South Africa: Flipper Traces Reveal the Presence of Historic Seals On South Africa’s Coast

The world’s largest and heaviest dwelling carnivore is just not an enormous cat, a bear or a wolf: it is the southern elephant seal (Mirounga leonina). Bulls of this species may be 5 metres lengthy and may weigh as much as 3,500kg. The Cape fur seal, in the meantime, can develop to three.9 metres and weigh as much as 360kg. A big African lion, by comparability, weighs 250kg.

So that you would possibly assume that the traditional ancestors of those and different giant seals would depart ample proof of their presence within the fossil document. That is partly true; there’s an extensive global body fossil record for seals. However, till now, there’s been no documented proof of fossilised seal traces – the tell-tale indicators of those massive animals dragging their flippers whereas hauling themselves alongside historical seashores.

Our new research, from South Africa’s Goukamma Nature Reserve on the nation’s Cape south coast, modifications that. The traces we found and described are from two websites that date again about 75,000 years.

This provides to our present data about what sorts of animals roamed this panorama way back, in addition to what the panorama might have appeared like – an necessary a part of understanding what’s modified over time and the way it would possibly change because the local weather shifts.

Many various creatures

The Cape south coast ichnology venture began in 2008. Ichnology is the examine of tracks and traces. Since then our staff has recognized greater than 300 vertebrate tracksites alongside a 350 km stretch of the South African coastline. The tracks and traces date again to the Pleistocene epoch, which began round 2.6 million years in the past and ended 11,700 years in the past.

The tracks and traces are present in aeolianites (the cemented stays of dune surfaces) and cemented seashore deposits. The fossil websites have offered a census of which creatures left traces of their passage on these historical dunes and seashores: elephants, crocodiles, large birds – and even hominins, human ancestors. There have been tiny members of this diversified neighborhood, too; we have reported on gerbil and spider tracks and traces.

Seals’ absence from the worldwide ichnology document can most likely be defined by these mammals spending a lot of their time within the ocean, and to a choice for rocky islands, cliff-side ledges, and pebble seashores once they do come ashore. None of those environments would protect fossil traces of seals.

Nevertheless, giant colonies may be discovered on distant sandy seashores, and particular person seals usually haul up on seashores, each of which could depart a hint fossil document.

Two websites

One of many websites we studied was located on a north-facing slope of a sand-bar and exhibits a furrow created by sliding down the slope, full with hind-flipper drag marks. There are parallel grooves and nested grooves adjoining to it, per front-flipper traces. Taken collectively, these options are extra per traces of a fur seal than these of an elephant seal. Each species happen on the shoreline right now, however Cape fur seals are much more frequent.

Cape fur seals usually collect into dense rookeries, a few of which include a whole bunch of hundreds of seals; one such rookery may be discovered at Cape Cross in Namibia. Seals in rookeries on seashores might create depressions within the sand which can be moulds of their outlines, and that is what the proof on the second web site suggests. 4 giant impressions are per moulds of juvenile seals, and one in all these incorporates what seems to be a flipper impression.

Microscopy of skinny sections sampled from the rock surfaces enabled us to establish that each websites are from seashore fairly than dune environments. This helped to corroborate our interpretation of the tracks as seal traces. In the meantime, optically stimulated luminescence dating studies carried out on the College of Leicester indicated that the seals inhabited these seashores about 75,000 years in the past.

Extra to search out?

The notion of seal traces, made so way back on these seashores, being evident on rock surfaces right now may be considered exceptional. Our findings assist to fill what was a considerable hole within the world ichnology document. Our discoveries will hopefully spur researchers elsewhere to search for related traces to higher perceive what components of the traditional world seals occupied, and when.

Charles Helm, Analysis Affiliate, African Centre for Coastal Palaeoscience, Nelson Mandela College