Miraculously, life appeared on earth nearly 3.5 billion years ago in the form of microbes. By the time of the Cambrian explosion, life forms were highly developed.
Consider the trilobite. (If you’ve been following my blog you know it’s one of my personal favorites!) It has a chitinous covering that was made of dozens of armor-like plates that allowed it to curl into a ball when stimulated and in need of protection. Trilobites had many legs, the three lobes that inspired its name, and a clear head, thorax and “tail” known as the pygidium. Its most highly developed organ was its eye, seen here on one of our favorite giant models. Yet, on the timeline of life, it’s one of the earliest noted species, living from approximately 520 mya until they died out at the great Permian mass extinction around 250 mya.
It is generally known that the most important remnants of the Cambrian animal explosion are found in the Burgess Shale, discovered in 1909 by Charles Wolcott of the Smithsonian Institution in the Canadian province of Alberta. Here, with the presence of more than 150 species, is the evidence of the Cambrian explosion of life. The Burgess Shale is notable not only for the number of species but also for the fossil remains that include rarely fossilized soft body parts.
But I’ve often wondered about the simplest animal forms? What did they look like? How did they relate to the Cambrian fossils of the Burgess Shale?
Enter the graptolite! When we first encountered this early colonial species, they didn’t visually impress. But the more we learned the more we thought our personal collection would be remiss without at least a few specimens of this animal group. For amateurs like ourselves, it took a while before we stumbled upon a place where the graptolites were plentiful enough that soon they will become part of our student collections! In the meantime, we are learning all we can about this early species and I’ll share bits and pieces of this learning over the next few blog posts.
As I began my research, the graptolite got my attention when I learned that it belongs to the phylum Hemichordata. Remembering my early days with the Montessori Chinese Box of the Animal Kingdom, I was excited to now have an animal I knew as part of this phylum. Scientists place it as an extinct subclass of the class Pterobranchia, a group of worm-like animals that live in tubes on the floor of the ocean. They are filter feeders.
So far in my studies, the most interesting fact is how they got their name. Based on Greek root words, the name literally means “written on rocks” (graptos: “written” and lithos: “rocks”), aptly chosen because the fossil remains look a lot like hieroglyphs. They were discussed, drawn and labeled by Linneaus as possibly plant fossils or crusts formed on rocks that merely resembled fossils. The new fossils we’ve found are truly beautiful “pictures” of real, simple, early animals that got their start in the middle Cambrian period.