OCR Text |
Show 894 SI R V. KROOKE ON THE [Nov. 19, In this Table, showing the geographical distribution of the Cervidae exclusive of the Elk and Reindeer, which have a circumpolar range, the following are the most important facts observable. Out of a total of 61 species 39 are confined to the Old and 22 to the New World. Of the 39 Old-world species 33 are found in the Eastern Palaearctic and Indian regions, the latter containing 22 species, a much larger number than that contained in any one of the remaining four regions. Of the 22 species confined to the N e w World, 8 are found to the north and 14 to the south of the Isthmus of Tehuantepec, the division adopted by Mr. Sclater between the Nearctic and Neotropical regions. These figures cannot, however, be taken as affording a just estimate of the relative degree of specialization of the Cervidae in the Nearctic and Neotropical regions respectively. On the one hand, the three species of Cariacus in the latter are undoubtedly immigrants from the former region ; and on the other hand, the species contained in the subgenera Coassus and Furcifer are, as far as the antlers are concerned, amongst the least-specialized of existing species. Out of the eleven genera into which the Old-world Deer are divisible, there is only one (Darna) which has not a representative in either the Palaearctic or Indian region. Owing to the exceeding paucity of Palaeontological material, any attempt to account for the present differentiation and distribution of the Cervidae must be considered as purely tentative ; and I venture to put forward the following hypothesis, more to provoke investigation and criticism, which may possibly bring new and more correct ideas to light, than from any great confidence that I feel in its approximation to completeness. In order to avoid unnecessary recapitulation, and to indicate as clearly as possible the interdependence of the facts and hypothesis, I shall place the facts and theory in two columns, numbering the former, and merely introducing the number attached to each fact before the deduction or deductions which are drawn from it. Facts. (1) So many characters are common to the Cervidae and Bovidae that it is very difficult to lay down definitions distinctive of the families. (2) Dremotherium, the earliest known Cervine form, was without antlers and tetradactyle. Hypothesis. (1) A very high degree of specialization had been attained by the common ancestor of the Cervidae and Bovidae, especially in the structure of the skull, dentition, and limbs; hence the possibility of divergence of character in its descendants was much restricted. (2) For a long period the early ancestors of the Cervidae, which were tetradactvle, |