Canadian and British scientists studying 300-million-year-old fossil sites in Atlantic Canada and Europe have concluded that a sudden, global warming-driven collapse of rainforests actually helped catapult the Earth’s earliest reptiles — the distant ancestors of dinosaurs and mammals alike, including humans — to the top of the era’s evolutionary pecking order.
The apparent “burst” of reptile biodiversity during what’s called the Carboniferous age was identified by the researchers after they probed evidence from the UNESCO World Heritage fossil site at Joggins, N.S., and other telltale locales.
The scientists believe the biological turning point occurred when the collapse of rainforest ecosystems created remnant pockets of treed habitat where species adapted in relative isolation, ultimately strengthening the reptilian gene pool.
“Climate change caused rainforests to fragment into small ‘islands’ of forest,” University of London paleontologist Howard Falcon-Lang said in a summary of the findings. “This isolated populations of reptiles and each community evolved in separate directions, leading to an increase in diversity.”
The process was a “classic ecological response to habitat fragmentation,” said co-author Mike Benton of the University of Bristol. “You see the same process happening today whenever a group of animals becomes isolated from its parent population.”
The lead author of the study, published in the latest issue of the journal Geology, was Canadian scientist Sarda Sahney, also at the University of Bristol.
“It is fascinating that even in the face of devastating ecosystem-collapse, animals may continue to diversify through the creation of endemic populations,” Sahney stated in the summary. But she warned that “life may not be so lucky again in the future, should the Amazon rainforest collapse” in a period of extreme climate change.
Last week, in another new study detailing a seismic shift in the ancient evolution of species, a team headed by scientists from the University of Alberta detailed how mammals surged in size and distribution following the disappearance of dinosaurs.
In the current study, fossil beds in Atlantic Canada served as “three of our most important sites in the database,” Falcon-Lang told Postmedia News on Monday, noting how preserved plant and animal remains at Horton Bluffs and Sydney, N.S., were also key to reconstructing the primordial environment.
“Joggins is ‘home’ to the oldest known reptile — Hylonomus lyelli,” he stated via email, referring to a 20-centimetre-long fossil species found by famed Canadian geologist William Dawson in 1859.
The extinct animal is considered a bridge between amphibians and their more complex reptile cousins, which eventually gave rise to ancestral mammals and — about 200 million years ago — to the dinosaur branch of the reptile family.
“In a sense, the whole story starts at Joggins with the origin of reptiles,” said Falcon-Lang.
During the time when reptiles emerged at sites such as Joggins, the world’s continents were fused in a single supercontinent called Pangaea and the future landmasses of Canada and northern Europe were located in tropical climes near the Earth’s equator.
“When reptiles first evolved (about 315 million years ago) they were adapted to dry conditions, because reptiles lay eggs with hard shells rather than spawn in ponds like frogs,” said Falcon-Lang. “However, when rainforests collapsed around the tropical belt (about 305 million years ago), the reptiles were ‘ready’ and got their ‘big break,’ rapidly diversifying.”
Falcon-Lang has been involved in several other landmark finds in Eastern Canada. Earlier this year, he was part of a team that announced the discovery of fossilized reptile footprints left behind 318 million years ago in present-day New Brunswick.
Those ancient trackways along the Bay of Fundy shore are believed to be the world’s earliest evidence of reptilian life, and also the first known signs of vertebrates — animals with a backbone — living in what was then a continental interior, far from any ocean coast.