Carnegie Museum of Natural History

For more information, contact: Leigh Kish
Carnegie Museum of Natural History
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KishL@carnegiemnh.org

November 5, 2014

   

Largest-known Mammal from Age of Dinosaurs Described Today in the Journal Nature
Carnegie Museum of Natural History scientist part of research team

Pittsburgh, Pennsylvania…New research published online today in the journal Nature by an international team—including Curator of Mammals John Wible from Carnegie Museum of Natural History—describes a well-preserved skull of a Vintana sertichi, a strange fossil mammal known as a gondwanatherian that lived in Madagascar just before the extinction event that killed the dinosaurs, 66 million years ago. With large teeth, a small brain, and looking a bit like a large groundhog, Vintana is the largest-known mammal from the Age of Dinosaurs, weighing in at a hefty 20 pounds. Not just big in size, Vintana is big in impact on scientists’ understanding of the paleo world: the creature, once placed on the mammal Tree of Life, illuminated new evolutionary relationships between other primitive mammal taxa that had previously been unlinked. Further, Vintana sertichi shows both primitive and developed characteristics, showing the effects of evolution during a time of shifting supercontinents to the continents that we recognize today.

“Gondwanatherians have been the big question mark in textbooks of life on Earth in the past,” says Wible. “Now based on the discovery of Vintana, we can fill in that big question mark.”


Placing Gondwanatherians on the Tree of Life  

Gondwantherians are poorly-known fossil mammals that straddled the extinction event 66 million years ago that marked the end of the Age of Dinosaurs. As their name implies, they are only known from Gondwana, the southern supercontinent that broke from Pangea some 180 million years ago and produced the continents in the Southern Hemisphere today, along with India and the Arabian Peninsula. The first gondwanatherian was discovered in 1979: a single, highly unusual tooth found in Patagonia, Argentina, that was thought to be related to living armadillos. Since that initial discovery, gondwanatherians have been reported from more isolated teeth and a few lower jaw fragments. This dearth of fossil evidence has made it nearly impossible to conclude where gondwanatherians fit on the mammal tree of life or what their biology was like.

The new anatomical information provided by the skull of Vintana helped place gondwanatherians on the mammal tree of life. They are not related to armadillos as once thought, but to another much more diverse and longer lived extinct group of mainly Laurasian mammals (from the northern supercontinent Laurasia) called multituberculates. These mammals also have a very bizarre dentition with cheek teeth with multiple cusps in rows, which is the origin of their name. Multituberculates are an older group, originating in the Jurassic Period in the north, which hypothesizes gondwanatherians into a similar time in the south. Vintana presents a mosaic of very ancient features reflective of this deeper Mesozoic origin coupled with its very bizarre specializations. During Vintana’s time 70–66 million years ago, Madagascar had been isolated from the other Gondwanan land masses for millions of years (16–22 million years from India and 40–50 million years from the others). In addition to Vintana, this isolation produced some other strange bedfellows, including massive predatory frogs, herbivorous crocodiles, and specialized theropod dinosaurs. After the demise of Vintana, other unrelated mammals somehow made their way to isolated Madagascar and evolved into one of the world’s most unique faunas of today with diverse radiations of lemurs (primates like no other), tenrecs (spiny hedgehog-like forms related to elephants), and Malagasy civets (carnivores related to mongooses). There is no place on Earth like Madagascar today as was true more than 66 million years ago.


Characteristics of Vintana  

Vintana was a monster mammal for its time; its contemporaries were shrew-sized, but Vintana was about 20 pounds. It was also a monster in that it seems to have been constructed from different parts of other mammals. It had two pairs of large, curved, ever-growing upper incisors separated from the cheek teeth by a wide gap, like a rabbit; its molars faced laterally as much as ventrally, like some rodents; and it had enormous scimitar-like bony flanges on its zygomatic arches for chewing muscles, like some sloths. Study of the enamel on the teeth along with a reconstruction of the chewing muscles predict that Vintana produced very high bite forces for an animal of its size and likely had a mixed diet that included large, hard, and/or abrasive food items, such as roots, seeds, or nut-like fruits. CT scanning allowed for a reconstruction of the brain and inner ear, which showed Vintana to have a small brain for its size, a highly acute sense of smell, and hearing sensitive to high frequencies. Vintana had large eyes coupled with the angulation of its semicircular canals suggesting a vestibular system for balance that was highly sensitive to head accelerations, which may have evolved to stabilize the large eyes during rapid and/or agile locomotion.


Finding and Naming the Fossil Mammal  

Unlike most fossils, the skull of Vintana was not discovered in the field, but by happy accident when a large block collected in Madagascar was brought to the lab for CT scanning. Because of the nature of the discovery the animal is called Vintana sertichi, for the name of the discoverer of the block, Joe Sertich, and the Malagasy word for luck, vintana.


Collaborators  

The research team was led by Dr. David Krause of Stony Brook University. In addition to Dr. Wible of Carnegie Museum of Natural History, other collaborators include Simone Hoffmann (Stony Brook University), E. Christopher Kirk (University of Texas at Austin), Julia A. Schultz (Universität Bonn, Germany), Wighart von Koenigswald (Universität Bonn, Germany), Joseph R. Groenke (Stony Brook University), James B. Rossie (Stony Brook University), Patrick M. O’Connor (Ohio University), Erik R. Seiffert (Stony Brook University), Elizabeth R. Dumont (University of Massachusetts), Waymon L. Holloway (Ohio University), Raymond R. Rogers (Macalester College), Lydia J. Rahantarisoa (Université d’Antananarivo, Madagascar), Addison D. Kemp (University of Texas at Austin), and Haingoson Andriamialison (Université d’Antananarivo, Madagascar). The research on Vintana sertichi is supported by the National Science Foundation and the National Geographic Society.

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