Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine, with diets based on fish and invertebrates. Lutrinae is a branch of the Mustelidae family, which also includes weasels, badgers, mink, and wolverines, among other animals.
The sea otter is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg, making them the heaviest members of the weasel family, but among the smallest marine mammals. Unlike most marine mammals, the sea otter's primary form of insulation is an exceptionally thick coat of fur, the densest in the animal kingdom. Although it can walk on land, the sea otter is capable of living exclusively in the ocean.
Potamotherium an extinct genus of caniform carnivoran from the Miocene epoch of France and Germany. It has historically been assigned to the family Mustelidae, but more recent studies suggest that it represents a primitive relative of pinnipeds
An ecological cascade effect is a series of secondary extinctions that are triggered by the primary extinction of a key species in an ecosystem. Secondary extinctions are likely to occur when the threatened species are: dependent on a few specific food sources, mutualistic, or forced to coexist with an invasive species that is introduced to the ecosystem. Species introductions to a foreign ecosystem can often devastate entire communities, and even entire ecosystems. These exotic species monopolize the ecosystem's resources, and since they have no natural predators to decrease their growth, they are able to increase indefinitely. Olsen et al. showed that exotic species have caused lake and estuary ecosystems to go through cascade effects due to loss of algae, crayfish, mollusks, fish, amphibians, and birds. However, the principal cause of cascade effects is the loss of top predators as the key species. As a result of this loss, a dramatic increase of prey species occurs. The prey is then able to overexploit its own food resources, until the population numbers decrease in abundance, which can lead to extinction. When the prey's food resources disappear, they starve and may go extinct as well. If the prey species is herbivorous, then their initial release and exploitation of the plants may result in a loss of plant biodiversity in the area. If other organisms in the ecosystem also depend upon these plants as food resources, then these species may go extinct as well. An example of the cascade effect caused by the loss of a top predator is apparent in tropical forests. When hunters cause local extinctions of top predators, the predators' prey's population numbers increase, causing an overexploitation of a food resource and a cascade effect of species loss. Recent studies have been performed on approaches to mitigate extinction cascades in food-web networks.
Sea otter conservation began in the early 20th century, when the sea otter was nearly extinct due to large-scale commercial hunting. The sea otter was once abundant in a wide arc across the North Pacific ocean, from northern Japan to Alaska to Mexico. By 1911, hunting for the animal's luxurious fur had reduced the sea otter population to fewer than 2000 individuals in the most remote and inaccessible parts of its range. The IUCN lists the sea otter as an endangered species. Threats to sea otters include oil spills, and a major spill can rapidly kill thousands of the animals.
Cyrnaonyx is an extinct genus of Lutrinae, otters from the Pleistocene. It was originally described by Helbing based on materials from France and he also attributed material from Corsica to it. The latter appeared to belong to another species and genus, Algarolutra majori. The only species of Cyrnaonyx is C. antiqua. It is known from the Pleistocene of Europe: France, Germany, Netherlands, Southern England and probably Italy.
Enhydrocyon is an extinct genus of bone crushing canid which inhabited North America during the Oligocene and Early Miocene, 30.8—20.4 Ma, existing for approximately 11 million years.
Sardolutra ichnusae is an extinct species of otter from the Late Pleistocene of Sardinia. It was originally described as Nesolutra ichnusae. It was a rather small species of otter, probably living in the sea. Among its characteristics is a relatively very large baculum, larger than in any living otter. The species probably evolved from a species of Lutra, maybe L. castiglionis.
Satherium is an extinct genus of otters that lived in North America during the Pliocene and Pleistocene. Two species are known, Satherium piscinarium and Satherium ingens.
Enhydritherium terraenovae is an extinct marine otter endemic to North America that lived during the Miocene through Pliocene epochs from ~9.1–4.9 Ma. (AEO), existing for approximately 4.2 million years.
Leithia is an extinct genus of giant dormice from the Pleistocene of the Mediterranean islands of Malta and Sicily. It is considered an example of island gigantism. Leithia melitensis is the largest known species of dormouse, living or extinct, being twice the size of any other known species.
The sea otter, Enhydra lutris, is a member of the Mustelidae that is fully aquatic. Sea otters are the smallest of the marine mammals, but they are also the most dexterous. Sea otters are known for their ability to use stones as anvils or hammers to facilitate access to hard-to-reach prey items. Furthermore, out of the thirteen currently known species of otters, at least 10 demonstrate stone handling behaviour, suggesting that otters may have a genetic predisposition to manipulate stones. Tool use behavior is more associated with geographic location than sub-species. Most behavioral research has been conducted on Enhydra lutris nereis, the Californian otter, and some has been conducted on Enhydra lutris kenyoni, the Alaska sea otter. Sea otters frequently use rocks as anvils to crack open prey, and they are also observed to rip open prey with their forepaws. While lying on their backs, otters will rip apart coral algae to find food among the debris. The frequency of tool use varies greatly between geographic regions and individual otters. Regardless of the frequency, the use of tools is present in the behavioral repertoire of sea otters and is performed when most appropriate to the situation.
Enhydriodon is an extinct genus of mustelids known from Africa, Pakistan, and India that lived from the late Miocene to the early Pleistocene. It contains 9 confirmed species, 2 debated species, and at least a few other undescribed species from Africa. The genus belongs to the tribe Enhydriodontini in the otter subfamily Lutrinae. Enhydriodon means “otter tooth” in Ancient Greek and is a reference to its dentition rather than to the Enhydra genus, which includes the modern sea otter and its two prehistoric relatives.
Siamogale is an extinct genus of giant otter from the late Miocene-early Pliocene of eastern Asia. Three species are currently known, S. thailandica and S. bounosa from Thailand and S. melilutra from China.
Polydolopimorphia is an extinct order of metatherians, more closely related to extant marsupials than other extinct mammals. Known from the Paleocene-Pliocene of South America and the Eocene of Antarctica, they were a diverse group during the Paleogene, filling many niches, before declining and becoming extinct at the end of the Neogene. It is divided into two suborders, Bonapartheriiformes, and Polydolopiformes Most members are only known from jaw fragments, which have their characteristically generally bunodont teeth. The morphology of their teeth has led to proposals that polydolopimorphians may be crown group marsupials, nested within Australidelphia, though this proposal, and the monophyly of the order as a whole has been questioned, with other analyses finding them outside of crown-group Marsupialia. The group contained omnivorous, frugivorous and herbivorous forms.
Lutra castiglionis, the Castiglione otter or Corsican otter, is an extinct species of otter that was endemic to Corsica during the Pleistocene.
Enhydra macrodonta, the large-toothed sea otter, is an extinct mustelid known from the middle Pleistocene in California.
Bounodus is an extinct genus of ungulates native from South America, belonging to the order Litopterna. Its remains were found in Miocene rocks from the Urumaco Formation of northern Venezuela. The genus is only known from its holotype, AMU-CURS 44, a fragmentary right maxilla preserving teeth from the fourth premolar to the third molar and the alveolus of the third premolar, exhibiting a typical bunodont structure in the animal dentition, a characteristic shared with its close relative Megadolodus. The postcranial skeleton of the genus is unknown. Its dentition indicates that the animal was omnivorous, with teeth adapted to potentially eat shelled fruits, as well as the molluscs and crustaceans that thrived in the wetlands that covered most of North-West South America, including the Urumaco Formation, during the Neogene.
Protolipterna is an extinct genus of mammal, belonging to the order Litopterna. It lived during the Late Paleocene and the Early Eocene, in what is now South America.
Molinodus is an extinct genus of mammal of uncertain affinities, whose fossils were found at Tiupampa, in Bolivia, in terrains dated from the Paleocene.
