Monotremes are remarkable animals, a mosaic of anatomical and physiological features that reflect reptilian, avian, and mammalian traits. Given their inaccessibility, little is known of the molecular and cellular mechanisms that underlie their neurodevelopment. Strikingly the Platypus has a lissencephalic neocortex, whereas its closest relative the Echidna has a large gyrified brain. We hypothesize that this is due to a difference in the number, type, or output of neuronal progenitors. As primary tissue is not available to test this hypothesis, we will exploit advances in induced pluripotent stem cell (iPSC) generation and cerebral organoid technology. Specifically, the aims are to: (1) Generate induced pluripotent stem cells derived from the platypus and echidna; (2) Model monotreme brain development using cerebral organoids; and (3) Characterize these organoids with a focus on the proliferative ventricular zone. This characterization will employ single-cell sequencing as well as traditional histological analysis. By leveraging these state-of-the-art methods, we will shed light on conserved mechanisms underpinning gyration in humans, as well as their divergence in monotremes.