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Early land carnivore is herbivore’s ancestor, pushes back family history


From ScienceDaily:

Eocasea lived nearly 80 million years before the age of dinosaurs [300 mya]. “Eocasea is one of the oldest relatives of modern mammals and closes a gap of about 20 million years to the next youngest members of the caseid family,” says Fröbisch. “This shows that caseid synapsids were much more ancient than previously documented in the fossil record.”

It’s also the most primitive member and was carnivorous, feeding on insects and other small animals. Younger members were herbivorous, says Reisz, clear evidence that large terrestrial herbivores evolved from the group’s small, non-herbivorous members, such as Eocasea.

Eocasea is the first animal to start the process that has resulted in a terrestrial ecosystem with many plant eaters supporting fewer and fewer top predators,” he says.

Actually, we don’t know anything except that this animal family is older than thought. Next year we could find a still older carnivore ancestor than Eocasea, the “first animal to start the process.” If we found a herbivore ancestor, that’d upset the applecart altogether. But not so far.

The basic idea is sound, of course (that an abundance of plant life creates an ecosystem where many plant eaters support a few large predators). But this may not be the first time it happened. In general, predictions of having found the “first” of anything much have not worn well.

Here’s the Abstract Open access:

The origin and early evolution of amniotes (fully terrestrial vertebrates) led to major changes in the structure and hierarchy of terrestrial ecosystems. The first appearance of herbivores played a pivotal role in this transformation. After an early bifurcation into Reptilia and Synapsida (including mammals) 315 Ma, synapsids dominated Paleozoic terrestrial vertebrate communities, with the herbivorous caseids representing the largest vertebrates on land. Eocasea martini gen. et sp. nov., a small carnivorous caseid from the Late Carboniferous, extends significantly the fossil record of Caseidae, and permits the first clade-based study of the origin and initial evolution of herbivory in terrestrial tetrapods. Our results demonstrate for the first time that large caseid herbivores evolved from small, non-herbivorous caseids. This pattern is mirrored by three other clades, documenting multiple, independent, but temporally staggered origins of herbivory and increase in body size among early terrestrial tetrapods, leading to patterns consistent with modern terrestrial ecosystem. – Robert R. Reisz, Jörg Fröbisch. The Oldest Caseid Synapsid from the Late Pennsylvanian of Kansas, and the Evolution of Herbivory in Terrestrial Vertebrates. PLoS ONE, 2014; 9 (4): e94518 DOI: 10.1371/journal.pone.009451

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