SUMMER 2003 No. 17

Page 6

These new improved Carnivores fit into two major groups: the Feloidea, cat-like carnivores, which includes the civet, cat and hyena families, and the Canoids, the dog-carnivores such as the dog, bear, racoon, and mustelid families. Here, finally, with the early mustelids, we arrive at our first recognisable prototype otters. The earliest known otter-like species, hailing from prehistoric Europe at 30Ma, is Potamotherium (below) from the Upper Oligocene, described 30, 001, 957 years later in a scientific paper.

Miocene (25Ma-5Ma)

Potamotherium is found in Europe until the Late Miocene and in North America during the Late - Upper Miocene. From around 25Ma and the mid-Miocene another species, named Paralutra jaegeri, measuring about 1.5m long, appears in France. Palaeontologists believe Paralutra may have been ancestral to modern otters.

Certainly both species share the otter body plan, with elongated, flat, broad heads, short stocky limbs and streamlined, sinuous bodies, ending in a powerful tail. Of the senses, as revealed in the skull through the configuration of portals for nerve connections, smell was perhaps limited, but sight and hearing were acute.

Dentition consisted of sharp cutting teeth, which suggests that at this stage our proto-otters were largely piscivorous but, like modern mink, conceivably took other prey as well when opportunities arose. With their flexible backbones we can imagine these otter forerunners darting lithely through the riverside undergrowth of the Miocene, snapping up the odd bird, amphibian or small mammal while chasing some ancient species of freshwater fish.

From these riparian beginnings early otters discovered they could also feed on the hard-shelled invertebrates they found there, such as crabs and crayfish. By the end of the Miocene some otters had developed modifications for tackling this crunchy prey, in the form of blunter-cusped, shell-grinding teeth. These otters took up a new way of life at the river mouth and in estuarine habitats where such Crustacean and shellfish food was plentiful. These would become the precursors of coastal and marine 'clawless' otters such as Aonyx. The fossil record shows the modern otter genera Lutra, to which the European Otter belongs, and, possibly, Aonyx, originating in the Upper Miocene.

Pliocene (5-1.6Ma) and Pleistocene (1.6-0.01Ma [i.e. 10 000 years ago])

The two distinct groups – river and coastal otters – presumably diverged further throughout the Pliocene and Pleistocene. Europe underwent serial ice ages, with glaciers reaching as far south as The Wash. Meanwhile the otter picture is complicated: many fossil remains are known, with different experts recognising some 4-13 different species from the same range of specimens. From many Mediterranean fossil finds, Pleistocene Europe was evidently home to the Lutra river otters and the Aonyx coastal otters, as well as, discovered in the 1980s, the massive Megalenhydris, a huge otter akin to the US Sea Otter that was even larger than today’s Amazonian Giant Otter (Pteronura). Although Lutra evolved first, the Aonyx coastal otters, widely distributed across Africa, China and India since the Pliocene, were the dominant European otters until the Middle Pleistocene. At 95 000 years ago, we are now very close to the emergence of today’s European Otter Lutra lutra, though the available evidence is harder to interpret and there is some debate as to an immediate ancestor.