Crioceratites (Binelliceras) seitzi: This

Hoedemaeker, Philip, 2013, Genus Pseudothurmannia Spath, 1923 and related subgenera Crioceratites (Balearites) Sarkar, 1954 and C. (Binelliceras) Sarkar, 1977 (Lower Cretaceous Ammonoidea), Revue de Paléobiologie 32 (1), pp. 1-209 : 28

Crioceratites (Binelliceras) seitzi: This species has four

ornamental ontogenetic stages:

1. The ribbing of the first stage consists of two intermediate ribs to one main rib, and the main ribs are provided with lateral tubercles. This stage is equivalent to stage one of C. (Bi.) angulicostatus . This stage ends at a diameter of 12 mm, which is earlier in the ontogeny than in C. (Bi.) angulicostatus ; it has therefore accelerated in relation to the ontogeny of the latter species.

2. The ribbing of the second stage consists of 3-5 intermediate ribs to one main rib. The lateral tubercles disappear at a diameter of 16 mm. This stage is equivalent to stage two in C. (Bi.) angulicostatus , and ends at a diameter of 24 mm, that is, earlier in the ontogeny than in C. (Bi.) angulicostatus . It has accelerated in relation to the ontogeny of the latter species.

3. In this third stage every two main ribs are separated by three intermediate ribs. Splitting of ribs occurs. This stage ends at a diameter of 37 mm, which is earlier in the ontogeny than the equivalent stage three in C. (Bi.) angulicostatus . Therefore, this stage also has accelerated in relation to the corresponding stage of the ancestor.

4. The ribbing of the last stage has only 1-2 ribs to one main rib. Only just before the aperture this number suddenly augments to 3-4; a similar increase in number of intermediate ribs occurs just before the aperture of C. (Bi.) angulicostatus .

Conclusion ( Fig. 7): The three species of the angulicostatus group form a harmonious, stepped cladogenetic peramorphocline. Owing to the rarity of these species, their total ranges are obscure, but thanks to this peramorphocline their phylogeny became clear. The ancestor of this group is not known, but should be sought for in the neighbourhood of the ancestor of C. (Bi.) binelli .