Cranial allometry in Adinotherium ovinum (Notungulata, Toxodontia)

FLORES, D.; G. CASSINI; S. VIZCAINO; S. BARGO

Punta del este

Congreso; 9º International Congress of vertebrate Morphology; 2010

Toxodontidae constitute a clade of endemic South American ungulates which include large (above 44 kg) to very large animals (including megammamals, i.e. 1000 kg or more). Adinotherium with approximately 120 kg is the smaller Santacrucian toxodont (Santa Cruz Formation, late-early Miocene) along the Atlantic coast of southern Patagonia. The larger amount of specimens recorded, and quality of preservation (including very young animals) allows a morphometric study of cranial ontogeny. For this purpose we measure 17 cranial variables on an ontogenetic series of 27 specimens of A. ovinum. Bivariate analysis (Reduced Major Axis) was done in order to obtain the coefficients of allometry considering the condylo-basal length of the skull as independent variable. Our results indicate that most measurements considered are highly correlated with the independent variable, except the postorbital breadth and the heigth of the occipital plate. From the 17 variables eight show isometric trend, seven exhibit positive allometry and only one variable, height of the orbit, exhibit negative allometry. Contrarily expected neurocranial variables, (braincase length and breadth, orbit length and occipital plate height) are positively allometric or isometric. Respect to the splachnocranium, most variables related with the rostrum and palate grow with positive allometry, except the height and breadth of the muzzle, which are isometric. Lastly, variables related with the masticatory muscles, as zygomatic breadth and masseteric fossa length, show different trends (isometry and positive allometry). Is remarkable that variables related to trophic apparatus grows positively allometric suggesting strengthening of the cranium traits related to mastication in adults.