Seirocrinus subangularis

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Seirocrinus subangularis
Seirocrinus subangularis 3334.jpg

Seirocrinus subangularis

Temporal occurrence
Pliensbachium to Toarcium
190 to 175 million years
Locations
  • Europe
  • North America
  • Japan
Systematics
Trunk : Echinoderms (Echinodermata)
Class : Sea lilies and starfish (Crinoidea)
Order : Isocrinida
Family : Pentacrinitidae
Genre : Seirocrinus
Type : Seirocrinus subangularis
Scientific name
Seirocrinus subangularis
( Miller , 1821)

Seirocrinus subangularis is a fossil sea lily species from the Lower Jurassic . The species is known for its spectacular Posidonia schist finds, which are showpieces in museum collections. It is also significant in terms of research history: Eberhard Friedrich Hiemer (1682–1727) published a treatise on the "Swabian Medusa head" in 1724 in which he was one of the first to see animals not only as games of nature, but as the remains of something actually living but extinct Tiers treated. The species is the largest sea lily species from the Jura described so far. Seirocrinus subangularis is fossil of the year 2014.

features

Seirocrinus subangularis has the typical structure of sea lilies in stem and crown, with the crown consisting of a cup (calyx) and tentacles attached to it. The stem is usually about 60 to 90 centimeters, the crown 20 to 30 centimeters long. The largest pieces, however, have stem lengths of over fifteen meters and a crown diameter of one meter. Such pieces can be seen , for example, in the Paleontological Museum in Tübingen . Sea lilies are passive filter feeders that use their arms to filter out food particles from the moving water on which they feed. In Seirocrinus the crown is unusually finely branched. It consists of 20 main arms or podia (created from twice dichotomously branched arms), on which a large number of side arms (ramuli) sit on one side on the inside, which are aligned parallel to each other. According to the taphonomic findings, the parallel alignment of the ramuli was retained during embedding, which indicates that they were somehow fixed to one another.

The endoskeleton of sea lilies, which consists of calcium carbonate, has a high fossil conservation potential and also makes up a large part of the body volume, so that a fossil sea lily gives a realistic impression even without soft tissue conservation. The mouth as well as the anus opening of the living animal lay on the top, "on the bottom", of the cup. The skeleton consists of small calcareous plates that were connected to one another by connective tissue. The mostly more or less regular pentagonal skeletal elements of the calyx are called basalia, the marginal radalia. In Seirocrinus , additional elements (interradialia and interbrachialia) are inserted, which increase the area of ​​the calyx. The species even exhibited partial third-order branching on the outside. The stem was also divided into sections (columns), each bearing a skeletal element. Disarticulated stalk members of (other) sea lily species are often fossilized, sometimes rock-forming. The stalk members of Seirocrinus subangularis were rounded, pentagonal to round. Numerous stalk members carry extensions called cirrus, with which the animal u. a. could anchor to the base. The basal approximately 30 centimeters of the stem carried a dense mass of flexible cirrus.

Way of life

The animals are always attached to pieces of dead wood in the rock, sometimes very many to one piece of wood. Although some researchers consider a fixation on deadwood that has sunk to the seabed possible, today a specialization in floating driftwood is assumed as a base for the species. This indicates u. a. the fine structure of the stem, which was most mobile not near the calyx but near the point of attachment, as well as taphronomic findings, according to which animals were better preserved on the underside of the wood when embedded than on the top. This way of life is called "pseudoplanktonic" or "pseudopelagic". It has a number of consequences: The long handle is primarily subjected to tensile stress like a rope. Since the substrate has the same speed as the surrounding water, filtration is much more effective with a very long stem. The animals can be thought of as hanging from the drifting piece of wood, with the crown being dragged along.

Research history and taxonomy

The first scientific description of the species, which did not yet correspond to today's rules of nomenclature, comes from the Stuttgart court preacher Eberhard Friedrich Hiemer (1682–1727) after a stone slab found in Ohmden near Holzmaden (Württemberg). He noticed the resemblance to the "Medusa head" Gorgonocephalus caputmedusae (Linnaeus, 1758), discovered in the Indian Ocean in 1705 , so that he interpreted his find as the fossilization of a similar animal. He explained that it was carried off to Swabia with the “deluge, the torrent of which seemed large enough to bridge any distance.” Hiemer's adaptation attracted widespread attention at that time, his illustration was for example by Johann Jacob Scheuchzer , Johann Ernst Immanuel Walch and Carl von Linné accepted. Only later editors were able to explain that Hiemer's specimen belonged to a different, distantly related species (the first recent stalked sea lily Cenocrinus asterius (Linnaeus, 1767) was not known in Europe until 1761 through Jean-Étienne Guettard ).

The German-English natural scientist Johann Samuel Miller then obtained the first description, which is also sufficient today for taxonomic requirements, in 1821 as Pentarcinites subangularis . As type localities, he gives Württemberg and the famous fossil site Lyme Regis , Dorset. Miller's type material was destroyed in a German air raid on Bristol in 1940. In 2011, researchers declared the famous Hiemer plate, which, after having been lost for decades, had been rediscovered in Göttingen, to be a neotype of the species.

The genus Seirocrinus needs careful systematic revision. During the last systematic treatment by Simms, all the species described up to that point were synonymous under Seirocrinus subangularis and a new species was described at the same time. Other editors recognize up to five species of the genus, all of which come from the Jura. In addition, there is a suspicion that the genus may have to be synonymous with the (previously described) genus Pentacrinites . It has even been suggested that the short-stemmed Pentacrinites may have been Seirocrinus ' juvenile stages . If this suspicion can be confirmed, the species would have to be renamed. The family Pentacrinidae would then be monotypical.

Finds

Most and the most spectacular finds of the species come from the Black Jura of southern Germany, especially from Holzmaden . Showpieces from there are, for example, in the local Urwelt Museum Hauff and in the State Museum for Natural History in Stuttgart . Other finds come from England, Canada, Alaska, Siberia and Japan. The wide distribution of the species could be explained by the pseudoplanktonic way of life of the species. Simms also explains the species’s relative longevity. The evolution of the drill clams could have contributed to the extinction of the species, like the entire group of pseudoplanktonic sea lilies : According to this, the lifespan of driftwood would have subsequently decreased so much that the animals could not complete their life cycle.

The finds mostly come from fine-layered, bituminous slate, which indicates oxygen-free, hostile conditions at the place of embedding. They probably come from animals that were attached to pieces of driftwood that ultimately sank to the ground, whereupon the colonists perished.

swell

Individual evidence

  1. ^ A b Adolf Seilacher, Rolf Bernhard Hauff, Manfred Wolf: Firmly rooted in floating ground: driftwood sea lilies in Lias oil slate. Fossils 1/2014: 349–355.
  2. ↑ Hans Hagdorn, Xiaofeng Wang, Gerhard H. Bachmann, Gilles Cuny, Martin P. Sander, Chuanshang Wang (2005): On a raft trip through the Tethys - the pseudoplanktonic sea lilies Traumatocrinus and Seirocrinus. Reports of the Institute for Earth Sciences of the Karl-Franzens-University Graz / Austria 10: 29–31.
  3. ↑ a b c d Michael J. Simms (1986): Contrasting lifestyles in lower jurassic crinoids: a comparison of benthic and pseudopelagic Isocrinida. Palaeontology vol. 29 part 3: 475-493.
  4. ^ Mike Reich (2010): The Swabian Caput Medusae (Jurassic Crinoidea, Germany). Proceedings of the 12th international echhinoderm conference, Durham, New Hampshire, USA: 61-65.
  5. ↑ Mike Reich & Joachim Reitner: brought to light - "Swabian Medusenhaupt" (Crinoidea; Lower Jura). 3rd working meeting of German-speaking echinoderma researchers, 29. – 31. October 2004. Works & abstracts of the lectures and posters. University Press Göttingen 2004.
  6. ↑ JS Miller (1821): A natural history of the Crinoidea, or lily-shaped animals: with observations on the genera, Asteria, Euryale, Comatula & Marsupites. p. 59
  7. ^ A b Aaron W. Hunter, Tatsuo Oji, Yoshihiko Okazaki (2011): The occurrence of the pseudoplanktonic crinoids Pentacrinites and Seirocrinus from the Early Jurassic Toyora Group, western Japan. Paleontological Research vol. 15, no. 1: 12-22. doi : 10.2517 / 1342-8144-15.1.012
  8. ^ Umberto Nicosia (1991): Mesozoic crinoids from the north-western Turkey. Geologica Romana. 27: 389-436.
  9. ↑ a b Vladimir G. Klikushin (1982): Taxonomic survey of fossil isocrinids with a list of the species found in the USSR. Geobios Volume 15, Issue 3: 299-325. doi : 10.1016 / S0016-6995 (82) 80083-1
  10. ^ Russell L. Hall (1991): Seirocrinus subangularis (Miller, 1821), a Pliensbachian (Lower Jurassic) Crinoid from the Fernie Formation, Alberta, Canada. Journal of Paleontology Vol. 65, No. 2: 300-307.