The world’s largest and heaviest dwelling carnivore is just not an enormous cat, a bear or a wolf: it’s the southern elephant seal (Mirounga leonina). Bulls of this species might be 5 metres lengthy and might 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 you may suppose that the ancient ancestors of these and different massive seals would go away ample proof of their presence within the fossil report. That’s partly true; there’s an extensive global body fossil record for seals. But, till now, there’s been no documented proof of fossilised seal traces – the tell-tale indicators of these huge animals dragging their flippers whereas hauling themselves alongside ancient 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 current data about what varieties of animals roamed this panorama way back, in addition to what the panorama might have appeared like – an necessary half of understanding what’s modified over time and the way it may change because the local weather shifts.
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Many completely different creatures
The Cape south coast ichnology challenge began in 2008. Ichnology is the research 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 supplied a census of which creatures left traces of their passage on these ancient dunes and seashores: elephants, crocodiles, large birds – and even hominins, human ancestors. There have been tiny members of this assorted neighborhood, too; we’ve reported on gerbil and spider tracks and traces.
Seals’ absence from the worldwide ichnology report 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 these environments would protect fossil traces of seals.
However, massive colonies might be discovered on distant sandy seashores, and particular person seals usually haul up on seashores, each of which could go away a hint fossil report.
Two websites
One of the 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, according to front-flipper traces. Taken collectively, these options are extra according to traces of a fur seal than these of an elephant seal. Both species happen on the shoreline at the moment, however Cape fur seals are way more widespread.
Cape fur seals usually collect into dense rookeries, some of which comprise tons of of 1000’s of seals; one such rookery might be discovered at Cape Cross in Namibia. Seals in rookeries on seashores might create depressions within the sand which might be moulds of their outlines, and that is what the proof on the second web site suggests. Four massive impressions are according to moulds of juvenile seals, and one of these comprises what seems to be a flipper impression.
Microscopy of skinny sections sampled from the rock surfaces enabled us to determine that each websites are from seashore slightly than dune environments. This helped to corroborate our interpretation of the tracks as seal traces. Meanwhile, optically stimulated luminescence dating studies carried out on the University of Leicester indicated that the seals inhabited these seashores about 75 000 years in the past.
More to seek out?
The notion of seal traces, made so way back on these seashores, being evident on rock surfaces at the moment might be considered exceptional. Our findings assist to fill what was a considerable hole within the international ichnology report. Our discoveries will hopefully spur researchers elsewhere to search for related traces to raised perceive what elements of the ancient world seals occupied, and when.
Charles Helm, Research Associate, African Centre for Coastal Palaeoscience, Nelson Mandela University
This article is republished from The Conversation beneath a Creative Commons license. Read the original article.
