Constructing cranial ontogenetic trajectories: A comparison of growth, development, and chronological age proxies using a known‐age sample of Macaca mulatta

Abstract

Recent morphometric research has generated opposing conclusions regarding the ontogenetic trajectories of catarrhine crania, possibly due to the ontogenetic proxies used to calculate them. Therefore, we used three surrogates: size, molar eruption, and chronological age to generate trajectories in a known-age sample to produce ontogenetic trajectories and determine the similarities and differences between them. Forty-three landmarks from an ontogenetic series of 160 Macaca mulatta crania, with associated ages at death, were used to produce ontogenetic trajectories of cranial shape change. These were computed by sex through multivariate regression of Procrustes aligned coordinates against three surrogates for ontogeny: natural log of centroid size (growth), molar eruption stage (development), and chronological age. These trajectories were compared by calculating the angles between them. Each trajectory was also used to produce simulated adults from juveniles, which were then compared with each other and actual adults. The different trajectories are nearly parallel as each of the surrogates track similar aspects of ontogenetic cranial shape change, but chronological age was the most divergent. Simulated adults produced using the developmental stage trajectories were most similar to actual adults. When simulated adults were produced from opposite sex trajectories, they resembled the sex from which the trajectory was produced, not the sex of the juvenile specimen. We discuss properties of the trajectories produced from each of the surrogates, the possible reasons for previously opposing conclusions, how these properties can inform future investigations, and how our investigation bears on analyses of heterochrony.

Ontogenetic allometry and scaling in catarrhine crania

“…Due to the scarcity of subadult specimens available in museum collections for some species, and the need to obtain reasonable sample sizes, mixed‐sex samples were used to construct each species’ ontogenetic trajectory. The use of mixed‐sex samples to construct ontogenetic trajectories is justified by previous investigations which found that male and female ontogenetic trajectories do not typically diverge until late in ontogeny, and that mean juvenile cranial shapes are often indistinguishable between sexes (Collard & O’Higgins, 2001; Leigh, 2006; O’Higgins & Collard, 2002; O’Higgins & Jones, 1998; Simons & Frost, 2016; Singleton et al, 2010). However, it should also be noted that even closely related species can vary widely in levels of sexual dimorphism (see Schaefer et al, 2004), and, as this is a mixed‐sex sample, information about the scale of interspecific levels of sexual dimorphism is not accounted for in our study.…”

“…Analyses in the present investigation were performed on two aspects of cranial postnatal ontogeny: (a) trajectories of shape change associated with size (allometric trajectories), and (b) trajectories of shape change associated with molar eruption stage (ontogenetic trajectories). Although these trajectories track similar aspects of shape change associated with ontogeny (Simons & Frost, 2016; Holly Smith et al, 1994), we use both of them to address separate aspects of ontogenetic trajectories. That is, we use cranial size to compare patterns of allometry among taxa, and we use the amount of shape changes that occur over similar stages of development (ontogenetic trajectories), from the full eruption of the deciduous dentition to full adult dentition, to examine if taxa differ in the magnitude of ontogenetic shape changes.…”

Basicranial ontogeny comparison in Pan troglodytes and Homo sapiens and its use for developmental stage definition of KNM‐ER 42700

“…Dental age groups were used for basicranial development proxy instead of size. This facilitated the comparison of individuals at different ontogenetic stages irrespective of absolute size, which is known to differ between humans and chimpanzees in both the adult values and growth curves (Scott et al, ; Simons & Frost, ). A detailed description of the chimpanzee and modern human sample with information regarding every individual used here is provided in the excel sheet file as Supporting Information.…”

“…In order to analyze ontogeny, we use the same phenotypic trajectories approach. In our case, as different phenotypic levels, we use dental eruption stages, a reliable proxy for ontogenetic comparison (Simons & Frost, ). This approach allows us to investigate nonlinear trajectories that most often are difficult to quantify with conventional methods (Adams & Collyer, ; Collyer & Adams, , ; Gunz, Neubauer, Maureille, & Hublin, ; Mitteroecker et al, ; Mitteroecker, Gunz, & Bookstein, ; Scott et al, ).…”

Generalized Procrustes analysis of an ontogenetic series of modified crania: Evaluating the technique of modification in the Migration Period of Europe (4th–7th century AD)

“…The Hungarian juveniles and Georgian adults have strong variation in lnCS, but not so the Hungarian adults. Dental age provides a stronger variable than lnCS for simulating ontogenetic trajectory (Simons & Frost, ) and returned a stronger R 2 correlation of 0.467 for the Hungarian juvenile and adult crania, than the Hungarian juvenile and Georgian adult crania, which returned an R 2 of 0.363 (Table ). A correlation of PD and dental age with lnCS as a covariate increased the correlation to R 2 of 0.684 for the Hungarian juvenile and adult crania and R 2 of 0.61 for the Hungarian juvenile and Georgian adult crania.…”