Earliest ancestor of land herbivores discovered

Apr 16, 2014
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: Danielle Dufault

New research from the University of Toronto Mississauga demonstrates how carnivores transitioned into herbivores for the first time on land.

"The evolution of herbivory was revolutionary to life on land because it meant could directly access the vast resources provided by ," says paleontologist Robert Reisz, a professor in the Department of Biology. "These in turn became a major food resource for large land predators."

Previously unknown, the 300-million-year old fossilized juvenile skeleton of Eocasea martini is less than 20 cm long. Found in Kansas, it consists of a partial skull, most of the vertebral column, the pelvis and a hind limb.

By comparing the skeletal anatomy of related animals, Reisz and colleague Jörg Fröbisch of the Museum für Naturkunde and Humboldt-University in Berlin, discovered that Eocasea martini belonged to the caseid branch of the group Synapsid. This group, which includes early terrestrial herbivores and large top predators, ultimately evolved into modern living mammals.

Eocasea lived nearly 80 million years before the age of dinosaurs. "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.

Interestingly, Reisz and Fröbisch also found that herbivory, the ability to digest and process high-fibre plant material such as leaves and shoots, was established not just in the lineage that includes Eocasea. It arose independently at least five times, including twice in reptiles.

"When the ability to feed on plants occurred after Eocasea, it seems as though a threshold was passed," says Reisz. "Multiple groups kept re-evolving the same herbivorous traits."

The five groups developed the novel ability to live off plants in staggered bursts with synapsids such as Eocasea preceding reptiles by nearly 30 million years. This shows that herbivory as a feeding strategy evolved first among distant relatives of mammals, instead of ancient reptiles – the branch that eventually gave rise to dinosaurs, birds, and modern reptiles.

The adoption of plant-eating also caused dramatic shifts in the size of early herbivores. When the team mapped the animals on an evolutionary tree, they found that four of the groups showed a tremendous increase in size during the Permian Period, at the end of the Paleozoic Era.

Caseids were the most extreme example of this size increase, says Reisz. The oldest member of the group, Eocasea, was very small, less than 2 kilograms as an adult, while the youngest, last member exceeded 500 kilograms.

Reisz says that the discovery of Eocasea creates questions even as it answers them. "One of the great mysteries to my mind is: why did herbivory not happen before and why did it happen independently in several lineages? That's what's fascinating about this event. It's the first such occurrence, and it resulted in a colossal change in our ."

The research is published online in PLOS ONE.

Explore further: 'Steak-knife' teeth reveal ecology of oldest land predators

More information: Reisz RR, Fröbisch J (2014) The Oldest Caseid Synapsid from the Late Pennsylvanian of Kansas, and the Evolution of Herbivory in Terrestrial Vertebrates. PLoS ONE 9(4): e94518. doi:10.1371/journal.pone.0094518 . dx.plos.org/10.1371/journal.pone.0094518

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User comments : 4

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verkle
1 / 5 (12) Apr 16, 2014
Some nonsense comments in the article.

research demonstrates how carnivores transitioned into herbivores...

Nonsense! All this small fossil shows is an ancient herbivore. Anything additional is unscientific speculation.

The evolution of herbivory was revolutionary....

Nonsense! This one fossil does not purport anything related to evolution. Mere speculation.

Eocasea is the first animal to start the process...

Nonsense! There is no science that says that even such a process (aka evolution) existed. Figments of atheists' imaginations.

Real scientists will challenge all of evolution's hypotheses, and find that it does not stand up to scientific and mathematic challenges.

Shakescene21
5 / 5 (9) Apr 16, 2014
"Nonsense! This one fossil does not purport anything related to evolution."

@verlke -- one fossil by itself may not tell much about evolution, but in context with numerous other fossils, both more primitive and more advanced, it tells us a lot.
Captain Stumpy
4.3 / 5 (6) Apr 17, 2014
Nonsense! There is no science that says that even such a process (aka evolution) existed. Figments of atheists' imaginations.
@verkle
wrong. Read Shakescene21 above as well as these links

http://phys.org/n...lts.html

http://phys.org/n...tml#nRlv

http://phys.org/n...tml#nRlv

http://phys.org/n...tml#nRlv
Real scientists will challenge all of evolution's hypotheses
all that ended years ago. and real scientists learned that evolution really is real.
IOW - you're wrong. still.
jsdarkdestruction
5 / 5 (1) Apr 19, 2014
"Figments of atheists' imaginations."
A lot of supporters of evolution theory are not atheists. not everyone takes the bible as a literal science book that's straight from god so if anything contradicts it that thing against it is automatically wrong science and facts be damned like you do.

"Nonsense! There is no science that says that even such a process (aka evolution) existed."
You simply refuse to examine the science as your religious views say you have to as it contradicts your little "in the beginning" genesis creation story.

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