The earliest ancestor of all vertebrates (including us) appears to have been a tiny, worm-like fossil creature just 2 inches long. Much like the proverbial acorn & oak, however, from Pikaia Gracilens a mighty family tree would grow.
Ancestors in the Archaeological Attic
(image via: Meeresbucht)
From Darwin’s contemporary foes to Inherit The Wind, opponents of evolution have mocked, maligned and misconstrued the notion that Man descended from monkeys. Turns out the stick-in-the-mud faction was right… we’re actually descended from worms.
Well, not “worms” in the true sense – more like “worm-like” though semantics can hardly soothe some folks’ tender sensibilities. Consider, however, that 505 million years ago being worm-like put one at the forefront of basic body design.
Our erstwhile ancestor, Pikaia Gracilens, wasn’t the biggest proto-fish in the pond by any means but when it comes to evolution, it’s not how big you but how you use what you’ve got.
What Pikaia had was a select suite of anatomical attributes that would serve it and its descendants well in the years, centuries and eons to come: a vascular system, a notochord (a primitive spinal chord) and myomeres (muscle blocks ranged along the length of the body). This combination places Pikaia among the earliest Chordates, precursors to Vertebrates. The biblical phrase “the meek… shall inherit the earth” was never so appropriate.
Most Eel Logical!
“It’s very humbling to know that swans, snakes, bears, zebras and, incredibly, humans all share a deep history with this tiny creature no longer than my thumb,” stated Jean-Bernard Caron, co-author of a landmark study published in the science journal Biological Reviews. “The discovery of myomeres is the smoking gun that we have long been seeking,” added lead author Simon Conway Morris. “This study clearly places Pikaia as the planet’s most primitive chordate.”
(image via: FossilMuseum)
Though the study published in Biological Reviews is new, the discovery of the eel-like Pikaia is not. First noted by pioneering paleontologist Charles Doolittle Walcott in 1911, Pikaia was dismissed as an ancestral polychaete worm or leech while other creatures found along with it in Canada’s Burgess Shale fossil field (above) garnered much of the public and private attention.
The graphic above highlights how insignificant Pikaia seems alongside large predators such as Anomalocaris and bizarre organisms like the 5-eyed Opabinia and the aptly named Hallucigenia. Pikaia is rare as well, with only a few dozen complete specimens found (so far) in the Burgess Shale – that’s 0.03 percent of all the fossils recovered there to date.