Home › Some Early Mammals and the Story of the Horse › Some Early Mammals and the Story of the Horse: Secondary

Some Early Mammals and the Story of the Horse: Secondary

Fishes abounded in the waters of the Primary or Palæozoic era, while air-breathing amphibians appeared towards its close; reptiles flourished vigorously all through Secondary or Mesozoic times: and now we are about to show that a marvellous outburst of mammalian life appears to have taken place very early in the Tertiary or Cainozoic era. All this is in accordance with the "Law of Progress" throughout past times, and strongly confirms the theory of Evolution (see pp. 84, 106, 125, and 264). The student of geological history soon discovers that mammals of some kind, or kinds, did exist throughout the Secondary eraalthough, judging from their imperfect remains, they must have been of a low type.¹ But the great advance in our knowledge of 1 Perhaps some of the jaw-bones from Triassic and Jurassic strata represent creatures as low down in the scale as the Monotremes, represented at the present day by the Duck-bill Platypus and the Echidna of Australia. the world's extinct races which has taken place during the last quarter of a century ought to make us careful with regard to broad statements of the above kind, which may require to be modified by future discoveries.

Now, the tendency of all the later results of Palæontology is to show that some of the higher types of life appeared on the earth a good deal earlier than was formerly supposed. Thus the discovery of the jaw-bones of small mammals (possibly marsupials) in the Purbeck strata, in 1854, and afterwards in the Stonesfield slate (both of Jurassic age), came as a surprise to most geologists. Again, it is not long since birds were believed to have come into existence only in Tertiary times: now we have the Jurassic bird Archæopteryx (see p. 212), and Professor Huxley has recorded his opinion that some of us may live to see a fossil mammal of the remote Silurian age! It is, therefore, only prudent for geologists to be on their guard against assuming that all the Secondary mammals were of low types and few in numbers, as might be inferred from the phrase "Age of Mammals." That mammals, however, developed vigorously in many directions during the Tertiary era cannot be doubted. So, far, then the expression conveys important truth; but in science, as in other things, the "unexpected" often happens, so it is better to be prepared for surprises.

It would be impossible within the limits of a single chapter to give an account of all the leading orders of Tertiary mammals. We must therefore limit our present remarks to two or three, or more, reserving others for future chapters.