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Evolution Of Cetaceans
The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. Cetaceans are fully aquatic marine mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya. Cetaceans are thought to have evolved during the Eocene (56-34 mya), the second epoch of the present-extending Cenozoic Era. Molecular and morphological analyses suggest Cetacea share a relatively recent closest common ancestor with hippopotami and that they are sister groups. Being mammals, they surface to breathe air; they have 5 finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retain many skeletal features from their terrestrial ancestors.Thewissen, J. G. M., L. N. Cooper, J. C. George, and S. Bajpai. 2009. From land to water: the origin of whales, dolphins, and porpoises. Evolu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cetaceans
Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver. While the majority of cetaceans live in marine environments, a small number exclusively reside in brackish water or fresh water. Having a cosmopolitan distribution, they can be found in some rivers and all of Earth's oceans, and many species inhabit vast ranges where they migrate with the changing of the seasons. Cetaceans are famous for their high intelligence and complex social behaviour as well as for the enormous size of some of the group's members, such as the blue whale which reaches a maximum confirmed length of 29.9 meters (98 feet) and a weight of 173 tonnes (190 short ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mammalodontidae
Mammalodontidae is a family of extinct whales known from the Oligocene of Australia and New Zealand. There are currently two genera in this family: ''Janjucetus'' and ''Mammalodon''. After a new cladistic analysis by Fitzgerald (2010), ''Janjucetus'' was transferred into Mammalodontidae, thereby making Janjucetidae a junior synonym of Mammalodontidae. Analysing the jaw morphology of the toothed mysticetes, found eight mandibular characters unique to the members of Mammalodontidae: * the mandibular symphysis is short, has a rugose joint surface, but lacks a symphyseal groove. In archaeocetes the symphysis is long. In modern mysticetes, in contrast, the symphysis is very small, its joint surfaces are smooth, and there is a groove on the interior side of the mandible that accommodates the symphyseal ligament which enables them to open their mouth wide. * the external foramina on the mandible are relatively large (smaller or absent in later mysticetes) * the postcanines sit in a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protocetidae
Protocetidae, the protocetids, form a diverse and heterogeneous group of extinct cetaceans known from Asia, Europe, Africa, South America, and North America. Description There were many genera, and some of these are very well known (e.g., '' Rodhocetus''). Known protocetids had large fore- and hindlimbs that could support the body on land, and it is likely that they lived amphibiously: in the sea and on land. It is unclear at present whether protocetids had flukes (the horizontal tail fin of modern cetaceans). However, what is clear is that they are adapted even further to an aquatic life-style. In '' Rodhocetus'', for example, the sacrum – a bone that in land-mammals is a fusion of five vertebrae that connects the pelvis with the rest of the vertebral column – was divided into loose vertebrae. However, the pelvis retain a sacroiliac joint. Furthermore, the nasal openings are now halfway up the snout; a first step towards the telescoped condition in modern whales. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rodhocetus
''Rodhocetus'' (from ''Rodho'', the geological anticline at the type locality, and ''cetus'', Latin for whale) is an extinct genus of protocetid early whale known from the Lutetian of Pakistan. The best-known protocetid, ''Rodhocetus'' is known from two partial skeletons that taken together give a complete image of an Eocene whale that had short limbs with long hands and feet that were probably webbed and a sacrum that was immobile with four partially fused sacral vertebrae. It is one of several extinct whale genera that possess land mammal characteristics, thus demonstrating the evolutionary transition from land to sea. Description left, Size of ''Rodhocetus'' relative to a human. ''Rodhocetus'' was a small whale measuring long. Throughout the 1990s, a close relationship between cetaceans and mesonychids, an extinct group of cursorial, wolf-like ungulates, was generally accepted based on morphological analyses. In the late 1990s, however, cladistic analyses based on molecul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Remingtonocetus
''Remingtonocetus'' is an extinct genus of early cetacean freshwater aquatic mammals of the family Remingtonocetidae endemic to the coastline of the ancient Tethys Ocean during the Eocene. It was named after naturalist Remington Kellogg. History of discovery named '' Protocetus harudiensis'' based on a partial skeleton, the type specimen found in the Lutetian shallow subtidal mudstone in the Harudi Formation, India. renamed it ''Remingtononocetus harudiensis'' due to morphological differences from protocetus. ''Remingtonocetus domandaensis'' was named by based on a partial skeleton found in a Lutetian coastal shale in the Domanda Formation of Pakistan. ''Remingtonocetus'' is larger, has a broader rostrum, and longer premolars than '' Andrewsiphius''. It is smaller than, has more gracile premolars and molars than ''Dalanistes''. ''R. harudiensis'' differs from ''R. domandaensis'' in molar morphology. Description ''Remingtonocetus'' was a small cetacean with ''R. harudien ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Remingtonocetidae
Remingtonocetidae is a diverse family of early aquatic mammals of the order Cetacea. The family is named after paleocetologist Remington Kellogg. Description Remingtonocetids have long and narrow skulls with the external nare openings located on the front of the skull. Their frontal shields are narrow and their orbits small. Their mouth has a convex palate and an incompletely fused mandibular symphysis. The dental formula is . The anterior teeth are flattened mediolaterally, making them appear shark-like. In the postcranial skeleton, the cervical vertebrae are relatively long and the sacrum is composed of four vertebrae of which at least three are fused. The acetabular notch is narrow or closed and on the femoral head the fovea is absent. Cranial fossils are common but dental remains are rare. The postcrania morphology is based entirely on a single specimen of '' Kutchicetus'' which was small and had a long and muscular back and tail. Perhaps remintonocetids swam lik ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kutchicetus
''Kutchicetus'' is an extinct genus of early whale of the family Remingtonocetidae that lived during Early-Middle Eocene (Lutetian and Ypresian) in what is now the coastal border of Pakistan and India (, paleocoordinates ). It is closely related to ''Andrewsiphius'' with which it was synonymized by . proposed a new clade, Andrewsiphiinae, for the two species. Later authors, however, still accept both as separate genera. ''Kutchicetus'' is smaller than other remingtonocetids, and probably is the smallest Eocene cetacean. With its extremely narrow snout, it resembles ''Remingtonocetus'' and ''Dalanistes'', but its strong tail distinguishes it from both ''Remingtonocetus'' and ''Andrewsiphius''. Its limbs were short. ''Kutchicetus''' vertebral formula is 7, 15, 8, 4, 20–25. Its four fused sacral vertebrae were probably articulated to the hip bone and the numerous tail vertebrae were robust and elongated in contrast to its short and relatively gracile limb bones. This mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ambulocetidae
Ambulocetidae is a family of early cetaceans from Pakistan. The genus '' Ambulocetus'', after which the family is named, is by far the most complete and well-known ambulocetid genus due to the excavation of an 80% complete specimen of ''Ambulocetus natans''. The other two genera in the family, ''Gandakasia'' and '' Himalayacetus'', are known only from teeth and mandibular fragments. Retaining large hindlimbs, it was once thought that they could walk on land—indeed, their name means "walking whales"—, but recent research suggests they may have been fully aquatic like modern cetaceans. Description The most basal of marine cetaceans, ambulocetids lived in shallow near-shore environments such as estuaries and bays, but were still dependent on fresh water during some stage of their life. Some of the characteristics related to sound transmission found in the lower jaws of modern whales that were absent in pakicetids are present in ambulocetids. They probably swam by paddling their ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ambulocetus
''Ambulocetus'' (Latin ''ambulare'' "to walk" + ''cetus'' "whale") is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene (Lutetian). It contains one species, ''Ambulocetus natans'' (Latin ''natans'' "swimming"), known solely from a single, near-complete fossil. ''Ambulocetus'' is among the best-studied of Eocene cetaceans, and serves as an instrumental find in the study of cetacean evolution and their transition from land to sea, as it was the first cetacean discovered to preserve a suite of adaptations consistent with an amphibious lifestyle. ''Ambulocetus'' is classified in the group Archaeoceti—the ancient forerunners of modern cetaceans whose members span the transition from land to sea—and in the family Ambulocetidae, which includes ''Himalayacetus'' and '' Gandakasia'' (also from the Eocene of the Indian subcontinent). ''Ambulocetus'' had a narrow, streamlined body, and a long, broad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pakicetidae
Pakicetidae ("Pakistani whales") is an extinct family of Archaeoceti (early whales) that lived during the Early Eocene in Pakistan. Description described the first pakicetid, ''Ichthyolestes'', but at the time they did not recognize it as a cetacean, identifying it, instead, it as a fish-eating mesonychid. Robert West was the first to identify pakicetids as cetaceans in 1980 and, after discovering a braincase, Phillip Gingerich and Donald Russell described the genus '' Pakicetus'' in 1981. On October 26, 2016, a publication represented the idea that the emergence of cetacea in the Paleogene presents the best idea of microevolution that resulted in the phenotype of pakicetid. During the following two decades, more research resulted in additional pakicetid cranial material and by 2001 postcranial material for the family had been described. Though all parts of pakicetid postcrania are known, no complete skeleton from a single individual has been recovered. The pakicetid goldmine is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pakicetus
''Pakicetus'' is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to Pakistan during the Eocene, about 50 million years ago. It was a wolf-like animal, about to long, and lived in and around water where it ate fish and small animals. The vast majority of paleontologists regard it as the most basal whale, representing a transitional stage between land mammals and whales. It belongs to the even-toed ungulates with the closest living non-cetacean relative being the hippopotamus. Description Based on the sizes of specimens, and to a lesser extent on composite skeletons, species of ''Pakicetus'' are thought to have been to in length. ''Pakicetus'' looked very different from modern cetaceans, and its body shape more resembled those of land-dwelling hoofed mammals. Unlike all later cetaceans, it had four fully functional long legs. ''Pakicetus'' had a long snout; a typical complement of teeth that included incisors, canines, premolars, and mol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Raoellidae
The Raoellidae, previously grouped within Helohyidae, are an extinct family of semiaquatic digitigrade artiodactyls in the clade Whippomorpha. Fossils of raoellids are found in Eocene strata of South and Southeast Asia. An exceptionally complete skeleton of '' Indohyus'' from Kashmir suggests that raoellids are the " missing link" sister group to whales (Cetacea). All other Artiodactyla are relatives of these two groups. δO18 values and osteosclerotic bones indicate that the raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of ...-like ''Indohyus'' was habitually aquatic. However, it is still unclear if ''Indohyus'' primarily fed on land or in water. It is hypothesized that Cetaceans evolved from ancestors similar to ''Indohyus'' and later fully adapted to aquatic life. Taxono ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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