Convergent evolution—the repeated evolution of similar traits in multiple lineages which all ancestrally lack the trait—is rife in nature, as illustrated by the examples below. The ultimate cause of convergence is usually a similar evolutionary biome, as similar environments will select for similar traits in any species occupying the same ecological niche, even if those species are only distantly related. In the case of cryptic species, it can create species which are only distinguishable by analysing their genetics. Distantly related organisms often develop analogous structures by adapting to similar environments.
In animals
Mammals
Several groups of ungulates have independently reduced or lost side digits on their feet, often leaving one or two digits for walking. That name comes from their hooves, which have evolved from claws several times. For example, horses have one walking digit and domestic bovines two on each foot. Various other land vertebrates have also reduced or lost digits.The phylogeny of the ungulates - Prothero Similarly, laurasiathere perissodactyls and afrothere paenungulates have several features in common, to the point of there being no obvious distinction among basal taxa of both groups. Many aquatic mammals or marine mammals independently came to have adaptations to live in water, such as similar-looking tail flukes in dugongs and whales. Unrelated herbivores and carnivores have adapted to marine and freshwater environments. The flipper forelimbs of marine mammals (cetaceans, pinnipeds, and sirenians) are a classic example of convergent evolution. There is widespread convergence at the gene level. Distinct substitutions in common genes created various aquatic adaptations, most of which also constitute parallel evolution because the substitutions in question are not unique to those animals. The pronghorn of North America, while not a true antelope and only distantly related to them, closely resembles the true antelopes of the Old World, both behaviorally and morphologically. It also fills a similar ecological niche and is found in the same biomes. Members of the two clades Australosphenida and Theria evolved tribosphenic molars independently. The marsupial thylacine (Tasmanian tiger or Tasmanian wolf) had many resemblances to placental canids. Several mammal groups have independently evolved prickly protrusions of the skin – echidnas (monotremes), the insectivorous hedgehogs, some tenrecs (a diverse group of shrew-like Malagasy mammals), Old World porcupines (rodents) and New World porcupines (another biological family of rodents). In this case, because the two groups of porcupines are closely related, they would be considered to be examples of parallel evolution; however, neither echidnas, nor hedgehogs, nor tenrecs are close relatives of the Rodentia. In fact, the last common ancestor of all of these groups lived in the age of the dinosaurs.An Introduction to Zoology, Page 102, by Joseph Springer, Dennis Holley, 2012 The eutriconodont Spinolestes that lived in the Early Cretaceous Period represents an even earlier example of a spiny mammal, unrelated to any modern mammal group. Catlike sabre-toothed predators evolved in three distinct lineages of mammals – carnivorans like the sabre-toothed cats, and nimravids ("false" sabre-tooths), the sparassodont family Thylacosmilidae ("marsupial" sabre-tooths), the gorgonopsids and the creodonts also developed long canine teeth, but with no other particular physical similarities.Convergent Evolution: Limited Forms Most Beautiful, page 158, by George R. McGhee, 2011 A number of mammals have developed powerful fore claws and long, sticky tongues that allow them to open the homes of social insects (e.g., ants and termites) and consume them (myrmecophagy). These include the four species of anteater, more than a dozen armadillos, eight species of pangolin (plus fossil species), eight species of the monotreme (egg-laying mammals) echidna (plus fossil species), the Fruitafossor of the Late Jurassic, the marsupial numbat, the African aardvark, the aardwolf, and possibly also the sloth bear of South Asia, all unrelated. Marsupial koalas of Australia have evolved fingerprints, indistinguishable from those of non-related primates, such as humans. The Australian honey possums acquired a long tongue for taking nectar from flowers, a structure similar to that of butterflies, some moths, and hummingbirds, and used to accomplish the same task. The marsupial sugar glider and squirrel glider of Australia are like the placental flying squirrel. Both lineages have independently developed wing-like flaps (patagia) for leaping from trees, and big eyes for foraging at night. The North American kangaroo rat, Australian hopping mouse, and North African and Asian jerboa have developed convergent adaptations for hot desert environments; these include a small rounded body shape with large hind legs and long thin tails, a characteristic bipedal hop, and nocturnal, burrowing and seed-eating behaviours. These rodent groups fill similar niches in their respective ecosystems. Opossums and their Australasian cousins have evolved an opposable thumb, a feature which is also commonly found in the non-related primates. The marsupial moles have many resemblances to the placental talpid moles and golden moles.The Encyclopedia of Applied Animal Behaviour and Welfare, page 137, D. S. Mills and Jeremy N. Marchant-Forde Marsupial mulgaras have many resemblances to placental mice. Planigale has many resemblances to the deer mouse. The marsupial Tasmanian devil has many resemblances to the placental hyena or a wolverine. Similar skull morphology, large canines and crushing carnassial molars.devilsatcradle.com, Tasmanian Devil - Sarcophilus harrisii Taxonomy Marsupial kangaroos and wallabies have many resemblances to the springhares, the viscachas (rodents which are also related to chinchillas), the maras (a large rodent from the cavy family (Caviidae)), and rabbits and hares (lagomorphs).Bulletin of the American Museum of Natural History, Volume 27, page 382, By Joel Asaph Allen The marsupial lion, Thylacoleo carnifex, had retractable claws, the same way the placental felines (cats) do today. Microbats, toothed whales and shrews developed sonar-like echolocation systems used for orientation, obstacle avoidance and for locating prey. Modern DNA phylogenies of bats have shown that the traditional suborder of echolocating bats (Microchiroptera) is not a true clade, and instead some echolocating bats are more related to non-echolocating Old World fruit bats than to other echolocating species. The implication is that echolocation in at least two lineages of bats, Megachiroptera and Microchiroptera has evolved independently or been lost in Old World fruit bats.Yoon, Carol Kaesuk. " R. Griffin, 88, Dies; Argued Animals Can Think", The New York Times, November 14, 2003. Accessed July 16, 2010.D. R. Griffin (1958). Listening in the dark. Yale Univ. Press, New York. Echolocation in bats and whales also both necessitate high frequency hearing. The protein prestin, which confers high hearing sensitivity in mammals, shows molecular convergence between the two main clades of echolocating bats, and also between bats and dolphins. Other hearing genes also show convergence between echolocating taxa. A genome-wide study of convergence published in 2013 analysed 22 mammal genomes and revealed that tens of genes have undergone the same replacements in echolocating bats and cetaceans, with many of these genes encoding proteins that function in hearing and vision. Both the aye-aye lemur and the striped possum have an elongated finger used to get invertebrates from trees. There are no woodpeckers in Madagascar or Australia where the species evolved, so the supply of invertebrates in trees was large. Castorocauda, a Jurassic Period mammal and beavers both have webbed feet and a flattened tail, but are not related. Prehensile tails evolved in a number of unrelated species marsupial opossums, their Australasian cousins, kinkajous, New World monkeys, tree-pangolins, tree-anteaters, porcupines, rats, skinks and chameleons, and the salamander Bolitoglossa.Organ, J. M. (2008). The Functional Anatomy of Prehensile and Nonprehensile Tails of the Platyrrhini (Primates) and Procyonidae (Carnivora). Johns Hopkins University. . Pig form, large-headed, pig-snouted and hoofs are independent in true pigs in Eurasia, peccaries in South America and the extinct entelodonts. Tapirs and pigs look much alike, but tapirs are perissodactyls (odd-toed ungulates) and pigs are artiodactyls (even-toed ungulates).Dawkins, Richard (2005). The Ancestor's Tale. Boston: Mariner Books. p. 195. . Filter feeding: baleen whales like the humpback and blue whale (mammals), the whale shark and the basking shark separately, the manta ray, the Mesozoic bony fish Leedsichthys, and the early Paleozoic anomalocaridid Aegirocassis have separately evolved ways of sifting plankton from marine waters. The monotreme platypus has what looks like a bird's beak (hence its scientific name Ornithorhynchus), but is a mammal. However, it is not structurally similar to a bird beak (or any "true" beak, for that matter), being fleshy instead of keratinous. Red blood cells in mammals lack a cell nucleus. In comparison, the red blood cells of other vertebrates have nuclei; the only known exceptions are salamanders of the genus Batrachoseps and fish of the genus Maurolicus. Caniforms like skunks and raccoons in North and South America and feliforms such as mongoose and civets in Asia and Africa have both evolved to fill the niche of small to medium omnivore/insectivore on their side of the world. Some species of mongoose and civet can even spray their attacker with musk similar to the skunk and some civets have also independently evolved similar markings to the raccoon such as the African civet.The Behavior Guide to African Mammals: Including Hoofed Mammals, Carnivores, By Richard Estes River dolphins of the three species that live exclusively in freshwater, live in different rivers: Ganges and Brahmaputra Rivers of India, the Yangtze River of China, and the Amazon River. Mitochondrial and nuclear DNA sequence analysis demonstrates the three are not related.Encyclopedia of Marine Mammals, by William F. Perrin, Bernd Wursig, J. G.M. Thewissen Mangabeys comprise three different genera of Old World monkeys. The genera Lophocebus and Cercocebus resemble each other and were once thought to be closely related, so much so that all the species were in one genus. However, it is now known that Lophocebus is more closely related to baboons, while the Cercocebus is more closely related to the mandrill. Sperm whales and the microscopic copepods both use the same buoyancy control system. The wombat is a marsupial that is often considered to be the marsupial equivalent of the North American groundhog. The fossa of Madagascar looks like a small cat. Fossa have semi-retractable claws. Fossa also has flexible ankles that allow it to climb up and down trees head-first, and also support jumping from tree to tree. Its classification has been controversial because its physical traits resemble those of cats, but is more closely related to the mongoose family, (Herpestidae) or most likely the family Malagasy carnivores family, (Eupleridae). The raccoon dog of Asia looks like the raccoon of North America (hence its scientific name Procyonoides) due to its black face mask, stocky build, bushy appearance, and ability to climb trees. Despite their similarities, it is actually classified as part of the dog family (Canidae). Gliders or passive flight has developed independently in flying squirrels, Australian marsupial, lizards, paradise tree snake, frogs, gliding ants and flying fish and the ancient volaticotherium that lived in the Jurassic Period looked like a flying squirrel, but is not an ancestor of squirrels.