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Talos sampsoni: New Troodontid from Utah

Embargo is off; paper is online:


Zanno LE, Varricchio DJ, O'Connor PM, Titus AL, Knell MJ (2011) A New 
Troodontid Theropod, Talos sampsoni gen. et sp. nov., from the
Upper Cretaceous Western Interior Basin of North America. PLoS ONE 6(9): 
e24487. doi:10.1371/journal.pone.0024487

Abstract Top

Troodontids are a predominantly small-bodied group of feathered theropod 
dinosaurs notable for their close evolutionary relationship
with Avialae. Despite a diverse Asian representation with remarkable growth in 
recent years, the North American record of the clade
remains poor, with only one controversial species-Troodon formosus-presently 
known from substantial skeletal remains.
Methodology/Principal Findings

Here we report a gracile new troodontid theropod-Talos sampsoni gen. et sp. 
nov.-from the Upper Cretaceous Kaiparowits Formation,
Utah, USA, representing one of the most complete troodontid skeletons described 
from North America to date. Histological assessment
of the holotype specimen indicates that the adult body size of Talos was 
notably smaller than that of the contemporary genus
Troodon. Phylogenetic analysis recovers Talos as a member of a derived, latest 
Cretaceous subclade, minimally containing Troodon,
Saurornithoides, and Zanabazar. MicroCT scans reveal extreme pathological 
remodeling on pedal phalanx II-1 of the holotype specimen
likely resulting from physical trauma and subsequent infectious processes.

Talos sampsoni adds to the singularity of the Kaiparowits Formation dinosaur 
fauna, which is represented by at least 10 previously
unrecognized species including the recently named ceratopsids Utahceratops and 
Kosmoceratops, the hadrosaurine Gryposaurus
monumentensis, the tyrannosaurid Teratophoneus, and the oviraptorosaurian 
Hagryphus. The presence of a distinct troodontid taxon in
the Kaiparowits Formation supports the hypothesis that late Campanian dinosaurs 
of the Western Interior Basin exhibited restricted
geographic ranges and suggests that the taxonomic diversity of Late Cretaceous 
troodontids from North America is currently
underestimated. An apparent traumatic injury to the foot of Talos with evidence 
of subsequent healing sheds new light on the
paleobiology of deinonychosaurians by bolstering functional interpretations of 
prey grappling and/or intraspecific combat for the
second pedal digit, and supporting trackway evidence indicating a minimal role 
in weight bearing.

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
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
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