Cainozoic Research, 5(1-2), pp. 93-102, November 2006 A primitive species of Chilotherium (Perissodactyla, Rhinocerotidae) from the Late Miocene of the Linxia Basin (Gansu, China) Tao Deng Institute of VertebratePaleontology and Paleoanthropology, ChineseAcademy of Sciences, P. O. Box 643, Beijing 100044, China: e- mail: [email protected] Received 1 June 2003; revised version accepted March 2006 skull with its articulated attributed the Late Miocene of Linxia Basin A mandible to Chilotheriumprimigenius sp. nov. from the (Gansu, is described. This Late Miocene the earliest and in the with China), early species is most primitive genus Chilotherium.Compared the other Late Miocene of C. →C.wimani→other of Chilotherium is species Chilotherium, a tentative lineageof primigenius→ species pro- A C. posed. Late Miocene Asian radiationis suggested for this genus, starting fromLinxia primigenius. The origin and dispersal history ofthe genus Chilotherium are discussed and correlated with major faunal exchanges. The sequence ofthe Late Miocene Hipparion fauna in the Linxia Basin, which yields the remains described herein, is also discussed. KEY WORDS: Chilotherium, Late Miocene, Linxia Basin, new species. of of Introduction cies Chilotherium, leading to the description a new species. Late Cenozoic terrestrial deposits from the Linxia Basin (Gansu, China) have yielded many mammalian fossils. In these faunas, rhinocerotids are very abundant and species- Systematic palaeontology rich. The rhinocerotids have essentially been collected and studiedsince the 1980s(Qiu etal, 1987,1990;Qiu & Xie, Family RhinocerotidaeOwen, 1845 1998; Guan, 1988; Guan & Zhang, 1993). Recently, we Subfamily AceratheriinaeDollo, 1885 have collected many new rhinocerotid material (Deng, Tribe ChilotheriiniQiu etal., 1987 2002a, 2003; Qiu et al. 2002). Qiu et al. Genus ChilotheriumRingstrom, 1924 2001b, c, b, , (1987)attributed a skull with its articulatedmandiblefrom the Linxia Basin to Acerorhinus hezhengensis and consid- ered that it differed from the species ofthe genus Chiloth- Chilotheriumprimigenius sp. nov. erium. They established a newtribe Chilotheriini, including (Figures 1-2, Tables 1-3) the genera Acerorhinus and Chilotherium.Their material was recovered from unnamed Late Miocene deposits at Holotype — HMV 0102, an adultskull with its articulated Dashengou (Hezheng, Linxia Basin). Deng (2001a) de- mandible. This mandible lacks the posterior part of the scribed much more materialof Chilotheriumwimani from horizontal ramus, the lower part of ascending ramus and than and consid- Fugu (Shaanxi, China) Ringstrom (1924), the left anterior corner of symphysis. ered that C. wimani was the most primitive species of Chi- lotherium. The species of Chilotheriumform a group con- Etymology — The specific name, primigenius, is a Latin sidered be related the Acerorhinus and first. This is considered to closely to genus (Qiu word, means the new species etal., 1987). the most primitive species of Chilotherium. We have collected thousands ofmammalianfossils in the Linxia Basin, including carnivores, rodents, perissodactyls, Type locality — Zhongmajia (35° 24' 47.0"N, 103° 24' proboscideans, artiodactyls, and primates (Deng, 2001b, c, 30.6"E; altitude: 2218 m), 6 km southeast to the Hezheng 2002a, b, 2003; Qiu et ai, 2000, 2001; Wang and Qiu, County seat in Gansu Province, China. The specimen is 2002; An almost skull with its articulated collected from 2003). complete the gray green sandstoneand conglomerate broken mandible from a small and primitive species of in the bottom of the Liushu Formation. The bed bearing Chilotherium has been discovered at Zhongmajia in Hez- this fossil is of the early Late Miocene, corresponding to Its known heng. morphology is different from all the spe- early and middleMN 9. -94- — The braincase is Diagnosis Ventral surface ofmandibularsymphysis flat frontalbones is slightly erect. very narrow, Chiloth- with exterior walls. The is (different from concave surfaces of other known steep parietal crest slightly pro- erium species); parietal crests very slightly separated, form- jecting sideward to form a brim. The two parietal crests to ing a sagittal crest different from the broadly separated meet posteriorly form a sagittal crest with the smallest reach the lat- parietal crests of C. anderssoni, C. habereri, C. samium, C. width of 18 mm, from where they diverge to schlosseri and C. kowalevskii and also different from the eral ends ofthe occipital crest. The posttympanic process is , of with smoothanterior and surface. slightly separated parietal crests lacking a sagittal crest thin, a a rough posterior C. C. wimani C. and C. kiliasi. This sideward, and declines for- xizangensis, , persiae process expands slightly ward to fuse with the postglenoid process on the upper part — exists Description Skull: The skull face is high. The premaxil- of the latter. As a result, a pseudoauditory meatus The is thin larybone is retracted into a vertical flake with a sharp ante- between them. postglenoid process longitudi- incisors absent. Both ends of with transverse section. The interior rior end. The upper are pre- nally, a triangular sur- maxillary bones are in close proximity. In ventral view, the face of the postglenoid process is smooth, and the exterior surface vertical The end of the premaxillary bone is thin and sharp, and its end is at the has a groove posteriorly. forward. The same level with the nasal tip. The nasal notch is narrow and postglenoid process curves temporal condyle deep, and its bottom is located at the level of M1/P4 is flat and straight, and its interior margin spaces out the boundary. A large infraorbital foramen on the maxillary postglenoid process by a deep groove. The articular surface is with continuous face is located near the bottomof the nasal notch. The dis- behindthe temporal condyle narrow, a tance between the bottomof thenasal notch and the orbit is wide crest on its exterior and posterior margins to form a transverse flute to the The very short, 55.5 mm. The wide and prominent anterior parallel temporal condyle. margin ofthe orbit is located at the level of the middle of pterygoid bones are high, with a deep valley between them. M2, and connects downward with the anterior margin of The maxillary tubercle is well developed, with a sharp pos- zygomatic arch. A frontward face is in front of the large terior end. The palatal surface is smooth and narrowly ofthe is and and round orbit. The postorbital process is well developed arched. The posterior margin palate V-shaped, its bottom is located the level of the of M3. on the frontal bone, but absent on the the zygomatic bone. at protocone The supraorbital and lacrimal tubercles are relatively Mandible:There is a long distance between the ascending is notch between the and m3. The of anterior of the marked. There a postorbital process ramus upper part margin rounded. The coronoid and supraorbital tubercle, and there is another one between ascending ramus is thin and process the supraorbital and the lacrimal tubercles. The zygomatic is well developed, and strongly curved backward. The is wide and arch is projecting highly to form a strong facial crest with a condyloid process very transversely narrow right angle, and its anterior end is located at the level of longitudinally, especially narrower interiorly. Near the inte- there is marked P4/M1 boundary. This arch is constricted inward at the rior end of the condyloid process, a con- is striction. On the of the level of the postorbital process, while its posterior part posterior part condyloid process, is and with expanded outward as a semicircle. The widest part of the there a narrow deep transverse groove a sharp zygomatic arch is located at the level of the postorbital bottom and a well-developed transverse crest. the end of the arch, its In view, the mandibular process. On posterior zygomatic top symphysis expands strongly sideward form shovel. The alveolar is crest posterior upper corner is rounded, and its posterior margin to a margin a and its anterior is straight and inclined forward. In ventral view, the zygo- with a straight posterior part, part expands The outward to be close to i2. There is wide matic arch is very thin.The occipital elevationis high. a U-shaped valley occipital surface and lateral margins incline forward obvi- between the two alveolar margins. The posterior margin of mandibular is located the level of ously. The lower part of the occipital surface is broken. the symphysis at p3/p4 In front view, the alveolar between the The foramen magnum is onion-shaped, with a sharp upper boundary. margin shallow central second lower incisors is thinand The ventral end. The occipital crest has a wide and uplifted. sur- and its lateral corners are rounded. The lateral face of the mandibular is broad and flat, on groove, two symphysis nutrient foramina distributed margins ofthe occipital crest are straight and parallel each which there are some large other. The nuchal ligament depression is wide and shallow. densely and irregularly, four on the right side. The exterior lateral crest is strong, and a deep vertical de- Upper teeth: The premolars have been worn deeply to reach the The labialwalls ofthe cheek teeth pression is present between this crest and the lateral margin root. upper are the nuchal flat. DP 1 has root. The molars also have been worn of the occipital crest. The median crest on liga- a single M3 becomes ment depression connects with the upperend of the fora- to be close to the root. As a result, a quadran- On the molars, the is constricted; the en- men magnum. The cranial top is smooth and flat, and it is gle. protocone the widest at the level of the supraorbital tubercle. The trance ofmedian depression is wide, with some pillars; the and and extend and of and nasals are narrow long, flatly straight. lingual margins protocone hypocone are straight. is enamel board the The nasal top is convex, and its basehas a marked constric- There a well-developed on posterior tion.