Tetracyclus emarginatus

Tetracyclus emarginatus has been noted in both modern and fossil deposits across several localities. Specimens described and displayed above come from two fossil deposits: the Valles Caldera complex, New Mexico dating to the mid-Pleistocene (~400 ka) and the Nebraska Ashfall Fossil Beds in Antelope County dating to back to the mid-Miocene (~12 Ma). The Miocene-aged deposit from Ashfall is interpreted to be from a subtropical watering-hole environment, much like those found in African savannas today, that became covered in ash from a mega-eruption in the Bruneau-Jarbidge area of Idaho. The Pleistocene-aged deposit from the Valles Caldera straddles Glacial Termination V, where glacial conditions transitioned to interglacial conditions as Southwestern climate began to warm and precipitation decreased.

Original descriptions of T. emarginatus place it in Siberia and Mexico (Ehrenberg 1845) and later it was reported from the Gap of Dunloe, Killarney (Smith 1856). Subsequent records of T. emarginatus (Patrick and Reimer 1966, Williams 2007) are from from New Jersey and Oregon. Multiple authors described T. emarginatus as a freshwater diatom that prefers the cool waters of lakes and ponds found in mountainous regions (Smith 1865, Patrick and Reimer 1966, Williams 2007).