Abstract
BackgroundThe theropod dinosaur family Troodontidae is known from the Upper Jurassic, Lower Cretaceous, and Upper Cretaceous of Asia and from the Upper Jurassic and Upper Cretaceous of North America. Before now no undisputed troodontids from North America have been reported from the Early Cretaceous.Methodology/Principal FindingsHerein we describe a theropod maxilla from the Lower Cretaceous Cedar Mountain Formation of Utah and perform a phylogenetic analysis to determine its phylogenetic position. The specimen is distinctive enough to assign to a new genus and species, Geminiraptor suarezarum. Phylogenetic analysis places G. suarezarum within Troodontidae in an unresolved polytomy with Mei, Byronosaurus, Sinornithoides, Sinusonasus, and Troodon + (Saurornithoides + Zanabazar). Geminiraptor suarezarum uniquely exhibits extreme pneumatic inflation of the maxilla internal to the antorbital fossa such that the anterior maxilla has a triangular cross-section. Unlike troodontids more closely related to Troodon, G. suarezarum exhibits bony septa between the dental alveoli and a promaxillary foramen that is visible in lateral view.Conclusions/SignificanceThis is the first report of a North American troodontid from the Lower Cretaceous. It therefore contributes to a fuller understanding of troodontid biogeography through time. It also adds to the known dinosaurian fauna of the Cedar Mountain Formation.
Highlights
The family Troodontidae and its sister family Dromaeosauridae make up the clade Deinonychosauria [1]
The discovery of G. suarezarum adds to the known diversity of the dinosaur fauna of the Cedar Mountain Formation
As the only Lower Cretaceous troodontid reported from North America it increases the known temporal distribution of the family on the continent
Summary
The family Troodontidae and its sister family Dromaeosauridae make up the clade Deinonychosauria [1]. Deinonychosauria, the sister taxon to Avialae, is a member of the theropod clade Coelurosauria [1]. Members of Troodontidae are gracile bipeds with an enlarged ungual on the second toe of each foot. They have been reported from the Upper Jurassic and Lower Cretaceous of China [2,3,4,5], the Lower and Upper Cretaceous of Mongolia [6,7,8,9], and the Upper Cretaceous of North America [10]. We report the discovery of a troodontid maxilla from the basal Cedar Mountain Formation (Lower Cretaceous, Barremian?) of Utah. Before now no undisputed troodontids from North America have been reported from the Early Cretaceous
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