I know that a blog on the interwebz is not considered standard protocol in science but, well things are changing and the pace of discovery, spread of news and discourse is going up and since I already sort of said it over at Tet Zoo as well as hinting at it here I might as well put it up here as well. I am working on a paper (my first ever) that can hopefully get published and enter the literature. Because I have put it out on such visible mediums as Tet Zoo comments section and over here I do not think anyone will attempt to get the scoop on me, lest they want the scorn of academic dishonesty. But if you like what I am saying and want to help or have some pertinent papers shoot me a line in comments. But I have my work cut out for me.
The T-Handled Socket Wrench of Death (thanks Yodelling Cyclist)
I think the chief impetus in plesiosauromorph morphological evolution was predation on ammonites.
Ammonites were abundant, diverse, and widespread through out the Mesozoic.
We should expect that predators as long lasting and abundant as plesiosauromorphs would seek to exploit them.
While small ammonites could have been swallowed whole or crunched up and further ground up with gastroliths I think large ammonites were predated upon as well.
Plesiosauromorphs would have attacked these large ammonites not by crunching through the shell as pliosauromorphs and mosasaurids did but through a unique method of rotational feeding.
1) Attacking from below in a slow stealthy approach the plesiosauromorph would grab any exposed fleshy part of the ammonite before it could recoil into shell or jet away.
2) After the mouth established a good anchoring bite the plesiosauromorph would then roll it's neck into and against the ammonite shell and begin a series of death rolls.
3) The ammonite shell, being a buoyancy device, would maintain an upright position even as this occurred.
4) By leveraging against the shell of the ammonite and continuing to roll against it the plesiosaur would be able to ratchet the cephalopod out of it's shell. Keep in mind the brunt of the force is not on the small head- that is simply the anchoring point. It is the massive neck that takes and distributes the torque until the ammonite is pulled out of it's shell.
5) After the cephalopod is pulled out the plesiosaur could use rotational feeding to pull off bits to be swallowed or, if living in groups, pull it apart together.
Furthermore I do not think it a coincidence that Cenozoic oceans lack abundant shelled pelagic prey and also lack predators similar in design to long necked plesiosaurs.
The largest and most long necked plesiosaurs, the Elasmosaurids, were coincident with the largest ammonites during the Cretaceous.
The above scenario is of course very wild and not without a lot of speculation. But I believe it accounts for the strange anatomy of long necked plesiosaurs. As a mental exercise consider snakes that kill by constriction. If snakes were extinct today imagine the dilemma in reconstructing the feeding ecology of constrictors. Losing limbs imposes a lot of constraints on snakes, not the least of which is relatively slow movement. Why would a group of animals embark on this evolutionary course? Because the evolutionary advantage outweigh the disadvantages.
I also want to stipulate that this feeding strategy is part of a larger generalist strategy many of these animals employed. But I do think ammonites were the prime driver and after the neck evolved it was useful for other things as well.
I made some quick 5 minute sketches to hopefully allow you to visualize what I think was going on. Not done for artistry or even accuracy, just to help the concept. Would also love comments , feedback, criticism.
|Step 1. Bite and hold|
|Step 2. Initiate Spin after leveraging neck against shell|
|Step 3. Keep spinning until dinner is served!!|
All artwork Duane Nash. use with attribution for free.