Herbivorous, or plant-eating, mammals have bigger bellies than their usually slim carnivorous counterparts, according to a study led by University of Zurich researcher Marcus Clauss.
Hippo family in Botswana. Image credit: Hans Stieglitz / CC BY-SA 3.0.
Prof. Clauss and his colleagues from Germany and the UK studied the shape of the ribcage in 126 terrestrial tetrapods — from prehistoric times up to the present day.
With the aid of photogrammetry and computer imaging techniques, they compiled a dataset of digital 3D models of tetrapod skeletons.
“This resulted in 126 digital skeletons of tetrapods including 86 synapsids (10 fossil synapsids, or ‘mammal-like reptiles,’ and 76 fossil and extant mammals), 38 diapsids (six extant birds, 27 non-avian dinosaurs, five fossil and extant reptiles), and two amphibians,” the researchers said.
“Of these, 31 were categorized as carnivores and 95 as herbivores.”
Using the computer-based visual evaluation of this dataset, the team reconstructed the volume of the body cavity (torso), which is delineated by the spinal column, the ribcage and the pelvis.
Tetrapod skeletons. Image credit: University of Zurich.
“In the overall dataset, diet had a significant effect on the torso volume, with herbivores having about 1.5 times larger torso volumes than carnivores. This was due to a clear effect of diet in mammals,” Prof. Clauss and co-authors said.
“In mammals, herbivores again had about 1.5 times larger torso volumes than carnivores.”
Far more surprising, however, is the fact that this pattern is not evident among the remaining tetrapods.
“We were amazed that there wasn’t even the slightest indication of a difference between herbivores and carnivores in dinosaurs,” Prof. Clauss said.
“Numerous fossilized species were examined in our study — from the earliest amphibians to the largest herbivorous dinosaurs and mammoths.”
“On the one hand, the results can indicate that it is difficult to reconstruct dinosaur skeletons reliably,” Prof. Clauss noted.
“On the other hand, the discovery reveals that there’s a fundamental difference in morphological principles between mammals and other tetrapods.”
For instance, the authors suspect that a different respiratory system might be responsible for the divergent effect of the diet on the body structure in mammals and dinosaurs.
The team’s findings were published online Nov. 4, 2016 in the Journal of Anatomy.
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Marcus Clauss et al. Reconstruction of body cavity volume in terrestrial tetrapods. Journal of Anatomy, published online November 4, 2016; doi: 10.1111/joa.12557
