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Early Mammal Relatives Offer Insight On Evolution After Mass Extinctions

August 14, 2013
Image Caption: Reconstruction of the Permian anomodont Dicynodon lacerticeps. Credit: Marlene Donnelly, Field Museum of Natural History)

Brett Smith for redOrbit.com – Your Universe Online

With the continuous expansion of human activity around the world, many species are facing the increasing threat of extinction as their habitats shrink and shift. Yet life on planet Earth has faced even larger extinction threats in the past.

A new study int the journal Proceedings of the Royal Society B examines how a group of mammalian relatives called anomodonts coped with a mass extinction event of the prehistoric past as a way to glimpse into the potential future.f

While mass extinction events have created room for surviving species to evolve and flourish, the new study found that anomodonts did not evolve any new features after the largest mass extinction event in our planet’s history, suggesting that the catastrophic event may have actually constrained the animals’ evolution rather than driven it forward.

The international team of researchers focused on the end-Permian mass extinction, which occurred just over 250 million years ago. It resulted in the extinction of as many as 90 percent of marine and 70 percent of terrestrial species.

Before the mass extinction event the anomodont family flourished, with a wide range of body shapes and sizes. These animals ranged from land-dwelling plant eaters to specialized burrowers to a water-dwelling hippo-like species.

“The number of anomodont species increased during the Permian, sharply dropped during the end-Permian extinction event, and then rebounded in the Middle Triassic Period (about 240 million years ago) before the final extinction of the group at the end of the Triassic,” said study co-author Marcello Ruta, a life science researcher at the University of Lincoln in the UK.

“However, the variety of different anatomical features found in anomodonts – that is, their anatomical diversity – declined steadily over their history,” Ruta said. “Even in the aftermath of the mass extinction, when there should have been a lot of empty ecological space, anomodonts did not evolve any fundamentally new features. Rather than allowing them to move to a new evolutionary trajectory, the genetic bottleneck they passed through constrained their future evolution.”

The study authors said their findings could be used to refine models of modern species’ evolutionary trajectories in the face of extinction threats from habitat loss, poaching or climate change.

“This is the first study of its kind to address simultaneously changes in species number and anatomical diversity in anomodonts, and to quantify their response to the most catastrophic extinction on record,” said Michael Benton, a paleontologist at the University of Bristol in the UK. “Anomodonts are abundant, diverse, and well-studied, which makes them ideal models for evolutionary analyses.”

“The results underscore that recoveries from mass extinctions can be unpredictable, a finding that has important implications for the species extinctions being caused by human activity in the world today,” Benton added. “We cannot just assume that life will return to the way it was before the disturbances.”

Extinctions of just a few select animals can have effects that reverberate throughout an ecosystem. Another report published this week found that the massive die-off of large animals in the Amazon 12,000 years ago significantly altered the way nutrients were distributed across the landscape. The effects of these extinctions can still be seen today, the study researchers said.


Source: Brett Smith for redOrbit.com - Your Universe Online



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