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Cronopio, "saber-toothed" dryolestoid mammal from Cretaceous of Argentina

From: Ben Creisler

In the new issue of Nature:

Guillermo W. Rougier, Sebastián Apesteguía & Leandro C. Gaetano (2011)
Highly specialized mammalian skulls from the Late Cretaceous of South
Nature 479: 98?102 (03 November 2011) 

Dryolestoids are an extinct mammalian group belonging to the lineage
leading to modern marsupials and placentals. Dryolestoids are known by
teeth and jaws from the Jurassic period of North America and Europe, but
they thrived in South America up to the end of the Mesozoic era and
survived to the beginnings of the Cenozoic. Isolated teeth and jaws from
the latest Cretaceous of South America provide mounting evidence that, at
least in western Gondwana, dryolestoids developed into strongly endemic
groups by the Late Cretaceous. However, the lack of pre-Late Cretaceous
dryolestoid remains made study of their origin and early diversification
intractable. Here we describe the first mammalian remains from the early
Late Cretaceous of South America, including two partial skulls and jaws of
a derived dryolestoid showing dental and cranial features unknown among any
other group of Mesozoic mammals, such as single-rooted molars preceded by
double-rooted premolars, combined with a very long muzzle, exceedingly long
canines and evidence of highly specialized masticatory musculature. On one
hand, the new mammal shares derived features of dryolestoids with forms
from the Jurassic of Laurasia, whereas on the other hand, it is very
specialized and highlights the endemic, diverse dryolestoid fauna from the
Cretaceous of South America. Our specimens include only the second
mammalian skull known for the Cretaceous of Gondwana, bridging a previous
60-million-year gap in the fossil record, and document the whole cranial
morphology of a dryolestoid, revealing an unsuspected morphological and
ecological diversity for non-tribosphenic mammals.

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