It’s Spine is the Base Line
By the late 1970s scientists began a wholesale re-examination of the Burgess Shale fauna using modern investigational techniques. In 1979 Morris tentatively assigned Pikaia to the Chordates based on its very primitive notochord but other biologists weren’t ready to accept this designation. Pikaia had other features that gave researchers pause as well, such as short tentacle-like structures on its head.
(image via: ROM Expeditions)
The recent study led by Morris (above, left, with Derek Riggs) employed researchers from Cambridge University and colleagues in Canada who applied the latest scientific techniques on a total of 114 whole and/or partial Pikaia specimens. The results speak for themselves: tentacles or not, Pikaia is now firmly ensconced at the base of the Chordate family tree and, by extension, our own.
What was a typical day like for our great-to-the-power-of-N-removed granddaddy? Judging from the sizes, shapes and overall intimidating armor of the other boys in da hood, it’s safe to say gramps was lucky if he got through the day (or night) in one piece. Even a half-billion years ago, the law of the land (or sea, in this case) was “eat or be eaten”.
Cambrian, Saw & Conquered
(image via: Quarta Republica)
Pikaia itself didn’t seem like much of a threat to its neighbors, though. The 2-inch (5cm) long creature had no teeth, jaws, spines or claws with which to chow down on fauna or flora with. Instead, scientists think Pikaia was possibly a filter-feeder that may have used its stubby tentacles to manipulate pieces of food into its primitive mouth.
Regardless, just the fact that Pikaia had dedicated functional structures grouped at its leading end put it, er, head & shoulders above its competitors. The anterior end of Pikaia’s flexible notochord would eventually swell in order to control these functions to the point where it could be considered a brain.
Those myomeres we mentioned earlier? Grouped along the length of Pikaia’s body, these blocks of muscle tissue could be contracted in sequence allowing the creature to squirm through the sea like a snake slithers on land. There’s much more potential for speed, endurance and control in such a system compared to simply crawling about on legs or flailing finned appendages.
And that’s what Pikaia Gracilens was all about, really: potential. The Cambrian Explosion of complex, multi-cellular life was also an expression of various body plans scrawled onto the blank slate of history. With hindsight we can look back through the eons and trace today’s living creatures back to their roots. With Pikaia, unlikely as it may seem, our bi-symmetrical body plan sporting a central backbone supporting and protecting a central nerve trunk got thrown into the mix… and in time, succeeded to the max!