Dietary Change and Evolution of Horses in North America

Abstract

The evolution of high-crowned molars among horses (Family Equidae) is thought to be an adaptation for abrasive diets associated with the spread of grasslands. The sharpness and relief of the worn cusp apices of teeth (mesowear) are a measure of dietary abrasion. We collected mesowear data for North American Equidae for the past 55.5 million years to test the association of molar height and dietary abrasion. Mesowear trends in horses are reflective of global cooling and associated vegetation changes. There is a strong correlation between mesowear and crown height in horses; however, most horse paleopopulations had highly variable amounts of dietary abrasion, suggesting that selective pressures for crown height may have been weak much of the time. However, instances of higher abrasion were observed in some paleopopulations, suggesting intervals of stronger selection for the evolution of dentitions, including the early Miocene shortly before the first appearance of Equinae, the horse subfamily in which high-crowned dentitions evolved.

The phylogenetic signal in tooth wear: What does it mean?

“…In many cases, the diets of extinct taxa are also vastly different from those of extant taxa, despite being members of the same family (e.g. Kaiser, 2011, Mihlbachler, Rivals, Solounias, & Semprebon, 2011; DeSantis, Schubert, Scott, & Ungar, 2012). …”

Habitat changes and changing predatory habits in North American fossil canids

“…However, although predictive models can give important clues to short-term biotic reactions 4,5 , only the fossil record can provide empirical data on evolutionary responses during long periods of profound climatic and environmental change [6][7][8][9] . Here we demonstrate that the evolution of predatory behaviour in North American canids (for example, foxes and wolves; family Canidae) has been influenced by climatic and environmental transformation over the later Cenozoic (the past B37 million years (Myr ago)).…”

“…Plant silica microfossils (phytoliths) attest that open-habitat grasslands were well established in North America by the end of the Oligocene at B27-23 Myr ago 12 . This trend towards habitat opening had a strong impact on mammalian palaeocommunities, as evidenced by changes in ungulate (hoofed mammals) craniodental morphology indicative of feeding on more abrasive forage (for example, hypsodont (high-crowned) cheek teeth), and changes in limb morphology to the elongate limbs typical of present-day fast-running (cursorial) open-habitat ungulates 8,13,14 . However, while large herbivores are the faunal components directly impacted by vegetational change, the effect of such changes on large carnivores has been less studied.…”

“…Here we use the impressive and well-documented fossil record of North American canids [17][18][19] to test if their inferred locomotor/ predatory behaviour was influenced by Cenozoic environmental change towards open habitats, as has been documented in the contemporaneous large herbivores 8,11,14 . We test for direct association between predatory behaviour and environmental events, rather than an 'arms-race' hypothesis between predators and prey.…”

Eels, Beavers, and Horses: Human Niche Construction in the European Late Upper Palaeolithic

“…Horse remains are found at most bone-rich Magdalenian sites indicating they were one of, if not the, prime prey species for humans (Nitecki & Nitecki, 1987). These small sized horses were common in a variety of open-habitats and their dentition suggests they were adapted to grazing rather than browsing (Mihlbachler et al 2011). The high land cover of sedges and graminoids would have promoted large herds (Bignon et al 2005).…”