Background: Motor coordination in vertebrates is primarily regulated by cerebellum. Divergence of aves from reptilian ancestors results in noticeable improvement in the motor coordination. This study aims to explore anatomical innovations in the cerebellar cortex during the course of evolution of reptiles and aves.Methods: Three representative species each from reptilian and avian lineages were selected to represent both vertebrate classes. Complete brain was dissected out from the cranial cavity of each specimen after radiological assessment of its extent. After gross examination, the brains were subjected to detailed histological investigation using conventional and special strains. Micrometry of layer and cellular architecture of cerebellar cortex were undertaken digitally using ImageJ and statistically compared using GraphPad Prism.Results: Grossly, significant increase (p<0.0001) in brain mass, brain volume and cerebellar volume was observed in aves compared to reptiles. Histo-morphometric analyses of granular and molecular layers of cerebellum showed statistically significant decrease (p<0.0001) in the thickness of avian representatives compared to reptilian counterparts. Similarly significant decrease (p<0.0001) in the interpurkinje neuronal distance was observed in aves compared to reptiles. Conversely, increase cellular and neuronal count (p=0.0332 to <0.0001) count was observed in all three layers of avian cerebellum in comparison to reptiles. This suggests increased cellular packaging and/or density in the avian cerebellum compared to reptiles. Conclusion: In summary, significant increase in the cellular density and differentiation in the cerebellum of avian representatives may provide anatomical basis of increased motor coordination in aves compared to reptiles. Keywords: Cerebellum; Evolution; Granular Layer; Molecular Layer; Purkinje Laye
