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Thanks to this month’s Eontologists: Jake Hart, Jon Ivy, John Davison Ng, and Steve. If you’d like to join them in supporting us, go to Patreon.com/eons and make your pledge! In 1824, French naturalist Georges Cuvier became the first scientist to describe a strange specimen of an extinct crocodilian. But even he had no idea how truly odd this animal would turn out to be. The specimen was from central France and consisted of just a few teeth and bones, enough to tell that it was some kind of croc-like reptile, but one unlike any that had ever been discovered. Cuvier noted that the teeth were flat and serrated, completely different from the cone-shaped teeth found in modern crocodilians. This reptile seemed equipped more for biting through flesh, than grabbing prey and pulling it into the water, as many crocodilians do today. Cuvier described this animal as “the crocodile from the Marl of Argenton” which sounds a lot more regal in French. Today this animal is known as Boverisuchus. But it wasn't until almost two centuries later that the full body of this strange reptile was finally pieced together, revealing that those flat, sharp teeth belonged to one of the weirdest members of the order Crocodilia ever found. For one thing, its legs were much longer than those of most crocs today. And its hind legs were a lot longer than its front legs.
Plus, instead of claws, its toes were each capped with … hooves! -- much like those found on early horses at the time. So, yeah! There once was a crocodilian with hooves that could run down prey on land And some researchers think that it had another, even stranger ability, although other’s aren’t so sure. Now, how did this living nightmare, this “crocodile from the marl,” come to evolve? Basically, it’s the product of a whole lot of family competition. When I say Boverisuchus was a crocodilian, I don’t mean that it was a crocodile. But it was a member of the same Order as crocodiles, which is known as Crocodilia. And anything within that order, including modern animals like alligators and caimans, are called crocodilians. And members of the order Crocodilia have been around in one form or another since the late Cretaceous, around 100 million years ago. But after the extinction event at the end of the Cretaceous, the non-avian dinosaurs and other large archosaurs were gone. And that’s when crocodilians really began to diversify and flourish, taking on many of the niches that those animals had left empty. One such group of enterprising reptiles was the now-extinct family known as Planocraniidae , a group of crocodilians that are characterized by living mostly on land, instead of in the water, and having those strange blade-like teeth.
Planocraniidae first showed up in the Paleocene Epoch about 61 million years ago, starting with a species from China known as Planocrania hengdongensis . But the family soon spread and diversified. And by the middle of the Eocene Epoch, around 50 million years ago, its members could be found running around Germany and North America -- including the most widespread of them all: Boverisuchus. No matter where it lived, Boverisuchus usually wasn’t the only crocodilian around. And that might have been one of the driving evolutionary forces that turned it into the nightmare fodder that it became. After all, when a lot of carnivores are in the same place, it creates competition. And when that happens, sometimes you have to do something a little different to set yourself apart, in order to survive. A good example of this phenomenon is recorded in the coal-bearing layers of the 48-million-year old fossil site in Germany known as Geiseltal . This layer of swampy sediment preserves the bodies of 4 different genera of crocodilians, in addition to Boverisuchus. There was Asiatosuchus , which was nearly 3 meters long; the medium-sized Diplocynodon; and the tiny pug-faced Allognathosuchus at just over half-meter long. Studies of the teeth and skulls of these crocs showed that each genus had adapted to its own ecological niche.
Asiatosuchus, for example, was the biggest and ate large fish and sometimes ambushed mammals that came to drink from the swamp. But Diplocynodon ate small fish and frogs. And Allognathosuchus was more likely eating small invertebrates, like crayfish. But all three of these crocodilians were aquatic, or at least semi-aquatic. They had short legs, and long, fin-like tails. They weren’t built for running after prey on land. And there were some predators on land, but not nearly as many as you might expect. 48 million years ago, bears, cats, and dogs hadn’t evolved yet. Which means that a large niche for a predator had been left empty. And the land was full of potential prey – from big terrestrial birds to little, dog-sized horses. So any crocodilian that could take advantage of that wide-open niche on land would have a better chance of thriving, especially when there were already three other kinds of crocodilians patrolling the waterways. Ok but then how did Boverisuchus come to fill that niche? How did its ancestors become this running, razor-toothed predator? Well, the fossil record doesn’t really help us there. In the United States, Boverisuchus shows up fully-formed and ready to run in the early Eocene. It appears in the fossil record nearly simultaneously, about 55 million years ago, in Texas, Wyoming,
and Utah, before spreading to Europe. And there’s no sign of the ancestor that would eventually lead to Boverisuchus. But we can find clues to its origins by looking at some of its modern relatives. Because, the fact is, not all modern crocodilians are bound to the water. Some of them still do hunt on land – like one known as the smooth-fronted caiman. This caiman isn’t closely related to Boverisuchus or the other Planocraniids. But it does have a similar lifestyle. Not only does it tend to hunt on land but, like Boverisuchus, it can sprint for short distances. It even has teeth that are a bit more blade-like than other crocodilians’. So researchers think that whatever Boverisuchus descended from probably looked and behaved a lot like today’s smooth-fronted caiman. And that ancestor would have been primed for natural selection to increase its speed and biting power, making it better suited to life on land. Now, one key to that transition was in its teeth. Those flat, serrated teeth that Boverisuchus and other Planocraniids had are known as ziphodont dentition, and it made a big difference in how they could take down big prey. Many modern crocodilians drag their prey underwater. So they have conical teeth that can clench their prey in their mouths as they drown it. Which is..not how I want to go But terrestrial crocodilians needed sharp, slicing teeth to help them inflict a lot of
damage in single bites, killing their prey more quickly. Which is...not a better option Now, another adaptation that gave this reptile a leg-up for life on land was … its strange legs. Like I mentioned before, the legs of Boverisuchus were much longer than a typical crocodilian’s. And its back legs were longer than its front legs. And this is where things get even more interesting. And … pretty controversial. If you’ve ever heard of Boverisuchus, or heard of it by its other, older name, Pristichampsus, then you might have heard that this reptile had a very strange ability indeed: the ability to run on just two legs. On some TV shows and websites, it’s been depicted as being facultatively bipedal, meaning that it could at times, carry itself on its hind legs, so it could run even faster on land. This ability was proposed by a researcher in Germany, who thought that its unusually long back legs might have made this possible. After all, many reptiles with a body plan like this are capable of running on their hind legs, like basilisks and collared lizards. And if Boverisuchus really could have run on two legs, I’d be the first to say that it would’ve made this animal even more terrifyingly awesome. Or, awesomely terrifying? But we talked to a couple of experts in ancient crocodylians, including Dr. Christopher Brochu,
who re-classified Pristichampsus as Boverisuchus. And he and others are not at all convinced. They argue that the limb proportions of this animal aren’t nearly as extreme as they are in modern bipedal lizards, and that its center of mass was also too far forward for it to have been able to raise its upper body. If Boverisuchus wasn’t bipedal, I’d have to say I’d be disappointed. But also somewhat relieved? And in any case, Boverisuchus did have one more undisputed and equally unusual trait that helped it master life on dry land: its hooves. Most crocodilians have pointy fingers that are tipped in claws. But the claws of Boverisuchus were rounded and blunt – much like hooves. Pretty much the only difference between the hooves of Boverisuchus and the hooves of its prey, like early horses, was that its hooves were a little narrower. So with its hooved hands and feet, it would’ve been much better at pushing off the ground and adding bursts of speed to catch its prey. And the fossil evidence suggests that these running crocodilians were quite good at what they did. Several horse fossils found at Geiseltal in the 1950s appear to have crocodilian teeth embedded in them. And at another site in Germany, there’s even a primate jaw with bite marks and teeth that show evidence of going through the very acidic digestive tract of a crocodilian.
But despite the many adaptations that Boverisuchus had at its disposal, we don’t have any toothy, hooved, running crocodilians today. And I'm going to count that as a positive The last of the planocraniids, a species known as Boverisuchus vorax, went extinct between 40 million and 45 million years ago. It was, as they say, the end of an era -- but also the beginning of a new abundance of mammalian predators. The earliest members of the order Carnivora prowled the land around this time, as did the creodonts - an odd group of mammals that seemed at once catlike and doglike, though they weren’t actually related to either. It’s not clear whether these warm-blooded animals outcompeted the running crocodilians, but it’s possible. And a big environmental change was also underway in the last half of the Eocene, thanks to the chemistry of mountain-building. Earlier in the Eocene, the collision of the Indian Plate with the Eurasian Plate created the Himalayas, and the slow weathering of these new mountains gradually removed Carbon Dioxide from the air. These and other plate movements also changed the circulation of air currents, and together these forces caused the climate to cool. Crocodilian ranges started to shrink, retreating from as far north as Wyoming to areas closer to the equator. So perhaps Boverisuchus, in cooler weather, simply couldn’t compete with all these new
mammalian predators. Ancient Crocodylians like Boverisuchus owed much of their success to the competition that took place within their own family, which drove their evolutionary development after the extinction of the non-avian dinosaurs In the case of Boverisuchus, that resulted in a crocodylian that could run on land, on hooved feet. But when faced with competition outside its family, in a rapidly changing world, in the end, even this speedy reptile couldn’t keep up. Thanks for joining me today in the Konstantin Haase studio! And you might notice that I'm wearing our first ever Eons shirt. Complete with a pocket And you can find them at DFTBA.com, the link is in the description Now Boverisuchus was a fascinating reptile, but you haven’t seen anything until you’ve learned about drepanosaurs and the other strange reptiles that were unique to the Triassic. And you can do that right here!
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