A new study by an international research team about a never before discovered Mesozoic mammal was published in Nature on November 5th. Lead author Dr. David Krause, professor of anatomical sciences at Stony Brook University, was interviewed on November 10th about his research:
“We think of the Mesozoic Era as the age of reptiles and the Cenozoic as the age of mammals, but something like two-thirds of mammalian history took place in the Mesozoic,” says Krause, who has been seeking fossils of these mammals since 1993. Led by Krause, the recent analysis of a skull from the Late Cretaceous in Madagascar offers groundbreaking insights into their diversity and evolution.
Called Vintana sertichi, the newly-discovered species is believed to have resembled an oversized groundhog, although it is very distantly related to modern mammals. With a skull 4.9 inches long and an estimated body weight of about 20 pounds, it is the largest known Mesozoic mammal in the southern hemisphere and the second largest in the world. Krause’s then graduate student Joseph Sertich discovered its skull within a fossil filled sandstone block from Madagascar’s Maevrano Formation, where the remains of coastal floodplains 71.2-66 million years old have yielded hundreds of vertebrate fossils (largely fish and reptiles) to research teams over many expeditions.
Detailed analysis by Krause and his team at Stony Brook University, who used computer tomography and scanning electron microscopes, revealed an utterly unique combination of features. Large eye sockets and nasal spaces, an inner ear designed for maintaining balance well and hearing high-pitched sounds, plant-grinding molars, and attachment sites for large incisors and powerful jaw muscles – its estimated bite strength is twice that of the nutria, a similar-sized modern rodent – suggest an active, agile herbivore with exceptionally keen senses for its time, able to eat tough material such as roots and large seeds. But some parts of its palate, nasal structure, and inner ear are “primitive,” having never been found in other true mammals but only their near-mammalian relatives such as tritylodontids.
These features place Vintana in the suborder Gondwanatheria, of which few fossils have been found, inhabiting what was then the southern hemisphere continent of Gondwana. They also link Gondwanatheria to Multituberculata and Haramiyida, two orders of extinct mammals mostly found on the Northern Hemisphere continent of Laurasia. Multituberculata thrived across the world 155-35 million years ago (Late Jurassic Period into Oligocene Epoch), existing longer than any other mammal group. Haramiyida, the earliest known herbivorous mammals, appeared in the Triassic Period, and their mammalian status has long been contested. Combining these three into the group Allotheria confirms that mammals have inhabited Earth since before the supercontinent Pangaea split into Laurasia and Gondwana in the early Jurassic Period. Krause describes the Mesozoic Era as a time of great “experimentation” in mammal evolution, with a flourishing array of species which have no living descendants but were very successful in their time.
Artist’s reconstruction of Vintana sertichi. Credit: Gary Staab
Madagascar separated from the rest of Gondwana more than 20 million years before the Maevrano Formation was deposited, and has been producing endemic creatures ever since. Now largely inland, the formation’s rocks and fossils display a subtropical landscape of forests, seasonally flooding rivers, and tidal flats teeming with land and water life. According to Krause, this Vintana specimen probably died near the site where it was discovered, buried by a gentle river-flood of sediment. Its large size may have provided some protection against local predators, which included carnivorous dinosaurs, relatives of crocodilians, and the huge frog Beelzebufo ampinga.
Much remains unknown about Vintana’s relationships with other mammals. Krause will continue to seek fossils in Madagascar, probing the lesser-known mysteries of the Mesozoic world.
Krause, D. W., Hoffmann, S., Wible, J. R., Kirk, E.C., Schultz, J.A., von Koenigswald, W., Groenke, J.R., Rossie, J.B., O’Connor, P.M. Seiffert, E.R., Dumont, E.R., Holloway, W.L., Rogers, R.R., Rahantarisoa, L.J, Kemp, A.D., & Andriamialison, H. (2014) First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature 515, 512-517.
Rogers, R. R., Krause, D.W, Kast, S.C., Marshall, M.S., Rahantarisoa, Robins, L.C.R., & Sertich, J.W. (2013). A new, richly fossiliferousmember comprised of tidal deposits in the Upper Cretaceous Maevarano Formation, northwestern Madagascar. Cretaceous Research 44, 12–29
Weil, A. (2014) Mammalian evolution: A beast of the southern wild. Nature 515, 495-496.
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