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02/07/2013

Ancestor of placental mammals, including humans, looked like this

Animal

An artist's rendering of the hypothetical ancestor of placental mammals, the group of mammals that includues humans, dogs, whales, and many other animals. (Courtesy Carl Buell)

The earliest common ancestor of most mammals - including humans - was probably a toothy shrew-like creature who ate bugs, according to a study published today in Science.

This hypothetical ancestor also lived after the big extinction event that wiped out dinosaurs, the researchers believe.

Scientists have hotly debated whether primates and other “placental mammals” - the branch of mammals that includes humans, dogs, elephants and bats, among many others - ever walked the Earth beside dinosaurs.

While this study says no, others are likely to contest it - though the Science researchers crunched a huge amount of data to make that prediction.

The paper is the result of a lengthy attempt to assemble the largest, most complete family tree of placental mammals. The project included two study groups: those collecting molecular data (DNA) and those collecting morphological data (bones, fossils, and other anatomical information).

It also included a Canadian, University of Toronto Scarborough’s Mary Silcox. Silcox’s job was to analyze teeth and skulls (“I’m kind of an above the neck person,” she explains.)

Silcox, an assistant professor of anthropology, says the impetus for the project was plain old intellectual curiosity.

“This is one of the major questions that people have asked about the world around them: Who is related to who; what does that mean in terms of the past history of these groups?” In other words, what could the common ancestor of a whale and human look like?

“That’s the best reason to do it, because it helps to structure our understanding of the world around us," she says.

But, she adds: “No one has ever tried to do it on this scale before.”

The researchers collected thousands of pieces of information about 83 placental mammals. Using the power of that dataset, they were able to predict approximate what the common ancestor of placental mammals would have looked like, and also predict that it must have lived after the extinction of dinosaurs.

That makes intuitive sense, says Silcox, because the current explosion of mammalian diversity we see today would have been much more likely to occur after dominant dinosaurs had been wiped off the Earth.

 
Kate Allen is the Toronto Star’s global science and technology reporter. Follow her on Twitter @katecallen

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Interesting that the largest discovered prime number is an animal.

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