The survey suggests that across animals, carnivory is most common, including 63% of species. Another 32% are herbivorous, while humans belong to a small minority, just 3%, of omnivorous animals.
The researchers were surprised to find that many of today’s carnivorous species trace this diet back all the way to the base of the animal evolutionary tree, more than 800 million years, predating the oldest known fossils that paleontologists have been able to assign to animal origins with certainty.
“We don’t see that with herbivory,” said Wiens, professor of ecology and evolutionary biology and corresponding author of the study. “Herbivory seems to be much more recent, so in our evolutionary tree, it appears more frequently closer to the tips of the tree.”
So if the first animal was a carnivore, what did it prey on?Paper. (open access) – Cristian Román-Palacios, Joshua P. Scholl, John J. Wiens. Evolution of diet across the animal tree of life. Evolution Letters, 2019; 3 (4): 339 DOI: 10.1002/evl3.127 More.
The researchers think the original animals preyed on protists or one-celled animals (a shell eat cell world?). Plant-eating was a later development (along with plants?): “Herbivory may go hand in hand with new species appearing in certain taxa, but it clearly is not a universal driver of new species.”
A case could, of course, be made that omnivory explains why humans are so numerous compared to, say, pandas.
See also: Early Land Carnivore Is Herbivore’s Ancestor, Pushes Back Family History
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