This week’s fossil is one of the simplest to draw, but one of the most important in Earth’s history: Graptolites.
If you’ve ever seen thin, zig-zag lines or tiny saw-blade patterns in black shale, you’ve probably found a graptolite. They lived over 400 million years ago, floating through ancient oceans, or attached to seabeds, in colonies that looked like little combs of various shapes.
They might not look all that impressive, but graptolites are a palaeontologist’s dream. Because different species evolved quickly and all across the globe, they make for great age markers for the rocks they're in, so we can date the rock really quite accurately by which ones are there. A thin squiggle in the rock can tell you exactly which slice of the Paleozoic you’re looking at. (Not that I could interpret that code myself though without a very good reference book)
Now although they may look like simple 'scribbly' combs, these things were pretty complex, and not just a single creature. Each “tooth” was the opening of a tiny living chamber, with tiny organisms called Zooids living inside making up a whole colony of them inhabiting the skeletal structure that we see in the rocks today.
Fun fact: The name graptolite means “written in stone,” because early geologists thought they looked like fossilised pencil marks. Quite apt that today I've just sketched one in pencil
