If you follow science headlines at all, you have doubtless heard about Ida, the diminutive 40 million year old primate who was unveiled to the world this week with nearly unprecedented publicity. Google even got into the excitement with an Ida-themed Google header.
So, what's so special about this find? Is it the "missing link" in human evolutionary history as many mainstream news headlines have suggested?
Well, to the extent that "the missing link" is coloqually used to refer to the most recent common ancestor of humans and chimps, not even close. Ida is more than four times older. Any most paleontologists still aren't sure that the species she belongs to is in our line of ancestry at all. This graphic from the New Scientist shows visually what's being argued about here. What is very much news here is that Ida may help answer some questions about the very, very early history of primates, when the ancestors of modern apes, monkeys and humans were diverging from those of modern lorises and lemurs. However, that's not as exciting a story, so the media seems to be blunding about in the fashion they often do in reporting any specialized field.
The other thing that's incredibly exciting about Ida is that she is an unusually well-preserved fossil, which among early primates is especially rare. (Given that good fossilization requires being quickly covered in fine sediment somewhere like a gentle river, you can see why tree dwelling creatures wouldn't get the treatment very often.) Ida was covered, immediately after her untimely demise, by solf volcanic ash which left a fossil which is 95% complete, fully articulated, and includes prints of her fur and organs.
The precise composition of the volcanic deposits in which Ida was found even allowed preservation of her soft tissue. “You can see the fur, the ears, all of the gut contents [leaves and a fruit], all the fingertips and toes,” Smith says.This has allowed us to get an unusually accurate view of what this early primate looked like. She's rather fetching, really.
Smith and her colleagues were able to guess Ida’s age based on the fossil’s teeth. “She was just turning over and replacing her baby teeth in the front of her face, and the molars were coming in the back,” Smith says. Because Ida had many teeth forming at the same time, Smith thinks the primate must have grown up fast, developing much quicker than a human would. Ida died before she was 1 year old, Smith and her colleagues suggest. Comparisons with a similar animal, the squirrel monkey, led the researchers to guess that Ida might have lived for 15 or 20 years had she not met an early demise.
The full paper on her (from which that sketch comes) can be found here.