Asteroceras

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Asteroceras
Taxon of the genus Asteroceras

Taxon of the genus Asteroceras

Temporal occurrence
Rhätium to Sinemurium
205.6 to 189.6 million years
Locations
Systematics
Cephalopods (cephalopoda)
Ammonites (ammonoidea)
Ammonitida
Psiloceratoidea
Asteroceratidae
Asteroceras
Scientific name
Asteroceras
Hyatt , 1867

Asteroceras is a genus of medium to large, ribbed, subvolute, sometimes involute ammonites . It is a key fossil and occurswidelyfrom the Rhaetian to the end of the Sinemurian .

Initial description and naming

The genus Asteroceras was first described by Alpheus Hyatt in 1867 . Its name is a word created from the Greek words ἄστρον ástron (star) and κέρας keras (horn).

Way of life

The individuals of the genus Asteroceras were fast-swimming marine carnivores that populated the shallow, open subtidal in front of the beach , but could also be found up to the shelf slope .

Systematics

Asteroceras obtusum from Lyme Regis

The genus Asteroceras belongs to the family of the Asteroceratidae (subfamily Asteroceratinae ) within the superfamily of the Psiloceratoidea . The following taxa are known from her:

As a sister species act Aegasteroceras , Arctoasteroceras , Bagnolites , Caenisites , Eparietites , Epophioceras , Euerbenites , Parasteroceras , Protechioceras , Ptycharietites and Tmaegophioceras .

Ammonite zone

Asteroceras stellare , type fossil from the Nuremberg region

The genus Asteroceras is a key fossil in the Obtusum zone (named after Asteroceras obtusum ) of the upper Sinemurium ( Lotharingium ) - but remains limited to the lower two biozones. The Obtusum Zone follows the Turneri Zone (named after Caenisites turneri ) of the outgoing lower Sinemurian. In turn, it is overlaid by the Oxynotum zone (named after Oxynoticeras oxynotum ).

The obtusum zone is subdivided as follows (from hanging wall to lying ):

description

Asteroceras is one of the richest genera in the Asteroceratidae family. Their most highly developed taxa approach the sister genus Aegasteroceras - so both genera show important, coincident, interspecific characteristics. Some species can become very large, up to 40 centimeters. Your phragmocone is circular to slightly elongated when viewed from above. The turns gain height very quickly and are quite thick in cross-section. Your sides are more or less bulged and clearly converge towards the belly side. The ornamentation remains - if present - quite sparse and only roughly indicated, tubercles are missing. The rather prominent ribs are thick and rounded in most taxa and taper towards the vent. A keel runs centrally over the vent, which is accompanied on both sides by indentations (sulci) and shoulder wings. These latter elements differ depending on the taxon or stage of development; mostly they are rounded and therefore do not appear much. The lines of praise are not cut very deep.

Obtus tone formation

Obtususton from Hüttlingen

The Obtususton formation in the southern German Jura was named after the key fossil Asteroceras obtusum .

Occurrence

Occurrences of the genus Asteroceras can be found in Germany on the Swabian Alb in the Obtususton Formation, for example near Mundelfingen in Baden-Württemberg and near Bielefeld in North Rhine-Westphalia . In Austria , the area around Adnet in the State of Salzburg and sites north of Dalaas and near Lorüns in Vorarlberg are to be mentioned . In Switzerland , the genus Asteroceras can be found north of Jaun in the canton of Friborg .

In France , the genus Asteroceras appears in Burgundy at Antigny-le-Château , at Beaune and at Posanges ( Département Côte-d'Or ) and at Semur-en-Auxois , the type region of the Sinemurium. Finds from England come from Lyme Regis and Charmouth in Dorset and from Glastonbury , Limington , Marston Magna near Yeovil and Tintinhull (all in Somerset ). In the Eastern Carpathians of Romania , the genus Asteroceras is found on the Praşca mountain .

Outside of Europe, the Queen Charlotte Archipelago in British Columbia , the Gabbs Valley Range in Nevada and the Antimonio Formation in Sonora in Mexico are to be cited.

literature

  • WJ Arkell et al .: Mesozoic Ammonoidea. Treatise on Invertebrate Paleontology. Geological Society of America and University of Kansas Press, 1957.

Individual evidence

  1. ↑ JJ Sepkoski: A compendium of fossil marine animal genera . In: Bulletins of American Paleontology . tape 363 , 2002, p. 1-560 .
  2. ^ J. Blau and C. Meister: Upper Sinemurian ammonite successions based on 41 faunal horizons: an attempt at worldwide correlation . In: GeoResearch Forum . tape 6 . Zurich 2000, p. 3-12 .
  3. ↑ Jean-Luc Dommergues: Les ammonites you Sinémurien supérieur de Bourgogne (France): biostratigraphy et remarques paléontologiques . In: Revue de Paléobiologie . Vol. 12 (1). Muséum d'Histoire Naturelle de la ville de Genève, 1993, p. 121 .
  4. ↑ M. Gruner: Dynamic paleoecology and taxonomic treatment of the Lower Jurassic (Hettangian to Lower Sinemurian) on the Swabian Alb . In: Profile . tape 11 . Stuttgart 1997, p. 1-197 .