Pseudothurmannia (Kakabadziella) ohmi ohmi, 1868

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 : 16-17

Pseudothurmannia (Kakabadziella) ohmi ohmi :

This species is the third descendant species in the

peramorphic part of the heterochronocline, but also the

first apaedomorphic species of the paedomorphic part

of the mosaïc heterochronocline; it has four ornamental

ontogenetic stages:

1. The balearis stage with fine dense uniform ribbing ends at a diameter of 11 mm, and is accelerated in relation to the ontogeny of the ancestor.

2. The second stage, which has coarser and differentiated ribbing with two intermediate ribs to one main rib, is equivalent to stage two in P. (K.) mortilleti . The ornamental stages one and two in combination with a small umbilicus are united in the so-called mortilleti stage, which ends at a diameter of c. 40 mm. Stage two merges into the third stage.

3. This third stage is characterized by more intermediate ribs per main rib and by an irregular distribution of main and intermediate ribs. This irregularity is an acceptable variation with respect to the more regular distribution in ontogenetic stage three of P. (K.) mortilleti ; it ends at a diameter of c. 105 mm. This early end may be a small heterochrony in the ontogeny of the second and third descendant produced by acceleration.

4. The adult ornamentation of the macroconch consists of very strong distant main ribs with distinct umbilical tubercles separated by 6-7 intermediate ribs.

The young stage of P. (K.) ohmi ohmi below a diameter

of 25 mm closely resembles P. (K.) mortilleti , and can with difficulty be distinguished from the latter. The early egression of the whorls differentiates them. Small uniform ventrolateral clavi occur on every rib in all ontogenetic stages.

As for the ontogeny with respect to the shape of the conch: the diameter at which the umbilical width is equal to the whorl height occurs at a diameter of 41-43 mm. This means that also in the ontogeny of proportions acceleration has occurred. The largest macroconch sampled has a diameter of 165 mm and is of the same size order as that of P. (K.) mortilleti . This species marks the end the peramorphic part and the beginning of the paedomorphic part of the mosaic heterochronocline towards P. (K.) tornajensis .

Pseudothurmannia (Kakabadziella) belimelensis: This species is provisionally regarded as the fourth descendant species of the heterochronocline, because it most resembles evolute P. (K.) ohmi ohmi , and because the latter is the only possible and most appropriate ancestor for P. (K.) belimelensis . However, the age of its appearance in relation to that of P (K.) ohmi ohmi is unknown, and possible adult features and size also are unknown. This species probably remained small. It totally lost the ornamental ontogenetic balearis and mortilleti stages, which may have disappeared through persistent acceleration; all the whorls, also the innermost, are advolute. Two ornamental ontogenetic stages could be recognized:

1. The ribbing of the first stage consists of two intermediate ribs to one main rib. This stage can be compared with stage two of P. (K.) ohmi ohmi .

2. The ribbing of the second stage consists of 3-5 intermediate ribs to one main rib. These stages may be compared with stage three of P. (K.) ohmi ohmi . No heterochrony in the ornamental ontogenetic stages can be detected between the two species. Small uniform ventrolateral clavi occur on every rib probably in all ontogenetic stages.

The diameter at which the umbilical width is equal to the whorl height is 47 mm, which means that there is no significant heterochrony in the ontogeny of the shape of the conch in comparison with P. (K.) mortilleti . However, the adult size is probably significantly less than the adult size of P. (K.) ohmi ohmi . The presumed smaller size and the loss of the two last ornamental stages may indicate the ontogenetic process of progenesis in relation to the ontogeny P. (K.) ohmi ohmi .

Pseudothurmannia (Kakabadziella) tornajensis: This species may be regarded as the fifth and last descendant species in this heterochronocline. It is not likely that P. (K.) tornajensis would be the young of P. (K.) belimelensis , because its ornamentation is more irregular than that of young P. (K.) belimelensis . Moreover, the advolute whorls of P. (K.) tornajensis increase much slower in height than

those of P. (K.) belimelensis . Therefore P. (K.) tornajensis cannot be the microconch of the latter. It is interpreted as a descendent of P. (K.) belimelensis , which exhibits only one ornamental ontogenetic stage, which is similar to the first ornamental stage in P. (K.) belimelensis , but a little more irregular. The only possibility seems to be that one has to do with the phenomenon of dwarfism (nanism) by ontogenetic progenesis (precocious sexual maturation for acquiring a demographical strategy of type r). Because of its smallness it could have been a favourite prey for predators.

The phylogeny of Crioceratites (Balearites) oicasensi : The first ornamental ontogenetic stage of this species is characterized by fine, dense ribbing like C. (B.) balearis and by the presence of lateral tubercles. As in C. (B.) balearis lateral tuberculation stops at a diameter of 10 mm, and between this diameter and a diameter of 20 mm there is only fine, dense ribbing. The difference with C. (B.) balearis is the appearance of slightly thicker, widely spaced ribs with small pointed umbilical tubercles from a diameter of 20 mm. These main ribs become more and more distant and are lined by constrictions from a diameter of 31 mm. C. (B.) balearis also has wide-spaced main ribs lined by constrictions from a diameter of 35- 40 mm. One may consider the appearance of main ribs earlier in the ontogeny of C. (B.) oicasensis as a case of predisplacement. If so, then C. (B.) oicasensis could be interpreted as a descendant of C. (B.) balearis . This species does not belong to the heterochronocline, but forms an individual phylogenetic side branch departing from C. (B.) balearis .

The phylogeny of Crioceratites (Balearites) pseudothurmannii : The ornamentation of this species fits best with the ornamentation of C. (B.) theodomirensis , and this is the reason why the author included it in subgenus Crioceratites (Balearites) as an individual side branch departing from C. (B.) theodomirensis . The heterochrony between the ontogenies of C. (B.) pseudothurmannii results from the process of acceleration of the ornamental ontogenetic stages one and two; the latter stage ends at a diameter of 22 mm instead of 36 mm.

Conclusion: Fig. 3. One may say that in this stepped cladogenetic mosaïc heterochronocline only the link between P. (K.) ohmi ohmi and P. (K.) belimelensis is uncertain. The five successive steps are not in contradiction to the starting points of the stratigraphic ranges of the various members of the heterochronocline. The heterochronocline consists of a first part from C. (B.) balearis to P. (K.) ohmi ohmi consisting of a stepped cladogenetic dissociated heterochronocline affected by different peramorphic processes, and a second part from P. (K.) ohmi ohmi to P. (K.) tornajensis consisting of a stepped cladogenetic paedomorphocline. The presence of C. (B.) balearis as well as P. (K.) mortilleti in the same heterochronocline does not mean that they should necessarily belong to one and the same genus, as many authors suggested.

The main distinction between the genera Crioceratites and Pseudothurmannia is the presence or absence of lateral tubercles in the first ontogenetic stage respectively. However, their presence in one and the same heterochronocline does support their close relationship, which has already been surmised by Nolan (1894). The author is convinced that the overstepping from Crioceratites to Pseudothurmannia is made from C. (B.) theodomirensis to P. (K.) mortilleti . The genus Pseudothurmannia forms a monophyletic group of species. A polyphyletic origin as advocated by Busnardo (2003) is untenable. In the course of the heterochronocline there is a remarkable increase in size from C. (B.) theodomirensis to P. (K.) mortilleti (a case of hypermorphosis), and a decrease in size from P. (K.) ohmi ohmi to P. (K.) tornajensis (a case of progenesis). The evolutionary tendency within the subgenus Pseudothurmannia (Kakabadziella) is from an involute to an evolute conch shape. C. (B.) oicasensis and C. (B.) pseudothurmannii are interpreted as individual side branches.

4.2. Anagenetic transitions: mortilleti-catulloi, mortilleti-caravacaensis and ohmi ohmi-ohmi valbonnettensis ( Fig. 4)

Ancestry of P. (K.) catulloi and P. (K.) caravacaensis: These species closely resemble P. (K.) mortilleti . In 1995 the author (Hoedemaeker, 1995) referred to the specimens that are herein united in P. (K.) caravacaensis as a variety or chronosubspecies of P. (K.) mortilleti . On the other hand, Vermeulen et al. (2002) and Company et al. (2003) considered P. (K.) catulloi a junior synonym of P. (K.) mortilleti . Both P. (K.) catulloi and P. (K.) caravacaensis have a small umbilicus, which is even slightly smaller than the umbilicus of P. (K.) mortilleti . The latter is the only species with a small umbilicus among the potential ancestors occurring before the first appearance of P. (K.) catulloi and P. (K.) caravacaensis . P. (K.) mortilleti is, therefore, the only possible ancestor of these two species. It should be emphasized that there are no intermediate forms between P. (K.) catulloi with strong, regularly distributed ribs and P. (K.) caravacaensis with fine, irregularly distributed ribs. The morphological separation is total, and they can, therefore, be considered separate species. These species are both anagenetically descended from one and the same ancestor at the same time and in the same sea. Do we have a case of sympatric or parapatric speciation?

Pseudothurmannia (Kakabadziella) catulloi: It was not possible to detect a significant heterochrony in the ornamental ontogeny between the chronospecies P.