Sentences with phrase «cretaceous placental mammal»
Along with post-Cretaceous marsupials identified in recent years from South America, Antarctica, Africa, and Australia, as well as a Late Cretaceous placental mammal from India reported in 1994, the new molar suggests that southern landmasses have an unexpected story to tell.
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The team found that the last common ancestor for all placental mammals lived in the late Cretaceous period, about three million years before the non-avian dinosaurs became extinct 66 million years ago.
If there were placental mammals in the Early Cretaceous of Australia, Krause says, it would «push back the record of placentals farther than we expected on any southern land mass and in many ways revolutionize our concept of early mammalian biogeography.»
Because so little is known about Gondwanan mammals, Krause is wary of dismissing Rich's interpretation «just because we don't expect, based on current knowledge of early mammalian evolution on Gondwana, to see a placental mammal in the Early Cretaceous of Australia.»
But he quibbled with the conclusion, noting that previous studies indicated that some placental mammals were present in the late Cretaceous.
«Of course you're excited when you find something well preserved from the Cretaceous [period 145 million to 65 million years ago],» says John Wible, curator of mammals at the Carnegie Museum of Natural History in Pittsburgh and senior author of a new report that concludes placental mammals originated around 65 million years ago, between the Cretaceous and Tertiary periods when dinosaurs disappeared.
In an attempt to determine whether it was a placental mammal, the scientists constructed a tree charting the evolution of placental mammals beginning well in the Cretaceous.
Some suggest that rabbit - or ungulate - like placental mammals existed early in the Cretaceous period, whereas other researchers push for a more recent origin, circa 65 million years ago — around the time when dinosaurs disappeared.
These results are consistent with the hypothesis that the Cretaceous - Paleogene mass extinction of non-avian dinosaurs played an important role in the diversification of placental mammals.