The mechanisms underlying mammalian neural tube closure remain poorly understood. We report a unique cellular process involving multicellular rosette formation, convergent cellular protrusions, and F-actin cable network of the non-neural surface ectodermal cells encircling the closure site of the posterior neuropore, which are demonstrated by scanning electron microscopy and genetic fate mapping analyses during mouse spinal neurulation. These unique cellular structures are severely disrupted in the surface ectodermal transcription factor Grhl3 mutants that exhibit fully penetrant spina bifida. We propose a novel model of mammalian neural tube closure driven by surface ectodermal dynamics, which is computationally visualized. Display omitted •Non-neural ectodermal cells form multicellular rosettes during mouse PNP closure.•Rosette-forming cells generate convergent F-actin protrusions and cable network.•Rosettes and protrusions are disrupted in the surface ectodermal Grhl3-KO mutants.•Computational modeling visualizes the stepwise closure of mouse PNP.