Reptiles stood upright after mass extinction

Sep 15, 2009
Reptiles stood upright after mass extinction
Moschops lived before the end-Permian mass extinction. Photo by © Jim Robins

(PhysOrg.com) -- Reptiles changed their walking posture from sprawling to upright immediately after the end-Permian mass extinction, the biggest crisis in the history of life that occurred some 250 million years ago and wiped out 90% of all species.

In a detailed study of 460 fossil tracks of reptiles from below and above the boundary, Tai Kubo and Professor Mike Benton from the University of Bristol have found that before the Permian extinction all the reptiles moved with their arms and legs held sideways in a sprawling posture, just like and do today.

After the mass extinction, the medium-sized and large reptiles of the subsequent Triassic period, walked with their legs tucked underneath their bodies, just like modern mammals.

Professor Benton said “Dinosaurs - and later the mammals - owe their success to being upright. An upright animal, like an elephant or a Diplodocus, can also be very large because its weight passes directly through the pillar-like legs to the ground. In addition, other upright animals, such as monkeys, could use their arms for climbing or gathering food.”

Walking upright can have great advantages - it means the stride can be longer and the animal can move with much less stress on the knee and elbow joints. Upright walking was the key to the success of the dinosaurs, which originated 25 million years after the great end-Permian crisis. The first dinosaurs were all bipeds and they also became very large. Sprawlers cannot become too big or their legs collapse.

Reptiles stood upright after mass extinction
Reptile posture before and after the mass extinction. Photo by © Simon Powell

Up to now, the transition from a sprawling to an upright was seen as long-term, possibly lasting some 20-30 million years, but the new evidence suggests that the event was much more rapid, and was perhaps initiated by the crisis.

This new understanding shifts the evolutionary assumptions as well. “If the replacement of sprawlers by upright animals had been a long drawn-out affair, then we’d be looking at some process of competitive replacement,” said Professor Benton.

“As it is, the new footprint evidence suggests a more dramatic pattern of replacement, where the sprawling animals that dominated Late Permian ecosystems nearly all died out, and the new groups that evolved after the crisis were upright. Any competitive interactions were compressed into a short period of time.”

The results are published today in Palaeontology.

More information: Kubo, T. and Benton, M.J. 2009. Tetrapod postural shift estimated from Permian and Triassic trackways. Palaeontology. 52, 1029-1037.

Provided by University of Bristol (news : web)

Explore further: 110-million-year-old crustacean holds essential piece to evolutionary puzzle

add to favorites email to friend print save as pdf

Related Stories

Recovering from a mass extinction

Jan 18, 2008

[B]The full recovery of ecological systems, following the most devastating extinction event of all time, took at least 30 million years, according to new research from the University of Bristol[/B] The ful ...

Luck gave dinosaurs their edge

Sep 11, 2008

By comparing early dinosaurs to their closest competitors, the curuotarsans, Steve Brusatte of the American Museum of Natural History and colleagues have found that dinosaurs had no special ability to dominate ...

Did dinosaurs hold their heads up?

May 27, 2009

Some dinosaurs may have held their heads up, like a giraffe, rather than in a more horizontal position, University of Portsmouth scientists report today.

Recommended for you

Fish eye sheds light on color vision

Dec 23, 2014

A fish eye from a primitive time when Earth was but one single continent, has yielded evidence of color vision dating back at least 300 million years, researchers said Tuesday.

Study sheds new light on the diet of extinct animals

Dec 22, 2014

A study of tooth enamel in mammals living today in the equatorial forest of Gabon could ultimately shed light on the diet of long extinct animals, according to new research from the University of Bristol.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

otto1923
not rated yet Sep 15, 2009
Perhaps only those animals whose mouths were sufficiently far enough above the muck and ash, and disease-causing pathogens from rotting plants and animals lying in fetid water, survived the extinction event.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.