But if you compare honestly
age with age, one at a time, I fearlessly maintain that, so far from
there being any falling off in the average bigness of things generally
in these latter days, there are more big things now living than there
ever were in any one single epoch, even of much longer duration than the
'recent' period.
I suppose we may fairly say, from the evidence before us, that there
have been two Augustan Ages of big animals in the history of our
earth--the Jurassic period, which was the zenith of the reptilian type,
and the Pliocene, which was the zenith of the colossal terrestrial
tertiary mammals. I say on purpose, 'from the evidence before us,'
because, as I shall go on to explain hereafter, I do not myself believe
that any one age has much surpassed another in the general size of its
fauna, since the Permian Epoch at least; and where we do not get
geological evidence of the existence of big animals in any particular
deposit, we may take it for granted, I think, that that deposit was laid
down under conditions unfavourable to the preservation of the remains of
large species. For example, the sediment now being accumulated at the
bottom of the Caspian cannot possibly contain the bones of any creature
much larger than the Caspian seal, because there are no big species
there swimming; and yet that fact does not negative the existence in
other places of whales, elephants, giraffes, buffaloes, and hippopotami.
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