Oldest Known Mammalian Tooth Marks

Science Daily is reporting on the finding of the oldest known tooth marks left by a mammal. They write:

The researchers believe the marks were made by mammals because they were created by opposing pairs of teeth -- a trait seen only in mammals from that time. They think they were most likely made by multituberculates, an extinct order of archaic mammals that resemble rodents and had paired upper and lower incisors. Several of the bones display multiple, overlapping bites made along the curve of the bone, revealing a pattern similar to the way people eat corn on the cob.

So by the late Cretaceous, mammals were considering some dinosaurs food. There is a good deal of suspicion that these were done by scavenging rather than predation—a squirrel-sized rodent would not ordinarily take on a five-foot dinosaur with teeth.

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The Evolution of Mammalian Hearing

The Pittsburgh Tribune-Review has an article detailing research on early mammalian hearing. Mike Cronin writes:

Though it weighed 2 ounces and was 5 inches long, the chipmunk-like mammal that lived 123 million years ago had something its dinosaur predators didn't: middle ear bones partially independent of its jaw bone.

That evolutionary development helped Maotherium asiaticus have more sensitive hearing.

"This made it possible for mammals to be active in the night," said Dr. Zhe-Xi Luo, the Carnegie Museum of Natural History associate director of science and curator of vertebrate paleontology, in an e-mail from Germany.

"In the Mesozoic (Era), when dinosaurs dominated the world, this is a key adaptation for the survival of mammals," he said.

Neat!

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As Climate Changes, So Do Animals' Diets

A story in e! Science News reports that researchers from The University of Florida have conducted a study of mammalian teeth and discovered that, as climate changes, the diets of many mammals shift to accommodate the changes:

Led by Florida Museum of Natural History vertebrate paleontologist Larisa DeSantis, researchers examined fossil teeth from mammals at two sites representing different climates in Florida:

a glacial period about 1.9 million years ago and a warmer, interglacial period about 1.3 million years ago. The researchers found that interglacial warming resulted in dramatic changes to the diets of animal groups at both sites. The study appears in the June 3 issue of PLoS ONE.

"When people are modeling future mammal distributions, they're assuming that the niches of mammals today are going to be the same in the future," DeSantis said. "That's a huge assumption."

Co-author Robert Feranec, curator of vertebrate paleontology at the New York State Museum, said scientists cannot predict what species will do based on their current ecology.

"The study definitively shows that climate change has an effect on ecosystems and mammals, and that the responses are much more complex than we might think," Feranec said.

We know that when the African climate shifted toward the end of the Miocene, the monkeys adapted to the savannas while the higher apes adapted to the jungles. Rather than do either, one group likely exploited the forest/fringe environment, which allowed them to be more generalists. It is probably this group that gave rise to the earliest hominids.