The late Miocene Hemphillian NALMA begins at approximately 9 Ma with the immigration of mammals from Asia and South America (Tedford et al. 2004; part of the larger Interchange Event 10 of Woodburne and Swisher 1995). The immigration event of the late early Hemphillian (Hh2, approximately 7.5 to 6.8 Ma of Tedford et al. 2004) marks the arrival of the first bovid, Neotragocerus, to North America (Matthew and Cook 1909). Its affinity to other bovids has yet to be adequately established, yet it is the only bovid in North America during the late Miocene.
Deposits in the Yushe Basin of Shanxi Province, China, show major periods of faunal turnovers. The first takes place over a short period of time across the Mahui-Gaozhuang hiatus at approximately 5.8 to 5.9 Ma (Flynn et al. 1991; Tedford et al. 1991; chronology updated in Flynn 1997). Large mammal faunas show an abrupt turnover at the transition between Gaozhuang and Mazegou Formations (dating approximately 4.0 Ma) and illustrate a distinct immigration event (Flynn et al. 1991). Another major turnover event takes place during the Mazegou-Haiyan hiatus, which cannot be pinpointed but falls in the interval of 3.0 to 2.0 Ma (Tedford et al. 1991).
These turnover events in eastern Asia and North America not only illustrate extinctions, but also reflect faunal exchange between the two continents. We infer that the new species of caprine from the Panaca Formation described here immigrated from the general region of northeastern Asia during the latest Miocene or earliest Pliocene, i.e., late late Hemphillian, Hh4 equivalent (Tedford et al. 2004).