(A) Average subclass proportions of neuronal classes (whiskers, standard deviation across individuals). Significant differences in proportions compared to human (two-sided t-tests; Benjamini-Hochberg corrected * P < 0.05, ** P < 0.01, *** P < 0.001). (B) UMAPs of L5/6 IT Car3 neurons labeled by individual, CUX2 expression, and subtype. (C) Conserved marker gene expression of High-CUX2 and Low-CUX2 subtypes. (D) Average proportions of L5/6 IT Car3 neuron subtypes (whiskers, standard deviation across individuals). (E) Laminar distributions of subtypes across great apes estimated based on layer dissections. (F) L5/6 IT Car3 neurons labeled in situ based on marker expression in human and macaque MTG and in the matching regions in marmoset cortex (TPO and TE3). Low-CUX2 neurons are enriched at the layer 5/6 border in human and macaque. Red asterisk, area of low probe density due to a technical artifact. STG, superior temporal gyrus. Au, auditory cortex. (G) UMAPs of CUX2 expression in L5/6 IT Car3 neurons from matched cortical regions in humans (purple, high expression) and marmosets (dark orange, high expression).