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Fruitadens anatomy in PLoS ONE



From: Ben Creisler
bcreisler@gmail.com


New in PLoS ONE:

Butler, R.J., Porro, L.B., Galton, P.M. & Chiappe, L.M. (2012)
Anatomy and Cranial Functional Morphology of the Small-Bodied Dinosaur
Fruitadens haagarorum from the Upper Jurassic of the USA.
PLoS ONE 7(4): e31556.
doi:10.1371/journal.pone.0031556
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0031556



Background

Heterodontosaurids are an important but enigmatic and poorly
understood early radiation of ornithischian dinosaurs. The
late-surviving heterodontosaurid Fruitadens haagarorum from the Late
Jurassic (early Tithonian) Morrison Formation of the western USA is
represented by remains of several small (<1 metre total body length,
<1 kg body mass) individuals that include well-preserved but
incomplete cranial and postcranial material. Fruitadens is
hypothesized to represent one of the smallest known ornithischian
dinosaurs.

Methodology/Principal Findings

We describe the cranial and postcranial anatomy of Fruitadens in
detail, providing comparisons to all other known heterodontosaurid
taxa. High resolution micro-CT data provides new insights into tooth
replacement and the internal anatomy of the tooth-bearing bones.
Moreover, we provide a preliminary functional analysis of the skull of
late-surviving heterodontosaurids, discuss the implications of
Fruitadens for current understanding of heterodontosaurid monophyly,
and briefly review the evolution and biogeography of
heterodontosaurids.

Conclusions/Significance

The validity of Fruitadens is supported by multiple unique characters
of the dentition and hindlimb as well as a distinct character
combination. Fruitadens shares highly distinctive appendicular
characters with other heterodontosaurids, strengthening monophyly of
the clade on the basis of the postcranium. Mandibular morphology and
muscle moment arms suggest that the jaws of late-surviving
heterodontosaurids, including Fruitadens, were adapted for rapid
biting at large gape angles, contrasting with the jaws of the
stratigraphically older Heterodontosaurus, which were better suited
for strong jaw adduction at small gapes. The lack of wear facets and
plesiomorphic dentition suggest that Fruitadens used orthal jaw
movements and employed simple puncture-crushing to process food. In
combination with its small body size, these results suggest that
Fruitadens was an ecological generalist, consuming select plant
material and possibly insects or other invertebrates.