Researchers have discovered the fossilized remains of a small, lizard-like creature that is the missing ancestral link between human beings and the fish we evolved from millions of years ago.
The remains of the creature, dubbed ‘tiny,’ were found in the Scottish Borders in south eastern Scotland in a piece of rock smaller than a clenched fist, after people saw a small part of its skull sticking out.
‘Tiny’ was one of the first four-legged creatures to move onto land – making it our ancestor and filling in a 15-million year fossil gap when fish transitioned to becoming land dwellers.
Researchers have discovered the fossilized remains of a small, lizard-like creature dubbed ‘Tiny’ that is the missing ancestral link between human beings and the fish we evolved from millions of years ago. Pictured is a rendering of what Tiny might has looked like
The fossil, whose analysis was funded by the UK’s Natural Environment Research Council, is just one of many fossils discovered in the Scottish Borders.
About 360-345 million years ago, Scotland was a very different place.
It lay close to the Equator, when many of Earth’s continents and landmasses were connected.
Scotland’s land was hot, humid and experienced droughts and flooding.
It was here that tetrapods: backboned animals with four limbs, invaded land – a major evolutionary event.
For many years, scientists were not sure how this had happened because there was a 15 million year ‘gap’ in the fossil record – no four-legged fossils had been found dating from that time, so there was no evidence to show this step had taken place – except for the Tiktaalik rosae fossil, a lobe-finned fish that lived 375 million-year-old fossil and is considered by many researchers to be the best-known transitional species between fish and land-dwelling tetrapods.
That was until the late fossil hunter Stan Wood began excavations in the Borders area of Scotland, where he uncovered a haul of four-limbed creatures that help explain the evolutionary mystery.
Still, the question of why creatures move from water to land remains, but with every new find like Tiny, researchers say they’re coming closer to answering that question.
Illustration of tetrapods on land. About 360-345 million years ago, Scotland was a very different place. It lay close to the Equator, when many of Earth’s continents and landmasses were connected. Scotland’s land was hot, humid and experienced droughts and flooding
HOW FINS BECAME LEGS
The Tiktaalik rosae was a lobe-finned fish that lived in the late Devonian period, but had features similar to four-legged animals.
A 375 million-year-old fossil Tiktaalik roseae fossil was discovered in 2004 on Ellesemere Island in Nunavut, Canada.
It represents the best-known transitional species between fish and land-dwelling tetrapods – until the discovery of the more recent ‘Tiny’ fossil.
A fish with a broad flat head and sharp teeth, Tiktaalik looked like a cross between a fish and a crocodile.
The Tiktaalik Roseae fossil shows how animals moved from sea to land. This photo released by Nature shows the preserved remains of what was once described as the ‘missing evolutionary link’ between fish and tetrapods
It had gills, scales and fins, but also had tetrapod-like features such as a mobile neck, robust ribcage and primitive lungs.
In particular, its large forefins had shoulders, elbows and partial wrists, which allowed it to support itself on ground.
In 2013, researchers re-evaluated the fossil and discovered that the fossil had a well-preserved pelvis and fin.
The find challenged the theory that large, mobile hind appendages were developed only after vertebrates transitioned to land.
Previous theories, based on the best available data, propose that a shift occurred from “front-wheel drive” locomotion in fish to more of a ‘four-wheel drive’ in tetrapods.
The first ‘fish’ to walk out of the sea 375 million years ago was able to survive out of water because it had developed a neck, wrist and elbow. The crocodile-like Tiktaalik Roseae had fins and gills but also features found only in land-living animals
But experts claim this shift actually began to happen in fish, not in limbed animals.
For example, the team discovered the Tiktaalik’s pelvic girdle was nearly identical in size to its shoulder girdle.
It had a prominent ball and socket hip joint, which connected to a highly mobile femur.
Crests on the hip for muscle attachment indicated strength and advanced fin function.
And although no femur bone was found, pelvic fin material – including long fin rays – indicate the hind fin was at least as long as its forefin.
David Millward, a geologist at NERC’s British Geological Survey, said: ‘Every specimen tells us something new.
‘Tetrapods are our ancestors.
‘They are the missing evolutionary link from fish and on to lizards, then ultimately to birds, dinosaurs, mammals and to us as people today.
‘If tetrapods had not made that fundamental step we would not be where we are today.’
Millward suggested one theory of why creatures moved to the land:
‘There were some very big, carnivorous fish in the lakes and creeks and no large predators on land so developing limbs to live on land would give any creature an advantage.’
Millward says that he is sure there are numerous other specimens worldwide, though the only other major site where tetrapods have been found so far is in Canada – where the Tiktaalik fossil was found.
Unlike in Scotland, researchers in Canada have also discovered well-preserved footprints which are helping to create a better understanding of how these ancient animals moved on land.
‘We haven’t found good footprints here yet,’ Millward says, ‘but we’re still looking.’