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Posted by Adam Britton on March 09, 2003 at 20:18:31:
In Reply to: ISO positioning posted by caimankid on March 09, 2003 at 14:29:08:
That's a good question. Crocodylidae ancestors clearly had these ISOs, whereas Alligatoridae ancestors did not. Whether one group lost them or the other gained them isn't known, and unless there are some good skin print impression fossils we're not likely to ever find out.
The trouble is, we're not quite sure how these body ISOs function in modern crocs, hence it's difficult to create a viable hypothesis about why one group doesn't have them! Some have said they are pressure receptors like those on the jaws, others have noted various differences in their structure from those on the jaws and hence postulate a different role. It's even been suggested that they might detect salinity levels. As you can see, nobody really knows yet. I've suggested to Daphne Soares (who elucidated the function of the facial receptors) that this should be her next project!