Mesosaurus brasiliensis

Réptil fóssil de cerca de um metro de comprimento, corpo alongado provido de grande cauda, hábito aquático, com longos dedos que indicam que eram dotados de membranas natatórias.    Apresentava longos e finos dentes que não se destinavam a devorar peixes, somente um peixe minúsculo poderia atravessar garganta tão estreita. Provavelmente alimentava-se de crustáceos que se fossilizaram nas mesmas rochas. Seus fósseis são assinalados nas bacias do Karroo (África) e do Paraná, nesta ultima na Formação Irati. Por este motivo, este réptil fóssil foi utilizado como argumento para a hipótese da união dos continentes Sul Americano e Africano no Permiano Superior (Gondwana) ocorrendo em camadas com cerca de 245 milhões de anos. O primeiro espécime foi descrito no início do século por Mc Gregor em 1908.    O Mesosaurus brasiliensis foi por muito tempo confundido com o Stereosternum tumidum, mas a similaridade é apenas superficial, pois eles diferem no formato e tamanho da cabeça, número de vértebras e caracteres dentários, sendo sua maior diferença o tamanho do arco dorsal. Outro réptil de grande semelhança foi descrito por Shikama & Ozaki (1966, apud Oelofsen & Araújo 1983), esta terceira forma foi designada de Brazilosaurus sanpauloensis.     Os fósseis mais antigos representantes da espécie Mesosaurus brasiliensis datam do Carbonífero Superior, cerca de 290 milhões de anos. Segundo Oelofsen & Araújo(1983), Mesosaurus brasiliensis, Stereosternum tumidum e Brazilosaurus sanpauloensis foram contemporâneos no primitivo Mar Irati, o primeiro adaptado a regiões centrais mais profundas da bacia e os dois últimos às porções marginais mais rasas. (Heracto Kuzycz Assunção; Mário Sérgio de Melo)    Referências Bibliográficas: PETRI, Setembrino; FÚLFARO, Vicente José. Geologia do Brasil. 1ª ed. São Paulo: Editora da Universidade de São Paulo, 1988. OELOFSEN, B. & ARAÚJO, D. C. Palaeoecological Implications of the Distribution of Mesosaurid Reptiles in the Permian Irati Sea (Paraná Basin), South America. In: Revista Brasileira de Geociências. N.º 13 pg. 1-6 .1983. Mesosaurus Learn more about this article Mesosaurus (meaning "middle lizard") is an extinct genus of anapsid reptile from the Early Permian of southern Africa and South America. Along with the genus Stereosternum, it is a member of the family Mesosauridae and the order Mesosauria. Mesosaurus was one of the first marine reptiles, and had many adaptations to a fully aquatic lifestyle. Description Mesosaurus fossil at the Geological Museum in Copenhagen   Mesosaurus had a long skull that was larger than that of Stereosternum and had longer teeth. The teeth are angled outwards, especially those at the tips of the jaws.[1] The bones of the postcranial skeleton are thick, having undergone pachyostosis. Mesosaurus is unusual among reptiles in that it possesses a cleithrum. A cleithrum is a type of dermal bone that overlies the scapula, and is usually found in more primitive bony fish and tetrapods. The head of the interclavicle of Mesosaurus is triangular, unlike those of other early reptiles, which are diamond-shaped.[2] Palaeobiology Life restoration of Mesosaurus. Mesosaurus was one of the first reptiles to return to the water after early tetrapods came to land in the Late Devonian. It was around 1 metre (3.3 ft) in length, with webbed feet, a streamlined body, and a long tail that may have supported a fin. It probably propelled itself through the water with its long hind legs and flexible tail. Its body was also flexible and could easily move sideways, but it had heavily thickened ribs, which would have prevented it from twisting its body.[3] Mesosaurus had a small skull with long jaws. The nostrils were located at the top, allowing the creature to breathe with only the upper side of its head breaking the surface, in a similar manner to a modern crocodile. The teeth were originally thought to have been straining devices for the filter feeding of planktonic organisms.[3] However, this idea was based on the assumption that the teeth of Mesosaurus were numerous and close together in the jaws. Newly examined remains of Mesosaurus show that it had fewer teeth, and that the dentition was suitable for catching small nektonic prey such as fish.[1] Early reconstruction of the skeleton of M. brasiliensis showing many small teeth in the jaws (MacGregor, 1908).[4]   The pachyostosis seen in the bones of Mesosaurus may have enabled it to reach neutral buoyancy in the upper few meters of the water column. The additional weight may have stabilized the animal at the water's surface. Alternatively, it could have given Mesosaurus greater momentum when gliding underwater. While many features suggest a wholly aquatic lifestyle, Mesosaurus may have been able to move onto land for short periods of time. The elbows and ankles had restricted movement, making walking impossible. It is more likely that if Mesosaurus moved onto land, it would push itself forward in a similar way to living female sea turtles when nesting on beaches.[2] Distribution Location of Mesosaurus remains shown in blue. Mesosaurus was significant in providing evidence for the theory of continental drift, because its remains were found in southern Africa and eastern South America, two far away places. As Mesosaurus was a freshwater animal, and therefore could not have crossed the Atlantic Ocean, this distribution indicated that the two continents used to be joined together. References Parker, Steve. Dinosaurus: the complete guide to dinosaurs. Firefly Books Inc, 2003. Pg. 90 ^ a b Modesto, S.P. (2006). "The cranial skeleton of the Early Permian aquatic reptile Mesosaurus tenuidens: implications for relationships and palaeobiology". Zoological Journal of the Linnean Society 146 (3): 345–368. doi:10.1111/j.1096-3642.2006.00205.x. ^ a b Modesto, S.P. (2010). "The postcranial skeleton of the aquatic parareptile Mesosaurus tenuidens from the Gondwanan Permian". Journal of Vertebrate Paleontology 30 (5): 1378–1395. doi:10.1080/02724634.2010.501443. ^ a b Palmer, D., ed (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 65. ISBN 1-84028-152-9. ^ MacGregor, J.H. (1908) Mesosaurus brasiliensis nov. sp. IN: White, I.C. (1908) Commission for Studies on Brazilian Coal Mines - Final Report; (Bilingual report, Portuguese & English), Imprensa Nacional, Rio de Janeiro, Brazil, 617 p.: Part II, pp. 301-336. Carroll, R. L. (1988). K. Behrensmeyer/K. Behrensmeyer/J. Alroy. ed. Vertebrate Paleontology and Evolution. W.H. Freeman and Company. Sepkoski, J. J. (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology 363: 1–560. Modesto, Sean Patrick (March 2006). "The cranial skeleton of the Early Permian aquatic reptile Mesosaurus tenuidens: implications for relationships and palaeobiology" ([dead link]). Zoological Journal of the Linnean Society (Blackwell Publishing) 146 (3): 345–368. doi:10.1111/j.1096-3642.2006.00205.x. http://www.ingentaconnect.com/bsc/zoj/2006/00000146/00000003/art00002. Margulis, Lynn; Clifford Matthews and Aaron Haselton. Environmental Evolution: Effects of the Origin and Evolution of Life on Planet Earth. Contributor Clifford Matthews, Aaron Haselton (2nd ed.). pp. 338. ISBN 0262631970, 9780262631976. LeGrand, Homer Eugene (1988). Drifting Continents and Shifting Theories: The Modern Revolution in Geology and Scientific Change (illustrated ed.). Cambridge University Press. pp. 313. ISBN 0521311055, 9780521311052.