[2] In 2006 Strömberg examined the independent acquisition of high-crowned cheek teeth (hypsodonty) in several ungulate lineages (e.g., camelids, equids, rhinoceroses) from the early to middle Miocene of North America, which had been classically linked to the spread of grasslands.
[3] In 2008 Mendoza and Palmqvist determined the relative importance of grass consumption and open habitat foraging in the development of hypsodont teeth using a dataset of 134 species of artiodactyls and perissodactyls.
[1][4][5] Analysis of dental microwear patterns of hypsodont notoungulates from the Late Oligocene Salla Beds of Bolivia showed shearing movements are associated with a diet rich in tough plants, not necessarily grasses.
Hence the relationship between high-crowned mammals and the source of tooth wear in the fossil record may not be straightforward and the spread of grasslands in South America, traditionally linked with the development of notoungulate hypsodonty, was called into question.
For example, hadrosaurs, a group of herbivorous dinosaurs, likely grazed on low-lying vegetation and microwear patterns show that their diet contained an abrasive material, such as grit or silica.