Crioceratites (Binelliceras) binelli

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 : 25

mostly resembles C. (Bi.) binelli and could be typified

as a coarse issue of C. (Bi.) binelli . However, they do not

occur together, but follow each other in time in the Río

Argos succession and in the Angles section (observation

of the author). Therefore, they presumably represent two

chronospecies of an anagenetic lineage. C. (Bi.) krenkeli

has three ornamental ontogenetic stages.

1. The first stage consists of 1-3 intermediate ribs to one trituberculated main rib. Large ventrolateral tubercles are present. The first trituberculate stage ends at a diameter of 16 mm and gives room for stage two.

2. Stage two consists of fine uniform flexuous ribbing. The umbilical bullae give rise to fascicules, and between every two fascicules are c. seven intermediate ribs.

3. From a diameter of 42 mm the third stage begins with 2-3 intermediate ribs to one main rib. With growth, the main ribs become more and more differentiated from the intermediate ribs and become more wide- ly spaced. This results in an adult ornamentation of well-differentiated, regularly-separated, widelyspaced main ribs, of which every two are separated by 4-6 intermediate ribs. So, the inner whorls, up to a diameter of 42-45, are similar to C. (Bi.) binelli , but after this diameter, the ribbing becomes gradually coarser and more regularly differentiated into main and intermediate ribs. This change in ribbing can be interpreted as ‘adult variation’ by which varieties, races and chronospecies can be distinguished. No heterochrony is involved.