Le Bassin de Yuanmou (Province de Yunnan, Sud-Ouest de la Chine) est bien connu pour son Homme de Yuanmou (Homo erectus), représenté par deux incisives supérieures et daté de ca 1.7 Ma [9]. La recherche de nouveaux matériaux d'hominidés dans le bassin dans les années 1980 a résulté en la découverte d'hominoïdes [3,20] et d'une faune associée près du village Xiaohe [4]. Les fouilles récentes dans le bassin, de 1998 à 2000, ont livré des hominoïdes et de la faune. Une nouvelle localité d'hominoïdes à Leilao (Fig. 1), à environ 8 km au sud du village Xiaohe, a été reconnue pendant les dernières fouilles dans le bassin. L'étude des micromammifères de Leilao montre que les niveaux livrant des hominoïdes peuvent être datés du Miocène supérieur (ca 9 Ma) [7] ; cependant que l'étude paléomagnétique permet de les dater de ca 8.2–7.1 Ma [19]. On peut considérer pour le moment que l'âge des niveaux livrant des hominoïdes est de ca 9–7 Ma. Parmi les nombreux et intéressants grands mammifères, une nouvelle espèce de muntjak, Muntiacus leilaoensis sp. nov. a été identifiée. Elle est très proche des muntjaks actuels, bien qu'il s'agisse du plus ancien représentant de ce genre.

The Yuanmou basin (Yunnan Province, southwestern China) is well known for its Yuanmou Man (Homo erectus), which is represented by two upper incisors and was dated ca 1.7 Ma [9]. The research of further hominid material in the basin in the 1980s resulted in the discovery of many hominoid materials [3] and [20] and associated fauna near Xiaohe Village in the Yuanmou Basin [4]. The recent extended excavations in the basin from 1998 to 2000 yielded new hominoid and fauna materials. A new hominoid locality at Leilao (Fig. 1), about 8 km south of Xiaohe Village, was discovered during the latest excavations in the basin. The study of micromammals from Leilao showed that the hominoid bearing layers at Leilao could be correlated to the Late Miocene or dated as ca 9 Ma [7]; the paleomagnetic study showed that the hominoid bearing layers were dated ca 8.2–7.1 Ma [19]. The chronological range of the hominoid layers can be considered as ca 9–7 Ma for the time being. The large mammals from Leilao are also very rich and interesting. During the recent systematic study on the large mammals, a new muntjak species, Muntiacus leilaoensis sp. nov. has been identified. It is very close to the extant muntjaks and is the earliest record of Muntiacus.

Mammalia Linnaeus, 1758.

Artiodactyla Owen, 1848.

Cervoidea Gray, 1821.

Cervidae Gray, 1821.

Muntiacinae Pocock, 1923.

Muntiacus Rafinesque, 1815.

Type species: Muntiacus muntjak Zimmermann, 1780.

Diagnosis of the genus: Small muntiacines with a distinct longitudinal crest along the lateral margin of the frontal that joins the antler pedicle on males while on females this crest nearly reaches the parietal. Between these two crests, the frontal is strongly concave. Lachrymal fossae are frequently present and they are usually very large or equivalent in diameter to the orbit. Pedicles, which are very long, frequently extend to the posterior margin of the cranium. A burr is conspicuous. Antlers are bifurcated with a relatively short brow tine that is medially curved. The main beam is simple and unbifurcated with a tendency to curve medially. Male canines are long and sharp with a laterally curved tip. The P₄ is ‘primitive’ (unfused metaconid and paraconid), molars lack a Palaeomeryx fold and cingula. The taxon has plesiometacarpal forelimbs and lateral digits are frequently vestigial [17].

Muntiacus leilaoensis sp. nov.

Holotype: A nearly complete left antler with nearly complete pedicle and a small part of frontal (PDYV1762) collected in 1999 from Leilao hominoid locality.

Included specimen: A nearly complete right juvenile antler with complete pedicle and a small part of frontal (PDYV1833) collected in 1999 from Leilao hominoid locality.

Type-locality: Leilao hominoid locality, Yuanmou, Yunnan Province, southwestern China.

Stratigraphic level: Lower part of Xiaohe Formation, Upper Miocene.

Etymology: The new species is so named after the name of the type locality.

Diagnosis: A medium-sized muntjak. The pedicle is long and thin, inclines backward and extends on the frontal by a strong ridge. The shedding plane of the burr forms with longitudinal axis of the pedicle an angle about 70°. The main beam and the brow tine arise abreast from the burr but diverge from each other at a small distance from the burr. The main beam is relatively long, and is about the same length as the pedicle. Its middle and distal parts curve medially and inferiorly. The brow tine is quite small, being no more than a small tapering protuberance. The morphology of its antler is similar to that of the Early Pleistocene Muntiacus bohlini [12] and extant M. muntjak [10]. However, it differs from M. bohlini by its longer pedicle and main beam, and by its more curved main beam. And it differs from M. muntjak by its longer main beam and by the higher position of the brow tine.

Description: The holotype specimen PDYV1762 (Fig. 1 and Fig. 2) is a nearly complete left antler with nearly complete pedicle (see Table 1 for measurement). It has a grown brow tine and it is regarded as from an adult individual. The proximal end of the pedicle is still attached to a small part of the frontal. The proximal end of the pedicle extends to the frontal as a ridge. The pedicle is thin and long, arises from the frontal postero-dorsally. Its surface is smooth. Its proximal end extends on the frontal to form a developed ridge. Its cross section in the proximal part is oval, and that in the distal part is nearly circular. The burr is well preserved and formed by a series of bony tubercles and appears as an oval cluster of pearl ring. The maximum diameter of the antler base is located medial-laterally, and the minimum diameter anterio-posteriorly. The main beam and the brow tine arise abreast from the burr and bifurcate at 22.5 mm above the burr. The medial view of the main beam is much more curved than its anterior view (Fig. 1 and Fig. 2). The ornamentation of the antler is formed by well developed longitudinal grooves and crests on the surface of the antler crown.

The included specimen PDYV1833 (Fig. 2, 2a and 2b) is a nearly complete right antler with complete pedicle (see Table 1 for measurement). The main beam of the specimen is distorted during the fossilization. The proximal end of the pedicle is associated with a small part of the frontal. Judged by the thin and long pedicle and tiny brow tine, the specimen is from a juvenile individual. The proximal cross section of the pedicle is between oval and triangle, and the distal cross section is nearly circle. The maximum diameter of the antler base is located medial-laterally, and the minimum diameter anterio-posteriorly. The main beam is tapered and relatively long. The brow tine is elusive, just as a tiny bony protuberance on the burr (Fig. 2, 2a).

The juvenile antler (PDYV1833) is longer and thinner than the adult antler (PDYV1762). Such difference can be considered as intraspecific variation because the ontogeny of pedicle shows that with the growth of a cervid individual, the pedicle becomes thicker and shorter by every antler shedding and the size of annual antler is in function with the availability of food resources [5].

The main beam and the brow tine of the above described specimens are simple, they arise abreast from the burr and bifurcate from each other at a very short distance from the burr. It shows that they belong to a member of the Muntiacinae. Their developed burr distinguishes them from the Miocene Dicrocerus [2] and [15]. Their curved main beam distinguishes them from the Miocene Euprox and Heteroprox [11] and [14]. Their curved main beam and lower position of the brow tine are similar to that of Eostyloceros [13], but the latter has larger main beam and shorter pedicle. Their small size and slender pedicle distinguishes them from the other muntiacines, except Muntiacus [17]. The above described specimens are evidently different from the other cervids from the Yuanmou Basin [6] and [8]. The small antler, long pedicle, the pedicle ridge on the frontal, etc., all these characters are typical of Muntiacus [10] and [17] and they can therefore be attributed to Muntiacus. The phylogenetic relationship of Muntiacus with other muntiacines is hypothesized in Fig. 3.

Compared with the known fossil species of Muntiacus, the angle between the shedding plane of the burr and longitudinal axis of pedicle is nearly 90°, the main beam just curves inferiorly a little at the distal end, and the base of the main beam is very compressed in the Pliocene Muntiacus lacustris from the Yushe Basin in northern China [13]; the pedicle and main beam are much shorter in the Pliocene M. nanus from the Yushe Basin of northern China [13]; the curvature of distal part of the main beam is less complicated and the main beam and pedicle are shorter in M. bohlini from the Lower Pleistocene at Locality 18 of Zhoukoudian of northern China [12]; the main beam is less curved and smaller in M. cf. reevesi from the Upper Pleistocene in Sichuan of central China [17]; the pedicle is evidently longer than the main beam and the brow tine is lower in M. muntjak from the Middle and Upper Pleistocene in southwestern China [17]; the brow tine is much longer and the antler is robust in M. fenghoensis from the Lower Pleistocene in Fenhe of northern China [1]; the main beam is smaller but the brow tine is larger in M. hengduanshanensis from the Lower Pleistocene in the Hengduan Mountains area of southwestern China [21]. Finally, it is impossible to compare directly with M. szechuanensis from the Middle Pleistocene at Geleshan (formerly spelled as Goloshan) of central China [18] due to lack of antler in Geleshan specimens and lack of dental material in Yuanmou specimens. But the body size of Yuanmou species is similar to that of M. muntjak and the teeth of the latter are obviously smaller than those of M. szechuanensis. It implies that M. szechuanensis is larger than Yuanmou species.

Based on the above mentioned difference between Yuanmou species and the other species of the Muntiacus, it must be assigned to a new species. The phylogenetic relationship of the new species with other fossil muntjaks is hypothesized in Fig. 4.

The Muntiacus is an old, relatively primitive, persistent and conservative but diverse genus. There are six extant species in China [16]; their range extends from the southern to northern China. There were 8 fossil species; the newly discovered member is the ninth fossil species of Muntiacus. Like extant members, the fossil muntjaks range from the southern to northern China. Their chronological distribution is mostly Pleistocene, and only two species, M. nanus and M. lacustris, are found in the Pliocene [13]. The new species from Leilao of southwestern China is from the layers dated from ca 9 Ma to ca 7 Ma [7] and [19]. It is thus the earliest record of Muntiacus. Its morphology similar to some of the extant muntjaks shows that the genus are a persistent and conservative group in contrast with the other rapidly evolving cervids since ca 9–7 Ma.