A stumpy-legged creature that was half a metre long and boasted a surprisingly long toe on each of its hind feet has been discovered by experts analysing fossils from a prehistoric lake in Scotland.
The creature is thought to have lived around 330m years ago – a time when what is now Scotland sat on the equator and featured not only a warm climate but a wealth of vegetation and even volcanic eruptions.
Dr Timothy Smithson, co-author of the research at the University of Cambridge, said the rocks in which the fossils were found were laid down in an isolated lake, but that the animal would have lived on the land as the lake would have been too hot, or had the wrong chemical balance, to sustain life.
“There were no fish or other aquatic animals in the lake until much later,” he said, adding that a diverse array of fossils have previously been recovered from the quarry including scorpions, millipedes and a limbless snake-like creature.
“They seem to have fallen or been chased into the lake, were unable to get out, died either because it was hot water, or chemically unsuitable for survival, or they drowned and then sunk to the bottom,” said Smithson.
Writing in the journal Communications Biology, Smithson and colleagues report that they named the newly discovered creature Termonerpeton makrydactylus.
The moniker means “boundary crawler” and “elongated toe”, and refers to the boundary walls near the East Kirkton quarry where the late Scottish fossil collector Stan Wood is thought to have found the specimen in the mid-1980s, and the unusually long fourth digit of the creature’s hind feet.
Smithson said the creature would have looked a bit like a lizard, with big feet but stumpy legs, adding the creature’s long toe was unusual in an animal from that time.
“A similar long fourth toe is found in living lizards where it is thought to extend the stride length and thus allowing them cover ground more quickly. It may also help the animal negotiate a variety of substrates from firm ground to shingle and sand,” he said. “This may have been advantageous to Termonerpeton too, helping it to escape predators and also negotiate an area prone to volcanic ash falls as well as the firm soil and leaf litter.”
Smithson added the creature lived before the two modern groups of tetrapods – amphibians such as frogs and newts, and amniotes such as reptiles and mammals – evolved.
“It was on the line leading to reptiles, birds and mammals but was not a direct ancestor of any of these,” he said.
It is thought the fossil of the long toed-creature, which includes bones of the ribs, pelvis and left leg and hind foot among other features, sat in a drawer after it was donated by Wood to the University Museum of Zoology in Cambridge in the 1990s, and when it was first examined it was thought to be an example of another animal that had already been discovered. But the new analysis reveals it to be something different.
“It is exciting because it shows for the first time that early tetrapods were experimenting with different ways of growing their feet to deal with walking on land,” said Smithson.
“The finds at East Kirkton quarry represent the earliest evidence anywhere in the world of terrestrial tetrapods, animals that seemingly lived all their life on land,” he added. “They lacked any evidence of amphibious habits – although we have no evidence of how they may have reproduced.”
Dr Nick Fraser of the National Museums Scotland, which houses one of the other East Kirkton quarry fossils, but who was not involved in the study, said the findings were exciting, not least as they show the evolution of terrestrial locomotion in early tetrapods was complex, and did not follow a regular pattern.
“For me it also suggests that the amniotes had started to flourish somewhat earlier than previously thought,” he said. “We are seeing a much greater diversity of different types from this time period.”