Abstract
The few detached dermal elements recorded here document a new ostracoderm fauna comprising undeterminable species of one anaspid, two cyathaspids and a heterostracan which might have its closest relatives among the pteraspids. This fauna is derived from marine deposits of ultimate Wenlock or possibly Early Ludlow age at the top of the Lafayette Bugt Formation in its type section, in Washington Land, western North Greenland. It is probably equivalent to one of the undescribed faunas known from the Monograptus testis - M. nilssoni sequence of the Cape Phillips Formation in the Canadian Arctic Archipelago. Comparative material from Norway and Spitsbergen is considered in this study which prompted general comments on cyathaspid squamation, vestigial fin structure, cyathaspid systematics, their phyletic position relative to the pteraspids, system of stability control in swimming, their habitats and diets.
Highlights
The few detached dermal elements recorded here document a new ostracoderm fauna comprising undeterminable species of one anaspid, two cyathaspids and a heterostracan which might have its dosest relatives among the pteraspids
Examination of these, and comparison with other material including articulated specimens from the Palaeontological Museum (Oslo) collections, has stimulated general comments concerning the trunk-tail squamation of the Cyathaspida and several topics significant for vertebrate palaeozoology in general. These are presented belowas a prelude to the description of the Washington Land faunal assemblage
Structural vestiges in the adult body squamations of Irregulareaspis, Nahanniaspis, Dinaspidella and Homalaspidella, suggest that the vestigial ventrolateral fin-folds in cyathaspids extended far back on the side of the tail, obviously well beyond the position of the anal opening. This pattern is exactly similar to what is known in some other fossil agnathans and in many extant and extinct fishes
Summary
Structureless massive Structureless massive Even parallel laminat ion Lamin) and in many extant and extinct fishes With respect to similarity in swimming pattern, it is evident that this would require the
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