Year: 1995
Type: article
Abstract: Decay experiments were carried out on three Recent species of coleoid cephalopods (the squids Alloteuthis subulata and Loligo forbesi, and the sepiohd Sepiola atlantica ) over a period of 1 day to 50 weeks.The morphological sequence of degradation and the fate of the more decay resistant organs (beaks, radula, suckers, gladius, statoliths, eye lenses) were recorded.Crystalline magnesium phosphate precipitated, but tissue ultrastructure was not preserved.Sex and stage of maturity may influence rate of degradation.Differences in buoyancy mechanism, physiological changes during reproduction, and post-mortem decay processes affect the highly variable preservation potential of modern coleoids.Of the six genera ( Belemnotheutis , Mastigophora , Loligosepia, Geopeltis , Plesioteuthis and Trachyteuthis ) of exceptionally preserved Jurassic fossil coleoids examined for evidence of ultrastructural preservation, Mastigophora exhibits a continuous series of tissues from the outer tunic, through the mantle and gladius, to the muscular sheath of the digestive gland.In Belemnotheutis and Mastigophora the radial and circular muscle, the outer collagenous tunic and the supporting meshwork of intramuscular fibres are all preserved.Longitudinal fibres are evident in the arms and in the mantle of some specimens.The texture of the calcium phosphate replacing the soft-tissue varies even within a specimen.Muscles may be represented by the fibres, or only the sarcolemma.The microspheres of calcium phosphate are 1-2 pm. in diameter in the former (perhaps representing the microbes themselves), but only 0T /mi in the latter (where precipitation is induced by microbial processes).Microspheres in the tunic are 0-5-0-25 pm in diameter.Muscle, tunic, intramuscular fibres and ink are preserved in calcium phosphate.Gladius material is finely banded, with varying proportions of diagenetic calcium phosphate and calcium carbonate in each of the layers in Geopeltis from Charmouth.The mantle morphology found in Mastigophora and Belemnotheutis corresponds with that found in living coleoid cephalopods and indicates that this structure had evolved by the Early Jurassic.This calls into question the systematic position of Belemnotheutis as a member of the Belemnitida.It is clear that phosphatization of ultrastructural detail is not confined to a small number of unusual localities.There is considerable potential for histological investigations of the soft-tissues of a range of extinct organisms.The Coleoidea, typified by the extant squids, cuttlefish and octopus, rank alongside the Nautiloidea and Antmonoidea as the third major subclass of cephalopods.Whilst the nautiloids and ammonoids have a heavy external shell, most coleoids, with the exception of the living families Sepiidae and Spirulidae and the extinct order Belemnitida, have negligible mineralized tissue and are essentially soft-bodied.Nevertheless the soft tissues of coleoid cephalopods are preserved at a number of Jurassic localities (Table 1), e.g.Holzmaden (Toarcian), Germany; Christian Malford (Callovian), England (Donovan 1983;Allison 1988; Page 1991; Donovan and Crane 1992); Voulte-sur-Rhone (Callovian), France (Fischer and Riou 1982 a, b)\ Solnhofen (Tithonian), Germany (Bandel and Feich 1986;Mehl 1990), as well as in the Cretaceous (Albian) of NW Queensland (Wade 1993), the Carboniferous Mazon Creek biota of Illinois (Allison 1987) and possibly the Devonian (Ernsian) Hunsriickschiefer of Germany (Sturmer 1985).Whilst the morphology of a number of coleoids that preserve traces of the soft parts has recently been described in detail from these localities, the mineralization of the soft-tissues has only been subjected to preliminary investigation (Allison 1988 ;Mehl 1990).The aim of this study is to identify the tissue types preserved in coleoids, to determine the degree of morphological detail preserved, and to interpret this in the light of controlled decay
Language: English
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W6968286288