While omnivorous mammals weren't always that way, plant-eaters and meat-eaters have diversified within a more well-worn path.
Radical shifts were unlikely for these animals. Mammals that eat meat for a living, for example, didn't give up their taste for flesh without transitioning through an omnivorous stage first.
"Direct transitions from carnivory to herbivory were essentially nonexistent," said co-author Louise Roth of Duke University.
"It's an intuitive result because it takes very different kinds of equipment to have those kinds of diets."
"Plant- and animal-based foods require different digestive chemistries and different processing mechanisms in the mouth and stomach," said co-author Samantha Hopkins of the University of Oregon.
The kinds of teeth adapted for tearing and slicing meat are different than the large, flat-topped molars adapted for grinding nuts and roots.
"It makes sense that you couldn't easily transition from one to the other in one step," Price said.
The researchers also found that diet is linked to how fast mammals spawn new species.
As new species arise and others go extinct, the plant-eaters proliferate faster than their meat-eating counterparts, with omnivores lagging behind both groups.
"If there was an evolutionary race to evolve 100 species, it would take three times longer for omnivores compared to herbivores, and carnivores would be in the middle," Price said.
|Contact: Cheryl Dybas|
National Science Foundation