CUANTIFICACION DE LA CORTEZA CEREBRAL EN MOLDES ENDOCRANEANOS DE MAMIFEROS GIRENCEFALOS. PROCEDIMIENTO y APLICACION EN TRES MAMIFEROS EXTINGUIDOS

Juan C. Quiroga

Abstract


It is proposed a procedure for the estimation of surfaces of discrete areas and whole cortex on endocasts of gyrencephalic mammals, as well as the relative cortical size respecting to the average living mammals through a corticalization quotient (CQ). The cortical cast was studied in the litoptema Proterotherium cavum (Santacrucian Land Marnmal Age) and a Proterotheriidae indet. (somewhere between Chasicoan and Chapadmalalan Land Marnmal Ages) and in the borhyaenoid marsupial Thylacosmilus (one especimen of Monterhermosan and other of Chapadmalalan Land Mammal Ages). It was determined that proportionally, the Proterotheriidae indet. has, respecting to Proterotherium cavum, more dorsal cortex (more than 6%), where is located the visual representation, more lateral cortex (more than 3%), where is located the auditive representation, less frontal cortex (among 4%), where are the somatic representations and less (more than 9%) in the exposed paleocortex, where is the olfactive representation. In Thylacosmilus it was determined that the somatic area represents more than 27% of the whole cortex, the visual area among 18%, the auditive area may be among 7%, and the exposed paleocortex of more than 8%. In the somatic area, the mandibulooral area represents among the 42% of the whole area, being greater than the postcranial and maxilo-nasal areas. The greater relative cortical size is that of the Peoterotheriidae indet. (CQ = 0.7), then that of Thylacosmilus (CQ = 0,535) and that of Proterotherium cavum (CQ = 0,46). In a11the three specimens, the encephalization quotients were greater than the corticalization ones, presenting Thylacosmilus the smaller difference.

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