Opis

Remarks. — The only character that distinguishes the earliest clymenias from the co-occurring or slightly older protornoceratid goniatites is the dorsal location of their siphuncle. All other conch and septal morphology characters are virtually identical. This was the basis for indication of the tornoceratids as the clymenias’ ancestors. Exquisitely preserved material of the oldest clymenias from the Urals shows that in the larval conch the siphuncle perforated the first septum near the protoconch venter, centrally in the second, and centrodorsally in the third septum. Thus, not before the metamorphosis an early clymenia developed the diagnostic dorsal location of its siphuncle. This looks like a recapitulation of phylogeny in the early ontogeny and points towards Kirsoceras rotundatum (Perna, 1914) from the Cheiloceras Stufe of the Urals, having the siphuncle significantly departing from the venter in adult specimens, as the probable ancestor of the clymenias.
However, the typical members of the Tornoceratidae and the clymenias differ fundamentally from each other in their larval (ammonitella)  conch organization. The difference between the Tornoceras and clymeniid suture ontogeny was the main argument against any close relationship between these ammonoids. If K. rotundatum is truly a connecting link between evolute tornoceratids and the earliest clymenias, then its protoconch morphology has to be also transitional. The origin of clymenias from the tornoceratid goniatites implies that the ancestral forms were of a rather complex morphology, with a relatively involute conchs and marginally vaulted septum. This conch morphology continued, with a somewhat more complicated septum, in the most long-ranging lineage of Cymaclymenia. The vaulting of the septum in the evolute Clymenia and Kosmoclymenia is apparently rooted in this ancestral status. Also the lineages ending in the highly sophisticated septal morphologies of Dimeroclymenia and Gonioclymenia are rooted, idependently of each other, in the early vaulted cymaclymeniids. In the lineage of Cyrtoclymenia, the ancestral involute conch geometry with open umbilicus was preserved, but with a simplified (balloon-type) septum. A more evolute conch combined with simple septum characterize Platyclymenia. In the wocklumeriids, a complication of suture morphology developed de novo from a rather simple septal morphology.
The dorsal location of siphuncle makes its length significantly shorter in respect to the phragmocone than in goniatites. Some clymeniids (Biloclymeniidae) show unusually wide siphuncle, proposed to be an adaptation to preserve the area of contact of the siphonal tissue with  the cameral liquid similar to that in goniatites. Interestingly, they show also extremely long septal necks, a feature undoubtedly limiting fluid and gas exchange between the sipho and phragmocone chambers (like in the Tertiary nautiloid Aturia with dorsally located siphuncle, but also in the endoceratid nautiloids, having similarly wide siphuncle).

Synonimy
[klymenie]

Zasięg czasowy

Famennian 

Literatura

Dzik, J. 2006. The Famennian "Golden Age" of conodonts and ammonoids in the Polish part of the Variscan sea. Palaeontologia Polonica 63, 1-359.