Carnegie Museum of Natural History

One of the Four Carnegie Museums of Pittsburgh

mammals

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New Mammal Fossil Provides Insights on Early Placental Mammal Evolution

ambolestes zhoui fossil
The two halves of Ambolestes zhoui show the remarkable completeness of the specimen including the hyoid bones in the neck and a furry outline to the body.

An international team including scientists from Carnegie Museum of Natural History and Indiana University of Pennsylvania have announced a 126 million year old fossil in the placental mammal lineage. This new fossil, named Ambolestes zhoui, was found in Inner Mongolia, northeastern China, in rocks also known for their spectacular feathered dinosaurs. Placental mammals, including humans, comprise most of the 5,500 species of living mammals. The other types are marsupials and monotremes. Within the placental lineage, only a handful of fossils of a similar or older age have been found. Ambolestes zhoui is without a doubt the most complete of these earliest members of the placental lineage.

As with other fossils from Inner Mongolia, Ambolestes zhoui was discovered by splitting rocks, resulting in a specimen cleaved in two halves. Putting these halves back together, nearly every bone in the body is preserved, including some bones that have never been found in any mammal from the Age of Dinosaurs. Perhaps the most remarkable preservation concerns the complete hyoid apparatus, a string of delicate bones suspended from the base of the skull that provide attachment area for muscles of the tongue and neck. Humans have a single, U-shaped hyoid bone, but that of Ambolestes zhoui was more elaborate, composed of seven separate bones, as in some living mammals, such as squirrels.

“The hyoid is one of the least understood elements of the mammalian skeleton,” according to Carnegie Museum of Natural History Curator of Mammals John Wible, an author on the study. “Its form across living mammals is amazingly diverse and we have little understanding why.” Wible hopes that the discovery of the hyoid apparatus in such an early placental relative will spark interest by researchers working on swallowing, mastication, and vocalization to provide evidence about the hyoid’s role in these critical functions so integral to being a mammal.

Ambolestes zhoui
The Early Cretaceous Ambolestes zhoui sits in a gingko tree eyeing its next meal, an unsuspecting cicada.

The nearly complete skeleton of Ambolestes zhoui, roughly 10 inches in length (25 centimeters), allowed Carnegie Museum scientific illustrator Paul Bowden to make a detailed reconstruction of how this animal looked. The bones of its hand point to it being an adept climber and its teeth to an insectivorous diet. Consequently, Ambolestes zhoui is reconstructed in a gingko tree hungrily eyeing a cicada; both the tree and the insect are also present in the same fossil formation in Inner Mongolia. Co-author Dr. Shundong Bi of Indiana University of Pennsylvania said “because this new animal is so complete, it affords an amazing window on the early evolution and lifestyle of the mammal group that would become dominant after the demise of the dinosaurs 66 million years ago.”

CONTACT INFORMATION FOR RESEARCH TEAM

John Wible, Carnegie Museum of Natural History: 412.606.2708, wiblej@carnegiemuseums.org

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Geographic coverage of mammalian species is worldwide but…

bears in the hall of North American wildlife

Geographic coverage of mammalian species is worldwide but Carnegie Museum of Natural History’s collection’s strength is in North American material.

The collections from Pennsylvania and West Virginia are among the best in the world, and there are mammals from all 50 states. Holdings from the eastern Arctic are the best of any United States museum and include the holotype (specimen used to describe a new species) of a freshwater seal.

Recent acquisitions from Belize, Bonaire, Curaçao, Costa Rica, Dominica, El Salvador, Grenada, St. Vincent and the Grenadines, Guatemala, Honduras, Jamaica, Mexico, Puerto Rico, and Trinidad and Tobago augment historical specimens from Central America.

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Ask a Scientist

Ask a Scientist: Can you tell us the story of Harvey the big rabbit?

Our museum has a huge rabbit stored in the Section of Mammals. Collections Manager Suzanne McClaren compares it to other local rabbits and tells the story of how it came into our collection.

Ask a Scientist is a new short video series where we ask our research staff questions about the millions of amazing objects and specimens stored in our collection. Tune in on YouTube, and submit your own questions via Twitter @CarnegieMNH.

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Did you know?

platypus specimen

Did you know that there are currently five extant species of monotremes, two of which we have in our collection. We have the duck-billed platypus (Ornithorhynchus anatinus) and the short-beaked echidna (Tachyglossus aculeatus).

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All of the African mammals gathered around the watering hole…

Hall of African Wildlife

All of the African mammals gathered around the watering hole in the Hall of African Wildlife were collected on an early research expedition let by Childs Frick to British East Africa and Abyssinia (now Kenya and Ethiopia).

The official dates of that expedition were 1911–1912, and we can track almost all these specimens to that trip. However, in 1909–1910, Frick took an exploratory trip to part of the area covered in 1911–1912 to scope it out and probably collected the giraffe on that trip at the train stop in Voi.

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Why Do Some Shrews Have Dark Red Teeth?

skull and jawbone of a shrew with red teeth

By John Wible

Some shrews have white teeth, while others, including our local northern short-tailed shrew, Blarina brevicauda, have a mixture of dark red and white patches on all their teeth. The dark red marks the presence of iron in the tooth enamel, in contrast to the white without.

Why? It turns out that the concentration of iron is not uniform across all teeth, but is highest on those parts of the teeth that do the most crushing and grinding during chewing. Because of that, the iron in the pigmented enamel is thought to reinforce those high stress surfaces, helping to prolong the life of the tooth. That is important for an animal that is born with its adult (permanent) teeth, having shed its baby (deciduous) teeth in utero. And for an animal with a voracious appetite, where finding the next meal in a hurry is necessary to maintain its high metabolic rate. Interestingly, the shrews that don’t have dark red teeth have a lower metabolic rate than those with. The juxtaposition of dark red and white enamel also helps to keep cutting edges sharp as the softer white enamel wears faster than the dark red. There is only one other group of living mammals that has pigmented enamel, rodents, but unlike the shrews, it is only on their incisors and not all teeth.

No matter what it is for, the shrew’s dark red enamel makes for a mouthful of beautiful, non-pearly white teeth!

John Wible, PhD, is the curator of the Section of Mammals at Carnegie Museum of Natural History. John’s research is focused on the tree of life of mammals, understanding the evolutionary relationships between living and extinct taxa, and how the mammalian fauna on Earth got to be the way it is today. He uses his expertise on the anatomy of living mammals to reconstruct the lifeways of extinct mammals. John lives with his wife and two sons in a house full of cats and rabbits in Ross Township.