The Osteology of Alioramus, A Gracile and Long-Snouted Tyrannosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Mongolia

2012·85.2 MB·English

by  Stephen L. Brusatte

Scientific Publications of the American Museum of Natural History B
R
American Museum Novitates U THE OSTEOLOGY OF ALIORAMUS, A GRACILE
S
Bulletin of the American Museum of Natural History A
T AND LONG-SNOUTED TYRANNOSAURID
Anthropological Papers of the American Museum of Natural History T
E
Publications Committee E (DINOSAURIA: THEROPODA) FROM THE
T
Robert S. Voss, Chair A
LATE CRETACEOUS OF MONGOLIA
L
Board of Editors .:
O
Jin Meng, Paleontology S
T
Lorenzo Prendini, Invertebrate Zoology E
O
Robert S. Voss, Vertebrate Zoology STEPHEN L. BRUSATTE, THOMAS D. CARR,
L
Peter M. Whiteley, Anthropology O
G
Y AND MARK A. NORELL
Managing Editor

O
Mary Knight
F

A
L
I
Submission procedures can be found at http://research.amnh.org/scipubs O
R
A
M
U
All issues of Novitates and Bulletin are available on the web from
S
http://digitallibrary.amnh.org/dspace
Order printed copies from http://www.amnhshop.com or via standard mail from:
American Museum of Natural History—Scientific Publications
Central Park West at 79th Street
New York, NY 10024
This paper meets the requirements of ANSI/NISO Z39.48-1992 (permanence of paper).
A
M
N
H

B
U
L
L
E
T
I
N

3
6
6

On the cover: A life reconstruction of Alioramus
altai in the Late Cretaceous (Maastrichtian) Nemegt eco-
system. Artwork by Jason Brougham, American Museum of 2
0
1 BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY
Natural History. 2
THE OSTEOLOGY OF ALIORAMUS, A GRACILE
AND LONG-SNOUTED TYRANNOSAURID
(DINOSAURIA: THEROPODA) FROM THE LATE
CRETACEOUS OF MONGOLIA
STEPHEN L. BRUSATTE
Division of Paleontology
American Museum of Natural History
Central Park West at 79th Street
New York, NY 10024
Department of Earth and Environmental
Sciences
Columbia University, New York
THOMAS D. CARR
Department of Biology, Carthage College
2001 Alford Park Drive, Kenosha, WI 53140
MARK A. NORELL
Division of Paleontology
American Museum of Natural History
BULLETINOFTHEAMERICANMUSEUMOFNATURALHISTORY
Number366, 197pp., 82figures, 11tables
Issued February 29,2012
CopyrightEAmericanMuseumofNaturalHistory2012 ISSN0003-0090
CONTENTS
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Institutional Acronyms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Systematic Paleontology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Holotype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Type Locality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Preparation Details of the Holotype. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Diagnosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
The Skull. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Maxilla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Nasal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Lacrimal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Jugal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Postorbital . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Squamosal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Quadratojugal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Quadrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Palatine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Pterygoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Ectopterygoid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Epipterygoid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Dentary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Surangular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Angular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Prearticular. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Splenial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Supradentary/Coronoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
Hyoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Dentition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
The Axial Skeleton. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Cervical Vertebrae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
Atlas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Axis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
Postaxial Cervical Vertebrae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Dorsal Vertebrae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Sacral Vertebrae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Caudal Vertebrae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
Cervical Ribs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
Dorsal Ribs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Chevron. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
The Appendicular Skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Ilium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Ischium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Femur . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
Crus-Tarsal Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Tibia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Fibula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
Astragalus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Calcaneum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
Distal Tarsals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
2
Metatarsus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
Pedal Phalanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
The Validity of Alioramus: Alioramus Is Not Juvenile Tarbosaurus . . . . . . . . . . . . . 178
Extreme Skull Length Is a Diagnostic Feature of Alioramus . . . . . . . . . . . . . . . . 181
Alioramus Is Morphologically Different from Similarly Sized Subadult Tarbosaurus 182
Alpha-level Taxonomy: Alioramus altai and Alioramus remotus. . . . . . . . . . . . . . . . 183
Similarities between IGM 100/1844 and the Holotype of Alioramus remotus. . . . . 183
Differences between IGM 100/1844 and the Holotype of Alioramus remotus. . . . . 184
Discrete Character Changes during Tyrannosaurid Ontogeny . . . . . . . . . . . . . . . . . 186
Cephalic Ornamentation of Alioramus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
Evolutionary Development of the Long, Low Skull of Alioramus . . . . . . . . . . . . . . 188
Novel Body Plan and Presumed Ecological Habits. . . . . . . . . . . . . . . . . . . . . . . . . 190
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Appendix 1: Systematics of AMNH FARB 5434. . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
3
ABSTRACT
TheLateCretaceoustyrannosauridtheropodAlioramushaslongbeenoneofthemostpuzzling
largecarnivorousdinosaurtaxa,largelybecauseforseveraldecadesithasbeenrepresentedonly
byasingle,fragmentaryspecimenthatseemstorepresentalong-snoutedandgracileindividual
butisdifficulttointerpret.ThediscoveryofasubstantiallycompleteskeletonofAlioramusatthe
Tsaagan Khuushu locality in the Maastrichtian Nemegt Formation of Mongolia, recovered
duringthe2001AmericanMuseum–MongolianAcademyofSciencesexpeditionanddescribed
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
evidencethatAlioramusisanunusuallong-snouted,gracile, andslender-limbedtaxonwith an
unpredecented degree of cranial ornamentation among tyrannosaurids and an extremely
pneumatizedskeleton.
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
holotypespecimenofA.altaibelongstoayoungindividual,andmanydifferencesbetweenitand
theotherknownspecimenofAlioramus(theholotypeofA.remotus)mayrepresentontogenetic
variation.TheunusuallongirostrineskullofAlioramuswaslargelyproducedbylengtheningof
thesnoutbones(maxilla, nasal, dentary,lacrimal,jugal),rather thantheorbiotemporalbones
(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
muscularjaws,thickteeth,andinterlockingsuturesenabledindividualstobitewithenoughforce
tofracturebone.WhetheradultAlioramuscouldutilize‘‘puncture-pull’’feedingawaitsdiscovery
ofmatureindividualsofthegenus.Thecoexistenceofthelong-snoutedAlioramusandrobustand
deep-snouted Tarbosaurus, which are found together at the Tsaagan Khuushu locality,
demonstratethatmultiplelargetyrannosauridswereabletoliveinsympatry,likelybecauseof
nichepartitioningduetodifferencesincraniofacialmorphologyandfunctionalbehavior.
INTRODUCTION Later authors accepted the tyrannosaurid
affinities of the Alioramus type specimen
The Late Cretaceous tyrannosaurid Alior- and noted that it was smaller and more
amus haslong been oneof themost puzzling gracile than other tyrannosaurids, likely due
and poorly understood large carnivorous its immaturity (e.g., Currie, 2003a; Hurum
theropod dinosaurs. Kurzanov (1976) estab- and Sabath, 2003). However, subsequent
lishedthis genus,andnamed thetype species authors disagreed on whether it represented
A. remotus, based on a series of fragmentary anewtaxonorwasajuvenileofTarbosaurus
cranialbonesandlimitedpostcranialmaterial (e.g., Currie, 2003a), and if a valid taxon,
from the Late Cretaceous of Mongolia. The whether it could be referred to the Tyranno-
specimen was collected at the Nogon Tsav sauridaeproper(sensuSerenoetal.,2005)or
localityinBayankhnongorAimagandisnow represented a more basal taxon on the
housed in the Paleontological Institute in tyrannosauroid stem (Holtz, 2001, 2004;
Moscow, Russia (PIN 3141/1). Kurzanov Currieetal.,2003;HurumandSabath,2003).
(1976) recognized numerous similarities The discovery of a well-preserved and
shared between Alioramus and tyrannosaur- substantially complete Alioramus skeleton at
ids such as Tyrannosaurus and Tarbosaurus, the Tsaagan Khuushu locality in the Maas-
and formally assigned the new genus to this trichtianNemegtFormationofMongoliahas
iconicgroupofcolossalpredatorydinosaurs. clarified these riddles (fig. 1). Brusatte et al.
4
2012 BRUSATTEETAL.: OSTEOLOGY OFTYRANNOSAURID ALIORAMUS 5
Fig. 1. Skeletal reconstruction of the holotype specimen of the Late Cretaceous tyrannosaurid
Alioramusaltai(IGM100/1844).Bonesinlightgray(e.g.,skull)arepreservedandthoseindarkgray(e.g.,
forearm) are absent but reconstructed based on comparison to close relatives (Appalachiosaurus,
Tarbosaurus,andTyrannosaurusofsimilarbodysize).Entirescalebar52m.Reconstructiondelineated
byFrankIppolito,AmericanMuseumofNatural History.
(2009) described this specimen, which was morphology and body proportions than
discovered by Julia Clarke and collect- similarly aged members of other tyranno-
ed during the 2001 American Museum– saurid species, notably the contemporary
Mongolian Academy of Sciences expedition, Tarbosaurus, a taxon that also found at
as a new species of Alioramus, A. altai. The Tsaagan Khushu. Most importantly, Alio-
specimen was recovered within in a tan ramusissmaller(approximatelyhalfthebody
sandstone lens sandwiched between two mass) and more gracile than other tyranno-
indurated shelves of more coarse sandstone saurids, and possesses a long snout and
(fig. 2). Some of the skeleton was destroyed numerouscranialhorns(figs. 1,4).Nonethe-
by erosion previous to recovery and thou- less, phylogenetic analyses in the short
sands of fragments were exposed downslope. description and a subsequent publication
Preliminary excavation showed that while (Brusatte et al., 2010a) show that, despite
some of the skeleton was missing, most of itsdivergentmorphology,Alioramusisnested
the cranial elements were present, although within the tyrannosaurid clade and is more
disarticulated (fig. 2). Further excavation closely related to Tarbosaurus and Tyranno-
during the 2001 expedition revealed that saurusthantotaxasuchasAlbertosaurusand
these cranial elements were exquisitely pre- Gorgosaurus.
served (fig. 3), often retaining detailed sur- Here we present an exhaustive description
facetextureandthinflangesofbonelessthan of the skeletal osteology of the Alioramus
a few millimeters in thickness. The specimen altaitypespecimen(IGM100/1844),expand-
was collected in four blocks and prepared by ing on the short initial report of Brusatte
Amy Davidson (and others under her direc- et al. (2009). Surprisingly, such monographs
tion) in the AMNH preparation laboratory. have rarely been undertaken for individual
This specimen is critical because it is only tyrannosaurid taxa, despite the iconic status
the second fossil of Alioramus that has been of this clade, the rich fossil record of the
reported (although through the illicit com- group, and the popularity of tyrannosaurids
mercial trade others are known to exist) and as exemplary research models in paleobiolo-
offers a great improvement on the fragmen- gy.Mostexistingtyrannosauridmonographs
tary, poorly preserved, and often difficult to were completed long before the advent of
access A. remotus type specimen. In a brief phylogenetic systematics (e.g., Osborn, 1912;
report, Brusatte et al. (2009) described this Lambe, 1917; Parks, 1928; Russell, 1970;
specimen as belonging to an immature Maleev, 1974) or have focused specifically
individual that was substantially different in on the most famous tyrannosaurid of all,
6 BULLETIN AMERICAN MUSEUM OFNATURALHISTORY NO.366
Fig. 2. The Tsaggan Khuushuu locality in the Gobi Desert of Mongolia, where the holotype of
Alioramus altai (IGM 100/1844) was discovered in Maastrichtian-aged rocks of the Nemegt Formation
(top).Therightmaxilla,inmedialview,aspreservedinthefield(bottom).
2012 BRUSATTEETAL.: OSTEOLOGY OFTYRANNOSAURID ALIORAMUS 7
Fig.3. TheholotypeskullofAlioramusaltai(IGM100/1844)partiallypreparedintheoriginalfieldjacket.
Tyrannosaurus rex (Molnar, 1991; Brochu, wide-ranging comparisons between Aliora-
2003). Other taxa, such as Albertosaurus, mus and other tyrannosauroids, running the
Gorgosaurus, and Tarbosaurus, have been gamut from basal taxa such as Dilong,
revisedrecentlybuthavenotbeenthesubject Guanlong, and Eotyrannus to more derived
of exhaustive and fully illustrated descrip- tyrannosaurids.Thesecomparisonsarebased
tions (e.g., Carr, 1999, 2010; Currie, 2003a; extensively on firsthand specimen observa-
Hurum and Sabath, 2003). Furthermore, tions of basal tyrannosauroids (SLB, MAN,
most of these descriptions have focused on TDC) and tyrannosaurids (TDC, SLB).
the skull, and only limited information on The comparative aspect of this project was
tyrannosauridpostcrania,especiallytheaxial used as a foundation for the tyrannosauroid
skeleton,isavailableinthemodernliterature. phylogenetic analysis of Brusatte et al.
In this monograph, we provide a thor- (2010a), which was able to combine these
ough, bone-by-bone description of the skull new observations and information from
(excluding the braincase, whose most salient newly discovered taxa to greatly expand
features were described by Bever et al. [2011] taxonomic and character sampling relative
andwhichwillbefullydescribedinaseparate to previous studies. This monograph is, in
publication), axial skeleton, and appendicu- many ways, a companion to the phylogeneic
lar skeleton of the Alioramus altai type analysis of Brusatte et al. (2010a). Many
specimen.Suchadetaileddescriptionismade characters used in the analysis, which could
possible by the fine preservation and disar- only merit cursory description in the phylog-
ticulated nature of most of the skeleton, eny paper, are explained more fully here.
especially the skull. Following from our Aside from providing a robust phylogeny,
observations and descriptions, we present the comparative phylogenetic study also
8 BULLETIN AMERICAN MUSEUM OFNATURALHISTORY NO.366
Fig.4. SkullreconstructionoftheholotypespecimenoftheLateCretaceoustyrannosauridAlioramus
altai (IGM 100/1844). Scale bar 5 5 cm. Abbreviations: afen, antorbital fenestra; ang, angular;
den, dentary; emf, external mandibular fenestra; en, external naris; fr, frontal; jh, jugal horn; jug, jugal;
lac, lacrimal; lcp, lacrimal cornual process; max, maxilla; mf, maxillary fenestra; nas, nasal; orb, orbit;
pal, palatine; par, parietal; po, postorbital; pop, paroccipital process; psp, parasphenoid rostrum;
qj,quadratojugal;rug,rugositiesonthenasal;sang,surangular;sfor,surangularforamen;sq,squamosal.
Reconstructiondelineated byFrankIppolito,AmericanMuseumofNatural History.
illuminates patterns of character transition CMN Canadian Museum of Nature, Ot-
over the 100-million-year evolutionary histo- tawa, Ontario, Canada
ry of these quintessential dinosaurian preda- CMNH Cleveland Museum of Natural His-
tors, elucidating the major changes as small, tory, Cleveland, Ohio
nimblebasaltaxadevelopedintosomeofthe FDRC Fossil Research and Development
most colossal terrestrial predators to ever Center, Gansu Bureau of Geology
live. and Mineral Resources Explora-
tion, Lanzhou, People’s Republic
INSTITUTIONAL ACRONYMS of China
HMN Humboldt Museum fu¨r Natur-
Thefollowingacronymsareusedthrough- kunde, Berlin, Germany
out this work: IGM Institute of Geology, Ulaan Baatar,
AMNH FARB Fossil Amphibian, Reptile, Mongolia
and Bird Collections, American Mu- IVPP InstituteofVertebratePaleontology
seumofNaturalHistory,NewYork and Paleoanthropology, Beijing,
ANSP Academy of Natural Sciences, Phil- People’s Republic of China
adelphia, Pennsylvania LACM Los Angeles County Museum, Los
BHI Black Hills Institute of Geological Angeles, California
Research, Hill City, South Dakota, LH Long Hao Institute of Geology and
BMR Burpee Museum of Natural Histo- Paleontology,Hohhot,People’sRe-
ry, Rockford, Illinois public of China
CM Carnegie Museum of Natural His- MIWG Museum of Isle of Wight Geology
tory, Pittsburgh, Pennsylvania (Dinosaur Isle, Isle of Wight Muse-
2012 BRUSATTEETAL.: OSTEOLOGY OFTYRANNOSAURID ALIORAMUS 9
um Services, IWCMS), Sandown, TYPE LOCALITY: Maastrichtian Nemegt
England, United Kingdom Formation, collected at Tsaggan Khuushuu
NHM TheNaturalHistoryMuseum,Lon- (originally called Tsagaan Uul), Mongolia
don, England, U.K. (fig. 2).
NMMNH New Mexico Museum of Natu- PREPARATION DETAILS OF THE HOLO-
ral History and Science, Albuquer- TYPE: The specimen (IGM 100/1844) was
que, New Mexico prepared primarily by Amy Davidson at the
OUMNH Oxford University Museum of American Museum of Natural History, and
Natural History, Oxford, England, preparation records are held in the AMNH
U. K. Division of Paleontology database. Some
PIN Paleontological Institute, Moscow, techniques for preparation and curation that
Russia were used on the specimen are described in
RMM Red Mountain Museum, McWane three published abstracts (Davidson et al.,
Center, Birmingham, Alabama 2006; Davidson, 2008, 2009). The specimen
ROM Royal Ontario Museum Toronto, was consolidated with ButvarH B-76 (Mon-
Canada santo Company), a terpolymer of vinyl bu-
RSM Royal Saskatchewan Museum, Re- tyral, vinyl alcohol, and vinyl acetate mono-
gina and East End, Canada mers. Joins were made with ParaloidH B-72
SMNK Staatliches Museum fu¨r Natur- (Rohm and Haas Company), an ethyl meth-
kunde, Karlsruhe, Germany acrylate and methyl acrylate copolymer. The
UALVP University of Alberta Laboratory specimen is very brittle and archival supports
for Vertebrate Paleontology, Ed- for all the skull elements were made of
monton, Canada EthafoamH polyethylene foam, polyester bat-
ting, and TyvekH Soft Structure polyethylene
ZPAL Instytut Paleobiologii PAN, War-
fabric.
saw, Poland
DIAGNOSIS: A tyrannosauroid theropod
possessing the following autapomorphies: an
SYSTEMATIC PALEONTOLOGY
accessorypneumaticfenestraposterodorsalto
the promaxillary fenestra; large and elongate
Theropoda Marsh, 1881 maxillary fenestra (length:depth ratio of 1.9);
Tetanurae Gauthier, 1986 a conical and dorsally extending cornual
process (horn) on the lacrimal*; a laterally
Coelurosauria Huene, 1914
projectinghorn on the jugal; a thick ridge on
Tyrannosauroidea Osborn, 1905
the dorsal surface of the ectopterygoid; 20
TyrannosauridaeOsborn,1905(sensuSereno
dentary alveoli; an anteroposteriorly long
et al., 2005)
anterior mylohyoid foramen of the splenial;
TyrannosaurinaeOsborn,1905(sensuCurrie
a thin epipophysis on the atlantal neurapo-
et al., 2003)
physis that terminates as a sharp point; a
Alioramus Kurzanov, 1976
pneumatic pocket on the anterior surface of
Alioramus altai Brusatte et al., 2009
the cervical transverse processes; an external
HOLOTYPE: IGM 100/1844. Substantially pneumatic foramen on the dorsal ribs; a
complete skeleton found associated and posterior margin of iliac postacetabular pro-
belonging to a single individual, including a cess projecting posterodorsally*. Asterisks
nearly complete and disarticulated skull; the denote autapomorphies recognized here for
cervical series; dorsal, sacral, and caudal the first time, whereas characters without an
vertebrae; cervical and dorsal ribs; chevrons; asterisk were recognized by Brusatte et al.
right ilium; left and right ischium; left and (2009).
right femur; right crus, tarsus, and metatar- Two characters considered autapomor-
sus;variousmetatarsalsandpedalphalanges. phies of A. altai by Brusatte et al. (2009)
Completelyunknownaremanyofthedorsal, arenowknowntobemorewidelydistributed
sacral, and caudal vertebrae; shoulder girdle in tyrannosaurids, and therefore not unique
and forelimbs; the pubes; regions of the to A. altai. A palatine pneumatic recess that
hindlimbs;andsomepedalphalanges(fig. 1). extends posteriorly beyond the posterior