June 6, 2001 -- The advent of chewing by a group of herbivores 260 million years ago may have signaled one of the first great bursts of vertebrate life on land, say paleontologists from University of Toronto and Duke University.
"The real boost in the success of vertebrates on land started with the ability to process plant material efficiently," says U of T at Mississauga paleontology professor Robert Reisz in the June 7 issue of Nature, who co-authored the paper with graduate student Natalia Rybczynski, who later moved on to Duke University.
According to Reisz, the first terrestrial herbivore appeared on land about 290 million years ago. But herbivores then had a fairly rudimentary form of eating - they simply tore the leaves off the plant and swallowed them whole, leaving most of the processing to take place in the guts.
Suminia getmanovi, however, evolved a far more innovative and efficient way of eating by first chewing and shreddingthe leaves into small bits before swallowing, thereby allowing maximum absorption of the plant's energy and nutrients. The advent of chewing in this species of terrestrial herbivore is also associated with the Earth's first great burst in the diversity and number of terrestrial herbivorous vertebrates, says Reisz.
"There is a link between the time when land-dwelling herbivores started processing food in the mouth and a great increase in animal diversity," he notes. "So you can say that the evolution of the modern terrestrial ecosystem with lots of herbivores supporting a few top predators is based on animals efficiently eating the greenery on land."
This type of terrestrial ecosystem is mirrored in modern-day animals. Today we see an abundance of plant-eating herbivores like gazelles and antelope with relatively few carnivores, such as lions and leopards.
Discovered in 1990, the skull of Suminia looks something like that of a little monkey or a rodent, with huge eyes and very impressive teeth. This herbivore lived during the Upper Permian period of the Paleozoic era some 260 million years ago, about 50 million years before dinosaurs. The fossil specimens of Suminia were found in an area in Central Russia called Kotelnich, situated on the Vyatka River.
According to Reisz, what makes the discovery of Suminia really exciting is the herbivore's chewing ability - a development that modern-day mammals follow. The fact that efficient chewing occurred first in the group that gave rise to mammals is really interesting because today it is mainly mammals who chew their food extensively, particularly plants, he adds.
The advent of chewing in different lineages is repeated throughout history, first with Suminia and its later mammalian relatives, and some groups of herbivorous dinosaurs. The reason for that may lie in the fact that mammals (and perhaps dinosaurs) are "warm-blooded," Reisz suggests. To maintain a high body temperature and high metabolism, they must develop an efficient way to digest and absorb nutrients from food. Permian reptiles, like modern-day lizards, do not have the same energy requirements as mammals because they are so-called "cold-blooded."
This study was funded by the National Geographic Society and the Natural Sciences and Engineering Research Council of Canada.
New fossil finds are not new to Reisz. Last November, he was part of a team that discovered the existence of a bipedal reptile that predates dinosaurs by more than 60 million years. He was also the lead researcher on a recent paper published in the May 31, 2001, issue of Nature about a unique dental development in lungfish that has been conserved across a span of 360 million years.
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