Accommodation of Dental Variations During Jaw Growth in Ungulate Mammals

The growth of teeth and jaw bones is intimately linked in vertebrates, especially in mammals due to their specialized dentition and limited body growth. However, the relative patterns of growth and level of integration (i.e., co-variation) of these structures are insufficiently known, which hinders our ability to understand how the jaw bones accommodate the diverse dental shapes and eruption patterns observed in mammals. Here, we studied the cranial ontogenetic series of 23 ungulate species among artiodactyls, perissodactyls, and hyracoids having different dental shapes and eruption patterns. We evaluated the variation of the teeth-palate complex, as well as the co-variation of teeth and palate during growth using 3D geometric morphometrics. We found a major ontogenetic component common to all the species studied, corresponding to an elongated dental row relative to the palate in juveniles and vice versa in adults. This pattern agrees with the prolonged growth of the palate as compared to teeth during development but is also reminiscent of an intraspecific allometric pattern previously observed in some dwarf ungulates. Moreover, most artiodactyls, especially ruminants, departed from other ungulates in having a higher co-variation between the dental row and the palate. This stronger integration seen in ruminants might be associated with their inherited rapid growth and relatively fast eruption pattern. This is in contrast to ungulates with late eruption of last molars, whose teeth-palate complex might be less constrained, but further investigation is needed to substantiate these hypotheses and better understand the factors influencing covariations within the upper jaw.