Chalk another one up for Evolution; “Limbless” Lizard

26 03 2007

It seems that there are just as many new and exciting discoveries buried in dusty museum cabinets as there are still buried in the ground, and such is the case with Adriosaurus microbrachis, sitting for nearly 100 years in the Natural History Museum in Trieste, Italy. What’s bizarre about this aquatic lizard is that it had large and normally functioning rear limbs, the front limbs being lost first, and I would imagine the rear limbs would remain longer as they would aid in propulsion. While the scientists who discovered this creature have said it doesn’t count as the transitional form between lizards and snakes, it does shed some light onto how the change may have happened or manifested itself, and hopefully more research will find some of this creature’s kin.

I haven’t seen any images of the actual fossil as yet, but I am a litte put off by the reconstruction the LiveScience article provided. The reconstruction was likely done according to parsimony and available data (thanks to John for calling me on my error), it seems to have the transition from lizards to snakes in mind (especially in the rendering of the stomach scutes and flat, squarish head). I am not suggesting the drawing is bad, should be thrown out, or disregarded, but I do get an overall snake-like impression from it and I would have much preferred to see a photograph of the actual fossil.

I’m also amazed by how many fossils have been misidentified, misnamed, misplaced, etc. I would love to go through the massive collections of the American Museum of Natural History or other establishment in search of more hidden creatures (I’m sure hordes of graduate students could find plenty of thesis material in those archives), and it seems that these days we have more fossils than we know what to do with. Part of the tangled web of fossil animals also stems from the early days of fossil hunting (at least in America) where the goal was to name as many species as you can as fast as you can, a mess that is likely to confound paleontologists for some time to come. As I have frequently (often in exasperation) there is simply too much to know.




2 responses

26 03 2007
John Scanlon

You said:

The reconstruction was done with the transition from lizards to snakes in mind, and it seems that the idea biased the artwork a bit (especially in the renditing of larger stomach scutes and flat, squarish head).

The method of reconstruction is based on parsimony, using the closest available relatives to predict (interpolate) the missing bits of A. microbrachis. Heads, necks and skin impressions including expanded belly scales are known from other Cretaceous species of adriosaurs and dolichosaurs, so I don’t think you can infer a bias. Unless you would prefer a bias AGAINST adriosaurs being transitional to snakes? But how would you draw that??

26 03 2007

Hi John. Like I said in the post, the only thing that I’ve seen is the reconstruction and I’m always a little leery of reconstructions that seem to infer evolutionary links when I haven’t seen the actual fossils. I didn’t say the drawing is bad (and I’ll change my wording in the post to clarify things to make it clear this is my opinion) or wrong per se, but just my own skepticism when it comes to reconstructions; I would have much rather seen photos of the fossils to get a better understanding of what this animal looked like. Also, the article does not make it clear that this creature was a transition between lizards and snakes, but rather that its front limbs were highly reduced and such a pattern may illuminate how the transition from lizards to snakes occurred. If the skin impressions suggest certain scale patterns and other factors, then I have no quarrels with that aspect of the depiction, but I just try to keep on my toes when it comes to reconstructions in that they are merely that and I think it’s important to keep an open mind about how perceived lineages can influence reconstructions.

In this same vein, a painting of Proconsul from the American Museum of Natural History human evolution exhibit comes most immediately to my mind, being that it seems to have been drawn with a more human face than I had seen elsewhere. The same goes for the Austtalopithecene child Selam; reconstructions of her skeleton varied depending on what magazine you looked at. Again, I’m not saying that any of these reconstructions have no merit, are outright wrong, or should be discarded, but rather that in lieu of any image of the actual fossil I think it’s important to think critically about reconstructions of extinct animals. I’m not a very good artist (I wish I was) so I can’t say how I would draw the animal, but it does give me an overall snake-like appearance and from what the LiveScience article stated this animal does not seem to be a transition from lizards to snakes. Thank you, however, for your comments and I’ll edit my text to clarify things.

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