Longer in the tooth, shorter in the record? The evolutionary correlates of hypsodonty in Neogene ruminants

The acquisition of hypsodont molars is often regarded as a key innovation in the history of ruminant ungulates. Hypsodont ruminants diversified rapidly during the later Neogene, circa 15-2 Myr ago, and came to dominate the ruminant fossil record in terms of species diversity. Here we show that hypsodont clades had higher speciation and diversification rates than other clades. Hypsodont species had, on average, shorter stratigraphic durations, smaller range size and lower occupancy than non-hypsodont species. Within hypsodont clades, some species were very common and acquired large geographical ranges, whereas others were quite rare and geographically limited. We argue that hypsodont clades diversified in an adaptive radiation-like fashion, with species often splitting cladogenetically while still in the expansive phase of their occupancy history.