Wednesday, 7 March 2012

On The Origins Of Amphibians And Their Oldest Ancestor

Between 370 and 300 million years ago, Scotland and Canada were joined together as part of the single super-continent Pangaea. They were covered in a single, gigantic swamp forest the remains of which can be found in rocks across the whole of northern Scotland and Canada. It is likely that the Rhynie Chert in Scotland, the remains of an ancient peat bog and the first ever terrestrial ecosystem, was the spawn point for this forest, evolving into the first trees and ferns.
An artist's impression of 'Ribbo'

Both landmasses have a rich evolutionary heritage from plants, arthropods to animals. Some of the most prized fossils from this era in the Earth's history are of the first ever amphibians. Their evolutionary history is fascinating and has been constructed from fantastically well preserved fossils. 

In fact there is such a large time period between the most amphibian-like fish and the first amphibians that it has been named Romer's Gap, after the American palaeontologist Alfred Romer, who first noticed the distinct lack of fossil evidence back in the 1980s. However a collection of fossil finds from Scotland has filled in a period within Romer's Gap, from 360 to 345 million years ago. The fossils were found over a 20 year period by Scottish palaeontologist Stan Wood near the village of Burnmouth on the Scottish Border.
The five toed foot of 'Ribbo'

However they have not been properly researched or understood until now. It was previously thought that low oxygen levels in the atmosphere had restricted the diversity of life on the land, leading to Romer's Gap. However these new fossils show that the land was thriving in a primitive sense of the word. One specimen, nicknamed 'Ribbo' is particularly well preserved, with a prominent bone structure and four five toed feet. Such a creature would need a decent food source in order to sustain its existence on the land.

Therefore a thriving terrestrial ecosystem would have had to have been present. The fact that this creature is 20 million years older than any other amphibian fossil discovered previously shows that life may have gained a foot-hold on the land far earlier than previously thought. Nick Fraser, keeper of natural sciences at National Museum of Scotland said: 'these fossils aren't much to look at in and of themselves, but they may prove to be profoundly important in advancing our understanding of the earliest development of land-dwelling life as we know it today.'