Fernando
E. Novas, Federico L. Agnolín, Martín D. Ezcurra, Juan Porfiri and
Juan
I. Canale
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 fromthe Early Cretaceous through tothe
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 sauropodswere 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 newfamily 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 awhole.
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 theywere 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 Laurasianpattern differs fromthat 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.
Novas, F.E., Agnolín,
F.L., Ezcurra, M.D., Porfiri, J.D., Canale, J.I. 2013. Evolution
of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia.
Cretaceous
Research 45:174–215.
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