Crioceratites (Binelliceras) rotundatus: Three

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 : 26

Crioceratites (Binelliceras) rotundatus: Three

ornamental ontogenetic stages could be recognized in

this species.

1. The first stage consists of trituberculate main ribs with five intermediate ribs. Fibulation frequently occurs. This stage ends at a diameter of 10-11 mm. This stage ends earlier in the ontogeny than in the ontogenies of C. (Bi.) ibizensis and C. (Bi.) binelli .

2. This stage is followed by a second stage with fine, almost uniform ribbing up to a diameter of 25-30 mm. Fasciculation occurs. The second stage also ends earlier in the ontogeny than in C. (Bi.) binelli . The shifts in the ends of the first and second ornamental ontogenetic stages are the only heterochronies between the ontogenetic developments of C. (Bi.) rotundatus and C. (Bi.) binelli , and are probably due to acceleration.

3. Then follows the third stage, which persists up to the aperture and consists of prominent, rather regularly distributed main ribs, with 3-4 intermediate ribs to one main rib, rarely two or six. The largest C. (Bi.) rotundatus found is 127 mm in diameter. Small ventrolateral tubercles are present on every rib up to the aperture.

Conclusion: The species united by the author in the binelli group of the subgenus Crioceratites (Binelliceras) have the same succession of similar ornamental ontogenetic stages. This unites the group. Apart from the anagenetic transition from C. (Bi.) binelli to C. (Bi.) krenkeli ( Fig. 9), the other two species, C. (Bi.) ibizensis and C. (Bi.) rotundatus , do not show a harmonious heterochronocline with C. (Bi.) binelli . Therefore the author believes that these species do not form a heterochronocline with C. (Bi.) binelli , but represent two independent branches originating from C. (Bi.) binelli . There is an apparent evolutionary tendency from fine uniform ribbing to coarser differentiated ribbing in the binelli group of the subgenus Crioceratites (Binelliceras) .

4.6. Stepped cladogenetic peramorphocline in the angulicostatus group of subgenus Crioceratites (Binelliceras) ( Fig. 7)

The species of the angulicostatus group are here provisionally included in the subgenus Crioceratites (Binelliceras) , because the ontogeny of their ornamentation resembles the ornamental ontogeny of the species of the binelli group. However they show some primitive traits, viz. the presence of lateral tubercles up to a greater diameter, and the coarseness of their ribbing. They lack the fine-ribbed part with fasciculation of the ribs that characterizes the binelli group, and apparently do not have the close relation with Crioceratites (Balearites) balearis that the binelli group and Pseudothurmannia have. However, they exhibit rows of small ventrolateral tubercles, which are considered typical for Pseudothurmannia , Crioceratites (Balearites) and the binelli group of Crioceratites (Binelliceras) . Nevertheless, their phylogenetic relation to the latter three taxa is still obscure.

Vermeulen included C. (Bi.) angulicostatiformis and C. (Bi.) seitzi in Spathicrioceras Sarkar, 1955 , because of the similarities in the ornamentation, but Sarkar (1955) stressed the loose crioconic coiling of his new genus, while C. (Bi.) angulicostatiformis , C. (Bi.) seitzi and C. (Bi.) angulicostatus are characterized by a tight crioconic coiling. Their closest relatives are doubtless the species of the binelli group. Therefore the author inserted them