Diagnoza

The symmetrical tr element with smooth lateral surfaces, its inner margin sharp, in juveniles with smooth flanks, but in adults they may bear angulations. The ne elements robust , with a deep round incision above the base. All elements hyaline.

Porównanie

Two main element types were identified by LINDSTROM(1971), the apparatus reconstruction
ha  been further developed by VAN WAMEL (1974), LOFGREN (1978), and DZIK (1990). During the evolution of this Drepanodus lineage elements become more and more prominently ornamented along their inner edges. In the Arenig some rare specimens (usually large ones) bear three ridges along this edge but I was not able to find any with more el aborated ornamentation, which is
typical for later D. robustus. Somewhat arbitrarily, I assign to D. arcuatus the se populations transitional to D. robustus that still did not develop five ridges along the inner edge in adult elements.
"Protopanderodus n. sp. A" MCCRACKEN, 1989 from the P. serra Zone of Northern Yukon, Canada, may be a successor of D. arcuatus. Oblique bases make it superficially similar to some species of Protopanderodus which, however, have quite different "platform" series elements and less elaborated apparatuses.

Autekologia

Występowanie geograficzne

A few specimens of Drepanodus , collected by Dr. Wieslaw BEDNARCZYK from
the limestone bed once exposed in the Buk6wka quarry definitely belong to this species. None of the
two large tr elements pre sent in the sample ha s any lateral ridges (Text-fig. 8a). However, a specimen
of similar size from the borehole Buk6wka IG 1 (depth 83.5-84 m) shows five di stinct ridges. This
rather exceeds possible population variability and the sample seems thu s to be of different age,
probably closer to the base of the M6jcza Limestone where similar large elements occur. Somewhat
enigmatic is the presence in both Buk6wka samples of a few possible ke elements with a very convex
posterior side and prominent medial rib (Text-fig. 8a). There are too few specimens available to statewith ce rta inty whether they belon g to anot her sympatric spec ies of Drepanodus or perhaps they
represent ne e leme nts of a species of Protopanderodus.
To D. arcuatus I assign also population s from bel ow the di scon tinuity surface in M6jcza, with
e lements usu all y armed with thr ee sharp ridges. Elsewhere the typ ical D. arcuatus is co nf ined to the
Arenig .

Zasięg czasowy

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.