Plant-eating mammals have bigger guts than their carnivorous relatives

ZURICH, Switzerland, Nov. 4 (UPI) -- New research confirms, for first time, plant-eating mammals have larger bellies than their meat-eating peers.

Scientists have long theorized such a difference. Plants, being harder to break down, require a longer trip through digestive tract. But the theory had never been objectively measured until now.

The analysis -- carried out by scientists at the University of Zurich and the Technical University Berlin -- involved 120 tetrapods, prehistoric as well as modern species, including dinosaurs, reptiles, birds, mammals and mammal-like reptiles called synapsids.

Researchers created 3D models of the bellies of all 120 species. For extinct species, researchers used the fossil record to approximate body cavity volume based on spinal column, rib cage and pelvis size. The results showed herbivorous mammal species boast bellies twice the size of those of carnivores with similar body dimensions.

"This is clear evidence that plant-eating mammals actually have larger guts," Marcus Clauss, a professor at UZH, explained in a news release.

Surprisingly, the analysis -- detailed in the Journal of Anatomy -- failed to reveal a similar pattern among dinosaurs.

"We were amazed that there wasn't even the slightest indication of a difference between herbivores and carnivores in dinosaurs," Clauss said.

It's possible the inconsistencies of the fossil record render the calculation of dinosaur body cavities too inaccurate, but scientists suggest it's more likely there is a fundamental physiological difference between dinosaurs and other tetrapods.