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Stereosternum AI simulator
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Hub AI
Stereosternum AI simulator
(@Stereosternum_simulator)
Stereosternum
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 of the periosteal cortex, increased bone density, which was due to the bone becoming more compact, the absence of free medullary cavity and the remnants of calcified cartilage matrix. This kind of pachyostosis is called “pachyosteosclerosis”.
Another characteristic of Stereosternum is the length of the tail and the amount of caudal vertebrae. As counted by Osborn, there are about 60-64 caudal vertebrae, which is very predictable for an aquatic predator and these adaptations helped individuals to push and swim gracefully in the water. There are also about 34 presacral vertebrae, with 11 cervical and 23 thoracic-lumbar vertebrae. The presence of accessory articulations, like the zygantra and the zygosphenes, are there to supposedly to have dampened the twisting movements of the vertebral column. On the axial pleurocentrum, there is a process that is distinctly analogous to the odontoid structure found in mammals. This probably correlates with the presence of a long skull on a long neck that is found with Stereosternum and this process could have helped to minimize the stresses and movement between the skull and the neck.
Another characteristic of Mesosaurs was that they probably had webbing of skin on both their feet and their hands, analogous to that of a duck's foot. This paddle would have easily initiated movement within the water to swim and hunt for food. The phalangeal formula is noted to be 2-3-4-5-3 for the manus, giving them a paddle-like form to it. The pedes are described to have a 2-3-4-5-5 phalangeal formula. In Stereosternum, the humerus has well-developed proximal muscular processes, and the scapulocoracoid is early fused and the Iliac blade has a rounded dorsal margin, and the pubic foramen is early closed. The most distal end of the humerus is shown to be slightly less than 35 per cent of the total length of the humerus.
Many of the modifications of the bones within the skull seem to reduce drag and help propel the animal through an aqueous environment while swimming and feeding. The skull of Stereosternum is equal to the length of the neck and the anterior half of the skull is not as elongated as in Mesosaurus and this is due to the extension of the premaxilla, which dominates the snout. The position of the external naris is about halfway along the skull. The presence of the lower temporal fenestra is absent in these species. There are a total of 12 within the premaxilla and then 14 teeth in the maxilla. The teeth seem to decrease in size from the frontal to the back part in the skull. The tongue-like posterolateral process, however, angles more posteriorly than laterally. The presence of such a process is a mesosaurid apomorphy, distinguishing this animal from other closely related clades.[which?] The dentary is a very slender and long bone, holding up to about 45 teeth. There is also the presence of palatal teeth that are much smaller in size than the marginal teeth, and also being sharp, straight and with homodont structures.
Stereosternum had small teeth compared to Mesosaurus tenuidens, but it had larger teeth compared to Brazilosaurus sanpauloensis. The teeth of Stereosternum are 6 times the length of Brazilosaurus sanpauloensis, but has smaller teeth compared to Mesosaurus tenuidens, which has teeth that are 12 times longer than Brazilosaurus. These differentiations with tooth length possibly correspond to different ecological niches being filled. The way the teeth are positioned inside the jaw is a unique feature of this species; with the teeth more apically being inserted within the alveolar bone and the fully developed teeth show dental ankylosis. From looking at the teeth and how they are positioned, it seems that the replacement pulse occurred anteroposteriorly in Stereosternum, in a quasi-alternate polyphyodont pattern. Going more distally, the teeth seem to have periodontal ligaments connecting the teeth to the alveolar bone and then even more distally the tooth is connected by the anchorage trabeculae,[clarification needed] which is composed of cementum and probably the alveolar bone. The anchorage trabeculae structure acts as an additional structure to hold the teeth in place. Within the adult teeth, the pulp cavity is enclosed within on itself,[clarification needed] and inside those pulp cavities are canals that connect the tooth to the alveolar bone. Those canals were the spaces that were filled by blood vessels and nerves, which supplemented the growth of the tooth and gave the tooth some sensory abilities. During the early part of the development of the teeth, the roots would have been open, and the only connection that would have been facilitated would have been the cementum between the tooth and the alveolar bone, the periodontal ligament and the cementum made anchorage trabeculae would have mediated this connection. This complex, called the tripartite periodontium, during the life of Stereosternum, would have acted as a mechanism for keeping the teeth within the jaw, working against the lateral forces that could easily pull teeth out of the socket, given the size of these teeth. The teeth also have multiple different types of dentine and there are different orientations of the dentine tubules along the tooth, including mixed composition in the dentary wall. These adaptations helped to increase the tooth's resistance to tension forces, especially the lateral forces. The enamel-dentine junction of Stereosternum, as in other mesosaurs, is smooth.
Stereosternum
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 of the periosteal cortex, increased bone density, which was due to the bone becoming more compact, the absence of free medullary cavity and the remnants of calcified cartilage matrix. This kind of pachyostosis is called “pachyosteosclerosis”.
Another characteristic of Stereosternum is the length of the tail and the amount of caudal vertebrae. As counted by Osborn, there are about 60-64 caudal vertebrae, which is very predictable for an aquatic predator and these adaptations helped individuals to push and swim gracefully in the water. There are also about 34 presacral vertebrae, with 11 cervical and 23 thoracic-lumbar vertebrae. The presence of accessory articulations, like the zygantra and the zygosphenes, are there to supposedly to have dampened the twisting movements of the vertebral column. On the axial pleurocentrum, there is a process that is distinctly analogous to the odontoid structure found in mammals. This probably correlates with the presence of a long skull on a long neck that is found with Stereosternum and this process could have helped to minimize the stresses and movement between the skull and the neck.
Another characteristic of Mesosaurs was that they probably had webbing of skin on both their feet and their hands, analogous to that of a duck's foot. This paddle would have easily initiated movement within the water to swim and hunt for food. The phalangeal formula is noted to be 2-3-4-5-3 for the manus, giving them a paddle-like form to it. The pedes are described to have a 2-3-4-5-5 phalangeal formula. In Stereosternum, the humerus has well-developed proximal muscular processes, and the scapulocoracoid is early fused and the Iliac blade has a rounded dorsal margin, and the pubic foramen is early closed. The most distal end of the humerus is shown to be slightly less than 35 per cent of the total length of the humerus.
Many of the modifications of the bones within the skull seem to reduce drag and help propel the animal through an aqueous environment while swimming and feeding. The skull of Stereosternum is equal to the length of the neck and the anterior half of the skull is not as elongated as in Mesosaurus and this is due to the extension of the premaxilla, which dominates the snout. The position of the external naris is about halfway along the skull. The presence of the lower temporal fenestra is absent in these species. There are a total of 12 within the premaxilla and then 14 teeth in the maxilla. The teeth seem to decrease in size from the frontal to the back part in the skull. The tongue-like posterolateral process, however, angles more posteriorly than laterally. The presence of such a process is a mesosaurid apomorphy, distinguishing this animal from other closely related clades.[which?] The dentary is a very slender and long bone, holding up to about 45 teeth. There is also the presence of palatal teeth that are much smaller in size than the marginal teeth, and also being sharp, straight and with homodont structures.
Stereosternum had small teeth compared to Mesosaurus tenuidens, but it had larger teeth compared to Brazilosaurus sanpauloensis. The teeth of Stereosternum are 6 times the length of Brazilosaurus sanpauloensis, but has smaller teeth compared to Mesosaurus tenuidens, which has teeth that are 12 times longer than Brazilosaurus. These differentiations with tooth length possibly correspond to different ecological niches being filled. The way the teeth are positioned inside the jaw is a unique feature of this species; with the teeth more apically being inserted within the alveolar bone and the fully developed teeth show dental ankylosis. From looking at the teeth and how they are positioned, it seems that the replacement pulse occurred anteroposteriorly in Stereosternum, in a quasi-alternate polyphyodont pattern. Going more distally, the teeth seem to have periodontal ligaments connecting the teeth to the alveolar bone and then even more distally the tooth is connected by the anchorage trabeculae,[clarification needed] which is composed of cementum and probably the alveolar bone. The anchorage trabeculae structure acts as an additional structure to hold the teeth in place. Within the adult teeth, the pulp cavity is enclosed within on itself,[clarification needed] and inside those pulp cavities are canals that connect the tooth to the alveolar bone. Those canals were the spaces that were filled by blood vessels and nerves, which supplemented the growth of the tooth and gave the tooth some sensory abilities. During the early part of the development of the teeth, the roots would have been open, and the only connection that would have been facilitated would have been the cementum between the tooth and the alveolar bone, the periodontal ligament and the cementum made anchorage trabeculae would have mediated this connection. This complex, called the tripartite periodontium, during the life of Stereosternum, would have acted as a mechanism for keeping the teeth within the jaw, working against the lateral forces that could easily pull teeth out of the socket, given the size of these teeth. The teeth also have multiple different types of dentine and there are different orientations of the dentine tubules along the tooth, including mixed composition in the dentary wall. These adaptations helped to increase the tooth's resistance to tension forces, especially the lateral forces. The enamel-dentine junction of Stereosternum, as in other mesosaurs, is smooth.
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