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Triassic origin for Lepidosauria with fossil jaw from Vellberg, Germany (free pdf)



From: Ben Creisler
bcreisler@gmail.com


A new online paper in open access:


Marc E.H. Jones, Cajsa Lisa Anderson, Christy A. Hipsley, Johannes
Müller, Susan E. Evans and Rainer R. Schoch (2013)
Integration of molecules and new fossils supports a Triassic origin
for Lepidosauria (lizards, snakes, and tuatara).
BMC Evolutionary Biology 2013, 13:208
doi:10.1186/1471-2148-13-208
http://www.biomedcentral.com/1471-2148/13/208/abstract


Abstract (provisional)

Background
Lepidosauria (lizards, snakes, tuatara) is a globally distributed and
ecologically important group of over 9,000 reptile species. The
earliest fossil records are currently restricted to the Late Triassic
and often dated to 227 million years ago (Mya). As these early records
include taxa that are relatively derived in their morphology (e.g.
Brachyrhinodon), an earlier unknown history of Lepidosauria is
implied. However, molecular age estimates for Lepidosauria have been
problematic; dates for the most recent common ancestor of all
lepidosaurs range between approximately 226 and 289 Mya whereas
estimates for crown-group Squamata (lizards and snakes) vary more
dramatically: 179 to 294 Mya. This uncertainty restricts inferences
regarding the patterns of diversification and evolution of
Lepidosauria as a whole.

Results
Here we report on a rhynchocephalian fossil from the Middle Triassic
of Germany (Vellberg) that represents the oldest known record of a
lepidosaur from anywhere in the world. Reliably dated to 238--240 Mya,
this material is at least 11 million years older than previously known
lepidosaur records and is older than some but not all molecular clock
estimates for the origin of lepidosaurs. Using RAG1 sequence data from
77 extant taxa and the new fossil specimens two of several
calibrations, we estimate that the most recent common ancestor of
Lepidosauria lived at least 242 Mya (238--249.5), and crown-group
Squamata originated around 193 Mya (176--213).

Conclusion
A Early/Middle Triassic date for the origin of Lepidosauria disagrees
with previous estimates deep within the Permian and suggests the group
evolved as part of the faunal recovery after the end-Permain mass
extinction as the climate became more humid. Our origin time for
crown-group Squamata coincides with shifts towards warmer climates and
dramatic changes in fauna and flora. Most major subclades within
Squamata originated in the Cretaceous postdating major continental
fragmentation. The Vellberg fossil locality is expected to become an
important resource for providing a more balanced picture of the
Triassic and for bridging gaps in the fossil record of several other
major vertebrate groups.


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A news release:

http://phys.org/news/2013-09-oldest-lizard-like-fossil-hints-scaly.html