R. Glenn Northcutt

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Most of the morphological and functional differences between vertebrates and other chordates occur in the head and are derived embryologically from muscularized hypomere, neural crest, and epidermal (neurogenic) placodes. In the head, the neural crest functions as mesoderm and forms connective, skeletal, and muscular tissue. Both the neural crest and the(More)
Vertebrate body organization differs from that of other chordates in a large number of derived features that involve all organ systems. Most of these features arise embryonically from epidermal placodes, neural crest, and a muscularized hypomere. The developmental modifications were associated with a shift from filter-feeding to more active predation, which(More)
Specializations for electroreception in sense organs and brain centers are found in a wide variety of fishes and amphibians, though probably in a small minority of teleost taxa. No other group of vertebrates or invertebrates is presently suspected to have adaptations for electroreception in the definition given here. The distribution among fishes is unlike(More)
A morphotype of the forebrain of gnathostomes, i.e. those characters that must have been present in the forebrain of ancestral gnathostomes, was generated by using out-group analysis to identify the shared primitive characters present in the forebrains of extant gnathostomes. The nature of morphotypes and the steps in generating a morphotype are described.(More)
The development of neurogenic placodes in Xenopus laevis from the time of neural fold closure to larval stages is described. Placodes were reconstructed from camera lucida drawings of serial sections, and the spatiotemporal pattern of placodal neurogenesis was analyzed using in situ hybridization for the genes X-NGNR-1, XNeuroD, X-MyT1, and X-Delta-1, all(More)
The cytoarchitecture of nuclei in the preoptic area, ventral thalamus, dorsal thalamus, epithalamus, hypothalamus, posterior tuberculum, synencephalon, and pretectum and the accessory optic nuclei was analyzed in the clupeomorph teleost, Clupea harengus. Plesiomorphic (evolutionarily primitive) and apomorphic (evolutionarily derived) features of nuclei were(More)
Biotinylated dextran amine and fluorescent carbocyanine dye (DiI) were used to examine connections of the lateral (Dl) and medial (Dm) divisions of the goldfish pallium. Besides numerous intrinsic telencephalic connections to Dl and Dm, major ascending projections to these pallial divisions arise in the preglomerular complex of the posterior tuberculum,(More)
Four major questions can be asked about vertebrate brain evolution: 1) What major changes have occurred in neural organization and function? 2) When did these changes occur? 3) By what mechanisms did these changes occur? 4) Why did these changes occur? Comparative neurobiologists have been very successful in recognizing major changes in brain structure.(More)