Abstract:Mammalian molar crowns form a module in which measurements of size for individual teeth within a toothrow covary with one another. Molar crown size covariation is proposed to fit the inhibitory cascade model (ICM) or its variant the molar module cascade model (MMC), but the inability of the former model to fit across biological scales is a concern in the few cases where it has been tested in Primates. The ICM has thus far failed to explain patterns of intraspecific variation, an intermediate biological scale, … Show more
“…286 species were represented by one specimen, and 13 species by 2 specimens. The intraspecific variation of molar proportions, generally low in placental species (Vitek et al, 2020), was assumed to be negligible in comparison to the magnitude of the interspecific variation related to allometry for Placentalia (see Supplementary Material available on Dryad, http://dx.doi.org/10.5061/dryad.dfn2z34xq). The sample covered most extant placental orders, some being excluded for being edentulous or enamel-free taxa (Cingulata, Pilosa, Tubulidentata), having high-crowned teeth (Lagomorpha) (see Gomes Rodrigues et al, 2017 for reasoning), or supernumerary molars (Sirenia).…”
Section: Specimen Selectionmentioning
confidence: 99%
“…It is largely overlapping with that of Billet and Bardin (2019) and its construction is based on the same publications and rationale. We used the phylogenetic patterns obtained by Meredith et al (2011) andWible et al (2009) for interordinal relationships of extant taxa and for the placement of successive fossil outgroups to crown Placentalia, respectively. We used a combination of sources for dating the divergences on the reconstructed composite cladogram and followed the same rationale as Billet and Bardin (2019) for placing fossils (see Supplementary Material available on Dryad).…”
Iterative segments such as teeth or limbs are a widespread characteristic of living organisms. While their proportions may be governed by similar developmental rules in vertebrates, there is no emerging pattern as regards their relation to size. Placental mammals span eight orders of magnitude in body size and show a wide spectrum of dietary habits associated with size and reflected in their dentitions, especially molars. Although variation in size constitutes an important determinant for variation in biological traits, few major allometric trends have been documented on placental molars so far. Molar proportions have been intensively explored in placentals in relation to developmental models, but often at a small phylogenetic scale. Here, we analyzed the diversity of upper molar proportions in relation to absolute size in a large sample of placental species (n = 286) encompassing most of the group’s dental diversity. Our phylogenetically informed analyses revealed a twofold pattern of evolutionary integration among upper molars: while molars covary in size with each other, their proportions covary with the absolute size of the entire molar field. With increasing absolute size, posterior molars increase in size relative to anterior ones, meaning that large-sized species have relatively large rear molars while the opposite is true for small-sized species. The directionality of proportional increase in the molar row exhibits a previously unsuspected allometric patterning among placentals, showing how large-scale variations in size may have influenced variation in dental morphology. This finding provides new evidence that processes regulating the size of individual molars are integrated with overall patterns of growth and calls for further testing of allometric variation in the dentition and in other segmental series of the vertebrate body.
“…286 species were represented by one specimen, and 13 species by 2 specimens. The intraspecific variation of molar proportions, generally low in placental species (Vitek et al, 2020), was assumed to be negligible in comparison to the magnitude of the interspecific variation related to allometry for Placentalia (see Supplementary Material available on Dryad, http://dx.doi.org/10.5061/dryad.dfn2z34xq). The sample covered most extant placental orders, some being excluded for being edentulous or enamel-free taxa (Cingulata, Pilosa, Tubulidentata), having high-crowned teeth (Lagomorpha) (see Gomes Rodrigues et al, 2017 for reasoning), or supernumerary molars (Sirenia).…”
Section: Specimen Selectionmentioning
confidence: 99%
“…It is largely overlapping with that of Billet and Bardin (2019) and its construction is based on the same publications and rationale. We used the phylogenetic patterns obtained by Meredith et al (2011) andWible et al (2009) for interordinal relationships of extant taxa and for the placement of successive fossil outgroups to crown Placentalia, respectively. We used a combination of sources for dating the divergences on the reconstructed composite cladogram and followed the same rationale as Billet and Bardin (2019) for placing fossils (see Supplementary Material available on Dryad).…”
Iterative segments such as teeth or limbs are a widespread characteristic of living organisms. While their proportions may be governed by similar developmental rules in vertebrates, there is no emerging pattern as regards their relation to size. Placental mammals span eight orders of magnitude in body size and show a wide spectrum of dietary habits associated with size and reflected in their dentitions, especially molars. Although variation in size constitutes an important determinant for variation in biological traits, few major allometric trends have been documented on placental molars so far. Molar proportions have been intensively explored in placentals in relation to developmental models, but often at a small phylogenetic scale. Here, we analyzed the diversity of upper molar proportions in relation to absolute size in a large sample of placental species (n = 286) encompassing most of the group’s dental diversity. Our phylogenetically informed analyses revealed a twofold pattern of evolutionary integration among upper molars: while molars covary in size with each other, their proportions covary with the absolute size of the entire molar field. With increasing absolute size, posterior molars increase in size relative to anterior ones, meaning that large-sized species have relatively large rear molars while the opposite is true for small-sized species. The directionality of proportional increase in the molar row exhibits a previously unsuspected allometric patterning among placentals, showing how large-scale variations in size may have influenced variation in dental morphology. This finding provides new evidence that processes regulating the size of individual molars are integrated with overall patterns of growth and calls for further testing of allometric variation in the dentition and in other segmental series of the vertebrate body.
“…The molars would reflect a morphological and evolutionary gradient of character change. The absence of the metaconid in the m4 can be conceived as related to the functional reduction of the distal half of the lower molar in taxa with an equal number of upper and lower molariforms and the developmental factors controlling molar size gradient (Vitek et al 2020). In addition to the plesiomorphic retention of the metaconid, in Callistoe the talonid in the m1-3 (unknown until the discovery of the specimen IBIGEO-P 110), also conserves a plesiomorphic pattern composed by distinct hypoconid, entoconid, hypoconulid, and a well-delimited, thought small, basin.…”
We present a detailed description of the anatomy of the dentary and lower teeth of a new specimen of Callistoe vincei, a large carnivorous metatherian from the Eocene (?Ypresian) of northwestern Argentina. The recently collected specimen is a young adult represented by a partial right dentary with the canine, p1, roots of p3, and very well-preserved m1 to m4. The description includes a comparison with the holotype specimen, a much older individual, and other closely related large sparassodonts (e.g., Arminiheringia). The analysis of this new material allowed identifying plesiomorphic molar features in Callistoe, such as the presence of a reduced metaconid on the m3 and a tricuspated, basined talonid on m1–m3. We also described the mesowear facets in the lower dentition, showing that the self-sharpening facet typically present in extinct and extant placental and some marsupial carnivorous forms, was absent in Callistoe. The presence of a short-term cutting edge in the trigonid related to the thinness of the enamel layer, and the associated tooth wear susceptibility, were likely compensated by a dental mechanism (overeruption) to maintain occlusal contact among antagonist teeth. This process could explain the marked extrusion of the tooth roots observed in Callistoe as well as in other large closely related members of the group.
“…All these studies looked at predicted (mean) tooth morphologies. To generate an independent prediction of the IC model, Roseman and Delezene (2019) derived the expected variances and covariances of tooth dimensions and found that these predictions were generally not matched closely by data from primates (see also Vitek et al 2020). Figure 4.Area of third molar (M3) compared with the second molar (M2), each relative to the area of the first molar (M1).…”
The concept of evolvability—the capacity of a population to produce and maintain evolutionarily relevant variation—has become increasingly prominent in evolutionary biology. Paleontology has a long history of investigating questions of evolvability, but paleontological thinking has tended to neglect recent discussions, because many tools used in the current evolvability literature are challenging to apply to the fossil record. The fundamental difficulty is how to disentangle whether the causes of evolutionary patterns arise from variational properties of traits or lineages rather than being due to selection and ecological success. Despite these obstacles, the fossil record offers unique and growing sources of data that capture evolutionary patterns of sustained duration and significance otherwise inaccessible to evolutionary biologists. Additionally, there exist a variety of strategic possibilities for combining prominent neontological approaches to evolvability with those from paleontology. We illustrate three of these possibilities with quantitative genetics, evolutionary developmental biology, and phylogenetic models of macroevolution. In conclusion, we provide a methodological schema that focuses on the conceptualization, measurement, and testing of hypotheses to motivate and provide guidance for future empirical and theoretical studies of evolvability in the fossil record.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
