Pseudothurmannia (Kakabadziella) catulloi, Zone, Miravetes Formation, Rio Argos, Caravaca, 1995

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 : 20-21

P. (K.) catulloi at the same time or just after the latter succeeded P. (K.) mortilleti as chronospecies.

Pseudothurmannia (Pseudothurmannia) picteti: This species is the aperamorphic ancestor of this peramorphocline. The ornamentation of young P. (P.) picteti lacks the ornamental ontogenetic balearis stage, which may have disappeared through persistent acceleration. Only two ornamental ontogenetic stages could be distinguished. 1. The first stage of P. (P.) picteti is similar to the second

stage of P. (K.) catulloi , and consists of rather wide-

spaced main ribs and of 1-3 short intermediate ribs

between every two main ribs. This stage ends at a

diameter of c. 60 mm. 2. In the second stage, the ribbing coarsens and there

are mainly 1-2 intermediate ribs to one main rib; this

stage is similar to the third ornamental stage of P.

(K.) catulloi. This uniform and regular ornamentation

continues up to the adult aperture, which means that P.

(P.) picteti lacks the distinct adult ornamentation which

is present in its ancestor, P. (K.) catulloi . This also

means that adult P. (P.) picteti has an ornamentation

which characterizes a younger ontogenetic stage

of the ancestor. The ornamental ontogeny of P.

(P.) picteti is, therefore, retarded with respect to its

ancestor, and caused by the heterochronic process

of neoteny, because the adult size of P. (P.) picteti of

320 mm is of the same order as that of P. (K.) catulloi . On the other hand, in P. (P.) picteti a new ornamental character was introduced, which has been passed down to all subsequent members of the subgenus Pseudothurmannia (Pseudothurmannia) , viz. the development of lateral tubercles on main ribs. This ornamental ‘innovation’ starts at a diameter of 75 mm, but disappears at a diameter of 130 mm; the lateral tubercles are only present over three quarters of a whorl, and merely occur in a transitional ontogenetic stage. There is a clear heterochrony with respect to its ancestor in the shape of the conch; the umbilical width of P. (P.) picteti equals the whorl height at a diameter of 150 mm, which is significantly later than P. (K.) catulloi (at D = 123 mm). This means that the ontogenetic development of the shape of the conch is also retarded. This heterochrony is probably caused by neoteny. This paedomorphic evolutionary trend (paedomorphocline, which is partly anagenetic and partly cladogenetic) in fact proceeds from P. (K.) mortilleti via P. (K.) catulloi to P. (P.) picteti ; the latter is, however, the aperamorphic species of the peramorphocline within the subgenus Pseudothurmannia (Pseudothurmannia) .

Pseudothurmannia (Pseudothurmannia) simionescui: This species is the first descendant of the stepped cladogenetic dissociated peramorphocline, and its ornamentation closely resembles that of P. (P.) picteti . It has two ornamental ontogenetic stages.

1. The first stage consists of 1-3 intermediate ribs to one main rib and is equivalent to stage one of P. (P.) picteti .

2. In the second stage the ribbing gradually becomes stronger, rather uniform and regular, with mainly two intermediate ribs to one main rib; it begins at a diameter of 65 mm, is equivalent to stage two of P. (P.) picteti and continues at least to a diameter of 176 mm.

3. It is not known whether this species has a third stage with a crioceratites- like ornamentation as all the other descendants have, for the largest known P. (P.) simionescui has a diameter of only 176 mm, while all other members of the subgenus Pseudothurmannia (Pseudothurmannia) have an adult diameter of more than 300 mm and a third adult ornamental stage. Nevertheless, it is quite possible that a similar ornamental stage exists in P. (P.) simionescui .

The lateral tubercles inherited from P. (P.) picteti appear at a diameter of 55 mm, which is much earlier than in P. (P.) picteti, and continue up to the aperture. The apertural extension of the lateral tuberculation can be explained by ‘progressive deviation.’ This phenomenon does not produce heterochrony. However, the earlier start of the lateral tuberculation is interpreted to be due to the heterochronic process called ‘predisplacement’ (Alberch et al., 1979). Predisplacement concerns the beginning of a structure, which starts earlier in the ontogeny of the descendant than in the ancestor; the result of this heterochrony is the same as the process of acceleration.

There is a clear heterochrony in the shape of the conch; the inner whorls overlap only a little, and the whorl height equals the umbilical width at a diameter of 113 mm, which is earlier in the ontogeny than in P. (P.) picteti (at D = 150 mm). This could be interpreted as heterochrony produced by acceleration. Moreover, the last whorl becomes detached from the preceding whorl and is weakly crioconic; it is difficult to judge where the whorls stop touching each other. This detachment is a late innovation of the shape of the conch and the prelude to the crioceratites -like ornamentation in the adult of the descendants. Perhaps P. (P.) simionescui already has this ornamentation.