Stereosternum
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Stereosternum Temporal range: Cisuralian ~299–270.6 Ma |
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| Fossil in Naturmuseum Senckenberg | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | †Parareptilia |
| Order: | †Mesosauria |
| Family: | †Mesosauridae |
| Genus: |
†Stereosternum Cope, 1885 |
| Type species | |
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†Stereosternum tumidum Cope, 1885 |
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| Synonyms | |
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Mesosaurus tumidum (Cope, 1885) |
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Mesosaurus tumidum (Cope, 1885)
Stereosternum tumidum (meaning "rigid chest") (Stereos, Greek: “solid, firm”; Sternon, Greek: “chest, breastbone”) is an extinct genus of mesosaur marine reptile from the Early Permian of Brazil and also the Great Karoo Basin of South Africa. The taxon mesosaur is a monophyletic group containing Brazilosaurus sanpauloensis and Mesosaurus tenuidens.
For most of the 20th century, information of Stereosternum was reported as Mesosaurus. Unlike previous interpretations of Mesosaurs as filter feeding animals, later studies have shown that these animals were very much active aquatic predators.Stereosternum and Mesosaurus are the oldest reported reptile species to have had a range spanning two present-day continents, then joined as Gondwana and they represent the first record of reptile species shared by both Southern Africa and South America.
Stereosternum was about 80 centimetres (2.6 ft) in length as an adult, and some of the juveniles to get to sizes of 68 centimetres (2.23 ft) in length. Many of the ribs and the Haemal arches are thickened with bone or have a pachyostotic characteristic, which would have helped the animal to be able to dive deep in the water as a counteracting force against buoyancy.
One of the more unusual and unique characteristics about the anatomy of Stereosternum is the thickness of the dorsal ribs, which continues to increase in size until the fifth rib, which measures 47.5 millimetres (1.87 in) in width. The ribs are noted here to be holocephalous. With the pachyostosis of the postcrania elements and restricted movement at the appendicular joints, it has been suggested that mesosaurs could not have walked on land, but may have been able to push themselves across terrestrial substrates. When studying the histology of the ribs of Stereosternum and Mesosaurus, the kind of pachyostosis of these two species has, is very much characterized by hyperostosis
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