Eunotosaurus

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Eunotosaurus
Replica of a fossil of Eunotosaurus africanus with noticeably widened costal arches

Replica of a fossil of Eunotosaurus africanus with noticeably widened costal arches

Temporal occurrence
Permian ( Capitanium )
265.1 to 259.9 million years
Locations
Systematics
Land vertebrates (Tetrapoda)
Amniotes (Amniota)
Sauropsida
Diapsida
Pan-Testudines
Eunotosaurus
Scientific name
Eunotosaurus
Seeley , 1892
Art
  • Eunotosaurus africanus  Seeley, 1892

Eunotosaurus is a genus reptiles like sauropsids from the middle Perm (265.1 to 259.9  mya ) of the Karoo supergroup South Africa. Their representatives were characterized by widened and numerically reduced costal arches and a rounded body. The genus has historically and currently played an important role in the attempt to understand the evolution of turtles from their prehistoric ancestors. Many fossils had a semi-rigid, turtle-like rib cage, which presumably made tortoise-type locomotion necessary.

The ribs were wide and flat and touched so that they formed wide plates similar to the back shield of a turtle. In addition, the number, size and structure of the vertebrae were largely identical to those of many turtle species. In addition, Eunotosaurus seemed to have a windowless ( anapsid ) skull. Because of these properties, the genus was often assigned to the Anapsida or parareptiles and, within this group, was regarded as the direct ancestor of the turtles, traditionally also regarded as anapsids. However, with the knowledge that turtles belong to the diapsid family and that they have a secondary anapsid skull, which has emerged from molecular genetic relationships at the latest , the structure of the skull, the widened ribs and the similar spine in Eunotosaurus and turtles appeared only as a case of convergent evolution . However, recent research has shown that Eunotosaurus had a reduced diapsid skull and that its similarities with tortoises are based on homology rather than convergence.

Drawing life reconstruction of Eunotosaurus africanus

Fossil material

More than a century after it was first described, Eunotosaurus was known to have less than a dozen specimens and little surviving material from the skull. Despite the incomplete tradition, it was described in detail. Two additional specimens were excavated and described in the Karoo supergroup in 1999. These fossils are now on display at the Bernard Price Institute for Palaeontological Research in Johannesburg and the National Museum in Bloemfontein . Although relatively rare, eunotosaurus is common enough in the Karoo supergroup to be used as a biostratigraphic marker . Fossils can be found within the Beaufort group in the upper Tapinocephalus assemblage zone and the Pristerognathus assemblage zone above .

Taxonomy and systematics

Eunotosaurus was described in 1892 , but it was only proposed in 1914 as the ancestor of Chelonia , the order of turtles. The English zoologist D. MS Watson claimed that Eunotosaurus was a mosaic form between turtles and the Captorhinidae , which at that time were still called cotylosaurs. He compared Eunotosaurus with "Archichelone", a hypothetical ancestor of Chelonia, noting that its ribs were intermediate to those of both tortoises and other tetrapods . Watson's "Archichelone" had a pelvic belt that was pushed back on the spine and placed under the armor. However, the fossils of Eunotosaurus show that its pelvis was in a position normal for tetrapods over the ribs and not between them, as in modern turtles.

Until the late 1940s, Eunotosaurus was widely believed to be the ancestor of turtles. The American paleontologist Alfred Sherwood Romer claimed in 1956 in his book Osteology of the Reptiles on the basis of the available evidence that Eunotosaurus could not be placed among the Chelonia. Instead, he assigned Eunotosaurus to the anapsids, within which, however , he assumed an uncertain position .

Eunotosaurus was assigned to its own family , the Eunotosauridae, in 1954 . However, this classification is no longer in use today. In 1969 he was placed in a subordination of the anapsids, the captorhinomorpha , which is now located within the clade of Eureptilia . In 2000, Eunotosaurus was placed in the parareptile clade , where it occupies an independent position from the turtles and the cotylosaurs. A phylogenetic analysis of the parareptiles from 2008 found that Eunotosaurus is a sister taxon of the Milleretta and therefore belongs to the family of the Millerettidae .

Eunotosaurus was included in a phylogenetic analysis from 2010 that investigated the origin of the turtles. More recently, on the basis of genetic and phylogenetic knowledge, turtles have been viewed as diapsids and therefore more closely related to lizards , snakes , crocodiles and birds than to parareptiles or all other anapsids. However, the resulting phylogenetic tree, with the involvement of Eunotosaurus and the late Triassic Proganochelys , a member of the turtle tribe, places the turtles in a position similar to the turtles' original classification as anapsids. The study claims that Eunotosaurus shared inferred features of the ribs and vertebrae with the earliest tortoises, making it a mosaic shape . The study identified a number of characteristics that make it possible to combine Eunotosaurus with the turtles in a real clade. These common features included broad T-shaped ribs, ten elongated trunk vertebrae, cranial tubercles (small bumps on the surface of the skull), and a broad trunk. The clade from Eunotosaurus and the turtles was called "Pan-Testudines". More progressive representatives of the Pan-Testudines, such as B. Odontochelys , already have a belly armor .

This thesis was underlined by a study from 2013 which analyzed the osteological fine structure of the bones, compared it with the ontogenesis of recent turtles and weighted it statistically. She came to the conclusion that Eunotosaurus and the turtles form a monophylum and stand within the Parareptilia . Both studies thus contradicted molecular genetic studies that identify the turtles as a sister group of the archosaurs .

Another study from 2014 shows that Eunotosaurus already developed the peculiar breathing mechanism of turtles. Since the turtle's ribs are integrated into the shell, they are immobile and special muscles have to take care of the inflow and outflow of air. Computed tomographic examinations of various skulls of Eunotosaurus published in September 2015 showed that the animals had two temple windows behind the eyes, i.e. had a diapsid skull . This can be seen particularly clearly in young specimens, whereas in older specimens the temporal windows are almost completely covered. The cranial ontogenesis of Eunotosaurus thus shows how a diapsid skull develops into a secondary anapsid skull like the one found in turtles today. Possibly the ribs of Eunotosaurus broadened as an adaptation to a burrowing way of life.

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literature

Web links

Commons : Eunotosaurus  - Collection of images, videos and audio files

Individual evidence

  1. ^ A b c Ann Campbell Burke: The development and evolution of the turtle body plan: Inferring intrinsic aspects of the evolutionary process from experimental embryology. In: American Zoologist. Vol. 31, No. 4, 1991, ISSN  0003-1569 , pp. 616-627, doi : 10.1093 / icb / 31.4.616 .
  2. ↑ Stuart S. Sumida, Sean Modesto: A Phylogenetic Perspective on Locomotory Strategies in Early Amniotes. In: American Zoologist. Vol. 41, No. 3, 2001, pp. 586-597, doi : 10.1093 / icb / 41.3.586 .
  3. ↑ Facts About Turtles: Eunotosaurus And Turtle Evolution. ( Memento from September 12, 2010 in the Internet Archive ) In: All-About-Reptiles.com. Retrieved November 2, 2014.
  4. ^ A b G. S. Bever, Tyler R. Lyson, Daniel J. Field, Bhart-Anjan S. Bhullar: Evolutionary origin of the turtle skull. Nature. Vol. 525, 2015, pp. 239–242, doi: 10.1038 / nature14900
  5. ↑ a b Tyler Lyson R., Bruce S. Rubidge, Torsten Scheyer M., Kevin de Queiroz, Emma R. Schachner, Roger MH Smith, Jennifer Botha-Brink, GS Bever: fossorial Origin of the Turtle Shell. Current Biology. Vol. 26, No. 14, 2016, pp. 1887-1894, doi: 10.1016 / j.cub.2016.05.020
  6. ↑ Bruce S. Rubidge, Sean Modesto, Christian Sidor, Johann Welman: Eunotosaurus africanus from the Ecca – Beaufort contact in Northern Cape Province, South Africa - implications for Karoo Basin development. In: South African Journal of Science. Vol. 95, No. 11/12, 1999, ISSN  0038-2353 , pp. 553-555, digitized version (PDF; 1.11 MB) ( Memento from February 26, 2012 in the Internet Archive ).
  7. ^ David MS Watson : Eunotosaurus africanus Seeley and the ancestors of the Chelonia. In: Proceedings of the Zoological Society of London. Vol. 84, No. 4, Article 53, 1914, ISSN  0370-2774 , pp. 1011-1020, doi : 10.1111 / j.1469-7998.1914.tb07724.x , digitized .
  8. ^ Alfred Sherwood Romer : Osteology of the Reptiles. University of Chicago Press, Chicago IL 1956, p. 772 (Reprint with new preface and taxonomic table. Krieger Publishing, Malabar FL 1997, ISBN 0-89464-985-X ).
  9. ^ Sidney H. Haughton, Adrian S. Brink: A bibliographical list of Reptilia from the Karoo Beds of Africa. In: Palaeontologia Africana. Vol. 2, 1954, ISSN  0078-8554 , pp. 1-187.
  10. ↑ Christopher Barry Cox: The problematic Permian reptile Eunotosaurus. In: Bulletin of the British Museum (Natural History). Geology. Vol. 18, No. 5, 1969, ISSN  0007-1471 , pp. 167-196, digitized .
  11. ↑ Michel Laurin, Robert R. Reisz: A reevaluation of early amniote phylogeny. In: Zoological Journal of the Linnean Society. Vol. 113, No. 2, 1995, ISSN  0024-4082 , pp. 165-223, doi : 10.1111 / j.1096-3642.1995.tb00932.x .
  12. ↑ Sean P. Modesto: Eunotosaurus africanus and the Gondwanan ancestry of anapsid reptiles. In: Palaeontologia Africana. Vol. 36, 2000, pp. 15-20.
  13. ↑ Juan Carlos Cisneros, Bruce S. Rubidge, Richard Mason: Analysis of millerettid parareptile relationships in the light of new material of Broomia perplexa Watson, 1914, from the Permian of South Africa. In: Journal of Systematic Palaeontology. Vol. 6, No. 4, 2008, ISSN  1477-2019 , pp. 453-462, doi : 10.1017 / S147720190800254X .
  14. ↑ a b Tyler R. Lyson, Gabe S. Bever, Bhart-Anjan S. Bhullar, Walter G. Joyce, Jacques A. Gauthier: Transitional fossils and the origin of turtles. In: Proceedings of the Royal Society. Series B: Biological Sciences. Vol. 6, No. 6, 2010, ISSN  0080-4649 , pp. 830-833, doi : 10.1098 / rsbl.2010.0371 .
  15. ↑ Lyson 2013, pp. 5-6.
  16. ^ Tyler R. Lyson, Emma R. Schachner, Jennifer Botha-Brink, Torsten M. Scheyer, Markus Lambertz, GS Bever, Bruce Rubidge, Kevin de Queiroz (2014): Origin of the unique ventilatory apparatus of turtles , Nature Communications 5: 5211, DOI: 10.1038 / ncomms6211