Fig. 3 in Significance of intermediate forms in phyletic reconstruction of ammonites: Early Jurassic Phricodoceras case study

Fig. 3. Microconch (m) / macroconch (M) dimorphism expressed by scholtheimiid ammonoid Phricodoceras exemplified by the NW Europe forms in the Uptonia jamesoni to Tragophylloceras ibex chronozones. A. Phricodoceras lamellosum (Orbigny, 1844) (M), UBGD 277451, Mazenay, Saône et Loire, France, probably early Uptonia jamesoni Chronozone, in apertural (A1), lateral (A2), and ventral (A3) views. B. Phricodoceras lamellosum (M), Kircheim unter Teck, Baden−Würtemberg, Germany, Early Pliensbachian (from Schlegelmilch 1976: pl. 27: 4, modified; original from Quenstedt 1884: pl. 28: 24), in apertural (B1), lateral (B2), and ventral (B3) views. C. Phricodoceras taylori (Sowerby, 1826) (m), Corbigny, Nièvre, France, Uptonia jamesoni Chronozone, Phricodoceras taylori Subchronozone (from Dommergues 2003: pl. 1: 4), in lateral view. D. Phricodoceras aff. cornutum (Simpson, 1843) (m), Fresnayle−Puceux, Calvados, France, Early Pliensbachian (from Dommergues et al. 2008: pl. 3: 6, modified), in ventral (D1) and lateral (D2) views. E. Phricodoceras taylori (m), Fresnay−le−Puceux, Calvados, France, Early Pliensbachian (from Dommergues et al. 2008: pl. 3: 5, modified), in ventral (E1) and lateral (E2) views. The two specimens corresponding to A, B are incomplete phragmocones (juvenile or immature shells) but the three corresponding to C–E are adult microconchs with the major part of the body chamber. The end of the phragmocone is starred. Notice the progressive ontogenetic transformation from tubercle (t3) to faint shoulder (s3) in specimen B. Abbreviations: t2, tubercle in latero−ventral position; t3, tubercle in peri−siphonal position; s3, shoulder peri−siphonal position.