LOWER JAW OF HYÆNODON. (After Gaudry.)
But we have not yet learned all that Palæontology can teach us about the history of the Carnivora. In the Eocene and Lower Miocene beds are found animals referred to the genera Hyænodon, Pterodon, Palæonictis, and Proviverra which, not content with trespassing on the boundaries between existing families, actually wander outside the Carnivorous order altogether, and approach so nearly to the Marsupials (Kangaroos, Opossums, &c.) that many competent anatomists have proposed to place them in the latter group. The premolars and molars in these extinct animals have sharp cusps, and increase gradually in size from before backwards; so that, of the whole grinding series, the first premolar is the smallest, and the last molar the largest. Now we have seen that the rule among existing Carnivora is for the last molar to be a small tooth, and for the largest of the set to be the fourth premolar in the upper jaw, and the first molar in the lower jaw. On the other hand, the regular increase in size is very characteristic of the flesh-eating Marsupials, amongst which the Thylacine, or so-called Tasmanian Wolf, shows a considerable resemblance, as to its teeth, to Hyænodon and Pterodon, while Palæonictis and Proviverra are more nearly allied to the Opossums and to the Dasyure, or Tasmanian Devil. The brain-case in these forms was very small, and a cast of the interior of the skull of Proviverra, figured by M. Gaudry,[198] shows that the brain must have had an extremely low character.
SKULL OF PROVIVERRA. (After Gaudry.)
The roof of the skull is supposed to be cut away to show the form of the brain, as deduced from a natural cast of the interior of the skull.
We thus see that a considerable number of the existing genera of Carnivora took their origin in the Eocene epoch, where they co-existed with creatures curiously intermediate between the various existing families, and with others intermediate between Carnivora and Marsupials. In the rocks of the Secondary period (chalk, oolite, lias, &c.), none of the Carnivora have as yet appeared, and only Marsupial remains are found.
APPENDIX TO CHAPTER VI.
(VIVERRIDÆ, CIVET FAMILY.)
THE CYNOGALE.[199]
CYNOGALE.