Data from: Millions of years behind: slow adaptation of ruminants to grasslands

The Late-Cretaceous appearance of grasses, followed by the Cenozoic
advancement of grasslands as dominant biomes, has contributed to the
evolution of a range of specialized herbivores adapted to new diets, as
well as to increasingly open and arid habitats. Many mammals including
ruminants, the most diversified ungulate suborder, evolved high–crowned
(hypsodont) teeth as an adaptation to tooth–wearing diets and habitats.
The impact of different causes of tooth wear is still a matter of debate,
and the temporal pattern of hypsodonty evolution in relation to the
evolution of grasslands remains unclear. We present an improved
time–calibrated molecular phylogeny of Cetartiodactyla, with phylogenetic
reconstruction of ancestral ruminant diets and habitats, based on
characteristics of extant taxa. Using this timeline, as well as the fossil
record of grasslands, we conduct phylogenetic comparative analyses showing
that hypsodonty in ruminants evolved as an adaptation to both diet and
habitat. Our results demonstrate a slow, perhaps constrained, evolution of
hypsodonty towards estimated optimal states, excluding the possibility of
immediate adaptation. This augments recent findings that slow adaptation
is not uncommon on million–year time scales.