A conserved pattern of brain scaling from sharks to primates

Area of Science:

• Comparative neuroanatomy
• Vertebrate paleontology
• Evolutionary biology

Background:

• Mammalian brain allometry reveals predictable scaling patterns.
• Understanding brain scaling in non-mammalian vertebrates like sharks (chondrichthyans) is crucial for evolutionary insights.

Purpose of the Study:

• To investigate if mammalian brain allometry patterns apply to chondrichthyans.
• To analyze the scaling relationships of brain parts in sharks relative to total brain size.
• To explore the relationship between cerebellar size, foliation, and mammalian cortical gyrification.

Main Methods:

• Comparative analysis of brain structure and mass across shark species.
• Statistical examination of allometric scaling slopes for different brain regions.
• Correlation of cerebellar foliation with absolute and relative cerebellar size.

Main Results:

• Brain allometry patterns observed in mammals are conserved in chondrichthyans.
• Relative brain part size, except olfactory bulbs, is predictable from total brain mass.
• Telencephalon and cerebellum exhibit the highest scaling slopes.
• Cerebellar foliation correlates with cerebellar size, analogous to mammalian gyrification.

Conclusions:

• A fundamental vertebrate brain plan allows for conserved scaling across diverse taxa.
• Brain scaling is adaptable to phylogenetic and ecological factors without compromising core function.
• These findings highlight deep evolutionary conservation in vertebrate brain organization.