Cut-Grind or Grind-Cut? The Butter Battle Book of Prehistoric Mammals

An artist's rendering of what Pseudotribos robustus or a weasel-possum-lizard, might have looked like 165 million years ago

In the November 1st, issue of Nature, a joint American and Chinese research team announced the discovery of a long dead prehistoric mammal with an interesting set of chompers. Although the teeth were very similar in form to other teeth found at the time, they actually were arranged in a "grind-cut" pattern instead of the more common "cut-grind" pattern! Upon realizing what they were looking at, some of the female researchers fainted from embarrassment.

These days, mammals have very different types of teeth: from fruit eaters; to grain munchers; to ant slurpers; and countless others. However, it is believed that all of these teeth descended from a common archetypal tooth design. Paleodentologists (I made that up, but I bet Darren Naish over at Tetrapod Zoology has a certification in it) have long believed that tribosphenic teeth, ideal for shearing and grinding, and common among monotremes and marsupials of the Jurassic Period, were the papa tooth from which modern teeth derived. However, the discovery of Pseudotribos robustus, a feisty little insectivore that fed on worms and insects, has turned that neat little theory on its head. You see, Pseudotribos had, you guessed it, pseduotribosphenic teeth, which apparently evolved separately and were just like tribosphenic teeth, just arranged oppositely. This means that the mammals in this period were likely...

much more diverse than scientists ever suspected.

..."The pseudo-tribosphenic teeth and the true tribosphenic teeth are great examples of convergent evolution and a great manifestation of how dental and feeding adaptation can be achieved by different lineages of mammals," said Dr. Zhe-Xi Luo, a curator of paleontology at Carnegie Museum of Natural History and a member of the international team that made the discovery. This little guy was about 12 cm long and had very strong arms for digging.