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Nigersaurus: the complete picture



Greetings on this sauropoderific day!

Just got back from Paul Sereno's press conference at National Geographic,
where he revealed the articulated skull and skeleton of Nigersaurus, in
coordination with:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0001230

Sereno PC, Wilson JA, Witmer LM, Whitlock JA, Maga A, et al. (2007)
Structural Extremes in a Cretaceous Dinosaur. PLoS ONE 2(11): e1230.
doi:10.1371/journal.pone.0001230

Abstract

Fossils of the Early Cretaceous dinosaur, Nigersaurus taqueti, document for
the first time the cranial anatomy of a rebbachisaurid sauropod. Its extreme
adaptations for herbivory at ground-level challenge current hypotheses
regarding feeding function and feeding strategy among diplodocoids, the
larger clade of sauropods that includes Nigersaurus. We used high resolution
computed tomography, stereolithography, and standard molding and casting
techniques to reassemble the extremely fragile skull. Computed tomography
also allowed us to render the first endocast for a sauropod preserving
portions of the olfactory bulbs, cerebrum and inner ear, the latter
permitting us to establish habitual head posture. To elucidate evidence of
tooth wear and tooth replacement rate, we used photographic-casting
techniques and crown thin sections, respectively. To reconstruct its 9-meter
postcranial skeleton, we combined and size-adjusted multiple partial
skeletons. Finally, we used maximum parsimony algorithms on character data
to obtain the best estimate of phylogenetic relationships among diplodocoid
sauropods. Nigersaurus taqueti shows extreme adaptations for a dinosaurian
herbivore including a skull of extremely light construction, tooth batteries
located at the distal end of the jaws, tooth replacement as fast as one per
month, an expanded muzzle that faces directly toward the ground, and hollow
presacral vertebral centra with more air sac space than bone by volume. A
cranial endocast provides the first reasonably complete view of a sauropod
brain including its small olfactory bulbs and cerebrum. Skeletal and dental
evidence suggests that Nigersaurus was a ground-level herbivore that
gathered and sliced relatively soft vegetation, the culmination of a
low-browsing feeding strategy first established among diplodocoids during
the Jurassic.


Extremely cool, extremely weird stuff. You can read all about the details
online at PLOS. Some highlights:
* Based on the semicircular canals, the orientation of the skull was snout
downward most of the time.
* The temporal region of the skull has been shifted to the anterior surface.
* With the topology Rebbachisauridae + (Dicraeosauridae + Diplodocidae), a
low-browsing short-necked morph is the ancestral condition for
Diplodocoidea.
* Rate of replacement of teeth? About one per month!!

Not your father's diplodocoid, to be certain...

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Fax: 301-405-0796

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA