Mammals are born on a precocial–altricial continuum. Altricial species produce helpless
neonates with closed distant organs incapable of locomotion, whereas precocial species
give birth to well-developed young that possess sophisticated sensory and locomotor
capabilities. Previous studies suggest that distinct patterns of cortex development differ
between precocial and altricial species. This study compares patterns of neocortex
neurogenesis and maturation in the precocial guinea pig and altricial dwarf rabbit, both
belonging to the taxon of Glires. We show that the principal order of neurodevelopmental
events is preserved in the neocortex of both species. Moreover, we show that
neurogenesis starts at a later postconceptional day and takes longer in absolute
gestational days in the precocial than the altricial neocortex. Intriguingly, our data indicate
that the dwarf rabbit neocortex contains a higher abundance of highly proliferative
basal progenitors than the guinea pig, which might underlie its higher encephalization
quotient, demonstrating that the amount of neuron production is determined by complex
regulation of multiple factors. Furthermore, we show that the guinea pig neocortex
exhibits a higher maturation status at birth, thus providing evidence for the notions that
precocial species might have acquired the morphological machinery required to attain
their high functional state at birth and that brain expansion in the precocial newborn
is mainly due to prenatally initiating processes of gliogenesis and neuron differentiation
instead of increased neurogenesis. Together, this study reveals important insights into the
timing and cellular differences that regulate mammalian brain growth and maturation and
provides a better understanding of the evolution of mammalian altriciality and presociality