Large-Scale Study Reconstructs Earliest Mammalian Ancestor
February 7, 2013

Evolution Of Mammals: Large-Scale Study Reconstructs Earliest Mammal Ancestor

[Watch Video: Reconstructing Common Ancestor Of Placental Mammals]

Lee Rannals for — Your Universe Online

A team from Carnegie Museum of Natural History have completed the largest-ever study of mammalian ancestors, helping to construct what the common ancestor of all mammals may have looked like.

The six-year research project looked at the evolution of placental mammals, which are the largest branch of the mammalian family tree with over 5,100 living species. Afterwards, the team was able to construct our ancient ancestor.

Writing in the journal Science, the researchers revealed the most complete picture of mammalian history, giving science a huge dataset that will become the starting point for studies to answer a number of scientific questions.

"In the field of mammal research, there had been a big divide between people working with DNA and others working on morphology," said John Wible, PhD, Curator of Mammals at Carnegie Museum of Natural History and co-author on the paper. "They just weren't working with each other until now."

During the project, the team collected DNA sequences of living animals, and examined the anatomy of both living and extinct mammals. They only sampled living mammals, because genetic material cannot be extracted from fossils that are older than 30,000 years. Instead, they collected as many characters of morphology as possible, comparing their variation among dozens of species.

Once they produced the DNA and morphological datasets, they were able to have an unprecedented amount of information for each of the 83 mammals included in the study.

"It's not that we hadn't combined morphology with DNA before." said co-author Michelle Spaulding, PhD, the Rea Post-doctoral Fellow at Carnegie Museum of Natural History. "This time, we ratcheted up the amount of morphological detail phenomenally, providing a larger anatomical base for the study as compared with DNA than is typical."

The team is now able to take the anatomical information collected, and predict the appearance of the most common ancestor of all placental mammals.

"That's the power of 4,500 characters," says Wible. "We looked at all aspects of mammalian anatomy, from the skull and skeleton, to the teeth, to internal organs, to muscles, and even fur patterns."

He said the team was able to reconstruct what the common ancestor of all mammals looked like, by using the new family tree of mammals. An artist helped the team construct the approximate appearance of the ancestor, including body size, fur type and number of teeth.

"We focused our study on the time around the Cretaceous-Tertiary (KT) boundary, 65 million years ago," Spaulding said in a statement. "Molecular and morphological based studies differ on the age when placentals first appeared."

The team has made the matrix created during the study freely available online, providing anyone with a road map to the findings. They say this website marks a new era in scientific collaboration.

"We couldn't have accomplished this without Morphobank," Spaulding said of the site. "This website allowed members of the team, spread all over the globe, to work simultaneously."