From Randy Boswell:
Dozens of fossilized reptile footprints left behind 318 million years ago in present-day New Brunswick will rewrite the history of animal evolution on land, says a team of Canadian and British researchers.
Their discovery along a Bay of Fundy sea-cliff is detailed today in the journal Paleogeography, Palaeoclimatology, Palaeoecology.
The ancient trackways are not only the world's earliest evidence of reptilian life, they are also the first known signs of vertebrates -- animals with a backbone -- living in a continental interior, far from any ocean.
Older fossils of amphibian species -- ancestors to the reptiles -- have been documented by scientists probing primordial coastal environments.
But the new reptile footprints are proof that these creatures -- the ancestors of all dinosaurs and mammals, including humans -- had adapted to dry, inland ecosystems at a time when the world's continents were fused in a single mass called Pangaea and the future Canada was in tropical climes near the Earth's equator.
The footprints were found in 2008 by University of London paleontologist Howard Falcon-Lang as he searched for fossils among piles of boulders along the steep Fundy seacoast, near the southern New Brunswick town of St. Martins. Now at the edge of the Atlantic Ocean, the sandstone strand was once an inland riverbed 500 kilometres from the ocean when several reptiles up to 20 centimetres in length -- and looking "a bit like a gecko," says Falcon-Lang -- made their mark more than 300 million years ago.
"The footprints were found as I tripped and fell while climbing," he told. "The boulder I grazed my knee on was covered in reptile tracks."
Falcon-Lang, who has made several important discoveries in Eastern Canada over the years, added: "While looking at the rocks, I could imagine the earliest reptiles scampering around a contracting water hole -- the first pioneers to invade the dry continental interiors."
At least three separate creatures, all from the era when certain amphibian species were morphing into reptiles, are believed to have left trackways at the site: Hylonomus lyelli, Dendrerpeton and Calligenethlon.
The world's earliest reptile-body fossils come from a 315-million-year-old coastal setting in Nova Scotia. And reptile tracks of a similar age were found by Falcon-Lang and other scientists in New Brunswick in 2007.
The new find pushes back the history of reptile life by a "trifling" few million years, Falcon-Lang says. But more importantly, he argues, it represents the moment when such advanced species began colonizing inland environments -- a key stage in the evolution of animals from marine to terrestrial habitats. Key to this transition was the reptile's development of eggs with hard shells that could be laid on land, giving the creatures the freedom "to explore the heart of the Pangaean supercontinent," Falcon-Lang says.
"At first, life was restricted to coastal swamps where lush rainforest existed, full of giant ferns and dragonflies," co-author Mike Benton, a University of Bristol paleontologist, states in a summary of the study. "However, when reptiles came on the scene they pushed back the frontiers, conquering the dry continental interiors."
While relatively small and simple compared to later reptiles, says Falcon-Lang, the creatures that left the footprints were part of an animal-invasion wave "that gave rise to both the dinosaurs and the mammals, the group to which we belong. So the story we report of reptiles invading the continental interiors actually laid the foundations for all diverse land ecosystems that followed, including humans."
He added: "It was one small step for a reptile, but one giant leap for life on land."
No comments:
Post a Comment