Ctenosauriscus

Ctenosauriscus
The holotype of Ctenosauriscus . The vertebrae with the greatly elongated spinous processes and some ribs are preserved.
Temporal occurrence
late Olenekian ( Lower Triassic )
approx. 247 million years
Locations
Lower Saxony , Germany
Systematics
Archosauria Crurotarsi Paracrocodylomorpha Poposauroidea Ctenosauriscidae Ctenosauriscus
Scientific name
Ctenosauriscus
Kuhn , 1964
Art
Ctenosauriscus koeneni

Ctenosauriscus is an extinct genus of Archosauria from the group Poposauroidea . The only find so far comes from the middle red sandstone of Lower Saxony (late Olenekian , Lower Triassic ). Ctenosauriscus is the eponymous representative of the Ctenosauriscidae , a family that is characterized by a high back sail. Ctenosauriscus lived during the Olenekian (about 247 million years ago), making it one of the oldest archosaurs. The genus was firstdescribedas Ctenosaurus by Friedrich von Huene in 1902andrenamed Ctenosauriscus by Oskar Kuhn in1964.

description

Drawing life reconstruction of Ctenosauriscus koeneni .

The most striking feature of Ctenosauriscus is the dorsal sail, which is formed by the elongated spinous processes of the cervical and dorsal vertebrae. The spinous processes are bent slightly forward in the front area of ​​the sail and slightly backward in the rear area of ​​the sail. Some other representatives of the Poposauroidea, such as Lotosaurus and the Ctenosauriscids Hypselorhachis and Xilousuchus , also had elongated spinous processes - but the Ctenosauriscus sail was one of the largest of this group. Ctenosauriscus is most similar to Arizonasaurus from the Central Triassic of the southwestern United States. Both genera had spinous processes that were up to 12 times as high as the vertebral bodies . In Centosauriscus the ends of the spinous processes are wider than in related genera, and the post- and prezygapophyses (mechanical connecting elements of the vertebrae) were larger and more robust. The related Hypselorhachis also had enlarged spinous processes at the upper end; however, these were shorter than with Ctenosauriscus . Also Lotosaurus from the Middle Triassic of China shows extended spinous processes, but, even wider and were much shorter than in ctenosauriscus .

Systematics

Ctenosauriscus is the eponymous representative of the Ctenosauriscidae . Typical of this group are dorsal sails, which are formed from elongated spinous processes of the vertebrae. The Ctenosauriscidae were especially widespread in Eurasia and North America during the Lower and Middle Triassic . Representatives of the group include Arizonasaurus from the Moenkopi Formation in Arizona ( USA ), Hypselorhachis from the Manda Formation in Tanzania , Xilousuchus from the Chinese Heshanggou Formation , the little-known British Bromsgroveia from the Bromsgrove Sandstone Formation , as well as an unnamed one Copy from the German Röt formation with one. Butler et al. (2011) the Ctenosauriscidae defined as a trunk line based Taxon ( stem-based definition ), which includes all taxa with closer koeneni ctenosauriscus than gracilis poposaurus , Effigia okeeffeae , Postosuchus kirkpatricki , Crocodylus niloticus , Ornithosuchus longidens or Aetosaurus Ferratus are related.

The Ctenosauriscidae are placed in the Poposauroidea . The sister taxon of the Ctenosauriscidae forms an unnamed group of derived genera of the Poposauroidea, such as Poposaurus , Sillosuchus and Shuvosaurus . The relationships within the Ctenosauriscidae are unclear. A cladogram according to Butler et al. (2011):

Poposauroidea	Lotosaurus      Sillosuchus      Poposaurus      Shuvosaurus      Effigia   Ctenosauriscidae   Hypselorhachis      Ctenosauriscus      Arizonasaurus      Bromsgroveia      Hypselorhachis      unnamed Ctenosauriscide

History of research and discovery

Location of the place where Ctenosauriscus and the unnamed Waldshut Ctenosauriscid were found

Ctenosauriscus is only known from a single find ( holotype , specimen number GZG .V.4191), which consists of a partial postcranial skeleton including an incomplete spine, ribs and possibly some elements of the shoulder girdle. The find is preserved on four sandstone slabs. The first plate (cataloged as A1) contains the dorsal vertebrae, while the second plate (B1) contains the caudal, sacrum, and the most posterior vertebrae. Two further plates (A2 and B2) form the counter plates to A1 and B1.

The find was found at the beginning of 1871 in a quarry in the Bremketal valley southeast of Göttingen . It comes from the Solling building sandstone , a unit of the Solling formation of the Middle Buntsandstein . Later in the same year it was donated to the University of Göttingen by the architect Eduard Freise . The first description as Ctenosaurus koeneni published Friedrich von Huene in 1902, but only on the basis of a photograph of the fossil. Von Huene later traveled to Göttingen himself to examine the fossil directly and published a more extensive description in 1914.

Edaphosaurus and Platyhystrix , two land vertebrates with sails from the lower Permian . Ctenosauriscus was classified first as Pelycosauria like Edaphosaurus and later as Temnospondyli like Platyhystrix .

Von Huene suspected that C. koeneni was a late pelycosaur - a synapsid distantly related to mammals . Such basal synapsids are mainly known from the Pennsylvania (Upper Carboniferous) and Lower Permian . Von Huene justified this assignment with the similarity of this animal to sail-bearing pelycosaurs such as Dimetrodon . The Austrian palaeontologist Othenio Abel classified C. koeneni as an amphibian from the Temnospondyli group , which should have been closely related to the Platyhystrix , which, like Dimetrodon, comes from Unterperm.

It was later found that the name Huene had chosen, Ctenosaurus, was already taken and referred to the black iguanas (now Ctenosaura ), which is why the genus was renamed by the paleontologist Oskar Kuhn in 1964. B. Krebs re-described the holotype in 1969 and recognized Ctenosauriscus as a representative of the Archosauria, based on similarities with the sail-bearing pseudosuchier Hypselorhachis from the Central Triassic Tanzania .

Ctenosauriscus was found in the Solling Formation , which is dated to an age of 247.5 to 247.2 million years. This dating is based on radiometric methods as well as on measurements of the Milanković cycles .

A research team led by Richard J. Butler published a new description of the holotype in 2011. While it did not recognize any autapomorphies (unique features), it found that the holotype can be distinguished from other ctenosauriscids by a unique combination of features. Ctenosauriscus is one of the oldest archosaurs ; Vytshegdosuchus from Russia was about the same age and probably also Xilousuchus , a Ctenosauriscidae from China.

Paleobiology

Bipedie

A study by Ebel and colleagues (1998) concludes, ctenosauriscus had bipedal running ( biped ) moves, with the extended spinous processes of the vertebrae should have cushioned the forces that occur when running on two legs. Although no leg bones have survived, these researchers suspect that the forces acting on the tops of the spinous processes were focused on a point below the spine, which may have been the knee joint. Butler and colleagues (2011) contradict this hypothesis and argue that muscles must form a direct connection between the knee joint and the back in order to generate such forces between the knee joint and the spinous processes. Instead, however, the forces would be transferred from the hind legs to the pelvic bones and sacrum, and not to the vertebrae. In addition, the sail of Ctenosauriscus would have shifted the center of gravity of the body forward, which would make two-legged locomotion difficult or even impossible.

Individual evidence

1. ↑ ^{a b c d e f g h i j k} Richard J. Butler, Stephen L. Brusatte, Mike Reich, Sterling J. Nesbitt, Rainer R. Schoch , Jahn J. Hornung: The sail-backed reptile Ctenosauriscus from the latest Early Triassic of Germany and the timing and biogeography of the early archosaur radiation. In: PLoS ONE . Vol. 6, No. 10, 2011, e25693, doi : 10.1371 / journal.pone.0025693 .
2. ↑ ^{a b} Sterling J. Nesbitt: The early evolution of archosaurs: relationships and the origin of major clades (= Bulletin of the American Museum of Natural History. No. 352, ISSN  0003-0090 ). American Museum of Natural History, New York NY 2011, doi : 10.1206 / 352.1 , digital version (PDF; 32.69 MB) .
3. ↑ Richard J. Butler, Paul M. Barrett , Richard L. Abel, David J. Gower: A Possible Ctenosauriscid Archosaur from the Middle Triassic Manda Beds of Tanzania. In: Journal of Vertebrate Paleontology. Vol. 29, No. 4, 2009, ISSN  0272-4634 , pp. 1022-1031, doi : 10.1671 / 039.029.0404 .
4. ↑ ^{a b} Stephen L. Brusatte, Michael J. Benton, Julia B. Desojo, Max C. Langer: The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida). In: Journal of Systematic Palaeontology. Vol. 8, No. 1, 2010, ISSN  1477-2019 , pp. 3-47, doi : 10.1080 / 14772010903537732 .
5. ↑ Oskar Kuhn : Unsolved problems of the tribal history of amphibians and reptiles. In: Annual books of the Association for Patriotic Natural History in Württemberg. Vol. 118/119, 1964, ISSN  0368-4717 , pp. 293-325.
6. ↑ Klaus Ebel, Franz Falkenstein, Frank-Otto Haderer, Rupert Wild : Ctenosauriscus koeneni (by Huene) and the Rauisuchier von Waldshut. Biomechanical interpretation of the spine and relationships with Chirotherium sickerli Kaup. = Ctenosariscus koeneni (v. Huene) and the rauisuchian reptile from Waldsut. Biomechanical interpretation of the vertebral column and relations to Chirotherium sickleri Kaup (= Stuttgart contributions to natural history. Series B: Geology and Paläontologie. No. 261, ISSN  0341-0153 ). State Museum for Natural History, Stuttgart 1998, digitized version .