Cell type profiling in salamanders identifies innovations in vertebrate forebrain evolution III

The evolution of advanced cognition in vertebrates is associated with the expansion of specialized areas in the forebrain (the six-layered neocortex in mammals and the dorsal ventricular ridge in birds and reptiles). Both areas exhibit complementary higher order brain functions, but it remains debated whether they developed convergently, or descended from a brain region already present in the last common ancestor of amniotes. To reconcile these views, we investigated the development, molecular identity, and connectivity of telencephalic neuron types in the Spanish newt, Pleurodeles waltl. These reveal that major neuron classes are conserved in tetrapods. Additionally, a glutamatergic neuron type in the ventral pallium displays key characteristics similar to the reptilian dorsal ventricular ridge (aDVR) and the mammalian piriform cortex (PC), suggesting that brain areas for advanced cognition evolved independently in mammals and reptiles and birds. scRNAseq of Pleurodeles Waltl telencephalon