The Zokors of Yushe Basin

Abstract

Myospalacinae from the Yushe Basin include ten species representing two tribes: Prosiphneini and Mesosiphneini. Of four Prosiphneini, the late Miocene Prosiphneus murinus spans the Mahui Formation to the Taoyang Member, low in the Gaozhuang Formation (~6.5–5.7 Ma), Pliosiphneus antiquus n. sp. occurs in the middle of the Nanzhuanggou Member of the Gaozhuang Formation (~4.7–4.5 Ma), and Pliosiphneus lyratus spans the Nanzhuanggou Member of the Gaozhuang Formation to the lower Mazegou Formation (~4.7–3.6 Ma). The derived Eospalax fontanieri appears much later in the Lishi Loess and younger sediments. The record of six Mesosiphneini begins with Chardina truncatus in the Nanzhuanggou Member (~4.7–4.5 Ma). Mesosiphneus praetingi spans the Culiugou Member of the Gaozhuang Formation to the lower Mazegou Formation (~4.3–3.4), and is followed by Mesosiphneus intermedius higher in the Mazegou Formation (~3.4–2.9 Ma). The mesosiphneine Yangia trassaerti is present in the early Pleistocene Haiyan Formation and Y. tingi occurs higher in the Haiyan Formation, both pre-Reunion magnetostratigraphic event, estimated ~2.5 to 2.2 Ma. Yangia epitingi in the Pleistocene Wucheng Loess is the youngest Yushe mesosiphneine. Zokor distribution reflects the Teilhard de Chardin Yushe biostratigraphy: the Mahui Formation to the Taoyang Member of the Gaozhuang Formation is equivalent to Teilhard’s Yushe Zone I; the Nanzhuanggou and Culiugou members through the Mazegou Formation is equivalent to Yushe Zone II; and the Haiyan Formation represents Yushe Zone III. The data propose a lineage of Mesosiphneini evolving from a primitive form to extinction: Chardina truncatus → Mesosiphneus praetingi → M. intermedius → Yangia trassaerti → Y. tingi → Y. epitingi. The transformation from the rooted M. intermedius to the rootless Y. trassaerti (by the earliest Pleistocene) clearly reflects a major change in environmental conditions. Among the rooted myospalacines, specific differentiation is recognized by sudden increases in tooth crown height. Among the rootless forms, taxa are distinguished by the increase of clinomegodonty (decrease in angle α), which is correlated with increased dental stress during feeding, likely due to changing environment.