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Juvenile Acrocanthosaurus from Cloverly Formation of Wyoming

From: Ben Creisler

A new online paper:

Michael D. D'Emic, Keegan M. Melstrom & Drew R. Eddy (2012)
Paleobiology and geographic range of the large-bodied Cretaceous
theropod dinosaur Acrocanthosaurus atokensis.
Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication)

A partial theropod skeleton from the Albian (ca. 105 ma) Cloverly
Formation of Wyoming is shown to exhibit many features in common with
members of Carcharodontosauria, and is referred to Acrocanthosaurus
atokensis on the basis of an autapomorphy and a unique combination of
characters. The absence of neurocentral fusion in dorsal and caudal
vertebrae and bone histology of the femur indicate that the specimen
is a juvenile. The circumferences of lines of arrested growth were
used to estimate mass over successive years of the animal's life.
These mass estimates suggest that early in ontogeny, Acrocanthosaurus
grew at rates on par with growth rates inferred in Allosaurus and most
tyrannosaurid theropods, which are similar to rates that would be
expected for scaled–up precocial birds. Histological data from adult
specimens suggest that Acrocanthosaurus reached adult body size in two
to three decades. Gigantism in Acrocanthosaurus likely evolved via
acceleration of growth rates relative to basal members of
Allosauroidea, a transition also observed within tyrannosauroid
theropods. Contrary to previous assessments, there is only evidence
for one large-bodied theropod species in the Early Cretaceous of North
America, though many fragmentary specimens are indeterminate to the
genus level. Aptian–Albian and Maastrichtian–aged dinosaur communities
were more similar to one another than to those of the intervening
Campanian stage in that both seem to have featured a single, extremely
large–bodied, fast growing, geographically widespread theropod