AMERICAN MUSEUM NOVITATESI Published by Number 1207 THE AMERICAN MUSEUM OF NATURAL HISTORY November 12, 1942 New York City NOTES ON THE LESSER ONE-HORNED RHINOCEROS, RHINOCEROS SONDAICUS 2. THE POSITION OF RHINOCEROS SONDAICUS IN THE PHYLOGENY OF THE GENUS RHINOCEROS By EDWIN H. COLBERT Although there is a fairly extensive tions as to its relationships to some of the literature on the so-called Javan rhinoceros, Asiatic Pleistocene forms became at once Rhinoceros sondaicus, this form has been apparent, thereby affording a much clearer generally neglected in discussions having picture of the phylogenetic development of to do with the phylogenetic development the genus Rhinoceros than had previ- of the Rhinocerotidae. It is true, of ously been envisioned by the writer. Con- course, that various authors have recog- sequently it has been thought advantage- nized Rhinoceros sondaicus as an animal less ous to discuss briefly the evolution of "specialized" or less "modified" than the Rhinoceros (using the term in a strict sense) Indian rhinoceros, Rhinoceros unicornis in an effort to show how Rhinoceros (Osborn, 1898; Matthew, 1931), but be- sondaicus may be related to other species of yond such general statements as to its the genus. phylogenetic relationships there has been In the first place, it might be well to indi- little or no effort made to discuss in a de- cate the limits of the genus Rhinoceros. tailed way the affinities of this extraor- This genus has been used, particularly by dinarily rare and interesting mammal. palaeontologists, to include a great number Perhaps this neglect of Rhinoceros sondaicus of species ranging in age from the Miocene in the more general discussions of phy- through the Pleistocene and into Recent logeny within the family Rhinocerotidae has times. Indeed, during the early history been due, to a considerable extent, to the of vertebrate paleontology it was the prac- comparative rarity of the species in muse- tice to designate almost every fossil rhino- ums, or at least to the lack of acquaint- ceros'6f post-Oligocene age as Rhinoceros, ance with this animal by palaeontologists. since in those days students of fossils For it is only through a palaeontological naturally were but little concerned with the background, particularly a knowledge of criticalt limitations for genera and species the late Tertiary and Quaternary rhinocer- that have developed with the refinement of oses of Asia, that the true position of the science. Rhinoceros sondaicus in its relationships to Obviously this is wrong and has been so other rhinoceroses can be' completely recognized with the increasingly detailed appreciated. studies that have been made in later years It was the good fortune of the present on fossil vertebrates. Consequently at the author to be engaged in a study of the ex- present time most of the fossil species tinct rhinoceroses from the Pleistocene of formerly designated as Rhinoceros have China-as part of a general study of the been allocated to other genera, and the Pleistocene mammalian fauna from the genus has thus become strictly limited ac- limestone fissures of Szechwan-when the cording to the evidence of its anatomical skull of Rhinoceros sondaicus in the Ameri- characters, which, as far as the osteology of can Museum came to light. When this the skull and the dentition are. concerned, recent skull was examined, certain implica- are as follows: 2 AMERICAN MUSEUM NOVITATES [No. 1207 1. Expansion of the nasal bones into a Recent of the Sundarbans, eastern Bengal, boss or eminence, upon which is borne the Assam, Burma, Malay Peninsula, Sumatra single nasal horn. and Java. 2. Incisors present, and of large size. 3. Skull short, with occipital plane in- Rhinoceros sivalensis Falconer and Cautley, clined forward. 1847. 4. Auditory meatus closed inferiorly by Synonym: R. palaeindicus. fusion of the post-tympanic and the post- Pleistocene of the Siwalik Hills of India. glenoid processes. Rhinoceros sinensis Owen, 1870. 5. Cheek teeth sub-hypsodont. Synonyms: R. plicidens, R. simplicidens. Upon the basis of the above limitations, Pleistocene of southwestern China. the genus Rhinoceros includes four good It might be well at this place to indicate species, two of which are of recent age, and the distinctions in the skull, jaw and denti- two of which are extinct. There are other tion between the two recent species, fossil species of doubtful validity which Rhinoceros unicornis and Rhinoceros son- need not be considered at this place. The daicus, since many of these distinctions are four species with which we are concerned of considerable importance in the following are: discussion of the phylogenetic position of Rhinoceros unicornis Linnaeus, 1758. Type each species in relation to the other. of genus. Moreover, by calling attention to these Synonyms: R. indicus, R. asiaticus,. R. osteological differences between the two stenocephalus. modern species it may be that some aid will Pleistocene and Recent of India. Now be afforded to workers in the future who very limited in range. may have occasion to examine skulls and teeth of Rhinoceros. Rhinoceros sondaicus Desmarest, 1822. Flower (1876) published a paper in which Synonyms: R. javanicus, R. inermis, R. he described many of the distinguishing nasalis, R. floweri. traits between the two living species of Possibly Pleistocene (of Borneo) and Rhinoceros, while Osborn in his monograph SKULL, MANDIBLE AND DENTITION Rhinoceros unicornis Rhinoceros sondaicus 1. Large and robust. 1. Smaller and lighter than R. unicornis. 2. Nasals expanded into large, rounded horn 2. Less expansion in the nasals; horn boss boss. pointed rather than rounded, and very small in female. 3. Ascending ramus very high. 3. Ascending ramus not extremely heightened. 4. Occipital surface high and narrow. Skull 4. Occipital surface comparatively low and deep. broad. Skull comparatively shallow. 5. Deep "saddle" in profile of skull, between 5. Rather shallow saddle in cranial profile. nasals and occipital vertex. 6. Zygomatic arch rounded at posterior ter- 6. Zygomatic arch angular at posterior ter- mination. mination. 7. Posterior margin of palate concave, or with 7. Posterior margin of palate with median small median projection. projection. 8. Mesopterygoid fossa, basisphenoid and basi- 8. Mesopterygoid fossa, basisphenoid and basi- occipital bones narrow. occipital bones comparatively broad. 9. Pterygoids compressed and grooved. 9. Pterygoids flattened and laterally expanded. 10. Vomer thick and united to sides of pterygoid 10. Vomer thin, lamelliform, pointed and free. processes. 11. Premaxillaries broad. 11. Premaxillaries relatively narrow. 12. Teeth strongly sub-hypsodont. 12. Teeth less hypsodont than in R. unicornis. 13. Ectoloph of cheek teeth rather flat. 13. Ectoloph of cheek teeth sinuous. 14. Parastyle buttress suppressed. 14. Parastyle buttress prominent. 15. Well-developed crochet and crista, united in 15. Crochet present but crista generally absent. worn tooth to enclose a medifossette. 19421 NOTES ON RHINOCEROS SONDAICUS. 2 3 Fig. 1. Comparison of the skull and jaw of (A) Rhinoceros unicornis, (B) Rhinoceros sondaicus and (C) Gaindatherium browni. Lateral views of right side showing, from C to B to A: (2) increase of nasal horn boss, (3) increase in height of ascending ramus, (4) increase in height and for- ward inclination of occiput, (5) in- crease in depth of "saddle" in cranial profile. Compare the items with these same numbers on page 2. Figures one-eleventh natural size A and B from Osborn, 1898; C from Colbert 1934. I1 on "The Extinct Rhinoceroses" (1898) dis- works and original observations of the cussed briefly certain differences to be seen American Museum specimens of Rhin- between the living species of Rhinoceros, oceros, the accompanying comparison has and in addition presented a very useful been drawn up (see p. 2). comparative figure in which lateral views This comparison of the characters in the of the skulls and mandibles of all the living two modern species of Rhinoceros is inter- rhinoceroses were shown to scale. UJpon esting in that it shows what might be called the basis of these previously published a "harmonic" specialization of Rhinoceros 4 4AMERICAN MUSEUM NOVITATES [No. 1207 unicornis over Rhinoceros sondaicus. The 5. Shallower saddle in cranial profile. one species is advanced beyond the 6. Zygomatic arch more angular at posterior other termination. not by virtue of a few isolated characters 7. Posterior margin of palate with small but in all features throughout the structure median projection. of the skull, jaws and dentition; every 11. Premaxillaries narrow. (Two incisor teeth, character listed above for the distinction of a primitive character.) 12. Teeth more brachyodont than in R. sondai- the two forms shows an advance in the cus. Indian rhinoceros over its expression in the 13. Ectoloph of cheek teeth sinuous. Javan form. It is not possible on the basis 14. Parastyle buttress prominent. of the material available to compare skele- 15. Neither crista nor crochet present. tons of the two species, but it would seem It might be mentioned that in these likely that much the same picture would characters Gaindatherium in turn is more hold in a lesser degree in the post-cranial or less intermediate between Rhinoceros region. Certainly the external characters sondaicus and certain mid-Tertiary rhino- in the two species conform to this concep- ceroses such as Caenopus or Subhyracodon. tion of a general, all-round specialization The reason that Gaindatherium