Apparatus of Drepanodus robustus Hadding, 1913

Diagnoza

The ne elements robust , with almost flat surfaces along the posterior ex ternalridge .
Mature elements prominently costate, the tr element usually bear five inner ribs (even in some juveniles). All the elements hyaline with rudimentary white matter .

Porównanie

The apparatus of D. robustus is of the same organization as that of D. arcuatus. The only difference consists in the ornamentation of the inner margins of mature elements. There are populations transitional between these two species but the evolutionary relations hips between them
are far from being clarified. They probably formed a network of all opatric, independently evolving lineages that occasionally interbred until a complete separation of the lineages at an unknown level of the Llanvirn, when along with the D. robustus lineage another line, leading from D. arcuatus to D. santacrucensis sp. n. was established. Juvenile elements of these species are hardly distinct morphologically. In consequence of a high developmental and population variability it is also not always possible to separate some morphologically close element types within the symmetry transition series .

Autekologia

Występowanie geograficzne

Th e species appea rs in the Mójcza limestone.

Zasięg czasowy

At the discontinuity surface and continues as high above as to 1.8 m above the bentonite (A . tvaerensis/superbus transition zone) . Rare,specifically unidentifiable elements of Drepanodus occur sporadically even higher in the section.

Materiały muzealne

Literatura