Hypsodontus sinensis, Jin & Jiangzuo & Wang, 2025

Jin, Yu-Qing, Jiangzuo, Qigao & Wang, Shi-Qi, 2025, The first discovery of Hypsodontus (Artiodactyla, Bovidae) from the Early Miocene of Linxia Basin, Gansu Province, China, Fossil Record 28 (2), pp. 231-239 : 231-239

Hypsodontus sinensis sp. nov.

Etymology.

From China, where the species was first discovered.

Holotype.

IVPP V 34116 , a right horn core with a broken frontal bone (Fig. 2 ).

Type locality.

Citan locality , Linxia Hui Autonomous Prefecture, Gansu Province, China (Fig. 1 )

Age.

Late Early Miocene (~ 17.2 Ma), possibly correlated to the early age of MN 4 in Europe.

Description.

IVPP V 34116 is a well-preserved right horn core, with only the lateral part of the base of the horn core and the pedicle slightly broken. As a whole, the horn is elongated (~ 126.4 mm in length) and evenly tapered upward, giving it a cylindrical appearance; the horn core is only slightly larger in diameter than the pedicle at the transition ring. It is uprightly inserted into the orbit and slightly inclined backward, whereas the tip of the horn core curves anteriorly. In medial view, a fragment of the frontal bone posteromedial to the horn core is preserved, exhibiting a slight inward tilt, resulting in a depression on the posteromedial aspect between the horn cores. In rostral view, the horn core displays marked homonymous twisting, exceeding 1 / 3 circle but less than 1 / 2 circle. The basal cross-section is nearly circular (Fig. 2 A ), with a transverse diameter (TD) to anteroposterior diameter (APD) of approximately 87.8 % (a length of 31.1 mm in APD and a length of 27.3 mm in TD). On the surface of the horn core, some faint longitudinal grooves are present, and the horn core surface is porous, especially along the transition ring between the horn core and the pedicle. A short anterior rib is present near the tip (Fig. 2 C ). The pedicle is rather long (~ 18.2 mm), with an oval supraorbital foramen at its base. Additionally, two sinuses occur at the bottom of the horn core: one is large and deep on the lateral side, and the other is small and shallow on the medial side (Fig. 2 E ); it is an advanced morphological trait in bovids as the frontal sinus enters the horn core ( Gentry 2010).

Comparison.

Up to now, the subfamily Hypsodontinae consists of four genera, among which all except Gobiocerus have yielded a considerable number of horn core specimens. As shown in Fig. 2 , the right horn core unearthed from the Citan locality exhibits pronounced homonymous twisting, indicating this specimen belongs to Hypsodontus . Contrasted with the type species, Hypsodontus miocenicus , the horn cores of Hypsodontus sinensis are moderately more robust, exhibit a smoother surface, and demonstrate stronger homonymous twisting, thereby precluding its assignment to H. miocenicus .

The earliest record of Hypsodontus in Europe west of the Belomechetskaya in the North Caucasus ( Stefanović and Mijovic 2004) was reported by Pavlović and Thenius (1959) from the Miocene strata at Prebreza, southern Serbia (the former Yugoslavia), where they documented an indeterminate species of this genus. Subsequently, Pavlović (1969) provided a comprehensive description of those materials and formally designated it as H. serbicus , despite some disagreements ( Cirić and Thenius 1959; Cirić 1960; Gentry 1970). The new specimen from the Citan locality actually does not differ much from H. serbicus , referring to the illustration plates ( Pavlović 1969; Tafel XVII-XVIII), but further comparisons are hindered by the lack of detailed morphological description and measurement data of H. serbicus .

H. pronaticornis is represented by the most extensive fossil record in this genus, and the horn cores of Hypsodontus sinensis share with the former several morphological features in terms of the shape of the cross-section and the degree of the upward tapering. Nevertheless, several diagnostic differences are evident: (1) the horn cores of Hypsodontus sinensis are significantly shorter than those of adult individuals of H. pronaticornis (measurements of horn cores in Köhler 1987, pp. 148), (2) the former exhibits less pronounced medial inclination; (3) there is no younger growth ring on the Hypsodontus sinensis , whereas always remarkably occurs in H. pronaticornis (manifesting as an obliquely outwards projection at ~ 30 ° on the posterior; Köhler 1987, fig. 16); (4) the growth trend and proportional length of the juvenile H. pronaticornis are comparable to those of Hypsodontus sinensis , whereas the presence of well-developed sinuses at the bottom of the Hypsodontus sinensis ruled out the possibility of juvenile H. pronaticornis . These collective morphological attributes support the recognition of Hypsodontus sinensis as a distinct species of Hypsodontus ; despite this, there is a closer phylogenetic affinity to H. pronaticornis than to other species.

Turcocerus was erected as a distinct genus by Köhler (1987) to distinguish it from Oioceros , which was widely recorded in Turolian (Late Miocene) deposits across Eurasia ( Chen 1988). The horn core of Hypsodontus sinensis differs from Turcocerus not only in terms of length and thickness but also in the twisting degree and the surface ornamentation: (1) among the various forms of Turcocerus , their horn cores are consistently shorter and thicker than those of Hypsodontus sinensis . For instance, T. grangeri , possessing the longest recorded horn cores within this genus so far, measures only approximately 110 mm in length ( Pilgrim 1934, pp. 25); (2) the horn cores of Turcocerus taper sharply from the base to top, displaying a conical profile in the lateral view, and they generally twist about 1 / 4 loop ( Ye et al. 1999) or less ( Köhler 1987), which is much weaker than those of the Hypsodontus sinensis ; (3) the horn cores of Turcocerus are characterized by prominent longitudinal grooves resulting in a rougher horn core surfaces; for example, there are covered with numerous anastomosing crests on the horn cores surface of the T. kekemaidengensis ( Ye et al. 1999) , and posterior longitudinal grooves occur between two well-demarcated ridges on the horn cores of T. grangeri , T. noverca , T. halamagaiensis and T. africanus ( Li et al. 2020; Geraads et al. 2023), while those of Hypsodontus sinensis are flat and smooth, with only a few short and indistinct grooves. Therefore, the new material from the Citan locality must not be affiliated with the Turcocerus .

Kubanotragus is characterized by the slender and well-proportioned horn cores, with a very weak homonymous twisting ( Gabunia 1973; Chen 1990). Although the length of the horn cores of Kubanotragus resembles that of Hypsodontus sinensis , the latter is distinguished by a more intense twisting. Additionally, the two taxa differ in basal cross-sections; the type species K. sokolovi displays a symmetrically elliptical cross-section with transverse compression ( Gabunia 1973), while Hypsodontus sinensis is nearly circular. Previous taxonomic uncertainty regarding the distinction between Hypsodontus and Kubanotragus stemmed from limited fossil records. Given this paucity of available data, the genera Hypsodontus and Kubanotragus were initially considered synonymous ( Gentry 1990). The differences in their horn corns have been variably interpreted as either a manifestation of ontogeny ( Köhler 1987) or sexual dimorphism ( Thomas 1984; Bonis et al. 1998). However, Geraads et al. (1995) argued the two share very few derived characters. Comparisons between the horn corns of H. sinensis and those of Kubanotragus species ( Gabunia 1973, fig. 34; Chen 1990, Plate I, fig. 1–8) also provide no clear evidence that would support the synonymization of the two genera.

Figures

Figure 1. Geographical context of the new specimen discovered from the Citan locality. A. Map of China; B. A meso-scale view of Linxia Hui Autonomous Prefecture, and Citan area is located in the southeastern part of Linxia City.

Figure 2. Hypsodontus sinensis sp. nov. from the Early Miocene of China. A. Anterior, with the cross section at 4.5, 36.4, and 80.0 mm distal to the base of the horn core; B. Posterior; C. Medial; D. Lateral; E. Bottom, represented by a photograph and sketch, with the medial side of the horn core facing left.