August 4, 2010 | 1
Modern crocodiles might have sharp, flesh-tearing teeth, but they cannot chew like us humans. In fact, mammals have cornered the market on mastication, leaving other life-forms to simply shred their food before ingesting it.
But a newly described Cretaceous crocodile relative (Pakasuchus kapilimai) seems to have been trying out a little chewing itself.
Whereas surviving members of the Crocodylidae family have mouths lined with uniformly menacing pointy teeth, this ancient creature had teeth of different shapes—and likely different functions. At the front of the small skull are conical fangs but the back contains flattened molarlike teeth that likely made contact to mash up food. A description of the toothy findings was published online August 4 in Nature (Scientific American is part of Nature Publishing Group).
"Those are teeth you might typically describe as very mammallike," Patrick O’Connor, of the Department of Biomedical Sciences at the Ohio University College of Osteopathic Medicine and first author of the study, said in a Monday press conference. "Unquestionably, they had more organization in that food-processing ability" than relatives with more standardized teeth, he said of P. kapilimai.
He and his team used a micro-CT scanner to analyze the short skull on the scale of microns. This detail allowed the scientists to digitally reconstruct the teeth and jaws—and hypothesize that the flat teeth likely came into contact with each other when the jaw closed, as they do when humans chew.
But the distinctive features of this notosuchian crocodyliform do not end with its dentition. This ancient croc was about the size of a house cat and likely lived mostly on land "instead of sitting down in the water" like modern crocodiles, O’Connor noted. It probably kept to small prey, such as big bugs and little animals.
Nevertheless, O’Connor asserted that it was a true crocodylian ancestor, with many "telltale crocodilelike characteristics," such as bone formation and spacing. The mammalianlike tooth organization is a "great example of convergent evolution," he said.
P. kapilimai lived some 65 million to 144 million years ago in what is now Tanzania and was then part of Gondwana, the southern landmass that had separated from Pangaea.
The diverse notosuchian crocodyliforms do not appear in the fossil record after the late Cretaceous. So even though P. kapilimai had arrived at what looks like the tooth and jaw arrangement that eventually proved successful for many mammals, the evolutionary experiment does not seem to have been enough to keep them around.
Image of Pakasuchus kapilimai in illustration courtesy of Mark Witton/University of Portsmouth; illustration of theorized jaw movement courtesy of Zina Deretsky/National Science Foundation; video courtesy of Patrick O’Connor/Ohio University