Scaling and adaptation of incisors' traits in caviomorph rodents

BECERRA FEDERICO; VASSALLO ALDO IVÁN; CASINOS PARDOS ADRIÀ

Punta del Este

Congreso; 9th International Congress of Vertebrate Morphology; 2010

International Society of Vertebrate Morphologists

The Caviomorpha (South American Hystricognathi) compose a diverse clade of rodents in terms of ecology and body size. Because of functional demands associated to different food habits, chewing modes, and particular locomotor habits –i.e. dentoexcavation--, the masticatory apparatus is highly diverse. We analyzed the incisors of 33 species belonging to nine caviomorph families, focusing on those traits affecting the resistance to bending stress (second moment of area: I), pressure distribution into alveolar bone (length of the incisor root), and incisors’ angle of attack (procumbency). Digital images taken form museum specimens were analyzed using the software ImageJ. Model I regressions were calculated using naso-occipital length as the independent variable. The sample included small forms such as Spalacopus, as well as big animals such as Hydrochaeris. A clear dependence of several incisor traits exists with respect to size, which included allometric coefficients not significantly departing from isometry. For example, allometric coefficient for I= 3.45 (2.39-4.50), R2=0.58; incisor root length= 0.83 (0.56-1.10), R2=0.54. However, residual analyses showed departures with respect to this general pattern. Representatives of the digging families Octodontidae and Ctenomyidae showed bigger I implying enhanced resistance to bending stress; the same was observed in the fossorial viscacha (Lagostomus; Chinchillidae), but not in species studied of Caviidae, which have slender incisors. Incisor procumbency was not significantly influenced by size. Digging species, in which an adequate angle of attack against the substrate represents a possible adaptation to dentoexcavation, display higher values; nonetheless non digging forms such as Cavia also has high procumbencies.