SOME REMARKS ON THE PLEISTOCENE MAMMALIA.
3
well to realise that just before man began to disturb them, they
attained their greatest size and most special development. Never
before or since had deer such large antlers, elephants such
unwieldy tusks, horses such effective grinders, or cats such power-
ful canine teeth. All "ran riot," so to say. Under these con-
ditions, they were all particularly variable in their most char-
acteristic features. We have thus to take into account not
only the variability due to differences in surroundings, but also
the inherent variability of overgrown parts.
Finally, we have to distinguish between the primitive Pleisto-
cene Mammals which exhibited this luxuriance of growth, and
some later local developments which may have been due only to
surrounding circumstances. At the present day in one part of
Alaska the bears, wolves, reindeer, and elk are all, for some
unknown reason, gigantic compared with most of the corres-
ponding animals in other parts of that territory. If their remains
were preserved in one deposit, and the bones of the other Alaskan
animals in another, it would be quite excusable to fail to recognise
them as contemporaneous.
While, therefore, it seems possible to determine the relative
age of whole faunas in Pleistocene deposits—while we are satis-
fied, for example, that the faunas at Grays Little Thurrock and
Clacton are older than that of Ilford—we cannot always decide
which race of any particular Pleistocene Mammal is the older
or the newer. On the whole, the earliest Pleistocene represen-
tatives of each genus are the largest and in many respects the
most specialised. Some of the earliest forms, as might be expec-
ted, also appear to be most nearly related to their immediate
predecessors in the Upper Pliocene fauna. The variations of
the successive forms, however, are so great, that even in com-
paratively well-known groups it is still impossible to trace clear
and definite lineages from the Pliocene period to the present
day.
It must further be remarked that although the Pleistocene
Mammals of this part of the world exhibit a curious mingling of
forms which to-day are confined respectively to the bleak wastes
of the Arctic Circle, to the steppes of Central Asia, and the
warmer climes of Africa, it by no means follows that these various
groups of animals always needed the climate and circumstances
which now appear to be essential for them. If, as we know, the