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RE: New Mei long (troodontid theropod) specimen found



An excellent paper with detailed description and high quality photos, sorely 
needed since the Mei holotype was described all too briefly eight years ago in 
one of the 'tabloids'.  I hope we get more osteologies like this of Liaoning 
taxa known from multiple specimens.  Too often, new specimens of known taxa are 
passed by because they're not exciting enough, but not only do they reveal 
previously unknown morphologies, they often show differences allowing us to 
code polmorphies.  Gao et al. are very explicit about both aspects for this 
specimen.  This is why I fully support the mission of PLoS ONE to publish good 
science that doesn't pretend to be more ground-breaking than it is.  It's so 
refreshing to read an abstract that doesn't claim to be the first of something 
or to "provide important insights into the origins/behavior/etc. of group X".

It is interesting that this specimen shows some previously unknown resemblences 
to dromaeosaurids.  The expanded postacetabular process sounds like the 
'lobate' morphology traditionally ascribed to unenlagiines, while the 
longitudinal ridge on the proximal femur reminds me of the morphology described 
by Xu (2002) in Sinornithosaurus.

Mickey Mortimer

----------------------------------------
> Date: Thu, 27 Sep 2012 14:09:07 -0700
> From: bcreisler@gmail.com
> To: dinosaur@usc.edu
> Subject: New Mei long (troodontid theropod) specimen found
>
> From: Ben Creisler
> bcreisler@gmail.com
>
>
> 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
> Taphonomy.
> PLoS ONE 7(9): e45203.
> doi:10.1371/journal.pone.0045203
> http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0045203
>
>
> 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.