Walking in footsteps of dinosaurs

NO dinosaur remains have been found in Ireland, or so I thought.

However, on a visit to Belfast’s Ulster Museum this month I was shown two pieces of fossilised bone, found by a teacher in County Antrim 20 years ago.

According to Dr Mike Simms, curator of palaeontology at the museum, one of them is from the leg of a bi-pedal meat-eater. The other belonged to a vegetarian known as a scelidosaurus.

My grandson Tommy, aged four, is an expert on the great beasts of the past. A book in his extensive dinosaur library has a picture of scelidosaurus. The four-metre long ‘limb lizard’ walked on all fours, its body encased in light armour. With hind legs slightly longer than the front ones, its back and tail were up in the air. This is the earliest dinosaur for which a complete fossil skeleton exists. Richard Owen, the anatomist who coined the term ‘dinosaur’, examined and named it in 1859, the year in which Darwin’s The Origin of Species appeared.

Sceldosaurus lived about 200 million years ago, when the great super-continent known as Pangaea was beginning to break up. What is now Britain and Ireland would become part of the land-bridge connecting Europe to North America but the continents did not finally separate until around 65m years ago. Being at a crossing point, this part of the great land mass had lots of dinosaurs. Many fossil specimens have been found in Britain but, oddly, not in Ireland.

Going back much further in time, however, we have evidence of a creature so ancient that it makes scelidosaurus look like a Johnnie-come-lately. Footprints on a stone pavement in Valentia Island were left by an animal from a period as remote from the dinosaur era as scelidosaurus is from ours. The Devonian tetra-pods, to which the Valentia animal belonged, were the first land animals.

Around 380m years ago all animals lived in the sea. Eighty million years later, legged fish-like creatures were out on land. The transformation from fish to amphibian was one of the most extraordinary in evolutionary history, more profound even than the subsequent development of reptiles birds and mammals. How the first tetra-pods evolved has been one of the hottest topics in palaeontology.

Until recently, there was an acute shortage of tetra-pod fossils. The most important one was found in Greenland by the Swedish scientist Erik Jarvic. According to an excellent documentary, transmitted recently on BBC 4, he worked on the specimen for decades but denied all other scientists access to it. Visits to Greenland required permits from the Danish authorities, who always refused requests from palaeontologists for fear of offending Jarvic. As a result, the field of tetra-pod research was moribund.

Ancient fish, Jarvic argued, made sorties onto land, much as mud-skippers do today. They used their fins to shuffle along. These then evolved into limbs with fingers and toes. Enter the British palaeontologist, Jennifer Clack. Having worked on a fossil from Bradford Museum she was interested in tetra-pods. Without access to a prime specimen her work was stalled. Then, in an extraordinary stroke of luck, she got hold of a fossil from Greenland which a geology student, unaware of its importance, had brought back to Cambridge. It was of a different species to Jarvic’s, so she argued that studying it would not encroach on his work. She met the reclusive Swede. They got on well and he relented. In due course the Danes issued the coveted permit. Clack’s expedition to Greenland would turn tetra-pod evolutionary theory on its head.

Early tetra-pod limbs, Clack showed, were not weight bearing. Fish living in swamps, she argued, used them to penetrate dense aquatic vegetation. Nor had they five digits. One species was shown to have seven, another eight; the limbs were webbed. Only later would they evolve into the legs that amphibians have today. Jarvic, however, insisted that his specimen had five digits but what he had thought were thumbs with cracks along the bones were, in fact, several digits close together.

If only we had a fossil of the Valencia tetra-pod!