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What is the world's favorite fossil? Why the orthoceras of course! Hank will tell why that is in this episode of SciShow. Find out how you can get your very own orthoceras fossil.

Hosted by: Hank Green
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If you're a fan of fossils, and I don't see why you wouldn't be, then you've probably seen one of these. It's the fossil of the shell of a skinny little cephalopod that lived nearly half a billion years ago. I'm holding it in my hand! That's crazy!

Today we know it as a method of the genus Orthoceras, and ever since scientists found a whole passel of these puppies in the mountains of Eastern Europe back in 1820, people have been captivated by them.

They're kind of funny looking, but they're very pretty when you polish them down, and in some parts of the world they seem to be everywhere. So let me tell you a little bit about the history of Orthoceras and how you can own a little piece of that history for yourself! 

Orthoceras lived in the massive primordial seas that covered a bunch of the Earth more than 450 million years ago. Paleontologists now know this time as the Ordovician era, but for most of the planet back then it was more like an eon long hangover from the giant underwater party that was the Cambrian Explosion - a huge blossoming of life that occurred more that 500 million years ago.

During the Cambrian the world’s oceans began to teem with life and many of the animal phyla that exist today came into being. And with all that competition for resources all sorts of awesome new evolutionary adaptations came along; claws and pincers for predation - which became a thing for the first time - and on the defensive side, shells!

That's where Orthoceras came in. As one of the earliest known kinds of cephalopod, called a nautiloid, whose few, living, direct descendants today include the nautilus. As its name, which means "straight horn", suggests, they had a long, narrow shell that probably made them look like floating squid-cream cones. But during the Ordovician they ruled the seas!

They were generally small, probably no more than 15 centimeters or so. They were mobile, and they were fast. And all this made them quite capable predators, thank you very much, so they likely ate stuff like plankton. They also probably fed on larger bottom-feeding animals, like those trilobites, and despite what you might have seen in some out-dated museum dioramas, Orthoceras didn't crawl around on the sea floor. It swam around, much like a modern nautilus, propelling itself with jets of water thrust from a feature called the siphuncle. Today if you get a good fossil specimen of them, you can actually see the siphuncle running down the length of the fossil, which I can actually see a little bit right here in this one. That's pretty cool.

So, how did these ancient trilobite-feasting squid-cones become one of the world's favorite fossils? Well, first of all, they are abundant. In some places where their fossil remains are commonly found, like Sweden and Morocco, their fossils are discovered hundreds, sometimes thousands at a time in a single place. For a long time this lead paleontologists to believe that Orthoceras were the victims of some weird confluence of sex and death, and that they all keeled over in huge mass die-offs after mating, which is sometimes seen in modern octopus and squid. But more research has shown that these big fossil beds are more likely the result of the animals dying over hundreds of millennia, their remains settling in layers with very little sediment in between. And of course it all makes sense that Orthoceras are so prevalent in the fossil record because, just like ammonites and trilobites, they had shells.

When they were alive their shells were made of a kind of carbonate called aragonite. Sometimes these shells stuck around long enough to fossilize into calcite. Other times they just lasted long enough to capture sand and soil and other sediments which fossilized into the shapes of all the chambers of the animals’ body. So, when you look at an Orthoceras fossil you're really, often, looking at a kind of mold of the animal's insides, all made of stone.

Now, if you'd like an Orthoceras fossil all your own, signed by yours truly, just head over to to subscribe, and if you have any questions or ideas for us please leave them in comments below or on Facebook and Twitter. Thank you for watching and continuing to get smarter with us here at Sci Show.