 Reference Base  Notes on the lesser one-horned rhinoceros, Rhinoceros son... |
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Colbert, E.H., 1942. Notes on the lesser one-horned rhinoceros, Rhinoceros sondaicus, 2. The position of Rhinoceros sondaicus in the phylogeny of the genus Rhinoceros. American Museum Novitates 1207: 1-5, figs. 1-3
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World |
| Subject: |
Taxonomy - Evolution |
| Species: |
Javan Rhino |
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Although there is a fairly extensive literature on the so-called Javan rhinoceros, Rhinoceros sondaicus, this form has been generally neglected in discussions having to do with the phylogenetic development of the Rhinocerotidae. It is true, of course, that various authors have recognized Rhinoceros sondaicus an animal less ?specialized' or less ?modified' than the Indian rhinoceros, Rhinoceros unicornis (Osborn, 1898; Matthew, 1931), but beyond such general statements as to its phylogenetic relationships there has been little or no effort made to discuss in a de- tailed way the affinities of this extraordinarily rare and interesting mammal.
Perhaps this neglect of Rhinoceros sondaicus in the more general discussions of phylogeny within the family Rhinocerotidae has been due, to a considerable extent, to the comparative rarity of the species in museums, or at least to the lack of acquaintance with this animal by palaeontologists. For it is only through a palaeontological background, particularly a knowledge of the late Tertiary and Quaternary rhinoceroses of Asia, that the true position of Rhinoceros sondaicus in its relationships to other rhinoceroses can be completely appreciated.
From these several comparisons certain facts emerge. Rhinoceros sondaicus may be distinguished from Rhinoceros unicornis by a large series of characters in the skull, the mandible and the dentition. In all of these characters the Javan rhinoceros is more primitive than the Indian form, so the development of the one from the other may be thought of as a ?harmonic' growth affecting virtually all portions of the cranial and dental anatomy and proceeding in a single direction. Indeed, this development in the characters from Rhinoceros sondaicus to Rhinoceros unicornis is so marked that certain Pleistocene species of the genus occupy positions intermediate between the two modern forms, Rhinoceros sinensis being a truly intermediate type, Rhinoceros sivalensis being somewhat closer to the Indian species.
Consequently, it would appear that Rhinoceros sondaicus, though recent in age, is truly a persisting primitive form and anatomically may be regarded as at about a Lower Pleistocene or perhaps an Upper Pliocene stage of development. It approaches the Lower Pliocene genus Gaindatherium, being intermediate between this latter form and the more advanced Pleistocene and Recent species of Rhinoceros mentioned above. Therefore, Rhinoceros sondaicus upon the basis of present evidence is to be regarded as the most primitive member of the genus Rhinoceros, embodying in its structure the features which by further complications and developments became diagnostic for the Pleistocene species, Rhinoceros sinensis and Rhinoceros sivalensis, and for the Recent Rhinoceros unicornis. It is a true living fossil.
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