FIG. 2 in False teeth: conodont-vertebrate phylogenetic relationships revisited

FIG. 2. — Histology of conodont element (showing continuous growth) vs vertebrate scale or tooth (odontode) formed in a papilla of mesenchymous cells: A, drawing of longitudinal section showing continuous growth with lateral additions and formation of serration of the conodont Gnathodus texanus Roundy, 1926 modified from Gross (1954: fig. 2, 1-5, subsequent addition of serrations) contra Donoghue (1998) Type 4 growth (reproduced in Reif 2006: fig. 4) where a basal body (or is it white matter?) apparently occurs in each serration (reproduced with permission from Senckenbergiana lethaea); B, B', longitudinal section through conodont "Ctenognathus" Pander, 1856 showing interrupted growth = "healing" (after Gross 1957: fig. 2D, F); C, schematic cross section to show continuous growth (arrows) of conodont element and basal filling (after Gross 1957: fig. 4); D, D', comparison of cross section of conodont element with osteichthyan (mammalian) tooth with pulp cavity (from Schultze 1996: fig. 2A, B; reproduced with permission from the author); E, E', formation of vertebrate odontodes in comparison to conodont growth in A. The odontode is formed by a papillary organ (with enamel organ, odontoblasts and osteoblasts in a single morphogenetic step). It cannot grow, but is enlarged instead by addition of a new odontode, that is formed by a new papillary organ resulting from a new interaction between ectoderm and mesenchyme (modified from Reif 2006: fig. 3a): thick line, enamel or enameloid; radiating lines, dentine with pulp cavity underneath; basal tissue, attachment bone = cement with thin lines of deposition. Note the presence of pulp in vertebrate examples. Abbreviations: al, lamellar tissue; b, basis; bb, basal body; bo, bone; b.gr, basal groove; brl, interruption = break of growth in lamellar tissue; bt, basis cone; ce, cement; de, dentine; e, enamel; f, fine fibers; la, lamellar tissue; tf, inner basal filling; t.gr, boundary between the two kinds of filling of the basal groove; w.m, albid tissue or white matter. a, b, from original author figures. Scale bars: 0.1 mm.