Monday 30 November 2015

Evidence of Shark predation on Whale bones from the Early Pliocene of South Africa.

Despite extending for almost 2000 miles, the west coast of South Africa is home to relatively few fossil-producing marine deposits. Two sites that are particularly productive are the Miocene-Pliocene deposits at Duinefontein and Langebaanweg, which have produced material attributed to a variety of different Whales and Sharks as well as Teleost Fish, other Marine Mammals and Birds, which are helping scientists to develop an understanding of the environment and ecological relationships present on the west South African Coast at that time.

In a paper published in the South African Journal of Science on 27 November 2015, Romala Govender of the Natural History Department at the Iziko Museums of South Africa, describes a series of fragmentary Whale bones from Duinefontein which show score marks attributed to the actions of Sharks.

The material comes from the Shark Tooth Bed at Duinefontein which is thought to be about 5 million years old, making it early Pliocene, and is extremely fragmentary, as well as showing wear signs consistent with having been roled on a beach prior to its eventual burrial, all of which prevents assignation of the bones to any particular Whale. The Shark Tooth Bed, as well as producing numerous Shark Teeth has produced a variety of Fish, Mammals and Birds, though most of the material is fragmentary; the bed is thought to have been laid down behind a barrier spit that was overtopped by spring tides or storm events, it has been suggested that it may even be a tsunami deposit.

The Cetacean (Whale) material from this site comprises vertebral centra, tympanic bullae, periotics, isolated teeth and cranial fragments. Several of the fragments, particularly those from the cranium and jaws, show score marks and patterns of groves consistent with a Shark having bitten down upon the bone then pulled backwards, a method of feeding common in the modern Great White Shark, Carcharodon carcharias.

 (a) CF2 bite marks on the lateral surface of cranial fragment (SAMPQMB-D-1342) (arrow 1, arrow 2). (b) CF2 bite mark on ventral surface of SAMPQMB-D-1342. (c) B1 bite mark on the lateral surface of a mandibular fragment (SAMPQMB-D-1182). (d) B2 bite mark on the small cranial fragment (SAMPQMB-D-1339) (arrow). (e) B2 bite mark on cranial fragment (SAMPQMB-D-1340) (inset close-up of damage). (f) B2 bite mark on the lateral surface of cranial fragment (SAMPQMB-D-1342) (inset close-up of damage). Govender (2015).

Such bite marks around the head are typical of Sharks feeding on dead Whales, which tend to concentrate their efforts around the head, where preferred food items such as the tongue are found, though this does not preclude the Whale having died as a result of a Shark attack. The exact nature of the attacker cannot be determined from the material, though it would have been a Shark with non-serated teeth such as a Great White, a species that specializes in this sort of feeding and the which numerous teeth of have been found at Duinefontein (and which is still present on the same area of coast today). Other Sharks known to have been present on the west South African Coast during the Early Pliocene include Mako Sharks, Isurus sp. and Cosmopolitodus hastalis, Ragged Tooth Sandtigers, Carcharias tarsus, Megalodon Carcharodon megalodon, and possibly Lemon Shark Negaprion brevirostris.

See also... megalodon: Did the Megashark get bigger over time?                                    The largest Shark ever to live was Carcharocles megalodon, which reached sizes of about eighteen meters and survived from the Middle Miocene until the end of the Pliocene. This was formerly thought to...
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