Suminia, a mammallike reptile, had large eyes and powerful, plant-grinding teeth (top). The remains of this pioneering plant-eater were found in the Vjatka region of Central Russia (above).
Photographs: Courtesy of Diane Scott/University of Ttoronto, Mississauga; Courtesy of Albert Khlupin
A stout set of teeth may have been key to the vertebrate conquest of dry land. So paleontologist Robert Reisz concluded after studying fossils found in Russia of Suminia getmanovi, a squirrel-sized reptile that lived 260 million years ago. Suminia is the oldest known vertebrate that could chew plants efficiently, says Reisz, who is based at the University of Toronto. And for evolution, that marked a great leap forward.
One hundred million years earlier, when the first vertebrates dragged themselves onto land, they faced an abundance of food they could not eat. Terrestrial plants were too tough for them to digest, so the creatures had to return to the water to dine on soft sea species. Around 300 million years ago, the first land herbivores had such rudimentary teeth they could only rip off large pieces of leaf. But Suminia's powerful teeth could shred vegetation with a shearing action, allowing it to extract juices and nutrients from cycads, conifers, and ferns. Such supershears touched off an explosion of vertebrate biodiversity.
The arrival of this true plant-eater also helped lay the foundation for the ecological pyramid found on land today, says Reisz, whose former graduate assistant Natalia Rybczynski analyzed the Suminia fossils. "You now have lots and lots of herbivores supporting a much smaller population of carnivores, and that happened almost exactly at the time when Suminia shows up," he says.