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The Sirenia, commonly referred to as sea cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The extant Sirenia comprise two distinct families: Dugongidae and Trichechidae with a total of four species. The Protosirenidae and Prorastomidae families are extinct. Sirenians are classified in the clade Paenungulata, alongside the elephants and the hyraxes, and evolved in the Eocene 50 million years ago (mya). The Dugongidae diverged from the Trichechidae in the late Eocene or early Oligocene.
Xenarthra is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Extinct xenarthrans include the glyptodonts, pampatheres and ground sloths. Xenarthrans originated in South America during the late Paleocene about 60 million years ago. They evolved and diversified extensively in South America during the continent's long period of isolation in the early to mid Cenozoic Era. They spread to the Antilles by the early Miocene and, starting about 3 Mya, spread to Central and North America as part of the Great American Interchange. Nearly all of the formerly abundant megafaunal xenarthrans became extinct at the end of the Pleistocene.
The Desmostylia are an extinct order of aquatic mammals that existed from the early Oligocene (Rupelian) to the late Miocene (Tortonian).
Osteosclerosis is a disorder that is characterized by abnormal hardening of bone and an elevation in bone density. It may predominantly affect the medullary portion and/or cortex of bone. Plain radiographs are a valuable tool for detecting and classifying osteosclerotic disorders. It can manifest in localized or generalized osteosclerosis. Localized osteosclerosis can be caused by Legg–Calvé–Perthes disease, sickle-cell disease and osteoarthritis among others. Osteosclerosis can be classified in accordance with the causative factor into acquired and hereditary.
Megatheriidae is a family of extinct ground sloths that lived from approximately 23 mya—11,000 years ago.
Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their lives hanging upside down in the trees of the tropical rainforests of South America and Central America. Sloths are considered to be most closely related to anteaters, together making up the xenarthran order Pilosa.
Mesosaurus is an extinct genus of reptile from the Early Permian of southern Africa and South America. Along with it, the genera Brazilosaurus and Stereosternum, it is a member of the family Mesosauridae and the order Mesosauria. Mesosaurus was long thought to have been one of the first marine reptiles, although new data suggests that at least those of Uruguay inhabited a hypersaline water body, rather than a typical marine environment. In any case, it had many adaptations to a fully aquatic lifestyle. It is usually considered to have been anapsid, although Friedrich von Huene considered it to be a synapsid, and this hypothesis has been revived recently.
Pistosaurus is an extinct genus of aquatic sauropterygian reptile closely related to plesiosaurs. Fossils have been found in France and Germany, and date to the Middle Triassic. It contains a single species, Pistosaurus longaevus. Pistosaurus is known as the oldest "subaquatic flying" reptile on earth.
Desmostylus is an extinct genus of herbivorous mammal of the family Desmostylidae living from the Chattian stage of the Late Oligocene subepoch through the Late Miocene subepoch and in existence for approximately 21.2 million years.
Sirenia is the order of placental mammals which comprises modern "sea cows" and their extinct relatives. They are the only extant herbivorous marine mammals and the only group of herbivorous mammals to have become completely aquatic. Sirenians are thought to have a 50-million-year-old fossil record. They attained modest diversity during the Oligocene and Miocene, but have since declined as a result of climatic cooling, oceanographic changes, and human interference. Two genera and four species are extant: Trichechus, which includes the three species of manatee that live along the Atlantic coasts and in rivers and coastlines of the Americas and western Africa, and Dugong, which is found in the Indian and Pacific oceans.
Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls, various groups of dinosaurs, phytosaurs, aetosaurs, placodonts, and hupehsuchians.
Dyrosauridae is a family of extinct neosuchian crocodyliforms that lived from the Late Cretaceous (Maastrichtian) to the Eocene. Dyrosaurid fossils are globally distributed, having been found in Africa, Asia, Europe, North America and South America. Over a dozen species are currently known, varying greatly in overall size and cranial shape. A majority were aquatic, some terrestrial and others fully marine, with species inhabiting both freshwater and marine environments. Ocean-dwelling dyrosaurids were among the few marine reptiles to survive the Cretaceous–Paleogene extinction event.
Thalassocnus is an extinct genus of semiaquatic ground sloths from the Miocene and Pliocene of the Pacific South American coast. It is monotypic within the subfamily Thalassocninae. The five species—T. antiquus, T. natans, T. littoralis, T. carolomartini, and T. yuacensis—represent a chronospecies, a population gradually adapting to marine life in one direct lineage. They are the only known aquatic sloths, but they may have also been adapted to a terrestrial lifestyle. They have been found in the Pisco Formation of Peru, the Tafna Formation of Argentina, and the Bahía Inglesa, Coquimbo, and Horcón formations of Chile. Thalassocninae has been placed in both the families Megatheriidae and Nothrotheriidae.
Stereosternum tumidum 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.
Palaeopleurosaurus is an extinct genus of diapsid reptiles belonging to the group Sphenodontia.
Pachyostosis is a non-pathological condition in vertebrate animals in which the bones experience a thickening, generally caused by extra layers of lamellar bone. It often occurs together with bone densification (osteosclerosis), reducing inner cavities. This joint occurrence is called pachyosteosclerosis. However, especially in the older literature, "pachyostosis" is often used loosely, referring to all osseous specializations characterized by an increase in bone compactness and/or volume. It occurs in both terrestrial and, especially, aquatic or semi-aquatic vertebrates.
Vivian de Buffrénil is a French histologist and paleobiologist who has been working at the Muséum National d'Histoire Naturelle in Paris since 1982. His doctorate (1980) and his doctorat d'état (1990), a diploma now replaced by the habilitation, were supervised by Armand de Ricqlès. His main fields of interest include basic histological descriptions, growth dynamics as recorded in bone growth marks, and adaptation of the tetrapod skeleton to a secondarily aquatic lifestyle. He is also interested in life history and population dynamics of exploited or threatened reptile taxa, especially among Varanidae and Crocodilia. He has published at least 92 papers, including 76 research papers, 10 reports on exploited or threatened species, and six popular papers.
Nothrotheriidae is a family of extinct ground sloths that lived from approximately 17.5 mya—10,000 years ago, existing for approximately 17.49 million years. Previously placed within the tribe Nothrotheriini or subfamily Nothrotheriinae within Megatheriidae, they are now usually placed in their own family, Nothrotheriidae. Nothrotheriids appeared in the Burdigalian, some 19.8 million years ago, in South America. The group includes the comparatively slightly built Nothrotheriops, which reached a length of about 2.75 metres (9.0 ft). While nothrotheriids were small compared to some of their megatheriid relatives, their claws provided an effective defense against predators, like those of larger anteaters today.
Eionaletherium is an extinct genus of ground sloth from the Late Miocene coasts of Venezuela containing one species: E. tanycnemius.
Pachyophis is an extinct genus of Simoliophiidae snakes that were extant during the Cenomanian stage of the Late Cretaceous period. More specifically, it was found to be from the Cenomanian Age about 93.9-100.5 million years ago in the suburb area of Bileca, Herzegovina.
References
- ↑ Domning, D. P. and V. Debuffrenil (1991). Hydrostasis in the Sirenia - Quantitative Data and Functional Interpretations. Marine Mammal Science 7(4): 331-368.
- 1 2 Houssaye, A. (2009). "Pachyostosis" in aquatic amniotes: a review. Integrative Zoology 4(4): 325-340.
- ↑ de Buffrenil, V., A. Canoville, R. D'Anastasio and D. P. Domning (2010). Evolution of Sirenian Pachyosteosclerosis, a Model-case for the Study of Bone Structure in Aquatic Tetrapods. Journal of Mammalian Evolution 17(2): 101-120.
- ↑ Amson, E., C. de Muizon, M. Laurin, C. Argot and V. de Buffrenil (2014). Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru. Proceedings of the Royal Society B-Biological Sciences 281.