Apparatus of Paltodus? venustus (Stauffer, 1935)

Diagnoza

The ne elemen ts with cusps of almost the same length as the base, tr element with sharp flat ribs along the external margin.

Porównanie

Like in all other known occurrences of the oistodontiform elements of this species there are no other elements in the Mójcza Limestone that could be easily matched with them on the basis of common occurence with expected frequency (that is dominating in numbers over the ne elements) . However, in two samples, MA-70 and MA-87, singular minute elements have been found that are identical with those proposed by NOWLAN et al. ( 1988) to belong to its apparatus. This reconstruction seems more probable than the alternative one that the rest of the apparatus of the species is identical with Drepanoistodus. The unusually high abundance of ne elements may result from their small size and special hydrodynamic properties.
As there is no inversion of the basal cavity in elements of P.? venustus, the species cannot be included in the genus Paroistodus, as provisionally chosen by NOWLAN et al. ( 1988) . The strong ribs arming element flank s and short lateral keels in symmetrical elements are highly primitive traits in the Distacodontidae. This is suggestive of a relationship with Early Ordovician Paltodus species .

Autekologia

Występowanie geograficzne

Zasięg czasowy

In Mójcza the species occurs from the level immediately below the bentonite (P.anserinus Zone) up to the top of the section. It may possibly occur also below the discontinuity but there the ne elements of this morphology are difficult to separate from associated Drepanoistodus species. In the North American Mid continent the species is common in the Lat e Ordovician while in the North Atlantic realm it seems to range from Arenig to Ashgill.

Materiały muzealne

Literatura

 Dzik, J. 1994a 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.