Psiloceras

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Psiloceras
Psiloceras planorbis

Psiloceras planorbis

Temporal occurrence
Hettangium
201.3 to 200.7 million years
Locations
Systematics
Cephalopods (cephalopoda)
Ammonites (ammonoidea)
Ammonitida
Psiloceratoidea
Psiloceratidae
Psiloceras
Scientific name
Psiloceras
Hyatt , 1867

Psiloceras is a genus of evolutionary, smooth-shelled ammonites from the Hettangium . It survived the mass extinction at the Triassic-Jura border 201.3 ± 0.2 million years ago. From it all Neoammonites (subordination Ammonitina ) and the subordination Lytoceratina emerged.

etymology

The name Psiloceras is a word created from the Greek words ψιλός psilos (naked) and κέρας ceras (horn).

description

Compared to other early ammonites, the genus Psiloceras had a smooth shell without any major ornamentation. Some taxa have simple, wavy-rounded ribs that can extend over the smooth venter. The genus consists of small to medium-sized forms, the average diameter of which is only 2.7 to 5.2 centimeters, with an average thickness of 0.67 to 0.95 centimeters ( Psiloceras distinctum even reached 11 centimeters). Its representatives were predominantly evolutionary, but involute forms are also known. Characteristic of Psiloceras is the simple, primarily slashed to phyllocerate-like suture and the one-piece anaptychus . The winding cross-section is highly oval to circular.

Way of life

The individuals of the genus Psiloceras were fast swimming marine carnivores . They populated the marginal marine , shallow subtidal , but were also found in the open marine area in siliciclastic basins and down to the shelf ramp in the deep subtidal.

Systematics

Psiloceras laevis

The genus Psiloceras belongs to the family of Psiloceratidae within the superfamily of Psiloceratoidea . It contains the following taxa:

Sister genera are Badouxia , Caloceras , Franziceras , Laqueoceras , Murihikuites , Neophyllites , Psilophyllites and Sunrisites .

phylogenesis

Most authors take the view that the genus Psiloceras is derived from the Phylloceratina or possibly goes back to Eopsiloceras . However, there is also the possibility that the Phylloceratina represent a completely separate line, which may be derived from the genus Rhacophyllites , which survived into the lowest Jurassic. The subordination of the Ceratitina expired with Choristoceras in the lower Jura.

Psiloceras spelae (or Psiloceras spelae tirolicum ) may have been the first Psiloceratide. Jean Guex and colleagues (2012) take the view that Psiloceras spelae evolved from the Phyllocerataceae 201.5 million years ago .

From this taxon the smooth-skinned Psiloceratiden around the group of Psiloceras planorbis emerged. In the 400,000 to 500,000 years after the first appearance of Psiloceras spelae, the Planorbis group had expanded explosively all over the world and occupied all ecological niches - from the deep water area of ​​the Pacific to Tethys deposits in Tibet to the epicontental area of ​​northwestern Europe. Such worldwide radiation enabled the group to be split into several main lines, such as the Schlotheimiidae , the Discamphiceratinae , the Arietitidae and the Lytocerataceae .

Thus further ammonite genera or superfamilies split off from the genus Psiloceras in the course of the lower Hettangium.

Very early in the Unterhettangian, around 201.3 million years ago, the genus Neophyllites and only a little later (around 201.2 million years ago) the genus Discamphiceras . In the middle Unterhettangian around 201 million years the genera Caloceras followed (from which the genus Alsatites emerged at the beginning of the Middle Hettangian around 200.2 million years ), Transipsiloceras , Euphyllites and Pleuroacanthites . In the upper Unterhettangian about 200.7 million years ago the genus chamber karites emerged . The genus Psiloceras ended at the same time .

At the beginning of the middle hettangian 200.2 million years ago, the superfamily of the Lytoceratoidea had developed from the Psiloceratoidea , followed at the beginning of the upper hettangian around 199.7 million years ago by the Arietitoidea with the genus Arietites .

All of this brings to mind the radiation of the Neoammonites that took place after the crisis at the Triassic-Jura border .

Ammonite zones

Psiloceras planorbis

The lowest ammonite zone of the Hettangium, the Tilmanni zone, is named after the taxon Psiloceras tilmanni . This begins with Psiloceras spelae tirolicum and defines the Trias / Jura border at the GSSP of the Kuhjoch in Tyrol . In the hanging wall of the zone then follow Psiloceras tilmanni and Psiloceras pacificum .

The Planorbis zone then appears in the hanging wall , which was established by Albert Oppel in 1856 and previously defined the beginning of the hettangium. In northwestern Europe it consists of the two subzones (English subchronozones ) Planorbis in the lying and Johnstoni (from Caloceras johnstoni ) in the hanging wall. The Planorbis subzone in turn contains the three biozones ( zonules ) Planorbis in the lying area, Sampsoni (or Psilonotum in the Alpine region) and Plicatulum in the hanging wall. The Planorbis biozone is then further subdivided into four horizons - Psiloceras erugatum in the lying wall , followed by Neophyllites imitans , Neophyllites antecedens and Psiloceras planorbis in the hanging wall .

In the Alpine area, the Planorbis zone is replaced by the Calliphyllum zone with the subzones of Psiloceras calliphyllum , Psiloceras costosum and Psiloceras naumanni .

Occurrence

Occurrences of the genus Psiloceras can be found in Germany near Bebenhausen , Nellingen , Pfrondorf and Rottweil in Baden-Württemberg , near Rottorf am Klei in Lower Saxony , near Bad Meinberg in North Rhine-Westphalia and on the Seebergen near Gotha in Thuringia .

As sites in Austria the GSSP act on Kuhjoch and the Ochsentaljoch little further west (both in Vorkarwendel ), the Hochalplgraben west of Hinterriß and the moat east of Hinterriß (all in Tyrol ). Other sites are the Fonsjoch on Lake Achensee in Tyrol, the Zlambach near Bad Goisern in Upper Austria and the Glasenbachklamm south of Salzburg .

In England the genus Psiloceras occurs in the Blue Lias of Watchet in Somerset and at Lyme Regis in Dorset . Occurrences in Northern Ireland are Collin Glen in south-west Belfast and Portrush in County Antrim . Occurrences of the genus Psiloceras are also known in France , Spain and Hungary .

Outside Europe, the genus Psiloceras is found in the Germig Formation of Tibet , on Roti ( Indonesia ), in New Zealand , in South America in Argentina , Chile and Peru ( Pucara Formation near Levanto ), in North America on the Queen Charlotte Islands of Canada and in New York Canyon in Nevada ( United States ).

literature

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

Individual evidence

  1. ↑ Axel von Hillebrandt: The ammonite fauna of the South American Hettangian (basal Jura), Part I, II, III . In: Palaeontographica . v. A257, 2000, p. 85-189 .
  2. ↑ Jiarun Yin, CA McRoberts: Latest Triassic-earliest Jurassic bivalves of the Germig formation from Lanongla (Tibet, China) . In: Journal of Paleontology . tape 80 (1) , 2006, pp. 104-120 .
  3. ↑ Axel von Hillebrandt, K. Kment: Psiloceratid ammonites from the Lower Hettangian of the Karwendel Mountains (Northern Calcareous Alps, Austria) and their biostratigraphic significance . In: New Yearbook of Geology and Paleontology, Treatises . tape 277 , 2015, p. 275-306 .
  4. ↑ Melchior Neumayr: To the knowledge of the fauna of the lowest Lias in the Northern Alps . In: Treatises of the Imperial Royal Geological Institute . tape 7 (5) , 1879, pp. 1-46 .
  5. ^ W. Lange: The lower Lias at the Fonsjoch (eastern Karwendel Mountains) and its ammonite fauna . In: Palaeontographica, Department A . tape 102 , 1952, pp. 49-162 .
  6. ↑ Jean Guex, David Taylor, Milos Rakus, Hugo Bucher: Deux nouveaux genres et quatre nouvelles espèces d'ammonites (Cephalopoda) du Lias inférieur . In: Bulletin de Géologie Lausanne . tape 339 , 1998, pp. 73-85 .
  7. ^ Jean Guex: Remarques preliminaires sur la distribution stratigraphique des ammonites hettangiennes du New York Canyon (Gabbs Valley Range, Nevada) . In: Bulletin de Géologie Lausanne . tape 250 , 1980, pp. 127-140 .
  8. ↑ Jiarun Yin, Paul L. Smith, József Pálfy, R. Enay: Ammonoids and the Triassic / Jurassic boundary in the Himalayas of southern Tibet . In: Palaeontology . tape 50 (3) , 2007, pp. 711-737 .
  9. ↑ W. Lange: On the paleogeography and ammonite fauna of the Lias together with a revision of the Nürtinger psilonote fauna . In: Journal of the German Geological Society . tape 77 , 1925, pp. 439-528 .
  10. ↑ Jean Guex et al .: Geochronological restraints on post-extinction recovery of the ammonoids and carbon cycle perturbations during the early Jurassic . In: Palaeogeography, Palaeoclimatology, Palaeoecology . tape 346-347 , 2012, pp. 1–11 , doi : 10.1016 / j.palaeo.201204030 .
  11. ↑ Jean Guex, David Taylor, Milos Rakus, Hugo Bucher: New data on the phylogeny of Liassic Ammonites . In: Bull. Soc. vaud. Se. nat. tape 87.2 , 2000, pp. 109-114 .
  12. ^ Axel von Hillebrandt, Leopold Krystyn: On the oldest Jurassic ammonites of Europe (Northern Calcareous Alps, Austria) and their global significance . In: N. Jb.Geol.Paleont. Depending on the band 253 / 2-3 . Stuttgart 2009, p. 163-195 .
  13. ↑ Kevin N. Page: The Lower Jurassic of Europe: its subdivision and correlation . In: Geological Survey of Denmark and Greenland Bulletin . tape 1 , 2003, p. 23-59 .
  14. ↑ M. Rakús: Lower Liassic (Hettangian) ammonites from Zlambach Graben near Bad Goisern, Upper Austria . In: Treatises of the Federal Geological Institute . tape 56 , 1999, p. 329-341 .
  15. ^ D. Bernoulli, HC Jenkyns: A Jurassic Basin: The Glasenbach Gorge, Salzburg, Austria . In: Negotiations of the Federal Geological Institute . 1970, p. 504-531 .