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Evolution Of Sirenians
Sirenia is the order of placental mammals which comprises modern "sea cows" (manatees and the Dugong) 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 (early Eocene-recent). 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. Origins Sirenians, along with Proboscidea (elephants), group together with the extinct Desmostylia and likely the extinct Embrithopoda to form the Tethytheria. Tethytheria is thought to have evolved f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trichechus Manatus Fg01
Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living species in the order Sirenia: the Amazonian manatee (''Trichechus inunguis''), the West Indian manatee (''Trichechus manatus''), and the West African manatee (''Trichechus senegalensis''). They measure up to long, weigh as much as , and have paddle-like tails. Manatees are herbivores and eat over 60 different freshwater and saltwater plants. Manatees inhabit the shallow, marshy coastal areas and rivers of the Caribbean Sea, the Gulf of Mexico, the Amazon basin, and West Africa. The main causes of death for manatees are human-related issues, such as habitat destruction and human objects. Their slow-moving, curious nature has led to violent collisions with propeller-driven boats and ships. Some manatees have been found with over 50 scars on the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continents of Asia and Oceania in the west and the Americas in the east. At in area (as defined with a southern Antarctic border), this largest division of the World Ocean—and, in turn, the hydrosphere—covers about 46% of Earth's water surface and about 32% of its total surface area, larger than Earth's entire land area combined .Pacific Ocean . '' Britannica Concise.'' 2008: Encyclopædia Britannica, Inc. The centers of both the |
Paenungulata
Paenungulata (from Latin ''paene'' "almost" + ''ungulātus'' "having Hoof, hoofs") is a clade of "sub-Ungulate, ungulates", which groups three Extant taxon, extant mammal Order (biology), orders: Proboscidea (including elephants), Sirenia (sirenia, sea cows, including dugongs and manatees), and Hyracoidea (hyraxes). At least two more possible orders are known only as fossils, namely Embrithopoda and Desmostylia. Molecular evidence indicates that Paenungulata (or at least its extant members) is part of the cohort Afrotheria, an ancient assemblage of mainly African mammals of great diversity. The other members of this cohort are the orders Afrosoricida (tenrecs and golden moles), Macroscelidea (elephant shrews) and Tubulidentata (aardvarks). Of the five orders, hyraxes are the most basal, followed by embrithopods; the remaining orders (sirenians and elephants) are more closely related. These latter three are grouped as the Tethytheria, because it is believed that their common ancest ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, the equivalent Latin term ''cladus'' (plural ''cladi'') is often used in taxonomical literature. The common ancestor may be an individual, a population, or a species (extinct or extant). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic. Some of the relationships between organisms ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hyracoidea
Hyraxes (), also called dassies, are small, thickset, herbivorous mammals in the order Hyracoidea. Hyraxes are well-furred, rotund animals with short tails. Typically, they measure between long and weigh between . They are superficially similar to pikas and marmots, but are more closely related to elephants and sea cows. Hyraxes have a life span from 9 to 14 years. Five extant species are recognised: the rock hyrax (''Procavia capensis'') and the yellow-spotted rock hyrax (''Heterohyrax brucei''), which both live on rock outcrops, including cliffs in Ethiopia and isolated granite outcrops called koppies in southern Africa; the western tree hyrax (''Dendrohyrax dorsalis''), southern tree hyrax (''D. arboreus''), and eastern tree hyrax (''D. validus''). Their distribution is limited to Africa, except for ''P. capensis'', which is also found in the Middle East. Characteristics Hyraxes retain or have redeveloped a number of primitive mammalian characteristics; in particular, they ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tethys Ocean
The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents of Gondwana and Laurasia, before the opening of the Indian and Atlantic oceans during the Cretaceous Period. It was preceded by the Paleo-Tethys Ocean, which lasted between the Cambrian and the Early Triassic, while the Neotethys formed during the Late Triassic and lasted until the early Eocene (about 50 million years ago) when it completely closed. A portion known as the Paratethys formed during the Late Jurassic, was isolated during the Oligocene (34 million years ago) and lasted up to the Pliocene (about 5 million years ago), when it largely dried out. Many major seas and lakes of Europe and Western Asia, including the Mediterranean Sea, the Black Sea, the Caspian Sea, and the Aral Sea are thought to be remnants of the Paratethys. Ety ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Condylarth
Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates. It is now largely considered to be a wastebasket taxon, having served as a dumping ground for classifying ungulates which had not been clearly established as part of either Perissodactyla or Cetartiodactyla, being composed thus of several unrelated lineages. Taxonomic history Condylarthra always was a problematic group. When Condylarthra was first described by , Phenacodontidae was the type and only family therein. , however, raised Condylarthra to an order and included a wide range of diverse placentals with generalized dentitions and postcranial skeletons. More recent researchers (i.e. post-WW2) have been more restrictive; either including only a limited number of taxa, or proposing that the term should be abandoned altogether. Due to their primitive characteristics condylar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tethytheria
Tethytheria is a clade of mammals that includes the sirenians and proboscideans, as well as the extinct order Embrithopoda. Though there is strong anatomical and molecular support for the monophyly of Tethytheria, the interrelationships between the included taxa remain disputed. The tethytheres are united by several characters, including anteriorly facing orbits and more or less bilophodont cheek teeth (double transverse ridges on the crowns of the teeth). Proboscidea and Sirenia are linked together based on auditory characters in their petrosal bones, but this link may be a homoplasy. Desmostylians, traditionally considered tethytheres, have been tentatively assigned to Perissodactyla, along with the Early Eocene family Anthracobunidae, which was considered a sister group to Tethytheria. Systematics Cladogram modified from and . Classification Classification modified from . * Clade Tethytheria ** order †Embrithopoda *** † Phenacolophidae *** †Arsinoitheriidae ** order ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embrithopoda
Embrithopoda ("heavy-footed") is an order of extinct mammals known from Asia, Africa and Eastern Europe. Most of the embrithopod genera are known exclusively from jaws and teeth dated from the late Paleocene to the late Eocene; however, the order is best known from its terminal member, the elephantine ''Arsinoitherium''. Description While embrithopods bore a superficial resemblance to rhinoceroses, their horns had bony cores covered in keratinized skin. Not all embrithopods possessed horns, either. Despite their appearance, they have been regarded as related to elephants, not perissodactyls. As tethytheres, the Embrithopoda have been believed to be part of the clade Afrotheria. However, a study of the basal arsinoitheriid, ''Palaeoamasia'', suggests that embrithopods are not tethytheres or even paenungulates, and that they need to be better sampled in an analysis of eutherian relationships to clarify if they are even afrotherians.[Erdal et al.'s inclusion of Embrithopoda in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desmostylia
The Desmostylia (from Greek δεσμά ''desma'', "bundle", and στῦλος ''stylos'', "pillar") are an extinct order of aquatic mammals that existed from the early Oligocene (Rupelian) to the late Miocene (Tortonian) (). Desmostylians are the only known extinct order of marine mammals. The Desmostylia, together with Sirenia and Proboscidea (and possibly Embrithopoda), have traditionally been assigned to the afrotherian clade Tethytheria, a group named after the paleoocean Tethys around which they originally evolved. The relationship between the Desmostylia and the other orders within the Tethytheria has been disputed; if the common ancestor of all tethytheres was semiaquatic, the Proboscidea became secondarily terrestrial; alternatively, the Desmostylia and Sirenia could have evolved independently into aquatic mammals. The assignment of Desmostylia to Afrotheria has always been problematic from a biogeographic standpoint, given that Africa was the locus of the early evoluti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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