Linda here –
Due to the global pandemic, much of the field work in almost all geoscience disciplines has come to a halt. While this means we cannot travel to discover new sites, collect new samples or do field experiments, this leaves us lots of time to commemorate all the exciting field experiences we’ve had in recent years.
Here I would like to introduce you to a small, but very important outcrop I visited a few years ago: the tetrapod trackway on Valentia Island (Co. Kerry, Ireland).
Valentia Island is a fairly small island in the eastern North Atlantic, just off the western coast of Ireland, it is in fact one of the westernmost points of the entire country. The outcrop itself is located on the northern coast of Valentia Island, and when I say on the coast, I don’t mean near the coast, I mean the literal edge of the island, partially under water.
The outcrop consists of Middle Devonian sandstones and slate called the Valentia Slate Formation. Life in the Devonian was very different from today, the first ammonites had just appeared, trilobites were common. Fish diversity was at an all time high, placoderms roamed the oceans.
On land, the first plants developed proper roots, leaves and seeds, by the end of the Devonian forests were widespread. And the tetrapods made their first steps on land, too.
A few of these very early steps have been recorded by the muddy sediments that later became the Valentia Slate Formation.
Unfortunately these imprints are quite rough, the shapes are irregular and no digits can be identified. Still, researchers have been able to determine that this creature must have been able to support its own weight on its four legs, because no body or tail drag marks are visible, it was clearly walking, not crawling or swimming. It’s approximate body length was 0.5-1m (20-40 inch) and its hands were probably smaller than its feet (Stössel et al. 2016).
A reconstruction of the tetrapod that has left these tracks for us to find is depicted on a sign on a path leading to this publicly accessible outcrop.
The outcrop is an Irish National Heritage Area, though it is threatened by erosion. When I visited, the tracks were actually filled with sea water and every once in a while a wave would wash over the outcrop. Fortunately, recently two more sites within the same formation have been discovered that contain very similar tracks and thus will aid us in our understanding of these very early tetrapods.
Stössel, I., Williams, E.A., and Higgs K. (2016) Ichnology and depositional environment of the Middle Devonian Valentia Island tetrapod trackways, south-west Ireland. Palaeogeogr. Palaeoclimatol. Palaeoecol., 462, pp. 16-40