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ANCIENT REPTILE WALKED ON TWO LEGS
By BBC News Online science editor Dr David Whitehouse
Thursday, 2 November, 2000, 19:07 GMT
A newly discovered fossil of a reptile that walked on two legs shows that
bipedal locomotion evolved long before the dinosaurs.
The exquisitely preserved, 290-million-year-old skeleton of Eudibamus
cursoris was dug up in a German quarry by an international team of
It is the oldest known member of the Parareptilia, a major group of
primitive reptiles. Eudibamus does not appear to be a direct ancestor to
later reptiles, including some dinosaurs, that adopted a bipedal posture and
This may indicate that the ability to walk upright on two legs arose several
times independently during reptile evolution.
Built for speed
Although only 26.1 cm (10.3 inches) long, the Eudibamus fossil contains a
wealth of clues about how the reptile moved.
Scientists say the creature's upper limbs were relatively short for its
overall size, while its lower limbs were relatively long. The reptile also
had an unusually long foot and tail, proportions usually indicative of
They think the long tail could have served as a sort of rudder, compensating
for changes in the animal's centre of gravity as it moved along in an
Other evidence of bipedalism comes from the arrangement of the hip, knee,
and ankle joints in the reptile's lower limb. The surfaces of these joints
are arranged so that the bones in the legs formed a straight line when the
hind limbs were fully extended.
Dinosaurs and mammals
This means that the creature's ankles and knees were able to flex and extend
in only one plane in a similar way to how human knees and ankles move mostly
back and forth, but not side to side.
Eudibamus cursoris appears to be the earliest known tetrapod, or four-legged
vertebrate, to adopt this distinctive posture and gait.
"This find is fascinating because it confirms that bipedalism is an
innovation that has happened several times," said Professor Robert Reisz, of
the University of Toronto at Mississauga.
"It happened in some dinosaurs, and their bird descendants, and it happened
in mammals, so it must be a good idea in terms of evolution."
Evolved several times
"There are only a couple of times in evolutionary history when animals have
gone from a sprawled posture like that of a four-legged lizard to an upright
posture when they tuck their limbs under the body.
"It happened once in dinosaurs and again with mammals. So to find an example
of an animal that did this before dinosaurs or mammals is particularly
According to the researchers, who report their work in the journal Science,
even on four legs, the creature's distinct posture would have distinguished
its movement from the sprawling gait used by the other tetrapods of the
Eudibamus belongs to an extinct family of early reptiles with an unusually
large geographic range, compared to its contemporaries in the early Permian
(about 290 to 268 million years ago).
"It was thought that the ability to run on two legs and stand upright first
emerged in dinosaurs and their relatives. But this discovery has shown
interesting and exciting things happening in the evolutionary history of
reptiles well before the advent of dinosaurs," said professor Reisz.
The teeth of Eudibamus indicate that it was a plant eater, so it was not
using its speed to chase food. Instead, it probably used its sprinting speed
to escape predators.
Professor Reisz and colleagues plan to continue excavations at the German
quarry, which has already yielded a number of other well-preserved fossils.
"It's a super site, a unique locality," said the palaeontologist,
"And it gives us a chance to show that some neat things were happening with
reptiles in the Palaeozoic, long before the appearance of dinosaurs."
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