Eunotosaurus
Replica of a fossil of Eunotosaurus africanus with recognizable widened rib cage
- Beaufort Group ( South Africa)
- Eunotosaurus africanus Seeley, 1892
Eunotosaurus is a genus of para reptiles from the Middle Permian ( 265.1 to 259.9 mya ) of the Karoo Supergroup of South Africa. Their representatives were characterized by broadened and numerically reduced costal arches and a roundish body. Originally, the genus was considered missing link between the turtles and their prehistoric ancestors. Many fossils exhibited a semi-rigid, tortoise -like chest, probably necessitating locomotion on the type of tortoises.
The ribs were broad and flat and touched, so that they were comparable wide plates the carapace of a turtle. In addition, the number, size and structure of the vertebrae were largely identical to those of many turtle species. Despite these many similarities to the turtles Eunotosaurus had a skull, which shared many characteristics with the skulls of primitive Anapsiden. Because of these properties Eunotosaurus will be provided to Para reptiles in many classifications and not considered a direct ancestor of turtles. According to this view represent the widened ribs and the spine like a case of convergent evolution dar.
Fossil material
More than a century after the first description was known with less than a dozen copies and with little überliefertem material from the skull Eunotosaurus. Despite the fragmentary tradition it was described in detail. Two additional specimens were excavated and described in 1999 in the Karoo Supergroup. These fossils are now on display at the Bernard Price Institute for Palaeontological Research, Johannesburg and at the National Museum of Bloemfontein. Although relatively rare, Eunotosaurus is often enough to be used as a marker biostratigrafisches in the Karoo supergroup. Fossils can be found within the Beaufort Group in the upper Tapinocephalus assemblage zone and the overlying Pristerognathus assemblage zone.
Taxonomy and systematics
Eunotosaurus was described in 1892, but in 1914 an ancestor of Chelonia, so the order of the turtle, is proposed. The English zoologist DMS Watson claimed that Eunotosaurus a mosaic form between the Captorhinidae had, which were then still called Cotylosaurier. He compared Eunotosaurus with " Archichelone ", a hypothetical ancestors of the Chelonia, where he remarked that his ribs intermediate to both where the turtles as to which were also other tetrapods. Watsons " Archichelone " had a pelvic girdle that was pushed back to the spinal column and placed under the tank. However, to show the fossils of Eunotosaurus that his pelvis in a normal position for tetrapods over the ribs and not between them, as in the modern turtles was.
Until the late forties Eunotosaurus was commonly called ancestor of turtles. The American paleontologist Alfred Sherwood Romer argued in 1956 in his book Osteology of the Reptiles basis of the evidence available, Eunotosaurus can not be called to the Chelonia. Instead, he arranged to Eunotosaurus the Anapsiden, but within which he occupied an insecure position.
Eunotosaurus in 1954 of his own family, the Eunotosauridae assigned. However, this classification is no longer used today. In 1969 he was placed in a subordination of Anapsiden, the Captorhinomorpha, which is now located within the clade of Eureptilia. In 2000 Eunotosaurus was placed in the clade of reptiles Para, where it occupies an independent position of the turtles and the Cotylosauriern. A phylogenetic analysis of the para reptiles from 2008 found that Eunotosaurus was a sister taxon of Milleretta and should therefore be put into the family of Millerettidae.
Eunotosaurus has been included in a phylogenetic analysis from the year 2010, which asked for the origin of turtles. In recent times, turtles are considered on the basis of genetic and phylogenetic insights than Diapsiden and therefore used as a closer with the lizards, snakes, crocodiles and birds than with the para reptiles or any other Anapsiden. However, the resulting phylogenetic tree placed the turtles with the inclusion of Eunotosaurus and the late Triassic Proganochelys, a stem group representative of the turtles, in a position similar to the original classification of the turtles as Anapsiden. The study claims that Eunotosaurus derived characteristics of the ribs and vertebrae with the earliest turtles shared what made him into a mosaic form. In the study, a number of features are identified that make it possible to combine Eunotosaurus in a true clade with the turtles. These common features included broad T-shaped ribs, ten extended dorsal vertebrae, cranial Tuberkele (small bumps on the surface of the skull ) and a wide body. The clade of Eunotosaurus and the turtles was called " Pan - Testudines ". More advanced representatives of Testudines, such as early Turtles Odontochelys already have a plastron.
This thesis has been emphasized by a study from 2013, which analyzed the osteological fine structure of the bone, with the ontogeny of extant turtles and compared statistically weighted. She came to the conclusion that Eunotosaurus and the turtles form a monophyletic group and are within the Parareptilia. Thus, both studies disagreed and molecular genetic studies which identify the turtles as the sister group of archosaurs.