Taxonomy, morphology and phylogeny of Lower Jurassic loligosepiid coleoids (Cephalopoda)
Abstract:Until today, gladii of loligosepiid vampyropods have been difficult to distinguished owing to their fragmentary state of preservation. Re-study of a large set of loligosepiids from different Lower Jurassic localities has shown that the preservation of growth lines is sufficient to provide an unambiguous determination. Especially the course of growth lines within the hyperbolar zone is a highly characteristic feature. Members of the Loligosepiidae (Loligosepia, Jeletzkyteuthis) display a deeply concave (V-shaped) hyperbolar zone. Members of the Geopeltidae, on the other hand, show weakly concave (Parabelopeltis), or even straightened (Geopeltis) growth lines. Gladii of Loligosepia can be distinguished from Jeletzkyteuthis by the transition lateral field/hyperbolar zone. The genus Loligosepia is characterised by abrupt backwards bent growth lines forming an elongated spine-like projection, whereas the transition is more arcuated in Jeletzkyteuthis. According to the present results, Loligosepia aalensis, Loligosepia bucklandi, Jeletzkyteuthis coriaceus, Geopeltis simplex, and Parabelopeltis flexuosa are re-described. In the course of taxonomic treatment, a lectotype of Jeletzkyteuthis coriaceus is designated and the morphologic independence of Parabelopeltis flexuosa reaffirmed. As can be inferred from the course of growth lines, Parabelopeltis and Geopeltis, members of the Geopeltidae, seems to be phylogenetically closest to Recent Vampyroteuthis infernalis.
Document Type: Research Article
Publication date: July 1, 2008
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