The Rise and Progress of Palaeontology
Page: 12

existing fishes; and that, not only among fishes, but in several
groups of the invertebrata which have a long palaeontological
history, the latest forms are more modified, more specialised,
than the earlier. The fact that the dentition of the older
tertiary ungulate and carnivorous mammals is always complete,
noticed by Professor Owen, illustrated the same generalisation.

Another no less suggestive observation was made by Mr. Darwin,
whose personal investigations during the voyage of the
Beagle led him to remark upon the singular fact, that the
fauna, which immediately precedes that at present existing in
any geographical province of distribution, presents the same
peculiarities as its successor. Thus, in South America and in
Australia, the later tertiary or quaternary fossils show that
the fauna which immediately preceded that of the present day
was, in the one case, as much characterised by edentates and, in
the other, by marsupials as it is now, although the species of
the older are largely different from those of the newer fauna.

However clearly these indications might point in one direction,
the question of the exact relation of the successive forms of
animal and vegetable life could be satisfactorily settled only
in one way; namely, by comparing, stage by stage, the series of
forms presented by one and the same type throughout a long
space of time. Within the last few years this has been done
fully in the case of the horse, less completely in the case of
the other principal types of the ungulata and of the carnivora;
and all these investigations tend to one general result, namely,
that, in any given series, the successive members of that series
present a gradually increasing specialisation of structure.
That is to say, if any such mammal at present existing has
specially modified and reduced limbs or dentition and
complicated brain, its predecessors in time show less and less
modification and reduction in limbs and teeth and a less highly
developed brain. The labours of Gaudry, Marsh, and Cope furnish
abundant illustrations of this law from the marvellous fossil
wealth of Pikermi and the vast uninterrupted series of tertiary