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Oldest mammal relative discovered in Kansas

The smallest and largest caseid: this is a reconstruction of 300-million-year-old tiny carnivorous Eocasea in the footprint of 270-million-year-old largest known herbivore of its time, Cotylorhynchus.
The smallest and largest caseid: this is a reconstruction of 300-million-year-old tiny carnivorous Eocasea in the footprint of 270-million-year-old largest known herbivore of its time, Cotylorhynchus.
Credit: Artwork by Danielle Dufault Usage Restrictions: None

The fossil of a carnivorous ancestor of modern mammals and herbivores has been discovered in the Dyke Museum of Natural History at the University of Kansas. The fossil is the most ancient relative of herbivores and mammals found to date and precedes dinosaurs by 80 million years. The fossil was evaluated by paleontologist Robert Reisz, a professor in the Department of Biology from the University of Toronto Mississauga, and Jörg Fröbisch of the Museum für Naturkunde and Humboldt-University in Berlin. The research was published in the April 16, 2014, edition of the journal Public Library of Science.

Eocasea martini arose about 315 million years ago. The animal is the most primitive ancestor of terrestrial herbivores and modern mammals found to date. The four pound animal ate insects and other small animals. The fossils included most of the spinal column, a partial skull, the pelvis, and a hind limb. Comparison of the anatomy of the fossil to ancient carnivores, the oldest known herbivores, and modern mammals indicates that this animal is the oldest ancestor of herbivores and mammals.

The discovery is important because it fills in a 20-million-year gap in the fossil record of both carnivores and herbivores. The evolution of herbivores prior to or coincident with the evolution of carnivores was necessary. The herbivores provided food for the developing carnivores and spread the seeds of the plants the animals ate across the entire world. Modern mammals are direct descendants of Eocasea martini and its relatives. The herbivores that arose from this lineage ranged in size from four pounds to more than 1,000 pounds.

This is the first documentation of the very first evolution of herbivores that were land dwelling. Different groups of herbivores evolved five separate times during the eons of ancient time. Eocasea martini and its later relatives are the first animals that opened the evolutionary door to herbivory in land dwelling animals.