Fig. 4 in Dimorphism in tetragonitid ammonoid Tetragonites minimus from the Upper Cretaceous in Hokkaido, Northern Japan

Fig. 4. Mature modifications recognised in tetragonitid ammonoid Tetragonites minimus Shigeta, 1989, from the Yezo Group in the Haboro, Kotanbetsu, Tappu, Nakagawa, Soya, and Yubari areas, Hokkaido, Japan. A, B. Changes in the shape of the body chamber: modification appeared at venter (A, MCM-W1591) and umbilicus (B, MCM-W1556). C. Shell thickening in the aperture, MCM-W1560. D. Septal crowding and increase in septal thickness, MCM-W1565; arrowhead indicates the last septum. Scale bars 2 mm.