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Leptorhynchos, new caenagnathid theropod from Late Cretaceous of North America



From: Ben Creisler
bcreisler@gmail.com


A new paper with a new genus of theropod:


Nicholas R. Longrich, Ken Barnes , Scott Clark , and Larry Millar  (2013)
Caenagnathidae from the Upper Campanian Aguja Formation of West Texas,
and a Revision of the Caenagnathinae.
Bulletin of the Peabody Museum of Natural History 54(1):23-49
doi: http://dx.doi.org/10.3374/014.054.0102
http://www.bioone.org/doi/abs/10.3374/014.054.0102

Caenagnathid theropods are a relatively common part of the theropod
fauna in the Late Cretaceous of Asia and North America, but have not
previously been described from the southernmost United States. Here,
we describe caenagnathid fossils from the late Campanian Aguja
Formation of West Texas, and revise the systematics of caenagnathids
from the Campanian of North America. Caenagnathids from the late
Campanian of Canada represent three species in three genera:
Caenagnathus collinsi, Chirostenotes pergracilis and Leptorhynchos
elegans gen. nov. Leptorhynchos is diagnosed by its small size, its
short, deep mandible, and the upturned tip of the beak. A single
caenagnathid is known from the late Campanian of Utah, Hagryphus
giganteus. Two caenagnathid species occur in the Aguja Formation,
?Chirostenotes sp. and Leptorhynchos gaddisi sp. nov. L. gaddisi
differs from L. elegans in that the tip of the beak is narrower and
less upturned. Phylogenetic analysis recovers Caenagnathidae and
Oviraptoridae as monophyletic sister taxa. Within Caenagnathidae, the
North American species seem to form a monophyletic assemblage, the
Caenagnathinae, within which Chirostenotes and Caenagnathus form a
clade to the exclusion of Leptorhynchos. The discovery of
Chirostenotes gaddisi provides more evidence for the existence of a
distinct dinosaurian fauna in southern North America during the
Campanian. Furthermore, the Aguja fossils show that caenagnathids were
widespread and highly diverse in the Late Cretaceous of North America.
This diversity was maintained in two ways. First, variation in body
size and beak shape suggests that diversity within formations is
maintained by niche partitioning, in a way analogous to Darwin's
finches. Second, diversity is maintained by high degree of endemism,
with different species of caenagnathids occurring in different
habitats.