Thursday, February 1, 2007

Monkey-Lizards and Birds: One Strange Alternate Theory

Dear Constant Readers,

When I first saw a page about Monkey-Lizards, I thought they were just made up. They were areal and chameleon-like, but had bird-like heads and (occasionally) anteater-like claws. Coupled with the strange name, I thought that they were part of a Spec World type project. How wrong I was. I should learn never to doubt the Hairy Museum of Natural History again! Monkey-Lizards are part of the bizarre group Avicephala, Diapsid reptiles considered by some as the alternate point of origin for birds. While Dinosaur origins are well supported, I like the idea of alternatives such as this post by Darren Naish on an equally strange theory for primates being flightless animals. Sure, they're almost certainly not right, but that doesn't mean that they aren't thought provoking.

There really isn't too much information out there for the poor Monkey-Lizards on the Internet. The most informative pages out there are from the HMNH and this page on Triassic Reptiles (see here too). These animal are generally considered to be highly derived aboreal Diapsids, but there is also theorizing of them being gliders or even aquatic. Coincidentally, one of Bruce Champaign's "Sea Serpent" types is a aquatic chameleon-like creature, which I drew, even more coincidentally. But that's a story for a different day. These creatures also survived the Permian-Triassic extinction, making them considerable for Connor's Island, but again, a story for another day.

The point is, these were some very weird animals. They're Diapsids like most (or all) modern reptiles, and overall somewhat converge upon chameleons. The front limbs had the 3 vs. 2 opposable digits of chameleons, but others had no opposable digits, or a gigantic claw similar to that of a pygmy anteater. The hind feet were somewhat unusual in that some specimens had an opposable digit, while others did not. Apparently, this is a very weird instance of sexual dimorphism, possibly breeding related. The tail was not as flexible in the vertical plane as a chameleon's, but a large hook on the end of the leaf-shaped tail probably compensated for this. Instead of capturing prey with a long tongue like a chameleon, Monkey-Lizards had a fairly long and flexible neck to capture prey, and muscles attached to an odd hump on the back. Strange as all of these features are, the most notable is the head. Instead of being lizard-like or chameleon-like it is bird like or even pterosaur-like. The lacked a fenestra present on Pterosaur heads, but some have argued that it may have secondarily closed. What's that? A potential relationship?

Before I get too caught up, I'd like to point out that most of the reconstructions are I can't post them here. However, I think I still can give links to them. Vallesaurus. Dolabrosaurus. Hypuronector (aboreal). Hypuronector (aquatic). Hypuronector (skeleton). Drapenosaurus. Drapenosaurus (skeleton). Megalanacosaurus. Megalancosaurus skeleton. Another Megalancosaurus skeleton.

And here's a link to papers on Drepanosaurs/Monkey-Lizards.

So as I implied, there are some that ally the Pterosaurs with the group containing Monkey-Lizards, the Avicephala. It would make sense to link flying animals with aboreal animals/gliders (getting to that), but I think it is mostly based on head structure. It is lacking a fenestra, and bird-like heads have evolved in the bizarre Effigia. Again, more on that weirdo later I'd imagine. So I guess for the time being, Pterosaurs are still too derived to determine where their ancestry is from.

Oh yes, and as I implied, the Avicephalans are also home to the group of the oldest gliding reptiles. Coelurosaurus was all the way from the Upper Permian, and unlike modern gliding groups, didn't support itself with ribs, but bony dermal rods. Obviously a mechanism like this is separate from modern flyers, but it at least demonstrates the tendencies of the group.

Things get very interesting when Longisquama enters the picture. There is a lot of controversy here, so it's going to be hard to try and sum up. It is apparently an aboreal creature with what appear to be "feathers" coming up from the back. These "feathers" or modified scales may also have been used to glide. Problem is, this animal is from the Early Triassic, before birds or even dinosaurs. This animal is sometimes regarded as being an Avicephalan, but opinion varies. Some individuals consider this to be an archosaur (or archosauromorph), but others consider it to be an early...theropod dinosaur! And not only that, but it is also theorized to be ancestral to modern day birds!

Of course, this creates a very interesting situation. Some then theorize that some animals regarded as bird-like dinosaurs are not dinosaurs at all but...flightless descendants of birds, which aren't dinosaurs. So basically, something like Velociraptor or maybe even Therizinosaurs aren't even really dinosaurs, but weirdo descendants from Longisquama. Things like Allosaurus are apparently still dinosaurs that converged upon them. Who knows what Tyrannosaurus, which is more bird-like than Allosaurus but not as bird-y as Velociraptor. I never heard of any clear cut off line, and I think this is the Achilles' heel of the theory. In all likelihood, the people that theorized this were...a little over-enthusiastic in turning all previous thought on its head. But that's how science gets stronger, all the possible theories get questioned and the strong one prevails. Tantalizing bizarre flightless pseudo-dinosaurs may be, it probably belongs in the realm of fiction. See here and here for extensive rebuttals, and Wikipedia for links to the major papers and a good summary.

Bird evolution is very interesting and quite complicated, even disregarding these Avicephalans. There are probably going to be a few more posts on this in the future...but I'm going to have to read up on it a lot before I can talk even somewhat coherently. Stupid reverse-birds and all. Well, more posts in the future, who knows on what.



Caitling said...

Of course monkey-lizards are real, the wicked witch of the west had some.

Geez, this is a crazy blog. Far too many things turn into completely different things as time goes by.

I also think that you're one of the few people in the world who can say that they just "stumbled upon" these things, and I believe you. There must be a search engine completely devoted to the outrageously bizarre.

Caitling said...

Mmmm, tastes like monkey-lizard!

Matt Celeskey said...

Nice summary, Cameron, and thanks for the links.

If you'd like to use any of the Monkey-Lizard artwork, feel free...for posting on a blog, all I ask is that you credit and link back--which you've already got covered!