Apparatus of Amorphognathus tvaerensis Bergstrom, 1962.

Diagnoza

The P₁ elements do not form a mirror-image pair, the sinistral one being more highly arched and bears an additional antero-internal lobe; branches of the posterior process of similar length, the external one being somewhat longer. The elements M with a low cusp that usually does not differ in size from neighbouring denticles .

Porównanie

The antero-internal lobe in the left P₁ element is the diagnostic feature. The lobe is usually armed with a single denticle in the earliest populations of the lineage in Mójcza. Gradually it becomes larger and larger and armed with a row of up to four denticles. It branches relatively late in ontogeny but in the course of evolution the branching developed earlier and earlier in organogeny as indicated by a migration of the point of branching towards the cusp. There is thus an acceleration of the ontogeny which also concerns the bifurcation of the posterior process. Its external lobe becomes more and more elongated in the course of evolution.

The right P₁ element is flat, with a wide platform and lacks any additional lobes on its inner process. However, in some rare specimens a denticle corresponding to that in the left element is present. Even if the denticle is present the left elements remain flat and clearly different from their right counterparts.

The denticulation in the M elements is extremely variable, usually with a group of 3-5 radially arranged denticles; the posterior process remains undenticulated or bears very small denticles. In early populations, the external process is prominently denticulated. In the course of evolution this denticulation gradually disappears and the process itself becomes smaller and smaller.

Autekologia

Występowanie geograficzne

Almost cosmopolitan.

Zasięg czasowy

The lineage immigrated to the Holy Cross Mountains area already in the Llandeilo. The early populations in Mójcza (1.0 m below the bentonite - the base of the P. anserinus Zone) are thus at least partially coeval with the Welsh  populations of Amorphognathus inaequalis, possibly being conspecific with them. Both the lower boundary of the typical (late) form of A. tvaerensis and its transition into the succeeding A. superbus is very unclear due to a great population variability of all the diagnostic characters. The first P1 elements without accessory lobes on their inner lobes appear 2.0 m above the bentonite, the last with the lobe occur 2.5 m above the bentonite. 

Materiały muzealne

ZPAL

Literatura

Dzik, J. 1994. Conodonts of the Mójcza Limestone. In: J. Dzik, E. Olempska, & A. Pisera. Ordovician carbonate platform of the Holy Cross Mountains. Palaeontologia Polonica 53, 43-128.