Sagittal crest morphology decoupled from relative bite performance in Pleistocene tapirs (Perissodactyla: Tapiridae)

Abstract

Bite force is often associated with specific morphological features, such as sagittal crests. The presence of a pronounced sagittal crest in some tapirs (Perissodactyla: Tapiridae) was recently shown to be negatively correlated with hard‐object feeding, in contrast with similar cranial structures in carnivorans. The aim of this study was to investigate bite forces and sagittal crest heights across a wide range of modern and extinct tapirs and apply a comparative investigation to establish whether these features are correlated across a broad phylogenetic scope. We examined a sample of 71 specimens representing 15 tapir species (5 extant, 10 extinct) using the dry‐skull method, linear measurements of cranial features, phylogenetic reconstruction, and comparative analyses. Tapirs were found to exhibit variation in bite force and sagittal crest height across their phylogeny and between different biogeographical realms, with high‐crested morphologies occurring mostly in Neotropical species. The highest bite forces within tapirs appear to be driven by estimates for the masseter–pterygoid muscle complex, rather than predicted forces for the temporalis muscle. Our results demonstrate that relative sagittal crest height is poorly correlated with relative cranial bite force, suggesting high force application is not a driver for pronounced sagittal crests in this sample. The divergent biomechanical capabilities of different contemporaneous tapirids may have allowed multiple species to occupy overlapping territories and partition resources to avoid excess competition. Bite forces in tapirs peak in Pleistocene species, independent of body size, suggesting possible dietary shifts as a potential result of climatic changes during this epoch.

Masticatory myology of the llama (Lama glama, Camelidae) and comparisons with other camelids and euungulates

“…The data analyzed here of Lama glama confirm that camelids possess relatively large M. temporalis, but in a less extreme degree than Camelus . The size of the zygomasseteric complex is almost identical than that of the M. temporalis, a proportion similar to that reached by other basal euungulates such as suines (Figure 5), and, although not quantified, probably similar to hippopotamus (Gratiolet, 1867) and non‐equid perissodactyls (e.g., tapirs; Bressou, 1961; Van Linden et al, 2022).…”

“…The large M. temporalis of early diverging artiodactyls represents a retention of the ancestral ungulate condition. This trait is also recorded in diverse extinct euungulates and, in different degrees, in generalized mammalian forms (Druzinsky et al, 2011;Ercoli et al, 2023;Janis, 1983;Joeckel, 1990;Lesbre, 1903;Popowics & Herring, 2006;Radinsky, 1985;Turnbull, 1970;Van Linden et al, 2022), including some non-ungulate herbivores (e.g., elephants, sloths; Druzinsky et al, 2011;Ercoli et al, 2023;Maglio, 1972;Naples, 1985;Turnbull, 1970). In line with this, the muscle reconstruction of two extinct artiodactyl entelodonts (Paleogene-early Neogene non-pecoran artiodactyls) performed by Joeckel (1990) indicates a larger M. temporalis (45 to 46%) than those of living artiodactyls (Figure 5).…”

“…Beyond the already discussed interpretation of a large M. temporalis in Camelidae and most of Suina as a plesiomorphic feature, the low and posteriorly extended temporal fossa in camelids and the tayassuid Catagonus, and dorsally extended coronoid process in camelids (invading the space of the temporal fossa and completely immersed within the M. temporalis), results in a mainly horizontal line of action of this muscle in these morphotypes (Ercoli et al, 2023;Herring, 1985;Joeckel, 1990;Schumacher, 1961, p. 162;Walton, 1865; see also Boas & Paulli, 1908:Plate 6). This functional trait should be considered as part of a derived reconfiguration, differing from other suines, hippopotamids, tapirs, and "archaic" artiodactyls, and in turn, resembling similar osteo-myological traits in other derived euungulates such as equids and pecorans (Allouch, 2018;Cuvier & Laurillard, 1849;Herring, 1985;Joeckel, 1990;Pérez-Barbería & Gordon, 1999;Popowics & Herring, 2006;Schumacher, 1961;Wang et al, 2022;Windle & Parsons, 1902;Van Linden et al, 2022). In this way, in camelids and some suines, the temporalis muscle, ancestrally dedicated to mainly vertical movements such as those involved in cutting and crushing functions (e.g., Joeckel, 1990;Turnbull, 1970), is recruited mainly as a retractor of the balancing side during the power stroke (Popowics & Herring, 2006;Williams et al, 2007).…”

Understand comprehensive perspectives of evolution

“…The study of the lumbosacral system of Emperor and Adelie penguins and Eocene giant Antarctic penguins using nondestructive CT imaging and geometric morphometrics, modularity, curvature, and wavelet analyses documents that the variability in the number of synsacro-lumbar vertebrae is evolutionarily conserved and traceable at least to the Eocene epoch, but the main synsacral canal differs in presentday and fossil penguins in regard to the observed complexity of periodicity patterns (Jadwiszczak et al 2022). Van Linden et al (2022) quantified bite force and sagittal crest height across modern and extinct tapirids us-ing the dry-skull method. Their results demonstrate a poor correlation between relative sagittal crest height and bite force.…”

“…Van Linden et al. (2022) quantified bite force and sagittal crest height across modern and extinct tapirids using the dry‐skull method. Their results demonstrate a poor correlation between relative sagittal crest height and bite force.…”