Alligators? In the sewers?

17 08 2007

I’m sure this is going to come as a huge shock to you all, but I was absolutely enthralled by dinosaurs as a child. The problem was, however, that the only place that they still “lived” was in my imagination, some dark corners, and maybe in a museum basement somewhere. Living crocodilians, however, were the next best thing, and one of the first movies I ever remember seeing was the John Sayles-penned 1980 horror flick Alligator, which utterly terrified and mystified me. Part of my reaction to the film probably was due to being a kid (“Why can’t alligators be living in the sewers?”), but a far greater part of my fascination was reinforced by paleontology. Even before seeing the wonderful b-film, I had come across black-and-white photos of Deinosuchus (formerly Phobosuchus) from the American Museum of Natural History, and the prospect that there were once enormous crocodilians that could swallow you hole (as in one memorable scene in an alley in Alligator) seemed very real.

Deinosuchus

Unfortunately, I don’t think I ever got to see the huge skull of Deinosuchus on display, and the skull is no longer on exhibit in the fossil halls of the AMNH. Looking up the paper describing the reconstruction the AMNH scientists had made, there seemed to be surprisingly little material from the skull of the giant crocodilian, most of the skull actually being a conjecture as to what the animal looked like in life (something like a Cuban Crocodile, Crocodylus rhombifer). This doesn’t mean that there are no giant toothy creatures in the display cases of the AMNH, however, and one of the most impressive “near-crocodile”* specimens is the skull of Machaeroprosopus gregorii.

*To the best of my knowledge no one is calling phytosaurs “near crocodiles”, but I think it’s an appropriate pop-monkier for them to help remember their overall close relationship despite their differences.

Giant Phytosaur
The gigantic (4′ 8″ long) skull of Machaeroprosopus gregorii, from Colbert et al., 1947. Studies of the phytosaurs Machaeroprosopus and Rutiodon. Bulletin of the AMNH ; v. 88, article 2

Part of the confusion surrounding phytosaurs is that they look so much like modern crocodiles even though they are not. Much like nimravids and true saber-toothed cats, phytosaurs and crocodiles share a close common ancestor, but there are some minor (but important) differences that separate the groups. Outside some features like a more primitive ankle structure, one of the sure-shot ways to tell you’ve got a phytosaur on your hands is if I has its nostrils back on the skull just above or just anterior-to the eyes, as is the case with Machaeroprosopus (and the obligate popular paleo-book inclusion, Rutidon). Although these animals seemed to have some measured success living in the semi-aquatic niches they occupied, they left no living descendants, dying out at the end of the Triassic. Crocodiles as we know them today, by contrast, would not appear until the Cretaceous, their ancestors occupying almost entirely terrestrial or marine niches.

What is interesting about the AMNH Colbert et al. paper is that it puts forth some hypotheses about the many “species” of Machaeroprosopus found in one particular area. Rather than representing various species evolving over time, it seems more likely to the authors that various stages of life of the giant phytosaur are represented, although the other specimens are not illustrated for comparison. Further, the authors contemplate some variations in the “robustness” of the skulls and prominence of perceived nasal ridges, which would seem to suggest some sort of sexual dimorphism. I’m a bit dubious about which would end up being the male or female (naturally the females are attributed the more refined or less-prominent characters), but they could be on to something there. In fact, such sexual differentiation based on visual cues would have been important, as recent research has suggested that phytosaurs (like many extinct archosaurs) could not have smelled, and therefore used, pheromones to find mates, define boundaries, etc. (Senter, 2002). After a quick search for papers, however, it seems that Machaeroprosopus has been all but forgotten, little to no resolution coming of the growth series of the Chinle Formation or possible sexually-selected characters. This lack of information, however, does leave open the door for anyone interested enough to pick up the trail, and I certainly hope that someone does.

Update: And I nearly forgot to say that this post was initially inspired by a story that Walt of the ever-wonderful Prehistoric Pulp mentioned today called “Gator” by Robert J. Sawyer. I would have much rather seen a Deinosuchus making its way through Manhattan sewers, but it’s a quick read if you’re into paleo-oriented SF. Be sure to check out some of Walt’s other recommendations, too.

About these ads

Actions

Information

7 responses

17 08 2007
Zach Miller

Really, when you really look at their skulls, phytosaurs are quite different from crocodilians. Wonderful animals, though, that figured out the modern croc lifestyle about 200 million years before it was cool.

17 08 2007
laelaps

Very true Zach; as I was looking at the picture I was noting all the bones right underneath the eyes in Deinosuchus that make up the palate and other parts of the back of the throat, especially the bones that slide against each other at the back of the mouth. Phytosaurs lack these specializations, and I would have made more of a point of it if I knew the names of those bones. I’ve still got a lot of anatomy to learn, but phytosaurs are indeed wicked buggers.

17 08 2007
DoubleW

That’s one big near-croc. And I was pleased to see you had already pointed out the nimravids, which I first encountered after reading The Big Cats and Their Fossil Relatives. To me, both have always represented “what ifs” of evolution. What if circumstances were different enough that we had phytosaurs today instead of crocs, or nimravids instead of true cats? What made these animals different enough that they didn’t make it? I admit that’s a simplistic take on evolution and the causes of extinction, but still, these questions have always interested me.

I remember watching Alligator as a kid also. Most of it anyway — didn’t make it past the kid in the swimming pool bit. Too scary. And given my parents had a swimming pool, let’s say I carefully checked the water every time I dived in for the next few days.

18 08 2007
laelaps

Phytosaurs and nimravids definitely are interesting, and I don’t think they get the popular attention they deserve. They are every bit as weird and wonderful as their more well-known counterparts, but I think part of that problem deals with historical science. Some nimravids (at least the most famous ones) were often lumped in with true saber-toothed cats for a while, and phytosaurs looked so much like crocodilians that many popular mentions of them never went beyond “That’s a phytosaur.” In the phytosaur/crocodile relationship it’s easier to understand why we have crocs today because there was a lag time when neither group was really occupying the semi-aquatic ambush predator niche, but as for nimravids, I really am curious why they didn’t make it.

As for Alligator, that movie definitely scared me. The scene in the alley when the “Great White Hunter” gets ambushed and swallowed whole always gave me nightmares, and some nights I would freak myself out thinking that I could hear the giant animal breathing just outside my room on the 1st floor of the house (if it could break through a sidewalk, why not a wall?). Crocodilians still scare me more than most animals, probably because they drag their victims into an alien environment in a vise-grip (which is hard to escape), and that they are one of the few animals that make no apologies about consuming people. I’m sure part of it as a mammalian bias, but I definitely would feel more comfortable around land-based predators than those at the water’s edge.

18 08 2007
johannes

Nice post on magnificent animals, that sadly don’t get the attention they deserve. Machaeroprosopus/Smilosuchus must have been the largest land (or at least semiaquatic) animal of its time.

> After a quick search for papers, however, it seems
> that Machaeroprosopus has been all but forgotten,

Perhaps using the alternative name Smilosuchus will be helpful. I don’t know which name has priority, but the use of Machaeroprosopus seems to have fallen out of fashion nowadays.

> Crocodiles as we know them today, by contrast,
> would not appear until the Cretaceous, their ancestors
> occupying almost entirely terrestrial or marine niches.

The lack of large jurassic freshwater predators outside southern Gondwana, where the temnospondyls still held sway, is very irritating. Such animals are usually among the most common fossils. They live in swamps, where the chance for fossilisation is good, and they are large and often armoured, with many hard parts. Phytosaurs are so common that they are used for biozonation. Could you really splash around in a Jurassic laurasian lake or river without encountering anything more dangerous than the poisonous spurs of a docodont (and even Castorocauda was probably from the lower Cretaceous rather than from the Jurassic)?

> but I definitely would feel more comfortable around
> land-based predators than those at the water’s edge.

Some of the ziphodont land-crocs where quite frightening, too. Another group of animals that is often sadly forgotten, because the public concentrates on dinosaurs and mammals (not that there is anything wrong with dinosaurs and mammals). But in a fight between Lybicosuchus and a dromaeosaur of similar weight, my money would be on the sebecid; one bite in the thorax of the feathered creature, and its lungs and air-sac system collapse…

18 08 2007
Hairy Museum of Natural History » Picking through The Boneyard

[…] which somehow missed out on inclusion in The Boneyard. I particularly recommend the bit about phytosaurs. File under Miscellany. Posted by Matt Celeskey round about 8:27 […]

27 08 2007
Protosuchus « Laelaps

[…] discussed in a recent post about Phytosaurs (creatures that occupied the niche crocodiles do today, only much earlier) however, crocodiles as […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s




Follow

Get every new post delivered to your Inbox.

Join 25 other followers

%d bloggers like this: