“IN SEARCH OF THE LOST CHORDATE”
FINDING THE ANCESTOR OF VERTEBRATES (AND OURSELVES)
530 million years ago
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| Early Chordates. The two animals swimming in the center are from the genus Pikaia, an early chordate that may be ancestral to all vertebrates, including humans. Actual length of the animal is about 2 inches. Credit: Illustration by John Sibbick, courtesy of John Sibbick Illustration. This illustration is used with permission. All rights reserved. |
The Cambrian explosion created all the major phyla of animals that we have today. This includes the phyla Chordata (chordates). Primitive forms are creatures with evidence of a notochord, a structural rod of cartilage and neural tissue running down the long axis of the body. This notochord was the early precursor to the spine in vertebrates (animals with a true backbone, like fish), and modern examples of simple chordates include sea squirts and lancelets. Two Cambrian fossil localities are of key importance here: Chengjiang in Yunnan Province, southern China, and the Burgess Shales in the British Columbia Rockies of Canada. Both of these localities have produced fossils classified as chordates. The Chinese forms include the forms Myllokunmingia and Haikouichthys (it has even been suggested these could be primitive vertebrate jawless fish). The Canadian form (somewhat later in the Cambrian period) is Pikaia, which especially resembles the modern lancelet.
Such primitive chordates, over time, would evolve into fish, amphibians, reptiles, mammals, and humans. The chordates emerged in the ocean waters of the Cambrian period.
HOW DO WE KNOW?
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| These Pikaia gracilens fossils are evidence that chordates were present on earth around 543 million years ago. They are the earliest known members of the phylum chordata, which is where humans are also classified. Credit: Photo by Dept. of Paleobiology, Smithsonian Institution. |
The fossil record contains specimens of early chordates from China (Chengjiang) and Canada (Burgess Shales) dated to between 530 to 505 million years ago. There is enough morphology in these specimens to identify the notochord running along the long axis of these early animals.
WHY SHOULD I CARE?
Humans are chordates and vertebrates. Incredibly, one of these these primitive, prehistoric two-inch creatures could be the direct ancestors to all later vertebrates – fish, amphibians, reptiles, birds, and mammals (which includes us). Although such a concept may be hard to believe for many people, is it really any more incredible than realizing that each of us started out as an independent sperm and an egg?
WEB RESOURCES
This is a video which shows the first vertebrate to breath with lungs and gills, Tektaalik. The video is from an Animal Planet series called Animal Armageddon.
https://www.youtube.com/watch?v=2-WV9vDcyvc&feature=fvw
Article about the oldest fossil of a vertebrate ever found. Posted October 23, 2003.
https://www.theage.com.au/articles/2003/10/22/1066631501521.html?from=storyrhs
This is a UC Berkley site which gives common information about the vertebrates as well as their ancestors.
https://www.ucmp.berkeley.edu/vertebrates/vertlh.html
