Evolution of bite performance in turtles

Abstract

Among vertebrates, there is often a tight correlation between variation in cranial morphology and diet. Yet, the relationships between morphological characteristics and feeding performance are usually only inferred from biomechanical models. Here, we empirically test whether differences in body dimensions are correlated with bite performance and trophic ecology for a large number of turtle species. A comparative phylogenetic analysis indicates that turtles with carnivorous and durophagous diets are capable of biting harder than species with other diets. This pattern is consistent with the hypothesis that an evolutionary increase in bite performance has allowed certain turtles to consume harder or larger prey. Changes in carapace length tend to be associated with proportional changes in linear head dimensions (no shape change). However, maximum bite force tends to change in proportion to length cubed, rather than length squared, implying that changes in body size are associated with changes in the design of the jaw apparatus. After the effect of body size is accounted for in the analysis, only changes in head height are significantly correlated with changes in bite force. Additionally, our data suggest that the ability to bite hard might trade off with the ability to feed on fast agile prey. Rather than being the direct result of conflicting biomechanical or physiological demands for force and speed, this trade-off may be mediated through the constraints imposed by the need to retract the head into the shell for defensive purposes.

Ontogeny of the Early Triassic Cynodont Thrinaxodon liorhinus (Therapsida): Cranial Morphology

“…However, the increase in the height of the sagittal crest would have increased the area for muscle attachment, and perhaps increased the bite force [see the study by Herrel et al (2002) of head height and biting performance in turtles]. Even though there was an increase in muscle volume, as indicated by the larger MTO in adults (Table 3) and an increase in sagittal crest height, the relative height and size of the coronoid process did not vary much with age (Fig.…”

The ontogenetic scaling of bite force and head size in loggerhead sea turtles (Caretta caretta): implications for durophagy in neritic, benthic habitats

“…Although head width in freshwater turtles has been shown to increase bite force as a result of a greater physiological cross-sectional area of the adductor mandibulae, an increase in head height has also been reported to increase bite force. Presumably, increased head height reduces the angle of the adductor mandibulae tendon line of action as it curves around the otic chamber of the skull (Gaffney, 1979;Herrel et al, 2002). This simple change would increase the mechanical advantage of the jaw lever system.…”

Anti-predator defenses of Brown Bullheads (<em>Ameiurus nebulosus</em>) and interactions with Snapping Turtles (<em>Chelydra serpentina</em>)

“…Based on our direct and indirect predation observations, it seems that Snapping Turtles do not necessarily discriminate against Brown Bullheads as prey items despite the risk posed by the defensive pectoral spines (i.e., the spines do not serve as a preemptive warning). Also, given the rapid predatory strike (Lauder and Prendergast 1992) and substantial bite force (Herrel et al 2002) of Snapping Turtles, the pectoral spines probably do not adequately protect Brown Bullheads (i.e., a landed strike would likely be fatal to the catfish, thereby negating the anti-predator significance of pectoral spines). As noted by Sismour et al (2013), the effectiveness of catfish pectoral spines as anti-predator defense depends on relative predatorprey size and predator aggressiveness.…”