Your teeth pattern rooted within the first reptiles struggling to turn into mammals. A new fossil mammal species from the Jurassic era, during the full blown dinosaur evolution, reveals that the basic tooth pattern encountered in all mammal species today emerged independently at least twice in the past, and also points that early mammals were much varied than previously believed.
The remains of Pseudotribos robustus were discovered in 165-million-year-old lakebeds in the Inner Mongolia (northeastern China). The 4.7in (12 cm) long mammal could have been a digger feeding on insects and plants. But what took by surprise the researchers were creature's molar teeth.
"This thing is very advanced in
terms of its tooth structure. It has departed considerably from the ancestral pattern where it could only cut up things; now it can grind things up," said Richard Cifelli, a paleontologist at the University of Oklahoma in Norman, not involved in this research.
This type of molar is believed to have boosted the high diversity of modern mammals, but Pseudotribos belongs to a long-lost lineage, with no connection with today's placentals and marsupials, thus its cut-and-grind molars must have evolved independently though convergent evolution. "It shows that this key feature ... evolved in two completely different ways but with the same functional outcome," said Hans-Dieter Sues, associate director for research and collections at the Smithsonian National Museum of Natural History in Washington, D.C., not involved in this research.
"It has long been supposed that the adaptation that allowed them (placentals and marsupials) to be so successful was a multifunction molar that can both cut and grind," said Cifelli. "For mammals you are what you eat with. Essentially all mammalian diversity is broken down pretty much by the different dental design that we each have," said co-author Zhe-Xi Luo, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania.
No matter the diet of today's mammals, the bone-crushing molars of the carnivores and the hay-grinding ones of the hoofed mammals, all evolved starting from the same basic teeth pattern.
The new discovery also shows that early mammals started to diversify much earlier than commonly believed, and it should be no wonder as two-thirds of mammalian existence occurred during the dinosaur age. The dinosaur age mammals are depicted as small, furry, nocturnal, insectivorous, at the periphery of a stage were the dinosaurs were the main actors. "Our general view of what happened is that they didn't really go into any extravagant ecological niches until dinosaurs became extinct. Now we're finding that wasn't the case." said Cifelli.
The same lakebed delivered fossils of gliding and swimming mammals 165 million years ago. "Along with the new find, the discoveries suggest that mammals underwent tremendous diversification during the middle of the Jurassic period. We're seeing a host of skeletal adaptations that say, hey, mammals were doing these wild and crazy things-they weren't just lying around in their little hidey holes," said Cifelli.