New basal iguanodonts from the Cedar Mountain formation of Utah and the evolution of thumb-spiked dinosaurs.
BACKGROUND
Basal iguanodontian dinosaurs were extremely successful animals, found in great abundance and diversity almost worldwide during the Early Cretaceous. In contrast to Europe and Asia, the North American record of Early Cretaceous basal iguanodonts has until recently been limited largely to skulls and skeletons of Tenontosaurus tilletti.


RESULTS
Herein we describe two new basal iguanodonts from the Yellow Cat Member of the Cedar Mountain Formation of eastern Utah, each known from a partial skull and skeleton. Iguanacolossus fortis gen. et sp. nov. and Hippodraco scutodens gen. et sp. nov. are each diagnosed by a single autapomorphy and a unique combination of characters.


CONCLUSIONS
Iguanacolossus and Hippodraco add greatly to our knowledge of North American basal iguanodonts and prompt a new comprehensive phylogenetic analysis of basal iguanodont relationships. This analysis indicates that North American Early Cretaceous basal iguanodonts are more basal than their contemporaries in Europe and Asia.
Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania, USA. mcandr@sas.upenn.edu
Andrew T
AT
McDonald
James I
JI
Kirkland
Donald D
DD
DeBlieux
Scott K
SK
Madsen
Jennifer
J
Cavin
Andrew R C
AR
Milner
Lukas
L
Panzarin
D000818:Animals; D001208:Asia; D044822:Biodiversity; D005075:Biological Evolution; D001842:Bone and Bones / Q000033:anatomy & histology*; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000145:classification / Q000254:growth & development; D005060:Europe; D005580:Fossils; D012863:Skeleton; D012886:Skull / Q000033:anatomy & histology; D013045:Species Specificity; D013997:Time Factors; D014589:Utah