Mammals in the British Isles. L. Harrison Matthews
of the species of this extensive list are typical of colder climates such as the ground squirrel, pine vole, glutton, and musk ox; and others of warmer ones such as the monkey, spotted hyaena and hippopotamus. The majority, on the other hand, are species that might live under a temperate climate like that of the present day in the British Isles. When the Cromerian stage drew towards its end the climate became cooler, and mixed oak forest was replaced by boreal forest with pines and birch, and with open heaths, until the Anglian glacial stage wiped out most of the flora and probably all of the mammalian fauna. The history of the present mammalian fauna of the British Isles must therefore start at the end of the Anglian glaciation, which wiped the slate clean for a new start, leaving us only a few tons of fossil bones from which to infer what had gone before.
It is not surprising that hardly any mammalian fossils are known from the Anglian glaciation, for at its severest the southern part of the country, the only part that was not covered by the deep ice sheet, was an arctic desert. The few that have been found are assigned to the early or late parts of the stage when glaciation was developing or retreating – a ground squirrel to the former and the red deer to the latter. As, furthermore, no vertebrate fossils of other classes are known from the Anglian the conclusion that the glaciation exterminated the entire mammalian fauna is inescapable. The deposits of the Anglian stage are a complicated series of tills, including the Boulder Clay, produced by the ice moving in different directions at different times as the glaciation proceeded.
When the ice at last retreated the temperate flora and fauna of the Hoxnian stage gradually moved in from the continent as the desert gave way to tundra, then to boreal forest followed by mixed oak forest. The fossils of this interglacial stage are preserved mainly in freshwater deposits, though some marine and estuarine deposits exist from its later part. It was during this stage, too, that man first made his way into the British Isles, for his palaeolithic flint artifacts have been found in several places. The former claim that man had been present at a much earlier time is now discredited – the ‘eoliths’ from the Crag that were supposed to be primitive tools are no more than fortuitously broken stones. The only skeletal remains of alleged palaeolithic man living in the Hoxnian stage that have been found in the British Isles are some fragments of a skull from the Thames terrace gravel at Swanscombe, Kent. One bit of the skull was found in 1935, another in 1936, and a third in 1955. Although Oakley in 1969116 tabulated the Swanscombe skull, among the ‘early Neanderthaloids’ dating from about a quarter of a million years ago, the fragments, the occipital and two parietal bones, are indistinguishable from those of modern man. Since then there has been some controversy about the dating of the Hoxnian interglacial119’ 127; but a dating of material from ‘a few centimetres below’ the horizon of the Swanscombe skull gave ages of up to more than 272,000 years.139 This, unfortunately, does not give irrefutable proof of the age of the skull, and still leaves open the possibility advocated by some that the skull fragments may have become included in the gravel as intrusions at a later date. With the possible exception of the Swanscombe skull, the earliest remains of man in the British Isles, apart from his artifacts, date from the middle of the Devensian glaciation, at least some two hundred thousand years later.
The Hoxnian mammalian fauna that moved in from the continent differed from that of the Cromerian, although many species were the same, or similar, such as the beaver, some voles, the wolf, marten, lion, boar, the straight-tusked elephant Palaeoloxodon antiquus, and the red, fallow, and roe deer. New arrivals included the arctic lemming, several voles, the cave bear, two species of rhinoceros replacing Diceros etruscus, Megaceros giganteus replacing several other species of giant deer, and the aurochs. Those that did not return, or were by then extinct, included the vole genus Mimomys, the sabre-tooth, the southern elephant, etruscuan rhinoceros, hippopotamus, zebrine horses, several species of deer, giant deer, and elks, the bison and musk ox.
When the climate became colder with the onset of the Wolstonian glaciation which reached its peak about 140,000 years ago, the fauna became more typically arctic, and those parts of the country not covered with ice were inhabited by hamsters, the arctic, Norway and steppe lemmings, the woolly mammoth, Mammuthus primigeneus, the woolly rhinoceros, Coelodonta antiquitatis, and the reindeer Rangifer tarandus.
At the end of the Wolstonian stage, about 120,000 years ago, the temperate Ipswichian interglacial stage began and lasted about 50,000 years. The climate and flora followed the usual sequence of an interglacial stage, the temperature reaching a peak higher, however, than that of the present day, and the flora progressing from arctic tundra to boreal forest, mixed oak forest and then regressing by similar steps to the onset of the next glaciation. Mammalian remains of the Ipswichian occur in river and lake gravels, muds, and brick earths, and in the deposits of some caves. Many of the mammals are species that form part of our present day fauna, and include the bank, water and field voles, the wood mouse, the red fox, badger, and wild cat, the red, fallow and roe deer; and some extinct only in historic times such as the beaver, wolf, brown bear, wild boar and aurochs. The cooler parts of the stage were also marked by the presence of ground squirrels, the woolly mammoth and the musk ox, whereas the warmer parts supported the spotted hyaena, the lion, the straight-tusked elephant, two kinds of rhinoceros, the giant deer, and the hippopotamus, the last indicating a comparatively high temperature as does the presence of the European pond-tortoise Emys orbicularis. Palaeolithic man, as shown solely by his artifacts, was present throughout the stage.
The following Devensian glaciation began about 70,000 years ago and lasted nearly sixty thousand years until it came to an end rather quickly about 10,000 years ago. It was the least severe of the three great glaciations as it left southern England and the midlands free of ice and thus a possible habitat for many species that can withstand a cold climate. During this stage the sea fell some three hundred feet below its present level so that England was widely connected with the continent over the site of the southern part of the North Sea, and northern Ireland was narrowly connected with southern Scotland. Stuart136 remarks that the vast majority of Pleistocene vertebrate remains found in the British Isles, excluding post-glacial material, is probably of Devensian age. Most of the remains are found in river gravels and caves, some of the later ones in lake sediments. The flora of the ice-free regions was mostly tundra or open grassland, with some patches of boreal forest during short interstadial recessions of glaciation.
The fauna is typical of cold regions, though it includes some species of our present fauna such as the common shrew, the bank, water and field voles, the mountain hare, the fox, stoat, polecat, and red deer. Some of the species are not now associated with severely cold climates but nevertheless can withstand more cold than might be supposed; these are the leopard, lion, and spotted hyaena. On the other hand there are many species typical of colder habitats: a pika Ochotona, ground squirrel, the arctic lemming, several voles including the northern and tundra voles Microtus oeconomus and M. gregalis, the arctic fox Alopex, polar bear, glutton, woolly mammoth which became extinct at the peak of the glaciation about 18,000 years ago, woolly rhinoceros, reindeer, and musk ox. Several other large mammals left abundant remains in gravel and cave deposits; they include the wolf, the brown and cave bears Ursus arctos and U. spelaeus, a sabre-tooth Homotherium, the horse, giant deer, elk, a bison Bison priscus, and the aurochs.
Man returned after the peak of the Devensian glaciation as shown by his artifacts and by a few skeletal remains.30 Some human teeth of middle Devensian age from Picken’s Hole cave in Somerset are the earliest human remains known in the British Isles apart from the Swanscombe skull whose alleged age has been challenged by some people. The largest find of palaeolithic man belongs to the late Devensian deposits of Aveline’s Hole in the Mendip Hills of Somerset, where bones representing thirty-one skeletons were excavated.
As the ice melted during the late glacial stage of the Devensian the climate became milder and reached a peak after about a thousand years in the Allerød interstadial or ‘amelioration’ as it is sometimes called, though amelioration could have a different meaning for a reindeer than for a red deer. Thereafter the climate again became colder until about 10,000 years ago when the ice finally disappeared inaugurating the Flandrian interglacial which has lasted until the present. By the end of the late glacial many of the large mammals had become extinct, although there appears to be no reason why they should