Aquatic adaptation
Encyclopedia
Several animal
groups have undergone aquatic adaptation, going from being purely terrestrial animals to living at least part of the time in water. The adaptations in early speciation tend to develop as the animal ventures into water in order to find available food. As successive generations spend more time in the water, natural selection causes the acquisition of more adaptations. Animals of later generations may spend the majority of their life in the water, coming ashore for mating. Finally, fully adapted animals may take to mating and birthing in water.
is a type of giant sea turtle
dating from the Cretaceous
Period, now long extinct. Its smaller cousins survive as the sea turtles of today.
Mesosaurus
(and other mesosaurids) were another group of anapsid reptiles to secondarily return to the sea, eschewing shells, and are also long extinct.
and Pliosaur
resembled crocodiles but were more strongly adapted to marine life. They became extinct within a few million years of the dinosaurs.
Modern diapsids which have made their own adaptions to allow them to spend significant time in the water include marine iguana
s and marine crocodile
s. Sea snakes
are extensively adapted to the marine environment, giving birth to live offspring in the same way as the Euryapsida (see below) and are largely incapable of terrestrial activity. The arc of their adaptation is evident by observing the primitive Laticauda
genus, which must return to land to lay eggs.
s adapting as fully as the dolphins they superficially resemble, even giving birth to live offspring instead of laying eggs, in other cases more to the extent of the seal, as with plesiosaur
s and placodont
s.
Epoch (about 55-65 million years ago), a group of wolf-like artiodactyls related to Pakicetus
began pursuing an amphibious lifestyle in rivers or shallow seas. They were the ancestors of modern whales, dolphins, and porpoises. The cetacea are extensively adapted to marine life and cannot survive on land at all. Their adaptation can be seen in many unique physiognomic characteristics such as the dorsal blowhole
, baleen
teeth, and the cranial 'melon' organ used for aquatic echolocation
. The closest extant terrestrial relative to the whale is the hippopotamus
, which spends much of its time in the water and whose name literally means "horse of the river."
and manatee
s first appeared in the fossil record about 45 to 50 million years ago in the ocean.
includes some aquatic adaptation, which has been said to explain human hairlessness, bipedalism, increased subcutaneous fat, descended larynx, vernix caseosa
, a hooded nose
and various other physiological and anatomical changes. The idea is not accepted by most scholars who study human evolution.
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
groups have undergone aquatic adaptation, going from being purely terrestrial animals to living at least part of the time in water. The adaptations in early speciation tend to develop as the animal ventures into water in order to find available food. As successive generations spend more time in the water, natural selection causes the acquisition of more adaptations. Animals of later generations may spend the majority of their life in the water, coming ashore for mating. Finally, fully adapted animals may take to mating and birthing in water.
Anapsid
ArchelonArchelon
Archelon is a genus of extinct sea turtle, the largest that has ever been documented.-Discovery:...
is a type of giant sea turtle
Sea turtle
Sea turtles are marine reptiles that inhabit all of the world's oceans except the Arctic.-Distribution:...
dating from the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period, now long extinct. Its smaller cousins survive as the sea turtles of today.
Mesosaurus
Mesosaurus
Mesosaurus is an extinct genus of reptile from the Early Permian of southern Africa and South America. Along with the genus Stereosternum, it is a member of the family Mesosauridae and the order Mesosauria. Mesosaurus was one of the first marine reptiles, and had many adaptations to a fully...
(and other mesosaurids) were another group of anapsid reptiles to secondarily return to the sea, eschewing shells, and are also long extinct.
Diapsid
Living at the same time as, but not closely related to, dinosaurs, the MosasaurMosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
and Pliosaur
Pliosaur
Pliosauroidea is an extinct clade of marine reptiles. Pliosauroids, also commonly known as pliosaurs, are known from the Jurassic and Cretaceous Periods. The pliosauroids were short-necked plesiosaurs with large heads and massive toothed jaws. These swimming reptiles were not dinosaurs but distant...
resembled crocodiles but were more strongly adapted to marine life. They became extinct within a few million years of the dinosaurs.
Modern diapsids which have made their own adaptions to allow them to spend significant time in the water include marine iguana
Iguana
Iguana is a herbivorous genus of lizard native to tropical areas of Central America and the Caribbean. The genus was first described in 1768 by Austrian naturalist Josephus Nicolaus Laurenti in his book Specimen Medicum, Exhibens Synopsin Reptilium Emendatam cum Experimentis circa Venena...
s and marine crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s. Sea snakes
Sea Snakes
Sea Snakes were a Canadian indie rock band, formed in 2002 and disbanded in 2005. The band consisted of vocalist and guitarist Jimmy McIntyre, guitarist Kristian Galberg, bassist and saxophonist Jeremy Strachan, keyboardist Shaw-Han Liem and drummer Nathan Lawr.Strachan played in the defunct band...
are extensively adapted to the marine environment, giving birth to live offspring in the same way as the Euryapsida (see below) and are largely incapable of terrestrial activity. The arc of their adaptation is evident by observing the primitive Laticauda
Laticauda
Laticauda is a genus of snakes from the family Hydrophiidae. Laticauda are the least adapted to sea life of all the members of Hydrophiidae; they retain the wide ventral scales typical of terrestrial snakes and have only a poorly developed tail fin...
genus, which must return to land to lay eggs.
Euryapsida
These marine reptiles had ancestors who moved back into the oceans, In the case of ichthyosaurIchthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
s adapting as fully as the dolphins they superficially resemble, even giving birth to live offspring instead of laying eggs, in other cases more to the extent of the seal, as with plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...
s and placodont
Placodont
Placodonts were a group of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. It is believed that they were part of Sauropterygia, the group that includes Plesiosaurs...
s.
Cetacea
During the PaleocenePaleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
Epoch (about 55-65 million years ago), a group of wolf-like artiodactyls related to Pakicetus
Pakicetus
Pakicetus is a genus of extinct terrestrial carnivorous mammal of the family Pakicetidae which was endemic to Pakistan from the Eocene .Pakicetus existed for approximately...
began pursuing an amphibious lifestyle in rivers or shallow seas. They were the ancestors of modern whales, dolphins, and porpoises. The cetacea are extensively adapted to marine life and cannot survive on land at all. Their adaptation can be seen in many unique physiognomic characteristics such as the dorsal blowhole
Blowhole
Blowhole may refer to:*Blowhole , the hole at the top of a whale's or other cetacean's head*Blowhole , a hole at the inland end of a sea cave*Blowhole Diversion Tunnel in Victoria, Australia...
, baleen
Baleen
Baleen or whalebone is a filter-feeder system inside the mouths of baleen whales. The baleen system works when a whale opens its mouth underwater and then water pours into the whale's mouth. The whale then pushes the water out, and animals such as krill are filtered by the baleen and remain as food...
teeth, and the cranial 'melon' organ used for aquatic echolocation
Echolocation
Echolocation may refer to:* Acoustic location, the general use of sound to locate objects* Animal echolocation, non-human animals emitting sound waves and listening to the echo in order to locate objects or navigate...
. The closest extant terrestrial relative to the whale is the hippopotamus
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
, which spends much of its time in the water and whose name literally means "horse of the river."
Sirenians
The ancestors of the dugongDugong
The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow , was hunted to extinction in the 18th century...
and manatee
Manatee
Manatees are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows...
s first appeared in the fossil record about 45 to 50 million years ago in the ocean.
Pinniped
The fossil records show that phocids existed 12 to 15 million years ago, and odobenids about 14 million years ago. Their common ancestor must have existed even earlier than that.Polar bears
Although still primarily a terrestrial animal, the polar bear shows the beginnings of aquatic adaptation to swimming (high levels of body fat and nostrils that are able to close), diving, and thermoregulation. Distinctly polar bear fossils can be dated to about 100,000 years ago. The polar bear has thick fur and layers of fat on its body to protect it from the cold.Humans
Proponents of the aquatic ape hypothesis believe that part of human evolutionHuman evolution
Human evolution refers to the evolutionary history of the genus Homo, including the emergence of Homo sapiens as a distinct species and as a unique category of hominids and mammals...
includes some aquatic adaptation, which has been said to explain human hairlessness, bipedalism, increased subcutaneous fat, descended larynx, vernix caseosa
Vernix caseosa
Vernix caseosa, also known as vernix, is the waxy or cheese-like white substance found coating the skin of newborn human babies.-Composition:...
, a hooded nose
Human nose
The visible part of the human nose is the protruding part of the face that bears the nostrils. The shape of the nose is determined by the ethmoid bone and the nasal septum, which consists mostly of cartilage and which separates the nostrils...
and various other physiological and anatomical changes. The idea is not accepted by most scholars who study human evolution.