The antiarch fish Asterolepis orcadensis from the Scottish Middle Devonian

[摘要] The Givetian (Middle Devonian) antiarch Asterolepis orcadensis was first described in 1932 based on a limited amount of material. Newly collected material has allowed the head to be described in more detail, especially the premedian plate which has an embayment at the centre of the anterior edge. Also, the anterior section of supra-orbital sensory line has been identified on the premedian plate. Other elements newly described include the pectoral appendages which are shown to be quite broad at their proximal ends. The anterior ventro-lateral plate has been described in detail for the first time, particularly structures associated with the attachment of pectoral appendages. The posterior median dorsal plate has been shown not to have had a more pointed posterior edge as depicted in the 1932 description, but a flatter posterior edge reminiscent ofAsterolepis saevesoederberghi which is shown to be closely related to A. orcadensis. The shortness of the posterior median dorsal plate has emphasised the broadness of the whole armour, making A. orcadensis one of the broadest species of Asterolepis. Whilst A. orcadensis is endemic to the Orcadian Basin of northern Scotland, it fits into a biostratigraphical column at the same level as A. saevesoederberghi so strengthening the evidence of a close relationship between these two forms.

[学科分类] 地质学

[关键词] Michael Newman;Jan den Blaauwen;David Leather;Givetian;biostratigraphy;morphology;placoderm;Scotland