3D model reveals how ancient creature got around
24 May 2012
An ancient four-limbed creature that's thought to be the first ever to walk on land couldn't actually walk at all, researchers have discovered.
Instead, they think the animal, which scientists call an early tetrapod, simply hauled itself out of the primordial ooze with its two front limbs, using its back limbs merely for balance.
"These early tetrapods probably moved in a similar way to living mudskipper fishes in which the front fins, or arms, are used like crutches to haul the body up and forward," explains Dr Stephanie Pierce from the Royal Veterinary College and the University of Cambridge, lead author of the study, published in Nature yesterday.
Pierce and co-authors, Professor Jennifer Clack from the University of Cambridge and Professor John Hutchinson from the Royal Veterinary College, made their discovery by creating the first ever 3D computer model of an early tetrapod's skeleton. Their aim was to work out how its limbs might have moved.
They scanned dozens of fossil specimens of a tetrapod that lived around 360 million years ago called Ichthyostega. They digitally separated the bones from the rock surrounding the fossils. Then they put each bone back together into a whole skeleton, "like a jigsaw puzzle," using animation software, before carefully manipulating the model to estimate each joint's range of motion.
To make sure their computer model was reliable, they built similar models of seals, salamanders, platypuses, crocodiles and otters and used the model to test their joint movements. They found that the model predicted a reliable amount of mobility.
Their model also revealed that the creature wouldn't have been able to move its hip and shoulder joints very much at all. Not just that, but its limbs couldn't rotate along their long axis, a movement that's essential for locomotion in today's land animals. This means it probably couldn't push its body off the ground and move each of its limbs in turn.
"All this points to the idea that limbs may have evolved before the ability to actually walk. It also shows that just because you have limbs, it doesn't mean you can walk," says Pierce.
"Our reconstruction demonstrates that the old idea, often seen in popular books and museum displays, of Ichthyostega looking and walking like a large salamander, with four sturdy legs, is incorrect," says Clack.
"Remarkably, earlier fishes (called tetrapodomorphs) had the ability to rotate their fins, so it seems that just as vertebrates were experimenting with terrestrial movement, the limbs became confined to mainly back-and-forth and up-and-down motions. It wasn't until tetrapods became more competent on land that they recovered the ability to rotate their limbs around their long axis," says Hutchinson.
The findings suggest that some of the 400 million-year-old footprints discovered in Poland two years ago - thought to have been made by similar tetrapods - may have been made by altogether different four-legged animals.
The study was funded by the Natural Environment Research Council (NERC).
NERC Press Office
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Polaris House, North Star Avenue
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Scientists' contact details:
Dr Stephanie Pierce
University of Cambridge and the Royal Veterinary College
Professor John Hutchinson
The Royal Veterinary College
Professor Jennifer Clack
University of Cambridge
1. This press release is based on the paper 'Three-dimensional limb joint mobility in the early tetrapod Ichthyostega', by Stephanie E Pierce, Jennifer A Clack and John R Hutchinson, published in Nature on 23 May 2012.
2. The Royal Veterinary College is the UK's first and largest veterinary school and a constituent college of the University of London. In the recent Research Assessment Exercise the RVC ranked as England's best school in the Agriculture, Veterinary & Food Science unit of assessment, for institutions whose research is exclusively veterinary related, with 55% of its submitted academics viewed as producing 'world class' and 'internationally excellent' research. The college provides support for veterinary and related professions through its three referral hospitals, diagnostic services and continuing professional development courses.
3. The University of Cambridge's mission is to contribute to society through the pursuit of education, learning and research at the highest international levels of excellence. Cambridge's reputation for excellence is known internationally and reflects the scholastic achievements of its academics and students, as well as the world-class original research carried out by its staff. Some of the most significant scientific breakthroughs occurred at the university, including the splitting of the atom, invention of the jet engine and the discoveries of stem cells, plate tectonics, pulsars and the structure of DNA. From Isaac Newton to Stephen Hawking, the university has nurtured some of history's greatest minds and has produced more Nobel Prize winners than any other UK institution with over 80 laureates.
4. NERC is the UK's main agency for funding and managing world-class research, training and knowledge exchange in the environmental sciences. It coordinates some of the world's most exciting research projects, tackling major issues such as climate change, environmental influences on human health, the genetic make-up of life on earth, and much more. NERC receives around £300m a year from the government's science budget, which it uses to fund independent research and training in universities and its own research centres.
Press release: 09/12
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