While searching for fish fossils in Madagascar four years ago, paleontologists discovered a well-preserved cranium of a mammal. The researchers believed that this mammal lived about 66 million to 70 million years ago, in the closing era of the mighty dinosaurs.
The discovery is known to be rare in the entire Southern Hemisphere and expected to provide new and important insights into early mammalian evolution. The ancient mammals’ fossil record in Madagascar is annoyingly thin. The researchers found just two other mammal skulls from the age of dinosaurs in the entire Southern Hemisphere – and both were from Argentina.
The study is published in Nature journal. The lead researcher of the study and a paleontologist at Stony Brook University on Long Island David W. Krause revealed that the fossil mammal is a distinct new genus and species, Vintana sertichi. Vintana means luck, which was smiling on Joseph Sertich, then a graduate student of Dr. Krause’s and now a curator at the Denver Museum of Nature and Science, in finding the slab of sandstone that held the skull.
Dr. Krause said in a statement, “No paleontologist could have come close to predicting the odd mix of anatomical features that this cranium exhibits.”
The five inches long cranium, which is twice the size of the one from the previous largest known mammal from the age of dinosaurs on the southern super-continent known as Gondwana. At that time, nearly all primitive mammals were no bigger than shrews and mice, cowering in the shadows of hulking reptiles.
Vintana is estimated to have weighed about 20 pounds, twice or even three times the size of an adult groundhog today.
However, the researchers sometimes described the specimen as groundhog-like. Vintana belonged to an ancestry without any known living descendants, Dr. Krause said. “It’s an entirely extinct ancestry, an early experiment in mammals that didn’t make it,” he said in an interview. “And I doubt Vintana was any better at predicting seasonal weather change than Punxsutawney Phil in Pennsylvania.”
Vintana belongs to a group of early mammals known as gondwanatherians, the only previous evidence for which were a few teeth and jaw fragments, researchers claimed.
Consecutively, these mammals were closely related to the multituberculates, which is an evolutionarily successful group of early mammals known almost solely from Northern Hemisphere fossils. All these relationships had been uncertain before now, researchers said.
Anne Weil, an anatomist at the Oklahoma State University Center for Health Sciences said in a commentary accompanying the Nature paper, the new findings offered “a profusion of data not only to solve” the mystery of the mammalian family tree “but also to reveal further amazing morphological diversity among early mammals.”
Other researchers independent of the discovery team endorsed the interpretation of the findings. Guillermo W. Rougier, a specialist in the early evolution of mammals at the University of Louisville, said the study is “a remarkable achievement” and the cranium “is exceptional.”
Zhe-Xi Luo, an anatomist at the University of Chicago who is also an expert in mammalian evolution, called Vintana “the discovery of the decade for understanding the deep history of mammals.”
The study “offers the best case of how plate tectonics and biogeography have impacted the animal evolution — an ancestry of mammals isolated on a part of the ancient Gondwana had evolved some extraordinary features beyond our previous imagination,” he added.
Joe Groenke, a technician working with Dr. Krause was the first person at Stony Brook to see the CT image of the cranium embedded in the sandstone. The specimen had wide eye sockets. Further analysis revealed teeth of a plant eater, and a nasal passage and inner ear of an animal with keen senses of smell and hearing.
Mr. Groenke said, “When we realized what was staring back at us on the computer screen, we were stunned.” He spent the next six months extracting the skull from the surrounding rock matrix, one sand grain at a time.