Ontogeny and sexual dimorphism in the Middle/Late Devonian rhomboentomozoid ostracod &amp;lt;i&amp;gt;Franklinella&amp;lt;/i&amp;gt;

Ewa Olempska

doi:10.1144/jm.21.1.9

Abstract

Abstract. A large number of three-dimensionally preserved, pyritized specimens of different instars of the rhomboentomozoid ostracod Franklinella (Franklinella) lysogorensis n. sp. were recovered from a mudstone of the Givetian/Frasnian transition beds at Wzdół in the Holy Cross Mountains, Poland. Seven growth stages are identified. Sexual dimorphism is manifested by differences of ribbing pattern in adults. Within the superfamily Entomozoacea, the presence of two types of sexual dimorphism is suggested: ornamental in rhomboentomozoids and domiciliar in entomoprimitiids. Formerly poorly known morphological features of the rhomboentomozoids, including the anteroventral indentation and a contact list ornamented by fine striation, are described.

Highlights

The rhomboentomozoids are a poorly known group of ostracods traditionally assigned to the superfamily Entomozoacea
More than twenty Franklinella species are known from the Middle Devonian to Lower Carboniferous strata from Europe, China, and North America, where they have proved useful in biostratigraphy
Another possible explanation was proposed by Triebel (1941) who suggested that dimorphism was the result of an ecological disparity between morphs and, according to Martinsson (1956) the sexes of some Palaeozoic ostracod species may have inhabited different biotopes

Summary

INTRODUCTION

The rhomboentomozoids are a poorly known group of ostracods traditionally assigned to the superfamily Entomozoacea They usually co-occur with entomozoids, in strata ranging from the Early Devonian to Early Carboniferous throughout the world. The possible presence of sexual dimorphism in entomozoids arose when Richter (1869) distinguished spherical and oval forms in Richteria serratostriata (Sandberger, 1845), Rabienella barrandei (Richter, 1869), and Richterina (Fossirichterina) costata (Richter, 1869). Preservation of the ostracod shells at Wzdół is variable They are preserved as moulds, but a few samples yielded undeformed, pyritized specimens.

Olempska

DISCUSSION

CONCLUSIONS