How skull (top) and tooth (bottom) shapes group marine tetrapods together. From Kelley and Motani, 2015.
Brian Switek has an interesting post on his Laelaps blog over at National Geographic. In it, he discusses a new Biology Letters study by marine tetrapod specialists Neil Kelley and Ryosuke Motani. They compared the skulls and teeth of marine tetrapods from many animals, including whales, turtles, crocodiles, seals, and even our friends the sauropterygians (plesiosaurs, pliosaurs, mosasaurs, and ichthyosaurs). What they found is that form followed function. Skull anatomy is a fairly good predictor of feeding strategy regardless of ancestry. Nice results that confirm what we all know about convergent evolution.
Kelley and Motani focused on skulls of marine tetrapods – descendants of the four-legged vertebrates that crawled out of the swamps over 360 million years ago. They’re an ideal group for such comparisons because all of them – from seals to turtles to whales – had terrestrial ancestors that eventually took on life in the seas. By combining skull, jaw, and tooth measurements from 69 living species with data on what they actually eat, Kelley and Motani were able to pick out how form relates to feeding.
As it turns out, skull anatomy is a fairly good predictor of feeding style regardless of ancestry. For example, herbivores like the marine iguana, green sea turtle have short skulls with larger areas of attachment for powerful jaws muscles to crop and crush vegetation. Species that snatch up fish and squid, on the other hand, tend to have longer, toothier snouts better-suited to “snap feeding” and swallowing prey whole. Apex predators such as the saltwater crocodile, leopard seal, and orca fell in-between, characterized by elongated jaws and relatively deep skulls that give them the power to tear apart larger prey.
The original paper is at The Royal Society.