A radiographic study of permanent molar development in wild Virunga mountain gorillas of known chronological age from Rwanda

Abstract

Despite sample limitations, our findings extend the known range of variation in radiographic estimates of molar formation timing in great apes, and provide a new age prediction technique based on wild specimens. However, mountain gorillas do not appear accelerated in radiographic assessment of molar formation compared to chimpanzees, as they are for other life history traits. Future studies should aim to resolve the influence of species differences, wild versus captive environments, and/or sampling phenomena on patterns observed here, and more generally, how they relate to variation in tooth size, eruption timing, and developmental life history.

Phylogenetic and environmental effects on limb bone structure in gorillas

“…Skeletal material was obtained from a number of museum collections, listed in the table. In addition, 72 specimens of G. b. beringei were obtained from collections of the Mountain Gorilla Skeletal Project (MGSP), a collaboration with the Rwanda Development Board's Department of Tourism and Conservation to recover and curate skeletal remains of recently deceased Virunga mountain gorillas (see Kralick et al, ; McFarlin et al, ). The majority of these specimens were measured in the Karisoke Research Center in Ruhengeri (Musanze), Rwanda; 21 specimens were measured while on loan to George Washington University.…”

“…Mandibular tooth crown and root development for immature individuals was assessed from radiographs as described in detail elsewhere (Kralick et al, ). Summed Boughner radiographic scores (Boughner, Dean, & Wilgenbusch, ) for the first and second molars (M1 and M2) were used to derive a polynomial regression equation for age estimation based on specimens of known age in the MGSP sample (Kralick et al, : Figure ; R 2 = 0.977; SEE = 0.477 years), and applied to the majority of the immature sample (56 G. g. gorilla , 18 G. g. beringei , 14 G. b. graueri ). Because of the timing of development of permanent molars, however, the equation is relatively less effective for discriminating between ages of very young infants.…”

“…It could be questioned whether the dental developmental equations, derived almost entirely from the G. b. beringei MGSP sample, can be validly applied to other gorilla taxa, given reported differences in timing of developmental events among gorillas (for discussion see Kralick et al, ). However, comparisons between Virunga mountain gorilla and common chimpanzee dental development show relatively small and inconsistent differences in timing, especially if wild chimpanzees are included (Kralick et al, ). This suggests that differences in dental developmental timing between gorilla taxa may also not be large.…”

Reassessment of the TM 1517 odonto‐postcranial assemblage from Kromdraai B, South Africa, and the maturational pattern of Paranthropus robustus

“…Judged against known age Virunga mountain gorillas at broadly the same stage of dental development, TM 1517 would fall between the ages of 10.69 and 14.94 years at the time of death (Boughner et al, 2012;Kralick et al, 2017) while, by assuming a Gorilla-like skeletal developmental model, TM 1517 would be younger than 8.5 years, if female, and between 9 and 12.5 years, if male (Leigh, 1992). When the Pan pattern is considered as a compatible model, TM 1517 would be 7.01-10.75 year old dentally (Boughner et al, 2012;Kuykendall & Conroy, 1996) and between 7.95 and 13.5 years old based on its skeletal maturation (Brimacombe et al, 2015(Brimacombe et al, , 2018Cameron et al, 2017).…”

A Simple and Environmentally Friendly Field Method for Fecal Analysis of Herbivore Diet

“…Alteration of fragments among age classes will be entirely due to the physiological and mechanical processes of digestion because the sieving and washing process does not degrade fragments. In the case of our study gorilla population, we would therefore expect larger vegetation fragments in age classes with lower chewing efficiencies, such as immature gorillas with incomplete tooth development and lower chewing forces (Kralick et al 2017, Fritz et al 2009. Data analysis and collection are greatly facilitated using our methods because digital images can be analyzed and measured directly from the digital microscope imaging software.…”