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Re: Alioramus (Theropoda) osteology in new AMNH Bulletin

From: Ben Creisler

The monograph has now been posted for free download:



Stephen L. Brusatte, Thomas D. Carr, and Mark A. Norell (2012)
The Osteology of Alioramus, A Gracile and Long-Snouted Tyrannosaurid
(Dinosauria: Theropoda) from the Late Cretaceous of Mongolia.
Bulletin of the American Museum of Natural History:1-197. 2012
doi: 10.1206/770.1

The Late Cretaceous tyrannosaurid theropod Alioramus has long been one
of the most puzzling large carnivorous dinosaur taxa, largely because
for several decades it has been represented only by a single,
fragmentary specimen that seems to represent a long-snouted and
gracile individual but is difficult to interpret. The discovery of a
substantially complete skeleton of Alioramus at the Tsaagan Khuushu
locality in the Maastrichtian Nemegt Formation of Mongolia, recovered
during the 2001 American Museum–Mongolian Academy of Sciences
expedition and described as a new species (Alioramus altai) in 2009,
definitively shows that this mysterious taxon is a distinct form of
longirostrine tyrannosaurid that lived alongside the larger and more
robust Tarbosaurus. Here we describe and figure this remarkably
preserved skeleton in detail. We provide exhaustive descriptions and
photographs of individual bones, and make extensive comparisons with
other tyrannosauroids. This monographic description provides further
evidence that Alioramus is an unusual long-snouted, gracile, and
slender-limbed taxon with an unpredecented degree of cranial
ornamentation among tyrannosaurids and an extremely pneumatized

Anatomical comparisons indicate that the long skull of Alioramus is an
autapomorphic feature that is proportionally longer (relative to femur
length) than in any other known tyrannosaurid specimen, including
juveniles, and that Alioramus is morphologically distinctive relative
to similarly sized individuals of the contemporary and sympatric
Tarbosaurus. The holotype specimen of A. altai belongs to a young
individual, and many differences between it and the other known
specimen of Alioramus (the holotype of A. remotus) may represent
ontogenetic variation. The unusual longirostrine skull of Alioramus
was largely produced by lengthening of the snout bones (maxilla,
nasal, dentary, lacrimal, jugal), rather than the orbiotemporal bones
(frontal, postorbital, squamosal, quadratojugal). The long snout,
gracile skull bones, comparatively small attachment sites for jaw
muscles, and lack of interlocking sutures and a robust orbital brow
would have precluded the holotype individual from employing the
characteristic “puncture-pull” feeding style of large-bodied adult
tyrannosaurids, in which the muscular jaws, thick teeth, and
interlocking sutures enabled individuals to bite with enough force to
fracture bone. Whether adult Alioramus could utilize “puncture-pull”
feeding awaits discovery of mature individuals of the genus. The
coexistence of the long-snouted Alioramus and robust and deep-snouted
Tarbosaurus, which are found together at the Tsaagan Khuushu locality,
demonstrate that multiple large tyrannosaurids were able to live in
sympatry, likely because of niche partitioning due to differences in
craniofacial morphology and functional behavior.