chang-Fu Zhou & Márton Rabi (2015)
A sinemydid turtle from the Jehol Biota provides insights into the
basal divergence of crown turtles.
Scientific Reports 5, Article number: 16299 (2015)

Morphological phylogenies stand in a major conflict with molecular
hypotheses regarding the phylogeny of Cryptodira, the most diverse and
widely distributed clade of extant turtles. However, molecular
hypotheses are often considered a better estimate of phylogeny given
that it is more consistent with the stratigraphic and geographic
distribution of extinct taxa. That morphology fails to reproduce the
molecular topology partly originates from problematic character
polarization due to yet another contradiction around the composition
of the cryptodiran stem lineage. Extinct sinemydids are one of these
problematic clades: they have been either placed among
stem-cryptodires, stem-chelonioid sea turtles, or even stem-turtles. A
new sinemydid from the Early Cretaceous Jehol Biota (Yixian Formation,
Barremian-Early Aptian) of China, Xiaochelys ningchengensis gen. et
sp. nov., allows for a reassessment of the phylogenetic position of
Sinemydidae. Our analysis indicates that sinemydids mostly share
symplesiomorphies with sea turtles and their purported placement
outside the crown-group of turtles is an artefact of previous
datasets. The best current phylogenetic estimate is therefore that
sinemydids are part of the stem lineage of Cryptodira together with an
array of other Jurassic to Cretaceous taxa. Our study further
emphasises the importance of using molecular scaffolds in global
turtle analyses.