Earliest
Evidence For Reptiles
Wednesday, October 17, 2007
Discovery of fossilized
footprints prove reptiles evolved earlier than previously
thought.
Top
Reconstruction
of Hylonomus lyelli
Photo
by Donald Agnew
|
Middle
One
of the metre-sized blocks of sandstone covered with fossil
reptile tracks
Photo
by Howard Falcon-Lang
Bottom
Close
up of a handprint showing five slender fingers, characteristic
of reptiles.
Photo
by Howard Falcon-Lang
Newly discovered fossilized
footprints provide the earliest evidence yet for the evolution of
reptiles – a major event in the history of life. They are
315 million years old, making reptiles up to 3 million years
older than previously thought.
The footprints were discovered
by Dr Howard Falcon-Lang from the University of Bristol in sea
cliffs, New Brunswick, Canada. The results of his study,
undertaken with UK and Canadian colleagues, are published today
in the Journal of the Geological Society of London.
Until now, the oldest reptile
fossils were skeletons found in 1859 by William Dawson in Nova
Scotia, and named Hylonomus lyelli after the nineteenth century
geologist, Sir Charles Lyell.
Falcon-Lang said, “The
new fossils were found in the same general region but at a level
in the rock strata almost a kilometer below Dawson’s
discovery. Consequently we can be confident the footprints are
older than the skeletons. They were preserved when reptiles
walked across the muddy bottom of a dry riverbed.
“The discovery was pure
luck. As I walked along remote sea-cliffs at the end of a long
day in the field, I passed a recent rock fall. One large slab of
rock was covered with hundreds of fossil footprints! The sun was
low in the sky and I probably wouldn’t have seen them if it
hadn’t been for the shadows.”
Unlike their amphibian cousins,
reptiles do not need to return to water to breed so they paved
the way for the widespread colonization of dry land, and the
establishment of diverse land-based ecosystems today. The
difficult part of the study was proving that the footprints were
actually those of reptiles and not just primitive amphibians.
“It was a bit like a
crime scene investigation,” said Falcon-Lang, “we had
found the footprints but who had made them?”
Professor Mike Benton, also of
the University of Bristol, who co-authored the study, added,
“There were only a few species capable of making prints
like this around at the time so we came up with a short-list of
suspects. However, the prints showed that the hands had five
fingers and scales, sure evidence they were made by reptiles and
not amphibians”.
The footprints prove that
reptiles evolved even earlier than previously thought and existed
in seasonally dry river-plains, a bit like those of northern
Australia today. As the first pioneers of dry continental
environments, they paved the way for the diverse terrestrial
ecosystems that exist today.
Source:
University of Bristol
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