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A good day for tyrannosaurs



October 5, 1905:

Tyrannosaurus rex, Dynamosaurus imperiosus, and Albertosaurus sarcophagus
are officially named.

October 5, 2009:

These guys are joined by their funny-looking cousin, Alioramus altai:

http://www.pnas.org/content/early/2009/10/01/0906911106.abstract

Brusatte, S.L., T.D. Carr, G.M. Erickson, G.S. Bever, and M.A. Norell. 2009.
A long-snouted, multihorned tyrannosaurid from the Late Cretaceous of
Mongolia. PNAS published online before print October 5, 2009,
doi:10.1073/pnas.0906911106

Abstract

Tyrannosaurid theropods are characterized by a generalized body plan, and
all well-known taxa possess deep and robust skulls that are optimized for
exerting powerful bite forces. The fragmentary Late Cretaceous Alioramus
appears to deviate from this trend, but its holotype and only known specimen
is incomplete and poorly described. A remarkable new tyrannosaurid specimen
from the Maastrichtian (Late Cretaceous) of Mongolia, including a nearly
complete and well-preserved skull and an extensive postcranium, represents a
new species of Alioramus, Alioramus altai. This specimen conclusively
demonstrates that Alioramus is a small, gracile, long-snouted carnivore that
deviates from other tyrannosaurids in its body plan and presumably its
ecological habits. As such, it increases the range of morphological
diversity in one of the most familiar extinct clades. Phylogenetic analysis
places Alioramus deep within the megapredatory Tyrannosauridae, and within
the tyrannosaurine subclade that also includes Tarbosaurus and
Tyrannosaurus. Both pneumatization and ornamentation are extreme compared
with other tyrannosaurids, and the skull contains eight discrete horns. The
new specimen is histologically aged at nine years old but is smaller than
other tyrannosaurids of similar age. Despite its divergent cranial form,
Alioramus is characterized by a similar sequence of ontogenetic changes as
the megapredatory Tyrannosaurus and Albertosaurus, indicating that
ontogenetic change is conservative in tyrannosaurids.

Congrats, guys!

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/
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

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