Aspectos da anatomia cerebral de cinodontes não-mammaliaformes e suas implicações na evolução do cérebro dos mamíferos

Abstract

Important studies have already been done regarding on paleoneurology of extinct animals due to the advancement of computed tomography techniques in recent years. This allowed more accurate studies and without the need to modify materials, especially non-mammaliaform cynodonts and basal mammals. However, these analyzes are limited by material preservation biases, often with absence of postcranium. Consequently, body mass estimations are required, which are necessary for calculations of quantitative analyzes regarding the evolution of the brain capacity of these animals. Considering this, in order to increase the data set about the evolution of the brain in Cynodontia, computed tomography of two skulls of the MCT/PUCRS (MCP 1600 PV Probelesodon kitchingi; MCP 3871 PV Massetognathus ochagaviae) were performed. We also calculated the specimens’ encephalization quotients (EQ), with and without the olfactory bulbs, using two formulas of body mass estimation. When the necessary data were available in the literature, the EQs were calculated for other synapids for comparative purposes. In relation to the morphology of the endocranial casts, no differences were observed in relation to previous described for other eucinodonts, in which there is still no enlargement of the cerebral hemispheres, as well as a development of the cerebellar region. The EQs obtained for M. ochagaviae and P. kitchingi do not differ representatively from those previously calculated for other materials of the same genus. For the calculations with and without the olfactory bulbs the same was observed. However, when comparing the encephalization quotients obtained with the application of the four formulas, significant differences were observed between the results. Therefore, it is not possible to compare the EQs obtained with the different methods, and only one is required.