title: Terreneuvian orthothecid (Hyolitha) digestive tracts from northern Montagne Noire, France; taphonomic, ontogenetic and phylogenetic implications.
abstract: More than 285 specimens of Conotheca subcurvata with three-dimensionally preserved digestive tracts were recovered from the Terreneuvian (early Cambrian) Heraultia Limestone of the northern Montagne Noire, southern France. They represent one of the oldest occurrences of such preserved guts. The newly discovered operculum of some complete specimens provides additional data allowing emendation of the species diagnosis. Infestation of the U-shaped digestive tracts by smooth uniseriate, branching to anastomosing filaments along with isolated botryoidal coccoids attests to their early, microbially mediated phosphatisation. Apart from taphonomic deformation, C. subcurvata exhibits three different configurations of the digestive tract: (1) anal tube and gut parallel, straight to slightly undulating; (2) anal tube straight and loosely folded gut; and (3) anal tube straight and gut straight with local zigzag folds. The arrangement of the digestive tracts and its correlation with the mean apertural diameter of the specimens are interpreted as ontogenetically dependent. The simple U-shaped gut, usually considered as characteristic of the Hyolithida, developed in earlier stages of C. subcurvata, whereas the more complex orthothecid type-3 only appears in largest specimens. This growth pattern suggests a distinct phylogenetic relationship between these two hyolith orders through heterochronic processes.
authors.affiliation: UMR 8217 Géosystèmes CNRS - Université Lille 1Villeneuve d'Ascq, France.
authors.forename: Léa
authors.initials: L
authors.lastname: Devaere
authors.affiliation: UMR 8217 Géosystèmes CNRS - Université Lille 1Villeneuve d'Ascq, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Clausen
authors.affiliation: Centro de Astrobiología, Instituto Nacional de Técnica Aeroespacial, Consejo Superior de Investigaciones Científicas, Torrejón de Ardoz, Spain.
authors.forename: J Javier
authors.initials: JJ
authors.lastname: Alvaro
authors.affiliation: Department of Earth Sciences (Palaeobiology), Uppsala University, Uppsala, Sweden.
authors.forename: John S
authors.initials: JS
authors.lastname: Peel
authors.affiliation: UMR 8217 Géosystèmes CNRS - Université Lille 1Villeneuve d'Ascq, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Vachard
mesh_terms: D000818:Animals; D005247:Feeding Behavior; D005580:Fossils; D005602:France; D041981:Gastrointestinal Tract / Q000502:physiology*; D005843:Geography; D005844:Geology; D007448:Invertebrates / Q000145:classification* / Q000502:physiology*; D010163:Paleontology; D010710:Phosphates / Q000737:chemistry; D010802:Phylogeny
chemical_list: D010710:Phosphates