One of the greatest challenges in all of evolutionary science is to figure out which species evolved into which over time. From our perspective, we would love to know how humans came to be, who our ancestors were, and what simpler animals gave rise to us.
Well, we don’t know this right now. We know a good portion of the fossil records, but — like anything that relies on fossils — there are gaps, referred to colloquially as missing links. One of the fun things to track is cranial capacity over time, and we find that Homo Sapiens‘ huge brains are recent developments.
And, as you can also see, there are gaps even in this relatively recent record. Did Homo Erectus evolve directly into Homo Sapiens? (Probably.) Is there a missing link? (Possibly.) But there are many, many gaps the farther back we go. The reason is simple: geology.
Everything that lives dies, but most dead things are recycled, not fossilized. We have to get lucky to find fossils, and we have to get luckier the farther back we go. And we get stopped about 600 million years ago (give or take) by the lifetime of sedimentary rock, which turns into metamorphic rock (and loses its fossils) on timescales longer than that. We know that the dinosaurs went extinct 65 million years ago, and that mammals rose after that. But how did humans come from that?
If we take a closer look, humans are great apes; we split off from them fairly recently. (And yes, there are missing links there.) Apes are primates, like dry-nosed monkeys and wet-nosed monkeys (like the lemur above) are. Scientists call the wet-nosers strepsirrhini and the dry-nosers haplorrhini. Note the dryness of your nose, and if you can’t, then wipe it for goodness’ sake!
Well, I’d like to introduce you to a long-lost cousin of yours. (And click to enlarge her.)
I probably can’t say ancestor, because she died before reaching adulthood, where she would have been just under 2 pounds. But she is the only complete primate from over 35 million years ago (she’s 43-47 million years old herself), and has a very special feature that is unique to her, but is found in apes and dry-nosed monkeys afterwards (and — again — click to enlarge):
Opposable digits!!! Yes, they’re on her feet instead of her hands, but these graspers are different than, say, cat claws. They are much more like modern opposable thumbs found on extant dry-nosed primates. She also had fingernails, ape-like teeth, and a body built for tree-dwelling.
And she just might be the oldest complete fossil of a species that evolved into us. So enjoy the awesome biology news, even if it is coming from an astrophysicist! And a special thanks to Bora Z, who pointed this research out to me! (And who — I’m sure — has a more detailed writeup of this!)