Functional Evolution of the Feeding System in Rodents

Abstract

The masticatory musculature of rodents has evolved to enable both gnawing at the incisors and chewing at the molars. In particular, the masseter muscle is highly specialised, having extended anteriorly to originate from the rostrum. All living rodents have achieved this masseteric expansion in one of three ways, known as the sciuromorph, hystricomorph and myomorph conditions. Here, we used finite element analysis (FEA) to investigate the biomechanical implications of these three morphologies, in a squirrel, guinea pig and rat. In particular, we wished to determine whether each of the three morphologies is better adapted for either gnawing or chewing. Results show that squirrels are more efficient at muscle-bite force transmission during incisor gnawing than guinea pigs, and that guinea pigs are more efficient at molar chewing than squirrels. This matches the known diet of nuts and seeds that squirrels gnaw, and of grasses that guinea pigs grind down with their molars. Surprisingly, results also indicate that rats are more efficient as well as more versatile feeders than both the squirrel and guinea pig. There seems to be no compromise in biting efficiency to accommodate the wider range of foodstuffs and the more general feeding behaviour adopted by rats. Our results show that the morphology of the skull and masticatory muscles have allowed squirrels to specialise as gnawers and guinea pigs as chewers, but that rats are high-performance generalists, which helps explain their overwhelming success as a group.

Diversity and evolution of femoral variation in Ctenohystrica

“…The adaptive diversity that characterizes the evolution of Ctenohystrica, and particularly the Caviomorpha, a group that dispersed from Africa to colonise South America (Poux et al, 2006;Rowe et al, 2010) and evolved on that continent during a period of splendid isolation in the Cenozoic, has been the subject of numerous morphofunctional and evolutionary studies (e.g. Verzi et al, 2010;Á lvarez et al, 2011a, b;Hautier et al, 2011Hautier et al, , 2012Cox et al, 2012;Geiger et al, 2013;.…”

Comparación de la morfología geométrica de la mandíbula de dos roedores africanos, Thryonomys swinderianus y Cricetomys gambianus (Rodentia: Thryonomyidae y Nesomyidae)

“…Some studies have pointed out the existence of a close relationship between feeding habits and skulls or mandibles morphology using classical and geometric morphometric tools for quantification of shapes Renaud et al, 2007;Samuels, 2009;Cox et al, 2012;Hautier et al, 2012). As the masticatory behaviors are important in evaluating biomechanical properties, we predicted that aspects of mandibular shape, as revealed in the principal components analysis, would separate C. gambianus and T. swinderianus.…”

Mandibular allometry in Hydrochoerus hydrochaeris (Linnaeus, 1766) (Hydrocherinae, Caviidae)

“…These specializations, plus a small number of cheek teeth used for chewing, are associated with a specialized musculature (Schumacher, 1961). To cope with the demands imposed by such an unusual dentition and propaliny (e.g., the mandible can be moved fore and aft) (Cox et al, 2012), the masticatory musculature of rodents has become highly specialized. The masseter is the dominant jaw-closing muscle, forming between 60% and 80% of the masticatory musculature (Sisson et al, 1982), and is divided into three layers in rodents: the musculus masseter (with a pars superficialis and a pars profunda) and the musculus zygomaticomandibularis (sometimes termed the medial masseter).…”