25 Tiny Bones Give Clues about our Earliest Primate Ancestors

When ancient primates reached India, they retained their primitive appearance — but their northern counterparts kept evolving.

54.5 million years ago, primates that were small enough to fit in the palm of your hand were living in trees of the ancient rainforests in what is now Gujarat, India. Reporting in the Journal of Human Evolution, researchers have discovered 25 of their tiny, well-preserved bones in a coalmine in Gujarat, which appear more primitive than any other primate bones found to date.

Based on their bones, primates can normally be assigned to one of two groups: the haplorhine group, which comprises monkeys and apes, including humans, or the strepsirrhine group, which contains lemurs, lorises, and bushbabies. Members of either group have distinct anatomical traits.

But the researchers had a tough time assigning many of the bones found in Gujarat to one group or another. “At first they all looked the same, and we could only sort them based on relative size,” study lead author Rachel Dunn of Des Moines University tells The Science Explorer. They began to suspect that these bones were relics that had maintained the appearance of the common ancestors to all primates, prior to their split into two groups.

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Counter intuitively, older fossils that have been found in North America, Europe and northern Asia appear more specialized than the Gujarat fossils. As study co-author Kenneth Rose, from Johns Hopkins University, explains in a press release, “the most likely scenario is that more primitive primates arrived in what is now India and retained their primitive, generalized skeleton, while their relatives on the northern continents continued to evolve.

“If our interpretation is correct, this research gives us new information about what the ancestor of all living primates might have looked like and how it behaved,” Dunn tells The Science Explorer. For example, the bones suggest that these early primates were well adapted for climbing in trees, but they probably weren’t leaping from branch to branch, like some modern-day lemurs.

The researchers hope to find more fossils in India, but Dunn notes that in the meantime, the 25 bones have been scanned in a microCT, and the resulting data are available for download on MorphoSource.org. “We hope that making the scans available to the larger research community will facilitate further research and lead to a better understanding of these little primates,” she says.

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