Thursday Morning Notes

2 08 2007

And so work on my amorphous project currently known as Memoirs from Deep Time has really begun to get going. Rather than read another 100 pages or so of White’s history of science/theology, I sat down with a stack of papers about a foot and a half high (about 5% of all the papers I have yet to print off my hard drive and read) and read through/took notes on 9 of them, essentially collecting bits of data that I’ll later string together when telling the story of evolution. Perhaps the most enjoyable/interesting read was Ryosuke Motani’s review article “Evolution of Fish-Shaped Reptiles (Reptilia: Icthyopterygia) in Their Physical Environments and Constraints.” Admittedly I don’t know as much about icthyosaurs as I would like, but the paper is well-illustrated and it’s easy to see the changes in groups through time, especially concerning the addition of phlanges/digits and the movement of the tail kink backwards to form the crescent-shaped tail so famous in later forms.

Then only real question I had concerning the article was the treatment of sclerotic rings in the eye. There shutter-shaped rings are found in many well-preserved icthyosaurs, and the author proposes they were an adaptation to varying pressures while swimming. When swimming, positive force would be exerted on the front of the eye, negative force on the trailing edge of the eye, so there would be two different pressures that would have to be stabilized, perhaps by the sclerotic ring. While I have no problem with this as an adaptation (it might have worked), I don’t know if such a scenario caused the evolution of the character (what about sclerotic rings known from other archosaurs?). I would think that the sclerotic ring was present in the early stages during the transition into the water at latest (and probably even before that), but this is all idle hypothesis; I need to do more research and dig up yet more papers.

Hopefully this weekend I’ll be able to knock out some more papers, although I probably should have organized them first so I could start working on one particular area instead of collecting random facts. Then again, things might be related that I might not realize at first, so taking the long way around might pay off. In any case, I’m glad to actually start getting down to business, and while not everything I read will end up being useful, at least I’ll be teaching myself and have some notes to refer back to.


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3 responses

3 08 2007
Zach Miller

As I’ve always understood it, sclerotic rings actually help focus the eye. They are mobile, and can “telescopically” collapse and enlargen, thus influencing the shape of the eye.

That’s what I’ve read and have been told, but that was like five years ago, so things have probably changed since then. It’s unfortunate that the only animals today with sclerotic rings are diapsids, and even some of THEM lost independantly lost their sclerotic rings.

4 08 2007
Kevin Z

I saw Montani’s job talk for the UC-Davis Geology dept. when I was an undergrad there. It was great and very visual. Needless to say he got the job, making one of my mentors there, Geerat Vermeij, happy to have another paleobiologist around.

I would like to reccomend to you Vermeij, G. J. 1977. The mesozoic marine revolution: evidence from snails, predators and grazers. Paleobiology 3:245-258.

I can email you the pdf if you don’t have it, as well as loads of his other stuff on invert paleo. Just shoot me a line.

4 08 2007
laelaps

Hi Kevin, thanks for the comment! I actually don’t have that paper, so if you could send it to evogeek AT gmail DOT com I would be much obliged. I’ve actually been meaning to get up on my invert paleo (especially ammonites), so I’d be more than happy to receive anything you’ve got. Thanks!

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