Morgan et al. (2011) recognized two species of Stegomastodon: the earlier S. primitivus and the late Blancan/Irvingtonian S. mirificus. The Caballo Local Fauna stegodont lacks specific characters and thus is recorded only as Stegomastodon sp. (Morgan et al. 2011).
Late Blancan: Caballo (Morgan et al. 2011).
Irvingtonian: Anza-Borrego (Murray 2008).
Literature. Morgan et al. 2011.
I follow Morgan and Lucas (2005, 2011) in recognizing one Irvingtonian species of Stegomastodon. However, Lucas et al. (2011) recognized that there may be merit in recognizing the derived Irvingtonian Stegomastodon as a separate species, S. aftoniae, but Morgan and Lucas (2011) retained S. mirificus for these advanced forms pending revision of the genus.
Although the teeth of Stegomastodon are far simpler than those of mammoths, Lucas et al. (2011) suggested that the evolution of the Stegomastodon lines indicates increasing adaptation to a grazing regime, evolution cut short with the invasion of mammoths. There is a lack of confirmed Stegomastodon younger than about 1.2 mya (Morgan and Lucas 2011).
Isolated teeth are reasonably common in the El Paso Valley. Common reports of finding bones of mastodonts in the Mesilla Basin and El Paso Valley generally turn out to be gomphotheres, and most likely represent this species, though Cuvieronius tropicus is a possibility.
Vanderhill (1986) described a palate (NMSU 75.2.4) with right and left M2-M3 from gravel pits east of Las Cruces, Doña Ana Co., NM, mentioning the presence of more than five cross-lophs on the teeth and a complex pattern of the enamel. Based on Vanderhill's description and measurements, the specimen in Fig. 1 is similar in age and size.
Fig. 1. Palate of Stegomastodon, anterior to left. Occlusal length of right anterior cheektooth, 105 mm. El Paso, private collection.
Late Blancan: Cal Tech (Morgan and White 2005); Curtis Ranch (Morgan and White 2005).
Irvingtonian: El Paso (UTEP; Private Collection); Taylor Gravel (Morgan and White 2005); Tortugas Mountain Gravel Pit (Morgan and Lucas 2005).
Literature. Lucas et al. 2011; Morgan and Lucas 2005, 2011; Morgan and White 2005; Morgan et al. 2011; Vanderhill 1986.
Last Update: 1 Apr 2014