Many high school biology students are taught to draw primate family trees, showing exactly how many millions of years ago chimps and gorillas diverged. New research, though, is sending students back to the drawing board, revealing new fossils that reconstruct the nature of primate origins and evolution.

In a study published last week in the Proceedings of the National Academy of Sciences, researchers used new skeletal evidence to change traditional conceptions about the roots of the primate family tree. Along with placing the earliest branch of primate evolution about 10 million years earlier than previously thought, the study also described two new members of the primate family.

The team of four researchers from Yale, University of Florida, Stony Brook University and the University of Winnipeg reanalyzed the issue of primate origins and their relationship to other mammals.

“This is the first study that brings different anatomical features and different animals all into a single analysis,” Yale anthropology professor and co-author Eric Sargis said. “It really gives us an idea of what the first years of primate evolution were like.”

In studying the new skeletal specimens, the authors found evidence that plesiadapiforms, a group of archaic mammals, are in fact the earliest primate species and are closely related to modern primates as well. The researchers were also able to correct many scientific misconceptions about the evolution of primate characteristics.

Study leader Jonathan Bloch, a vertebrate paleontology curator at the Florida Museum of Natural History, collected the fossils from limestone blocks in Wyoming. He said one of the most interesting and provocative aspects of the study is the discovery of these fairly complete skeletons, most of which have never been seen before.

“Before, we only had isolated teeth and fragments,” Bloch said. “These new findings allow us to reconstruct what primitive primates would have looked like.”

According to the study, there are five major defining traits of primates: grasping hands and feet, nails instead of claws, forward facing eyes, large brains and the ability to leap. This new research shows that the earliest primates had some, but not all, of these qualities, in contrast to the accepted “all-in-one-package” theory, which holds that all these characteristics evolved simultaneously. In light of these discoveries, scientists are able to better determine how, when and why certain traits evolved, Sargis said.

“Now that we have this new group [in the primate family], we’re getting a sense of the order in which these traits evolved,” Sargis said. “This new species also helps us understand why certain features evolved in primates, and proves many theories wrong.”

According to Sargis, one of the most important effects of the study is that it answers major questions about the diet and locomotion of primates. For instance, the new fossil evidence confirms the hypothesis that primates and flowers evolved at the same time.

Professors in the field, though, said the new information on the primate date of origin is not particularly significant in comparison with the rest of the findings, especially since the date will only continue to be pushed back as new evidence emerges.

But Yale anthropology professor Andrew Hill said that while the earlier date of origin is not surprising, the concrete evidence the research provides is important for understanding primates and for the future of anthropology in general.

“It establishes … that you can still find out a lot by finding new fossils,” Hill said. “Simply going out there, digging holes, and managing to find new stuff changes ideas a lot.”

Knowledge of the field will continue to expand as researchers uncover more and more skeletons from these freshwater limestones, Bloch said. Both he and Sargis are working to recover more varieties of specimens from the lake deposits in Wyoming, the pair said.

“It’s this completely new window into the past,” Bloch said. “There are a huge diversity of primitive primates and we fully expect that the skeletal diversity will be quite impressive.”

Sargis said the team is meeting this weekend with a larger group studying the entire mammalian tree to discuss new limestone block findings.