New fossils of small and medium-sized bovids from the Early Site of Shanshenmiaozui in Nihewan Basin, North China

TONG Hao-Wen, ZHANG Bei, CHEN Xi, WANG Xiao-Min

Vertebrata Palasiatica 2022, 60 (2): 134-168. DOI: 10.19615/j.cnki.2096-9899.220413

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Shanshenmiaozui site in Nihewan Basin in North China is a recently discovered Early Pleistocene site which yields rich and diverse mammalian fossils. In the fauna, the small and medium-sized bovid fossils are well represented and can be referred to the following taxa: Spirocerus wongi, Gazella sinensis, Ovis shantungensis and Megalovis piveteaui respectively, among which G. sinensis is the dominate species. S. wongi and G. sinensis are mainly represented by horn-cores and partial skull bones as well as mandibles; in addition, metacarpal and/or metatarsal bones were also recognized for all of the four species. The horn-cores are easy to be identified to the species level, while the dentitions and the postcranial bones underwent a series of examinations and comparisons before getting properly determined and referred to the most approximate taxa. Among the postcranial bones, the metapodials, especially to the metacarpal bones special attentions were paid, which are crucial not only for taxonomic identification, but also for phylogenetic and paleoecological reconstructions; the previously misidentified metapodial specimens in Nihewan fauna were reconsidered in this paper. In the SSMZ fauna, the bovid guild is dominated by Gazella and Bison, which indicates steppe was the most important biome in Nihewan Basin during Early Pleistocene.

Mc III+IV

Taxa

Sources

Length

Proximal width

Proximal APD

Distal width

Distal APD

Midshaft width

Midshaft APD

Index of stoutness (Distal width/total length) (%)

Bison palaeosinensis

Teilhard and Piveteau (1930)

231-248

72-74

28-29

Tong et al. (2018)

226-233

60-67.8

35-38.6

59-63.5

34.2-34.7

36-39.5

26-27.6

26-28

Megalovis latifrons

Viret (1954)

200

56.5

Megalovis latifrons

Radulesco and Samson (1962)

192

35.7

33.3

Megalovis piveteaui

This paper

212

27.8

Teilhard and Piveteau (1930); Schaub (1937); Radulesco and Samson (1962)

192-204

51-57

54-61

28-30^#

Megalovis wimani

Schaub (1937)

185

30.8^#

Ovis shantungensis

This paper

221

Teilhard and Piveteau (1930)

231-233

42-44

42-44.5

18-19

Ovis ammon

Fedosenko and Blank (2005)

218

Ovis shangi

Teilhard and Young (1936)

150

18.7

Spirocerus wongi

This paper

175

Spirocerus kiakhtensis

Sokolov (1959)

170

60.9^#

35.0^#

22.0^#

35.8

Gazella cf. G. lydekkeri

Zhang and Yang (2016)

141

Gazella sinensis

This paper

180

12.5

11.3

12.8

Gazella subgutturosa

Demircioglu and Ince (2020)

146.0(F)

18.4(F)

18.0(F)

10.5(F)

9.7(F)

150.7(M)

19.6(M)

18.9(M)

11.4(M)

9.9(M)

Procapra przewalskii

Boule et al. (1928)

142

18-21

12.7-14.8

Procapra gutturosa

Boule et al. (1928)

180

12.8

Procapra gutturosa

This paper (OV 1124)

146

15.5

8.0

16.7

12.1

8.7

7.0

11.4

Saiga tatarica

Prat (1966b)

153

18.5

25.5

13.5

17.7

Capra ibex

Prat (1966a)

126-155

28.5-38.5

20.5-27

31.5-43

19-24

20-27.5

(139.2)

(33)

(23.8)

(36.7)

(21.3)

(23.8)

Praeovibos priscus

Kahlke (1964)

193.7^#

Ovibos moschatus sussenbornensis

Kahlke (1961)

189.9^#

62.8^#

36.5^#

69.1^#

44^#

36.4

Mt III+IV

Spirocerus wongi

This paper

173.0

36.9

34.0

45.3

26.1

22.0

21.5

26.2

Mc III+IV: The Mc III+IV (Fig. 4A1-3) is a kind of short but robust one, with the distal end expanded. The cranial aspect is more rounded on the shaft while the caudal surface is more flat. At both the proximal and distal ends the medial side or Mc III looks prominently thicker than the lateral side. In proximal view, there are two large articular facets, the larger facet or magnum trapezoid facet is relatively wide and has a curved edge, which is articulated with the fused 2nd and 3rd carpals; the smaller facet or unciform facet is triangular and articulates with the 4th carpal; between the two facets there exists a groove or depression. The posterior medial tubercle is not developed. In anterior view, the vascular groove (or metacarpal gully) is nearly unobservable and the nutrient foramen is tiny. In posterior view, the shaft has a quite flat surface, except near the proximal end, there is a depression; a small nutrient foramen exists near the distal articular surface. The dimensions are shown in Table 4.

Mt III+IV (Fig. 4C1-3): In general view, the Mt III+IV has the very proximate length as the Mc III+IV, which is quite different from the common ungulates whose metatarsals are prominently longer than metacarpals belonging to the same individual; furthermore, the distal end expands more sharply relative to the shaft. In proximal view, the proximal surface has a polygon outline, and consists of four articular facets; the two anterior facets are large and kidney-shaped, but the two posterior facets are small and elongated. The mediolateral dimension of the proximal end is slightly larger than the anteroposterior dimension. The two large articular facets meet at the front middle part but diverge posteriorly; both of them have longer anteroposterior dimensions. The anteromedial facet articulates with the fused 2nd and 3rd tarsals; the anterolateral facet articulates with naviculo-cuboid. There are two smaller facets located near the posterior margin. The posterolateral facet has larger mediolateral dimension and articulates with naviculo-cuboid. The small roundish facet articulates with the 1st tarsal. The dimensions are shown in Table 4.

Mc III+IV: A complete left Mc III+IV (IVPP V 28688) (Fig. 4E1-4). In general, the bone is very slender; the cranial aspect is more rounded on the shaft and the caudal aspect is much flatter and slightly concave at the upper part; the distal epiphysis is not fused yet. In proximal view, there are two articular facets, the larger one or magnum trapezoid facet is prominently wider and deeper, which articulates with the fused 2nd and 3rd carpals; the smaller one or unciform facet is oval-like and is the articular surface for 4th carpal; between the two facets there exists a narrow ridge; no nutrient foramen can be observed at the proximal end (Fig. 4E3). In anterior view, a prominent tubercle (extensor carpi radialis insertion: Gentry, 1966: fig. 12) occurs at the cranial aspect of the proximal end; no vascular groove (or metacarpal gully) can be observed, while the nutrient foramen is clear but small and located near the epiphyseal suture; the widest portion lies at the epiphyseal suture rather than at the trochlea (Fig. 4E1). In posterior view, no prominent groove can be observed except the upper part; the articular facet for the vestigial 5th metacarpal is absent. A prominent nutrient foramen exists near the epiphyseal suture and a tiny nutrient foramen occurs at the mid-shaft (Fig. 4E2). The dimensions are shown in Table 4.

The metacarpal bone is prominently larger than such allied taxa, as Gazella subgutturosa and Procapra przewalskii, but with the same size as that of P. gutturosa (Table 4); in morphology, it has no peculiarity. The metapodial bone does have distinctive characters relative to those of the caprines in their extremely slenderness. Meanwhile, the BT (maximum breadth of trochlea) of the metacarpal of SSMZ specimen is 20.9 mm, which stands between those of the Gazella (15.1-20.1) and Procapra (21.5-21.6) (Wang et al., 2020).

Metacarpal: A right anterior canon bone (Mc III+IV) (IVPP V 28695) (Fig. 4K1-4). In general, both the proximal and distal ends expand to some extent, and the metacarpal bone is moderately stout. At both proximal and anterior aspects, the medial side or Mc III looks noticeably thicker than the lateral side. The two proximal articular facets are quite flat, and a narrow groove occurs between the facets. In anterior view, the shaft is roundish, and the vascular groove (or metacarpal gully) is very narrow at the upper par but widened around the nutrient foramen. In posterior view, the proximal portion of the shaft has a medial longitudinal depression, but the lower part is flat; a prominent nutrient foramen exists near the articular surface. The dimensions are shown in Table 4.

The genus Megalovis of the Villafranchian are thought by many to be similar to the ancestral form of Ovibos, if not directly ancestral (Crégut-Bonnoure, 1984). Actually, Teilhard de Chardin and Piveteau (1930) had indicated the close affinity of Megalovis piveteaui with Ovibos in the following aspects: cheek teeth without basal pillars, premolars quite hypsodont (Fig. 10A), upper molars with small enamel loops between the lobes at the lingual side (Fig. 10B). Furthermore, the present authors also think the upper molars are quite elongated in crown and the upper premolars with spurs (Fig. 10B). Although the cranial and cornual features are almost completely unknown, the close relationship between Megalovis and ovibovines is verified. On the other hand, the metapodials of Megalovis are also quite stout (Table 4), which resembles those of the recent Ovibos.

The bovid metacarpal bones unearthed at SSMZ site are quite diversified, and most of them are easy to be identified according to their size and proportion, whereas some of them are very similar to each other both in size and stoutness. Therefore, an index should be employed, that’s the robusticity index or stoutness index. Concerning the robusticity index, there exist two calculation methods: one is the relative dimensions of mediolateral diaphysis width and maximum length (SD/GL) ×100) (Maniakas and Kostopoulos, 2017), the other is the distal width/total length (Sher, 1997). Because it’s easier and more practical to measure the distal width, this paper follows Sher’s (1997) method to calculate the robusticity index, i.e. (distal width/greatest length) ×100. Based on the morphological observations and robusticity index calculations, the metacarpal bones of bovids from SSMZ site are quite clearly distinguished (Table 4; Fig. 11).

Megalovis piveteaui and Bison palaeosinensis have quite similar metacarpals both in size and proportion, the only difference is that the formers’ is slightly smaller. Moreover, the Nihewan specimens of M. piveteaui share the similar size and form with M. latifrons of European (Viret, 1954; Radulesco and Samson, 1962) (see Table 4). Megalovis was referred to Ovibovini, maybe its metacarpal is the largest, but less stout, among the ovibovine taxa. M. piveteaui should be larger than Spirocerus wongi in body mass.