Whoops, We’ve Been Looking at a Really Important Fossil Upside Down This Whole Time (2024)

Go back far enough in humanity’s family tree, and things start to get weird. After all, at some point, one of our ancestors had to break with tradition and grow a spine—literally. And it’s from this pioneering

creature that all known vertebrates descend.

Since its discovery in 1910, a creature from the Middle Cambrian known as Pikaia gracilens was widely believed

. Apart from its very primitive notochord—a flexible rod found in the embryos of chordates, and which eventually makes up part of the backbone—this eel-like specimen shares no other distinguishable qualities with hom*o sapiens. But that notochord was enough to hail this half-a-billion-year-old fossil a the beginning of the phylum Chordata.

That’s why it came as quite a surprise when researchers from the University of Cambridge and the University of Bristol reported in a study, published

, that the distinguished fossil Pikaia gracilens may have been viewed with the wrong perspective. Specifically, we may have been looking at it upside-down.

“We reinterpret the morphology of Pikaia, providing evidence for a gut canal and, crucially, a dorsal nerve cord—a robust chordate synapomorphy,” the researchers wrote in the study. “The identification of these structures underpins a new anatomical model of Pikaia that shows that this fossil was previously interpreted upside down.”

According to The New York Times, the study’s co-author Jakob Vinther from the University of Bristol came to this topsy-turvy conclusion when comparing high-resolution scans of P. gracilens to other vertebrate-like fossils discovered in Greenland. That’s when he noticed that the creature’s dorsal organ appeared to have sediment stains. The only organ that would’ve been open to the external world was the digestive tract, so Vinther flipped the specimen so that the dorsal fin ran along its belly. And according to Vinther, P. gracilens’ biology suddenly “[made] way more sense.”

This new perspective on the famous fossil also came with other new attributions for certain body parts. For example, a set of appendages that were originally believed to hang down from the creature’s head were now extending above it as if “feathery outgrowths of gills,” according to The New York Times. The researchers also discovered evidence of a nerve cord, once thought to be a blood vessel, that appeared to connect to a tiny brain—even stronger evidence that Pikaia was an early member of Chordata… but maybe not the first.

The University of Cambridge’s Giovanni Mussini, the study’s lead author, said that all vertebrates likely evolved from Cambrian sea creatures known as vetulicolians, which sort of look like swimming baskets.

“It so not so much a Big Bang, going to a fully fledged fish,” Mussini told The New York Times. “The vertebrate body plan probably had a much more protracted assembly than we thought.”

While this new study certainly provides a new perspective on the famous specimen, not everyone is convinced by the new orientation—especially because it raises yet more questions about the P. gracilens biology. But whether you’re convinced or not, the paper definitely highlights the immense difficulty of piecing together humanity’s distant family tree.