As a reward for winning our
Winter Trivia Contest,
Carla has requested a "Top Five Extinct
Crocodilians" post, and I was all too happy to oblige (but sorry it took so long)! Let's face it: living crocodilians are pretty awesome, and their extinct cousins? Even MORE so! And although some of the creatures that we will look at in this Top Five list may not be crocodilians by the strictest sense of the term, those that don't entirely fit the bill are very closely related. These "almost crocodilians," as well as the actual crocodilians, are all from a group of
reptiles that we call the
archosaurs. Archosaurs include many fascinating animals, including the crocodilians,
pterosaurs,
dinosaurs, and
birds, as well as their extinct ancestors. Some of the members of this list are critters that look a whole lot like crocodilians, but just weren't quite there yet, as most sources state that modern crocodiles did not evolve until the
Late Cretaceous. Some people refer to this large group of crocodile-like creatures, as well as the crocodilians and their ancestors, as "pseudosuchians," which is what is used to describe the first few animals that we are looking at today!
1. The phytosaurs are the first of these "pesudosuchian" groups. Although at a glance they look pretty similar to the modern day
Indian gharial, the phytosaurs lived in the
Late Triassic, right around the time that dinosaurs were first evolving too, about 200-220 MYA. We still have nearly 150 million years before the appearance of modern crocodiles! As you can see below, the phytosaurs definitely resembled the later crocodilians in many ways, but they were different, too. Just look at how far back on the skull those nostrils were!
2. Our next pseudosuchian is one of my favorites, named
Desmatosuchus. A member of the extinct group called the
aetosaurs,
Desmatosuchus was actually an herbivore! As you can see on the back of this animal,
Desmatosuchus is yet another one of those fascinating creatures that has evolved
dermal armor, similar to the
armadillo and the
ankylosaurs! The giant shoulder spikes of
Desmatosuchus definitely look a whole lot like those of the ankylosaurs, and served a similar defensive purpose. If you traveled back to the Late
Triassic period, you would have been able to find
Desmatosuchus in the southern
United States.
3. While
Poposaurus definitely looks a lot like a dinosaur, just like
Desmatosuchus and the ankylosaurs, this is simply another fascinating example of
convergent evolution!
Poposaurus, just like
Desmatosuchus and the first dinosaurs, lived during the Late Triassic Period, about 225 million years ago. For whatever reason, it was the poposaurs and not the dinosaurs that went extinct at the end of the Triassic Period. Apparently, the Triassic town wasn't big enough for these two groups of bipedal reptiles.
4.
Postosuchus, a member of another group of pseudosuchians called the rauisuchians, looked a lot like
Poposaurus, as this critter also is thought to have been able to walk on its hind legs.
Postosuchus and
Poposaurus also both lived at the end of the Triassic, and both disappeared in the mass extinction event that jumpstarted the
Jurassic. Apparently, when it was first discovered,
Postosuchus was thought to be a
tyrannosaur ancestor, an understandable mistake once you look at the skull of this creature!
5. This next crocodilian seems like a bizarre medley of different animals and, in some ways, it kind of is! Meet
Dakosaurus, a member of a group of extinct crocodilians called the metriorhynchids. The metriorhynchids display numerous physiological adaptations that suggest they were quite comfortable in marine environments, such as paddle-like front limbs, hypertrophied nasal salt glands (presumably to help keep the body from getting an excess of salt), and a hypocercal tail.* Unlike many other crocodilians, the metriorhynchids evolved sharp, serrated
teeth, similar to those seen in terrestrial predatory dinosaurs. These marine crocodilians also lost their dermal armor over the course of evolution, the tough, bony scales and scutes on the backs of modern day crocodiles that help defend them against attack from predators or other crocodilians. Presumably, this lack of dermal armor would have helped make the metriorhynchids even more hydrodynamic.
Dakosaurus has been discovered in
Europe,
South America and
Mexico, and lived during the
Late Jurassic and
Early Cretaceous.
*As you can probably tell from the complicated words used in these descriptions, the "hypertrophied nasal salt glands" and "hypocercal tail" are both direct quotes from the paper describing
Dakosaurus (click
HERE to check it out). I had a tough time determining the exact meaning of the term "hypocercal," but as I understand it, it is a condition seen in many extinct fish and other marine creatures, in which the vertebral column bends downwards in the tail, (as you can see in the picture of
Dakosaurus above), as opposed to where the vertebral column bends upwards, or simply doesn't protrude very far into the tail to begin with. Amongst other creatures, the
ichthyosaurs seem to have a very similar tail design, as you can see below. I'm not certain what, if any, the distinction is between hypocercal and reversed heterocercal; either way, this sort of tail definitely seems like it would be a good adaptation for swimming!
Works Cited:
