Evidence of strong stabilizing effects on the evolution of boreoeutherian (Mammalia) dental proportions

Abstract

The dentition is an extremely important organ in mammals with variation in timing and sequence of eruption, crown morphology, and tooth size enabling a range of behavioral, dietary, and functional adaptations across the class. Within this suite of variable mammalian dental phenotypes, relative sizes of teeth reflect variation in the underlying genetic and developmental mechanisms. Two ratios of postcanine tooth lengths capture the relative size of premolars to molars (premolar–molar module, PMM), and among the three molars (molar module component, MMC), and are known to be heritable, independent of body size, and to vary significantly across primates. Here, we explore how these dental traits vary across mammals more broadly, focusing on terrestrial taxa in the clade of Boreoeutheria (Euarchontoglires and Laurasiatheria). We measured the postcanine teeth of N = 1,523 boreoeutherian mammals spanning six orders, 14 families, 36 genera, and 49 species to test hypotheses about associations between dental proportions and phylogenetic relatedness, diet, and life history in mammals. Boreoeutherian postcanine dental proportions sampled in this study carry conserved phylogenetic signal and are not associated with variation in diet. The incorporation of paleontological data provides further evidence that dental proportions may be slower to change than is dietary specialization. These results have implications for our understanding of dental variation and dietary adaptation in mammals.

Mammal Molar Size Ratios and the Inhibitory Cascade at the Intraspecific Scale

“…A review of literature related to the inhibitory cascade recovered six publications that included sufficient data to evaluate intraspecific variation in molar ratios ( Labonne et al. 2012 ; Asahara 2014 , 2017 ; Asahara and Nishioka 2017 ; Monson et al. 2019 ; Roseman and Delezene 2019 ).…”

“…2019 ; Roseman and Delezene 2019 ). The resulting combined datasets consisted of 1593 length entries for 47 species ( Monson et al. 2019 ), 706 individual-level ( Labonne et al.…”

“…The second suggested measurement type is the MMC or relative mesiodistal length of each molar crown without the incorporation of buccolingual width ( Hlusko et al. 2016 ; Monson et al. 2019 ).…”

“…If the MMC is a more precise way of capturing the ICM, length measurements should match ICM predictions more closely than area measurements for the same specimens because there should be reduced pleiotropy and therefore lower likelihood of overprinting of other genetic modules ( Hlusko et al. 2016 ; Monson et al. 2019 ).…”

Patterns and magnitudes of craniofacial covariation in extant cercopithecids

“…The cranium contains most of the primary sensory organs, the mouth, and the brain (Ackermann & Cheverud, 2004; Cheverud, 1982), and as such, craniofacial morphology is a focal point for selection. Various aspects of the cranium, including dental morphology, tooth eruption sequence, and calvarial shape, are significantly associated with variation in life history, behavior, diet, body size, brain size, and other traits (Harvati & Weaver, 2006a, 2006b; Monson et al, 2019; Monson & Hlusko, 2018a, 2018b; Perez & Monteiro, 2009; von Cramon‐Taubadel, 2011; von Cramon‐Taubadel & Smith, 2012). The evolution of cranial variation in humans is of particular interest due to important adaptations associated with brain size and brain morphology in our lineage (Elton, Bishop, & Wood, 2001; González‐Forero & Gardner, 2018; Kaplan, Hill, Lancaster, & Hurtado, 2000; Kappelman, 1996).…”