The earliest known mammal (_microlestes_) is an isolated
forerunner of not very certain location, the real bulk of the mammalian
orders beginning in the Eocene. Seeing, too, how very closely one
Creative command is recorded to have followed on the other, it is not in
any way against the narrative that some land forms of crustaceans and
insects (and possibly others) began to appear at an early stage, when
the vegetable and water-animal forms had only progressed as far as the
Silurian and Devonian ages. Nor should we wonder if mammalian forms had
occurred earlier. I mention this because of the evident gap in the
geologic record between the Cretaceous and the Eocene, and because in
the article of December, 1885 (and elsewhere), Professor Huxley has used
language which suggests that mammals may have existed of which the rocks
give no sign. E.g. (p. 855): "The organization of the bat, bird, or
pterodactyle, presupposes that of a terrestrial quadruped ... and is
intelligible only as an extreme modification of the organization of a
terrestrial _mammal or_ reptile." The italics are of course mine. And
again (p. 855), "I am not aware that any competent judge would hesitate
to admit that the organization of these animals (whales, dugongs, &c.)
shows the most obvious signs of their descent from terrestrial
quadrupeds.
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