Besides the most famous evolutionary “missing link” (you know, the one between apes and humans), there are tons of places in the tree of life where scientists aren’t sure how one animal turned into another. One of those places is within a group of animals that don’t have spines but are closely related to animals that do, like humans.
The animal that fills that particular gap is a worm that Philippe Cousteau describes in the latest episode of The Aquatic World as, well, “phallus-shaped.”
The acorn worm has no eyes, no brain, no sense organs, and eats mostly dirt. It’s basically a giant, segmented earthworm, but one that lives underwater. Though it seems like an unlikely ancestor, approximately 70% of human genes trace back to acorn worms, Ashlan Gorse-Cousteau informs us.
The Cousteaus and crew find the acorn worm as it exists today below the waves, but the fossils that inspired the acorn-worm-as-missing-link theory were discovered far above ground, in the Canadian Rockies. The creature has remained almost unchanged for 500 million years, Jean-Bernard Caron, curator of invertebrate paleontology at the Royal Ontario Museum tells Philippe in a video call.
The acorn worms as well as many other odd prehistoric creatures were dug out of the Burgess Shale formation in British Columbia’s Yoho National Park (which you can explore on a guided hike). Just don’t expect to be able to take home a phallic fossil souvenir.