In the most common system of taxonomy, as we should all have learned in high school, human beings are Animalia Chordata Mammalia Primata Hominidae Homo Sapiens. The first bit essentially means that we eat something other than sunlight. The second bit means we are descended – like all other vertebrates – from Pikaia gracilens. This creature lived about 570 million years ago and was part of the Cambrian explosion: so spectacularly displayed in the Burgess shale near the border of British Columbia.
Pikaia was initially mis-categorized as a worm. Now, it seems that the combination of segments, muscles, and a flexible dorsal rod embodied in this little creature may mean that it was the first vertebrate: the template for all those alive today. From the first vertebrate species, all amphibians, reptiles, birds, and mammals evolved. From tuna fish to orangutan, we may all be descendents of Pikaia. Writing about the animal in Wonderful Life, Stephen Jay Gould highlights both its huge evolutionary legacy and the degree to which it arose as the result of many change occurrences. If we could go back all those millions of years and let time unroll again, it is highly likely that we would have a profoundly different world at the end.
You can begin to imagine how staggeringly different the contemporary world would be if this little creature hadn’t survived and spread. The old view of evolution as a linear and predictable progression towards ‘higher’ organisms – a surprisingly common teleological view – is laid to rest by the contemplation of the degree to which chance can nudge history down one or another track.
Here is a computer rendering of how Pikaia gracilens may have looked.
‘Pikaia gracilens and the vertebrates’ would be a wicked name for a band.
Here is a cool Pikaia descendant: the Green Turtle.
Pikaia gracilens (a primitive chordate)
Living among the variety of ancestral forms that make up the Burgess Shale community is this earliest known representative of the phylum to which we ourselves belong. Averaging about one and one half inches in length, Pikaia swam above the seafloor using its body and an expanded tail fin.
MAY 15, 2009
Fossil Discovery Is Heralded
By GAUTAM NAIK
In what could prove to be a landmark discovery, a leading paleontologist said scientists have dug up the 47 million-year-old fossil of an ancient primate whose features suggest it could be the common ancestor of all later monkeys, apes and humans.
Anthropologists have long believed that humans evolved from ancient ape-like ancestors. Some 50 million years ago, two ape-like groups walked the Earth. One is known as the tarsidae, a precursor of the tarsier, a tiny, large-eyed creature that lives in Asia. Another group is known as the adapidae, a precursor of today’s lemurs in Madagascar.
Based on previously limited fossil evidence, one big debate had been whether the tarsidae or adapidae group gave rise to monkeys, apes and humans. The latest discovery bolsters the less common position that our ancient ape-like ancestor was an adapid, the believed precursor of lemurs.
CALGARY — It seems an inglorious beginning, but some scientists are now convinced humanity’s origins can be traced to an ancient, flat, fishlike worm.
A team of researchers subjected the 505-million-year-old Burgess shale fossils of Pikaia gracilens to the latest technology and found evidence that could settle a decades-long debate about the primitive species.
Notably, that they had the seeds of a spine.
“We can see and discern the positive location of the notochord and the nerve chord. This was not obvious at all, you needed these techniques to see it,” said Jean-Bernard Caron, the curator of invertebrate paleontology at the Royal Ontario Museum.
Caron is the co-author of a study to be published Monday in the British journal, Biological Reviews. The lead author was English paleontologist Simon Conway Morris.
The earliest explorers of the Burgess shale collected specimens of Pikaia in 1911. But the creature was overlooked as an ancestor of the earthworm.
“They had no idea it might be something more important to us then, at first sight,” Caron said.
It wasn’t until the ‘70s that Morris first suggested the lancelet-like species could in fact be one of the earliest known members of Phylum Chordata — the class that spawned animals with spines. He noted what looked like a notochord, a primitive spine that forms in the embryos of all vertebrate animals, including humans.
Metaspriggina had large eyes (towards the left in the photograph) and, though boneless and therefore spineless, had a characteristic structure called a notochord running along its back to stiffen it. Backboned animals, too, have a notochord when they are embryos, though it disappears during development. Metaspriggina or one of its contemporaries was thus ancestral to mankind.