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Re: New Mei long (troodontid theropod) specimen found

Another sleeping specimen of Mei? Can laziness be used as an autapomorphy?



Dr. Mark Witton
Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk

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>>> Ben Creisler  27/09/12 10:09 PM >>>
From: Ben Creisler

New in PLoS ONE:

Chunling Gao, Eric M. Morschhauser, David J. Varricchio, Jinyuan Liu &
Bo Zhao (2012)
A Second Soundly Sleeping Dragon: New Anatomical Details of the
Chinese Troodontid Mei long with Implications for Phylogeny and
PLoS ONE 7(9): e45203.

A second nearly complete, articulated specimen of the basal troodontid
Mei long (DNHM D2154) is reported from the Early Cretaceous
(Hauterivian-Valanginian) lower Yixian Formation, Liaoning Province,
China. New diagnostic features of Mei long are identified, including:
a uniquely shaped maxilla, low with small, low maxillary fenestra;
sacrum with an extremely wide caudal portion and elongate 4th and 5th
sacral processes; and a large distal articular surface on the
tibiotarsus which continues caudally on the tibia. A phylogenetic
analysis including new data from the second specimen recovered Mei as
a basal troodontid, in keeping with previous analyses. Although the
skeleton exhibits several juvenile-like features including free
cervical ribs, unfused frontals and nasals, and a short snouted skull,
other attributes, full fusion of all neurocentral synostoses and the
sacrum, and dense exteriors to cortical bone, suggest a small, mature
individual. Microscopic examination of tibia and fibula histology
confirms maturity and suggests an individual greater than two years
old with slowed growth. Despite being one of the smallest dinosaurs,
Mei long exhibits multi-year growth and cortical bone consisting
largely of fibro-lamellar tissue marked by lines of arrested growth as
in much larger and more basal theropods. This Mei long specimen lies
in a similar but mirrored sleeping position to that of the holotype,
strengthening the hypothesis that both specimens were preserved in a
stereotypical life position. Like many Liaoning specimens, the new
specimen also lacks extensive taphonomic and stratigraphic data,
making further behavioral inference problematic.