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Theropod evolution during Cretaceous in Patagonia



From: Ben Creisler
bcreisler@gmail.com


A new online paper:

Fernando E. Novas, Federico L. Agnolín, Martín D. Ezcurra, Juan
Porfiri & Juan I. Canale (2013)
Evolution of the carnivorous dinosaurs during the Cretaceous: The
evidence from Patagonia.
Cretaceous Research (advance online publication)
doi:http://dx.doi.org/10.1016/j.cretres.2013.04.001,
http://www.sciencedirect.com/science/article/pii/S0195667113000608


Patagonia has yielded the most comprehensive fossil record of
Cretaceous theropods from Gondwana, consisting of 31 nominal species
belonging to singleton taxa and six families: Abelisauridae,
Noasauridae, Carcharodontosauridae, Megaraptoridae nov. fam.,
Alvarezsauridae, and Unenlagiidae. They provide anatomical information
that allows improved interpretation of theropods discovered in other
regions of Gondwana. Abelisauroids are the best represented theropods
in Patagonia. They underwent an evolutionary radiation documented from
the Early Cretaceous through to the latest Cretaceous, and are
represented by the clades Abelisauridae and Noasauridae. Patagonian
carcharodontosaurids are known from three taxa (Tyrannotitan,
Giganotosaurus and Mapusaurus), as well as from isolated teeth,
collected from Aptian to Cenomanian beds. These allosauroids
constituted the top predators during the mid-Cretaceous, during which
gigantic titanosaur sauropods were the largest herbivores.
Megaraptorans have become better documented in recent years with the
discovery of more complete remains. Megaraptor, Aerosteon and
Orkoraptor have been described from Cretaceous beds from Argentina,
and these taxa exhibit close relationships with the Aptian genera
Australovenator, from Australia, and Fukuiraptor, from Japan. The
Gondwanan megaraptorans are gathered into the new family
Megaraptoridae, and the Asiatic Fukuiraptor is recovered as the
immediate sister taxon of this clade. Although megaraptorans have been
recently interpreted as members of Allosauroidea, we present evidence
that they are deeply nested within Coelurosauria. Moreover, anatomical
information supports Megaraptora as more closely related to the
Asiamerican Tyrannosauridae than thought. Megaraptorans improve our
knowledge about the scarcely documented basal radiation of Gondwanan
coelurosaurs and tyrannosauroids as a whole. Information at hand
indicates that South America was a cradle for the evolutionary
radiation for different coelurosaurian lineages, including some basal
forms (e.g., Bicentenaria, Aniksosaurus), megaraptorans,
alvarezsaurids less derived than those of Laurasia, and unenlagiids,
revealing that Gondwanan coelurosaurs played sharply differing
ecological roles, and that they were taxonomically as diverse as in
the northern continents. The unenlagiids represent an endemic South
American clade that has been recently found to be more closely related
to birds than to dromaeosaurid theropods. Analysis of the theropod
fossil record from Gondwana shows the highest peak of origination
index occurred during the Aptian–Albian and a less intense one in the
Campanian time spans. Additionally, peaks of extinction index are
recognized for the Cenomanian and Turonian–Coniacian time spans. In
comparison, the Laurasian pattern differs from that of Gondwana in the
presence of an older extinction event during the Aptian–Albian
time-span and a high origination rate during the Cenomanian time-bin.
Both Laurasian and Gondwanan theropod records show a peak of
origination rates during the Campanian.