F is for Fossil

Fossil of plant-eating teeth, Morrison museum, photo by kajmeister

Fossils never excited me. Skulls do, but I could never find the thrill of a 1000-year-old imprint of a leaf. Imprint of a 200-million-year-old feather? Now you’re talking. Yet we wouldn’t know anything about the world that came before, without fossils. Everything we know about dinosaurs comes from fossils. You don’t get to know what T-rex ate, how a diplodocus withstood attack, how hadrosaurs laid eggs, or where the sauropods walked — without fossils. Fossils are the artifacts, the archive as the historians say, which prove that there was life before humans.

And they’re not really even bones.

Theseus’ Paradox

There’s a famous Greek philosophy idea about Theseus’ ship. Theseus sailed out to the island of Crete and slew the minotaur in the maze, plus had many grand adventures, which is why Athens was named for him. The story goes that the ship of his odyssey (no, that’s another guy) was put on display as a monument. Over time, the wood rotted, so a plank was replaced here, then there, then the mast…. Over a long time, all of the wood in the ship was replaced.

Theseus ship paradox. Graphic from Youtube.

So was it the same ship?

Is the ship the idea? the shape? or was it the physical ship? And what if the ship didn’t look entirely the same? The Internet, in some cases, says “yes, most definitely is the answer,” but this is a Greek zen koan. Not meant to have a simple answer. Another later philosopher, Thomas Hobbes, then wondered, if you gathered up all the discarded planks from the original ship and built another ship — was that Theseus’ ship as well?

If you’re thinking this has nothing to do with fossils, think about Diplodocus, plaster casts, and the fossils. Fossils are very much like Theseus’ ship.

Fossil Bone (Not Bone Bone)

There are several kinds of fossils, but the ones we most think about are the fossil bones. These are the fossilized remains of skulls, hips, teeth, claws from the original creature. This kind of fossil bone is created through permineralization, typically four steps. First, the dinosaur needs to die in a soft substance, like mud or sand at the bottom of a river. The bones need to be sheltered from wind and predators, which might erode it or rip it apart. It needs to decay carefully.

Muscles and flesh rot fairly quickly, although there have been a few cases where soft matter like skin and feathers–yes, feathers–get preserved if the mud dries a certain way. Even though bones are hard, they have blood vessels and organic tissue as well. Even at the cellular level, there is gas and air bubbles, which have openings. Between openings in the bones, cells, and blood vessels, there are places for minerals to be deposited. Mineralized water seeps into the openings and fills the holes, as the other organic matter decays. Over time, a long time, the mineral hardens and turn to rock, but it preserves a three-dimensional copy of the original dinosaur.

Preserved Camasaurus fossil, Quarry Exhibit, Dinosaur Nat’l Monument. Photo by kajmeister.

Fossils, then, are like a photographic negative of a dinosaur. They’re not bones; they’re rock. Fossil bones, as the scientists say. Arguably, they aren’t where the original bone was either–they’re where the original holes were in the bone. Close enough for scientific analysis. But like Theseus’ ship, they are a perfect copy of the original dinosaur skeleton, and not the original dinosaur skeleton.

So for the purists who only want to show original Diplodocus “bones” and not copies, those are neither bones nor originals.

By the way, the Quarry Exhibit at Dinosaur National Monument near Vernal, Utah and Grand junction, Colorado has amazing preserved fossil bones. If you like the dinos, that’s a bucket list trip for you, along with the Royal Museum in Alberta, the natural history museum in Albuquerque etcetera etcetera.


Still, perfectly preserved fossil bones are pretty cool. Almost any organic matter can be fossilized, and the more quickly the dinosaur was buried in the right kind of conditions, the more intact the fossil may turn out to be, like these gorgeous claws (I forgot to look up what kind, but predator most definitely.)

Fossil claws, photo by Mehmet Kaman.

Fossil bones are one kind of fossil, but there are tons of other kinds of fossils which carry the stamp of what the original animal was doing. These are “trace fossils,” i.e. traces of what the critters left behind. Ichnology is an entire branch of “ology” devoted to studying traces of what animals left behind.

A literal example of a stamp can be seen at the Dinosaur Ridge Trail in Morrison, Colorado. Here was where the sauropods trod through the mud. In this case, their footsteps sank deep into one kind of mud. The other kind of soil underneath eroded away and changes in geology exposed the rest to air. So we can see places where the dinosaurs walked.

Tramp of the sauropod feet, Dino Ridge Trail, CO. Photo by kajmeister.
Fossil footsteps, Dino Ridge Trail, CO. Photo by kajmeister.

Dinosaur footprints would be preserved in a different way. The mud that the dinos walked in has to be a harder dried soil than whatever fills it. The footprints get covered with sand, pebbles, or some other soil that is simply softer than where the print lay. Over time, yadda yadda, erosion, uplift, and bob’s your uncle, we can see the footprints.

Uplift isn’t related to fossils, but it’s a pretty important geological idea that helps scientists and tourists find dinosaurs. Fossils are buried. They’re buried all around us underneath layers and layers of rock. The only reason we know they exist is that in some parts of the world, mountains formed after the animals lived and died. The Rockies are a relatively young set of mountains and, as parts of them formed after the dinosaur age, they pushed up the fossil beds sideways, exposing them to any passing motorist. That’s why there’s all this dinosaur hunting in Colorado and Wyoming. There are similar places in Asia and South America where fossil beds have come to light partly due to uplift.

The Coprolite Industry

Almost any part of an animal could, in theory, be fossilized. Feathers might be imprinted in the right kind of mud, and eggs certainly have been found. Rock eggs of course. Fossil eggs.

Even coprolite has been found; coprolite is the sciency word for dinosaur poop. I’m not going to go much into the detailed biology of this, but theoretically the organic matter just needs to be more solid than whatever preserves it. Mineralization replaces the air bubbles in the material and voila! preserved dino dung.

Authentic coprolite, from wikipedia. Note a deer toe preserved in the dinosaur dung.

It’s interesting that at one point in the late 19th century in Cambridgeshire in southeastern England, there was a thriving coprolite industry. That is, they found plenty of what they termed coprolite–dinosaur feces–and its phosphate composition which made it still useful as fertilizer. They dug it up and used it for farming.

Nowadays, there’s another thriving coprolite industry on the Internet. People sell fake dinosaur poop. (Of course they do, because anybody will buy anything, which means anybody will sell anything.) If you try to get information about coprolite, or an accurate picture of coprolite, there are tons of fake sales offers out there. On the chat sites, people keep showing pictures of coprolite they bought, or are considering buying, and being told !Nope! Without confirming its composite of phosphates or seeing bits of digested animals inside, it would be very hard to tell.

No matter what, even authentic poop isn’t actual poop. It’s only a copy. If you made a cast of authentic coprolite, would it still retain the essence of dung? Wonder what Thomas Hobbes would think of that.

Archaeotpteryx fossil, note the feathers. Photo from Youtube.

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