370 MILLION YEARS AGO

Eventually however all of the great mountain range (the Calendonide) was eroded away and the sea came in again from the south. It was now 370 mya and much of Ireland basked in a shimmering warm shallow tropical sea. Sea life was abundant and as time passed the remains of corals and shellfish built up on the sea floor and became consolidated into limestone. In time this sea also retreated.
It is considered that the Tetrapod Tracks on Valentia Island were laid down around this time (maybe 350 million years ago) - these tracks are the oldest known evidence of the existence of a Tetrapod creature (see bottom right for an image of what the Tetrapod may have looked like).

Tetrapod recreation by BBC NI