Carnivora Skull Shape Depends on More Than Just Diet

by AMNH on Feb 7, 2018 2:07 pm

Typical skull shapes of carnivoran species living in dry areas, modeled above, may be different from those in rainier locales, because food availability varies.
© Z.J. Tseng et. al. 

It turns out, you’re not what you eat—at least, if you’re a mammal belonging to the order Carnivora.

New research has found that for this group of mammals—which includes species as varied as raccoons, pandas, and elephant seals—nondietary factors can be just as important, if not more so, in determining skull form and function.

[Poll: Which species has a skull that is more similar to a hyena’s—wolf, or mongoose? The researchers found more similarities in the overall shapes and biomechanical properties of the skulls of mongooses and hyenas. Congrats to all who you voted mongoose in our March newsletter poll!]

Skulls Reveal Clues to Evolution of Carnivoran Diversity

Published February 7, 2018

[HANDEL’S WATER MUSIC SUITE NO. 1 IN F MAJOR OVERTURE]

[An image of an 18^th century gentleman surrounded by an elaborately presented table.]

[TEXT: One of history’s most renowned food writers famously said,]

[Vintage French postcard of a woman serving an elaborate meal to a large man. At the next table is a miserly looking man eating bread and peas.]

[TEXT: “Tell me what you eat, and I shall tell you what you are.”]

[RECORD SCRATCH]

[The postcard is pushed away by split screen video of two scientists examining skulls.]

[TEXT: Two evolutionary biologists beg to differ.]

[Scientists are identified in on-screen text as Z. Jack Tseng from the University at Buffalo, and John Flynn from the American Museum of Natural History.]

[MODERN, LIGHTLY DRIVING MUSIC PLAYS]

[American Museum of Natural History Curator John Flynn sits behind a table in the Mammalogy collection. Various carnivoran skulls surround him, and he holds a hyena skull.]

JOHN FLYNN (Curator, Division of Paleontology): You think, basically, you are what you eat. And turns out, you’re not.

[A lioness chews on a carcass.]

[TEXT: From lions,]

[A raccoon in a field of clover chews on a piece of food.]

[TEXT: to raccoons,]

[Two giant pandas eat bamboo.]

[TEXT: to giant pandas,]

[A family of European badgers plays in the forest.]

[TEXT: mammals of the order Carnivora can vary greatly]

[A small greyish fox sits on a rock.]

[TEXT: from one species]

[A large walrus sits on a rock.]

[TEXT: to another.]

[Two red pandas in branches chew on bamboo.]

[TEXT: (And despite their name, they aren’t all meat eaters.)]

[An overhead shot of a desk with many Carnivora skulls. Hands open and close the jaws of one skull.]

[TEXT: Their skulls tend to take the form of just a few shapes—]

[Tseng and a grad student examine skulls in an office.]

[TEXT: a pattern scientists have long attributed to shared diets.]

[Tseng works at a violet-lit research station with several computers and a mechanical device.]

[TEXT: But new research from the University at Buffalo]

[Flynn pulls a skull from a specimen box in the American Museum of Natural History’s Mammalogy collection.]

[TEXT: and the American Museum of Natural History]

[On the left side of the screen, the skull of a fossa (Cryptoprocta ferox) is shown from front, side, and rear views.]

[TEXT: reveals that the evolution of Carnivora skull shape]

[Five carnivoran skulls and mandibles are lined up on a table. A microscope sits behind them.]

[TEXT: is much more complex.]

[A mother fox and her three kits play in a field.]

[TEXT: Factors like an animal’s age at sexual maturity]

[Rain falls around a wet margay (small cat) in a forest.]

[SOUND OF RAINDROPS]

[TEXT: and average rainfall where it lives]

[Close-up of a hyena skull and mandible with large teeth.]

[TEXT: influence skull form and function as much]

[TEXT: or even more]

[A giant otter eats a fish held in its paws.]

[TEXT: than what it eats.]

[Flynn sits behind a table in the Mammalogy collection. Various carnivoran skulls surround him, and he holds a hyena skull.]

FLYNN: We found more similarities in the overall shapes and biomechanical properties of-

[Flynn picks up a small mongoose skull]

FLYNN: of mongooses and hyenas—which look nothing alike—than this

[Flynn indicates the hyena skull]

FLYNN: might have to a wolf.

[Camera pans over a table of various carnivoran skulls.]

[TEXT: With data from more than 50 living species,]

[Tseng walks in the halls of the University at Buffalo.]

[TEXT: lead author Z. Jack Tseng,]

[Flynn holds a fossil skull and mandible in the Museum’s Paleontology collection.]

[TEXT: and co-author John Flynn]

[A large skull sits on a black circular plate. Blue light scans over the skull.]

[TEXT: created sophisticated shape and biomechanical models]

[Close up of skull scanned by blue light.]

[TEXT: of carnivoran skulls.]

[Camera tracks in to Tseng at desk, examining carnivoran skulls.]

[TEXT: They tested how skull size and shape correlate to]

[A monk seal swims underwater.]

[TEXT: habitat,]

[A bear eats a fish in a waterfall.]

[TEXT: diet,]

[A coyote, caught at night on a camera trap, sniffs the grass. Skyscrapers tower in the background.]

[TEXT: what time of day a species is active,]

[A mother hyena licks her cubs.]

[TEXT: life expectancy,]

[An ermine stands on its hind legs, and then runs across a grassy field.]

[TEXT: and how an animal moves.]

[A student works at a computer behind a camera pointed at a large skull.]

[TEXT: Combining digital modeling]

[Close up of Tseng’s hands holding a 3D print of a skull.]

[TEXT: and biomechanical analysis]

[Flynn examines a skull in the Museum Mammalogy collection.]

[TEXT: Tseng and Flynn pinpointed changes related to ecological factors,]

[A machine approximating bite pressure shatters a piece of bone.]

[TEXT: then tested the functional importance of those shape changes]

[An animated bite simulation of a carnivoran skull shows a “heat map” of pressure distribution.]

[TEXT: using bite simulations.]

[Close up of a raccoon skull and mandible.]

[TEXT: Their results show, for the first time,]

[A mother skunk and her kit walk around the base of a tree.]

[TEXT: that nondietary factors significantly influence]

[A meerkat stands on its hind legs, looking around.]

[TEXT: both skull function and form in Carnivora.]

[A young fox in a forest looks at the camera.]

[TEXT: Now that they’ve looked at modern species,]

[A rear view of a red fox as it jumps into a snow bank in search of prey.]

[TEXT: where do they go from here?]

[Flynn pulls out a drawer in the Museum’s Paleontology collection.]

[TEXT: They can start placing fossils into the analysis—]

[Close up of a smilodon skull.]

[TEXT: learning more about how different factors]

[An array of dire wolf skulls, mounted on a wall.]

[TEXT: interacting over deep time]

[A male lion walks down a road.]

[TEXT: led to the evolution]

[A black-footed ferret walks out of a ribbed plastic tube. The nose of another ferret appears behind it.]

[TEXT: of the wonderfully diverse carnivorans]

[A seal turns over in the water and slaps its flippers against its side.]

[TEXT: we see today.]

[A group of wolves play on snowy ground.]

[TEXT: Tseng, Z. Jack and John Flynn. Structure-function covariation with nonfeeding ecological variables influences evolution of feeding specialization in Carnivora. Science Advances, February 2018 : eaa05441]

[American Museum of Natural History logo and credits appear over footage of an otter.]

“For years, conventional thought surrounding carnivoran skull shape followed the ‘you are what you eat’ paradigm, where distantly related species evolve similar skulls because of shared dietary needs,” said Z. Jack Tseng, assistant professor of pathology and anatomical sciences in the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo and a research associate at the Museum. “We found that to be a dramatic oversimplification.”

Seven side-by-side comparisons of skulls and heat maps.

Pairs of skulls with shape changes based on factors including age at sexual maturity, diet, and others. Warmer colors indicate extruding shape change (expansion), while cooler colors show shrinking shape change (reduction).
© Science Advances/Z.J. Tseng et. al.

In a study led by Zheng and coauthored by John Flynn, Frick Curator of Fossil Mammals in the Museum’s Division of Paleontology, data from more than 50 living species was used to create shape and biomechanical models representing a wide range of diets, from exclusive carnivores like lions to herbivores like pandas and omnivores like raccoons.

The models allowed researchers to examine how skull size, shape, and bite performance varied when compared with nondietary factors such as habitat, life expectancy, and movement, among others.

A red panda, one of the omnivorous species in the mammalian order Carnivora, eating bamboo leaves.
Courtesy of Mathias Appel/ Flicker

Results showed that not only did nondietary factors influence skull shape and bite, but that variables such as age at sexual maturity and precipitation rates in a species’ environment can have a strong influence on bite performance.

“You wouldn’t think that how many raindrops fall on an animal’s head each year could tell you what their skull looks like, so that was definitely an unexpected finding,” said Flynn. “But this precipitation factor is probably a proxy for something else having to do with the species’ environment. For example, a wet forest might have greater food availability than a dry habitat, and that would influence the skull’s shape.”

The study was published today in the journal Science Advances.