Pseudothurmannia (Parathurmannia) edouardi: 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 : 24-25

Pseudothurmannia (Parathurmannia) edouardi: This species shows three ornamental ontogenetic stages.

1. The first stage is equal to the first one of P. (Pa.) sarasini and consists of fine ribbing with 5-6 long intermediate ribs between every two main ribs. Within this stage (at a diameter of c. 20 mm) small lateral tubercles appear which gradually become more prominent. These tubercles appear in an earlier stage than in P. (Pa.) sarasini , and this early appearance may be the result of the heterochronic process of predisplacement.

2. Stage two begins at a diameter of 40 mm, and consists of coarse, straight main ribs of which every pair is separated by two intermediate ribs. This stage is equivalent to stage two of P. (Pa.) sarasini , and begins at the same diameter as in P. (Pa.) sarasini , but significantly earlier in the ontogeny than in P. (Pa.) dissiticostata . It ends at a diameter of 130 mm [in the specimen of P. (Pa.) edouardi described by Thomel, 1965b].

3. The third stage exhibits strong main ribs with three intermediate ribs to one main rib. This stage is equivalent to stage three of P. (Pa.) sarasini . This implies that stage two proceeds to a larger diameter than in P. (Pa.) sarasini , but does not show significant ontogenetic difference with P. (Pa.) dissiticostata . This is probably a case of ‘progressive deviation’, which does not involve heterochrony.

The whorls of P. (Pa.) edouardi are not in contact and

it is not known whether the inner whorls are in contact

or not. The equality of whorl height and umbilical

width is reached at a diameter of 52 mm, which is much

earlier than in P. (Pa.) sarasini , but also earlier than in

P. (Pa.) dissiticostata . This may be interpreted as the

heterochronic process of acceleration.

Conclusion: Fig. 6. There is only one peramorphic trend apparent that involves all species of subgenus Pseudothurmannia (Parathurmannia) , viz. the acceleration of the start of the egression of the whorls monitored by the shift of the diameter at which the whorl height equals the umbilical width. In this trend the whorls of the successive species become more and more evolute and slightly crioconic in the end, as in subgenus Pseudothurmannia (Pseudothurmannia) . This means that P. (Pa.) sarasini is the ancestral stock. There may also be a tendency to increase in size. With respect to the shape and size of the successive species, one could possibly think of a peramorphocline.

However, as to the ornamental (= somatic) ontogenetic development, there is no clear heterochrony. Their ornamental ontogeny does not change in steps in one direction.

Be that as it may, it became clear that the three species P. (Pa.) sarasini , P. (Pa.) dissiticostata and P. (Pa.) edouardi are closely related, because they have similar ornamentations in the same ontogenetic order. But whether the three species form one lineage is not probable. It is more probable that P. (Pa.) dissiticostata and P. (Pa.) edouardi originate independently from P. (Pa.) sarasini .

4.5. Evolutionary trends in the binelli group of