Happy National Fossil Day!
As a paleontologist-in-training, I get really excited about fossils, and often believe that everyone else should be as well. Fortunately, the National Park Service, as part of Earth Science Week, hosts a National Fossil Day, a nation-wide celebration of these magnificent traces of prehistoric life.
I think most everyone would agree with me that fossils are pretty cool; without them, we wouldn’t know about dinosaurs, after all. But besides looking cool in a museum, what do they really tell us? Turns out, a lot of things. For instance, climate change over geologic time. Some shelly invertebrates, including tiny microfossils like forams, have different shell compositions at different water temperatures. This gets preserved in the fossil record, and can be compared to living forams to calibrate a climate history for hundreds of millions of years, as these critters first appeared in the Cambrian and are still around today.
Other fossils give us clues to climate change in the past as well. For instance, there are fossil leaves from Colorado that are 64 million years old, with drip tips. Today, the only plants with drip-tip leaves are found in the tropical rainforests. Therefore, apparently, there was a rainforest in Colorado barely 1 million years after the dinosaurs went extinct. How cool is that?
Fossils also tell us about our evolutionary past. We can guess at how living things are related based on their genetic code, using “molecular clocks” to try to determine how long ago the last common ancestor of two groups lived. But it’s nice to be able to check if those phylogenies, evolutionary trees, are correct. Fossils are the best resource we have to do that. For instance, based on molecular data, humans probably diverged from the other great apes around 6-7 million years ago. We find the first hominid fossils… 6-7 million years ago.
Along the same track, fossils also tell us about groups we could have never inferred from modern species. I’m not talking so much about dinosaurs, here. We certainly wouldn’t have been able to guess at the full diversity of dinosaurs, but if you mentally cross an ostrich and a crocodile (which we know are distantly related based on molecular data), you end up with something that looks an awful lot like a Velociraptor*. But, could you ever imagine something like this swimming in the sea, based on modern creatures:
No, that’s not some conceptual alien from the methane ocean of Titan. It’s called Opabinia, and it lived in the Cambrian sea 500 million years ago. It left no living descendants, and lived with a whole host of other weird things. They’re all animals; past that, scientists have no idea what these things are, where to put them on the evolutionary tree. And that’s part of what makes paleontology so exciting.
So, if you’ve found any of this interesting, I highly encourage you to explore the Earth Science Week, National Fossil Day, and the USGS websites. Go learn what a trilobite, a Tully Monster, a cycad, and a Protoceratops are. Visit your local natural history museum. And enjoy National Fossil Day!
*As a note, crocodiles actually diverged from the dinosaurs well before the first birds- they are not in any way evolved from dinosaurs. They are just the most closely related reptile group alive today. Most likely, you don’t care, but as a paleontologist I want to make that clear. Back