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Some early amphibians had legs strong enough to do press-ups, according
to American palaeontologists who have found the shoulder bone of an early
amphibian in Pennsylvania. The bone, which is 365 million years old, shows
markings where strong muscles were once attached.

Only one older amphibian is known: the 370-million-year-old Scat Craig
fossil found three years ago in Scotland. However, scientists were unable
to study the creature’s legs because the fossil was too fragmentary.

Amphibians evolved more than 370 million years ago from freshwater fish
that had bony lobe-shaped fins, similar to those in lungfish. The new amphibian,
named Hynerpeton, is described by Edward Daeschler of the Academy of Natural
Sciences of Philadelphia in Science (vol 265, p 639). When taken together
with other fossils, Daeschler says it points to the evolution of a range
of amphibians, instead of there being just a single evolutionary path.

So far, Daeschler has found only the shoulder and some skull fragments.
However, according to his colleague, Neil Shubin of the University of Pennsylvania,
the shoulder is the bone that reveals the most about early amphibians.
Marks on the bone show that the leg was strongly muscled, and could pivot
for walking. There is no sign of a ridge where gills attached in other amphibians,
indicating that Hynerpeton was adapted to breathing air.

The creature was up to a metre long, and weighed about 10 kilograms.
It lived in a flat, marshy tropical area beside a stream. Early amphibians
may have evolved strong limbs to move in shallow water, and then moved toward
the land, which plants and insects had colonised. Some specialists think
amphibians came ashore to exploit food resources, but Daeschler suggests
the real advantage was escaping predators. ‘It was a fish-eat-fish world,’
he says.