New materials of Exallerix pustulatus (Erinaceidae, Eulipotyphla) from Nei Mongol and other Brachyericinae of China

LI Lu, LI Qiang, WANG Xiao-Ming

Vertebrata Palasiatica 2025, 63 (4): 335-349. DOI: 10.19615/j.cnki.2096-9899.250910

Abstract （981）

HTML （20）

PDF（pc）（2341KB）（227）

This article describes new fossil material of Exallerix pustulatus from the early Late Oligocene of Nei Mongol, China. The specimens supplement and clarify certain mandibular and lower dental morphological features of this species, allowing for further comparisons with other short-faced hedgehogs. Previously, E. pustulatus had only been recorded from the Hsanda Gol Formation at Taatsiin Gol, in the Valley of Lakes, Mongolia. This discovery of new material from Sonid Left Banner marks the first occurrence of the genus Exallerix in China. In addition, discussions of other short-faced hedgehog fossils from Chinese localities confirm the validity of Metexallerix gaolanshanensis, which lived during the late Late Oligocene, approximately 25 Ma. Furthermore, the short-faced hedgehog specimens from locality Damiao 16 in Nei Mongol are tentatively referred to Synexallerix junggarensis, rather than M. gaolanshanensis.

The m1: as noted by Ziegler et al. (2007), the trigonid of the m1 is relatively short anteroposteriorly and wide transversely. The ratio of trigonid length to width ranges from 1.05 to 1.32 (Fig. 2). This ratio is significantly higher than that of Metechinus from North America and comparable to or lower than that of other short-faced hedgehogs (Lopatin and Zazhigin, 2003). The trigonid is fully open lingually. The ratio of talonid length to trigonid length ranges from 0.48 to 0.60 (Fig. 4), which is slightly higher than in other species of Exallerix (Lopatin and Zazhigin, 2003). The talonid is approximately equal in width to the trigonid. The metaconid sits close to the protoconid, and the two cusps are separated by a shallow depression. The entocristid is low, with a height approximately equal to that of the cristid obliqua and postcristid. The talonid lacks a hypoconulid, though some individuals have a metastylid (e.g., V 34183.6, Fig. 2F). The labial surface of the crown, particularly the paralophid and cristid obliqua, is unornamented in the upper third to quarter. The lingual surface of the crown is mostly unornamented except near the lingual opening of the trigonid. Enamel knobs or tubercles form at least three elongated longitudinal rows on the labial face of the crown and several shorter rows on the labial aspect of the roots. These rows are wavy and run approximately parallel to each other. Additional enamel tubercles are scattered between or along the margins of these rows.

As noted by Lopatin and Zazhigin (2003), Asian short-faced hedgehogs, including Synexallerix, Posterallerix, and Exallerix, exhibit a more derived dental morphology, specifically: 1) a narrower and more elongated m1 trigonid (Fig. 4); 2) a relatively shorter talonid on the m1 (Fig. 5); and 3) a smaller ratio of m2 length to m1 length (Fig. 6). In contrast, the dental features of Exallerix pustulatus show closer resemblance to those of North American short-faced hedgehogs.

Furthermore, the evolutionary trends in m1 morphology differ significantly between Asian and North American short-faced hedgehogs. In the former group, the trigonid tends to become increasingly elongated anteroposteriorly over time, whereas in the latter, the opposite trend is observed (Figs. 4, 5). The m2 appears to be relatively stable in both lineages (Fig. 6). However, due to the limited sample size and scarcity of comparative data, further analysis is not feasible.