Late Silurian–Early Devonian tessellated heterostracanOniscolepisPander, 1856 from the East Baltic and North Timan

T Märss,V Karatajūtė-Talimaa

doi:10.3176/earth.2009.1.05

Abstract

Late Silurian–Early Devonian tessellated heterostracan<i>Oniscolepis</i>Pander, 1856 from the East Baltic and North Timan

Highlights

Oniscolepis (= Strosipherus) was introduced in the pioneer work of Pander (1856), but still only a few features of this taxon, such as the composition of the exoskeleton of two types of mesomeric elements, tesserae and scales, and the histology of these elements, are known
The microstructure of scales of O. dentata specimens from the East Baltic and North Timan differs only slightly from that of scales from the type locality, Saaremaa Island, Ohesaare Cliff, which has fewer and finer dentine tubules and Sharpey’s fibre tubules than the specimens from North Timan
We have not succeeded to identify heterostracans either in Lõo Cliff or Kaugatuma Cliff (Kaugatuma Stage, Přidoli) situated nearby, large samples of several kilograms of rock have been dissolved

Summary

Introduction

Oniscolepis (= Strosipherus) was introduced in the pioneer work of Pander (1856), but still only a few features of this taxon, such as the composition of the exoskeleton of two types of mesomeric elements (or units), tesserae and scales, and the histology of these elements, are known. The type locality for Strosipherus was indicated by Pander as Leo (present name Lõo), Saaremaa Island, Estonia. We have not succeeded to identify heterostracans either in Lõo Cliff or Kaugatuma Cliff (Kaugatuma Stage, Přidoli) situated nearby, large samples of several kilograms of rock have been dissolved As the acid dissolution method was not known at that time, it is highly improbable that Pander found Strosipherus on rock slabs from Lõo Cliff. Oniscolepis dentata ranges from Přidoli (Upper Silurian) to Lower Lochkovian (Lower Devonian), and so far it has been found in the East Baltic, North Timan (Fig. 1), and in the boulders of the North German Lowland (Gross 1961; Karatajūtė-Talimaa 1970; Märss 1986)

Methods

Discussion

Conclusion