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. Unrelated organisms often develop analogous structures by adapting to similar environments.
The skulls of the thylacine (left) and the grey wolf, Canis lupus, are similar, although the species are only very distantly related (different infraclasses). The skull shape of the red fox, Vulpes vulpes, is even closer to that of the thylacine.
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. Among familiar animals, horses have one walking digit and domestic bovines two on each foot. Various other land vertebrates have also reduced or lost digits.
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.
Several mammal groups have independently evolved prickly protrusions of the skin – echidnas (monotremes), the insectivorous hedgehogs, some tenrecs (a diverse group of shrew-like Madagascan 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 was a contemporary of the dinosaurs. The eutriconodontSpinolestes that lived in the Early Cretaceous Period represents an even earlier example of a spined mammal, unrelated to any modern mammal group.
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.
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.
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.
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. Recently the first genome-wide study of convergence was published, this study analysed 22 mammal genomes and revealed that tens of genes have undergone the same replacements in echolocating bats and ceteaceans, with many of these genes encoding proteins that function in hearing and vision.
The monotremeplatypus has what looks like a bird's beak (hence its scientific name Ornithorhynchus), but is a mammal. It was thought that somebody had sewn a duck's beak onto the body of a beaver-like animal. Shaw even took a pair of scissors to the dried skin to check for stitches. 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.
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.
The Fossa of Madagascar looks like a small cat. Fossa have semiretractable 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).
Megaladapis, a genus of extinct lemur, bears a great resemblance to an indri or a koala (hence its nickname "Koala-Lemur") due to their stocky build, tufted ears, and short stumpy tail.
Palaeopropithecidae, a family of extinct lemurs, which are most likely related to the family Indriidae due to their morphology, have many similarities to sloths due to their appearance and behaviour, such as long arms, hooked fingers, and slow moving, giving them the nickname "Sloth-Lemurs".
Archaeolemuridae, another family of extinct lemurs, which are also most likely related to the family Indriidae, have many similarities to monkeys and baboons due to their body plans, which are both adopted to arboreal and terrestrial lifestyle, giving them the nickname "Monkey-Lemurs" or "Baboon-Lemurs".
Pterosaurian pycnofibrils strongly resemble mammalian hair, but are thought to have evolved independently.
The Pelycosauria and the Ctenosauriscidae bore striking resemblance to each other because they both had a sail-like fin on their back. The pelycosaurs are more closely related to mammals while the ctenosauriscids are closely related to pterosaurs and dinosaurs. Also, the spinosaurids had sail-like fins on their backs, when they were not closely related to either.
Also, Acrocanthosaurus and Ouranosaurus, which are not closely related to either pelycosaurs, ctenosauriscids or spinosaurids, also had similar, but thicker, spines on their vertebrae, and thus have humps, like the unrelated, mammalian camels and bison.
The thorny devil (Moloch horridus) is similar in diet and activity patterns to the Texas horned lizard (Phrynosoma cornutum), although the two are not particularly closely related.
Modern crocodilians resemble prehistoric phytosaurs, champsosaurs, certain labyrinthodont amphibians, and perhaps even the early whaleAmbulocetus. The resemblance between the crocodilians and phytosaurs in particular is quite striking; even to the point of having evolved the graduation between narrow- and broad-snouted forms, due to differences in diet between particular species in both groups.
Ostriches are large ratites specialised to cursoriality, having lost the first and second toes. Eogruids and geranoidids were crane relatives that also specialised for cursoriality in the same way, showing a reduction in the second toe's trochea, culminating in its disappearance in more derived taxa.
Vultures are a result of convergent evolution: both Old World vultures and New World vultures eat carrion, but Old World vultures are in the eagle and hawk family (Accipitridae) and use mainly eyesight for discovering food; the New World vultures are of obscure ancestry, and some use the sense of smell as well as sight in hunting. Birds of both families are very big, search for food by soaring, circle over sighted carrion, flock in trees, and have unfeathered heads and necks.
Flightlessness has evolved in many different birds independently. However, taking this to a greater extreme, the terror birds, Gastornithiformes and dromornithids (ironically all extinct) all evolved the similar body shape (flightlessness, long legs, long necks, big heads), yet none of them were closely related. They also share the trait of being giant, flightless birds with vestigial wings, long legs, and long necks with the ratites, although they are not related.
Certain longclaws (Macronyx) and meadowlarks (Sturnella) have essentially the same striking plumage pattern. The former inhabit Africa and the latter the Americas, and they belong to different lineages of Passerida. While they are ecologically quite similar, no satisfying explanation exists for the convergent plumage; it is best explained by sheer chance.
Seriemas and Secretary Birds very closely resemble the ancient dromaeosaurid and troodontid dinosaurs. Both have evolved a retractable sickle-shaped claw on the second toe of each foot, both have feathers, and both are very similar in their overall physical appearance and lifestyle.
Brood parasitism, laying eggs in the nests of birds of other species, happens in types of birds that are not closely related.
Fish that swim by using an elongated fin along the dorsum, ventrum, or in pairs on their lateral margins (such as Oarfish, Knifefish, Cephalopods) have all come to the same ratio of amplitude to wavelength of fin undulation to maximize speed, 20:1.
Mudskippers exhibit a number of adaptations to semi-terrestrial lifestyle which are also usually attributed to Tiktaalik: breathing surface air, having eyes positioned on top of the head, propping up and moving on land using strong fins.
Tiktaalik roseae - artistic interpretation. Neil Shubin, suggests the animal could prop up on its fins to venture onto land, though many palaeonthologists reject this idea as outdated
Acanthurids and mbuna are both aggressive, brightly colored fish that feed principally on aufwuchs, although the former is found only in marine environments, while the latter is only found in freshwater Lake Malawi.
Cichlids of South America and the "sunfish" of North America are strikingly similar in morphology, ecology and behavior.
The antifreeze protein of fish in the arctic and Antarctic, came about independently. AFGPs evolved separately in notothenioids and northern cod. In notothenioids, the AFGP gene arose from an ancestral trypsinogen-like serine protease gene.
Stickleback fish, there is widespread convergent evolution in sticklebacks.
Flying fish can fly up to 400 m (1,300 ft) at speeds of more than 70 kilometres per hour (43 mph) at a maximum altitude of more than 6 m (20 ft), much like other flying birds, bats and other gliders.
The praying mantis body type – raptorial forelimb, prehensile neck, and extraordinary snatching speed - has evolved not only in mantid insects but also independently in neuropteran insects Mantispidae.
Gripping limb ends have evolved separately in scorpions and in some decapod crustaceans, like lobsters and crabs. These chelae or claws have a similar architecture: the next-to-last segment grows a projection that fits against the last segment.
Proleg a fleshy leg on many larvae of insects is found in all the orders in which they appear, formed independently of each order by convergent evolution.
Parasitoid use of viruses, parasitoid wasps lay their eggs inside host caterpillars, to keep the caterpillar's immune system from killing the egg, a virus is also "laid" with the eggs. Two unrelated wasps use this trick.
Bivalves and brachiopods independently evolved paired hinged shells for protection. However, the anatomy of their soft parts is very dissimilar, which is why molluscs and brachiopods are put into different phyla.
Jet propulsion in squids and in scallops: these two groups of mollusks have very different ways of squeezing water through their bodies in order to power rapid movement through a fluid. (Dragonfly larvae in the aquatic stage also use an anal jet to propel them, and jellyfish have used jet propulsion for a very long time.). Sea hares (gastropod molluscs) employ a similar means of jet propulsion, but without the sophisticated neurological machinery of cephalopods they navigate somewhat more clumsily. tunicates (such as salps), and some jellyfish also employ jet propulsion. The most efficient jet-propelled organisms are the salps, which use an order of magnitude less energy (per kilogram per metre) than squid.
Hydrothermal vent adaptations like the use of bacteria housed in body flesh or in special organs, to the point they no long have mouth parts, have been found in unrelated hydrothermal vent species of mollusks and tube worms (like the giant tube worm.
Lichens are a partnerships of fungi and algae. Each "species" of lichen is make of different fungi and algae species, thus each has to come about independently.
Prickles, thorns and spines are all modified plant tissues that have evolved to prevent or limit herbivory, these structures have evolved independently a number of times.
Stimulant toxins: Plants which are only distantly related to each other, such as coffee and tea, produce caffeine to deter predators.
The aerial rootlets found in ivy (Hedera) are similar to those of the climbing hydrangea (Hydrangea petiolaris) and some other vines. These rootlets are not derived from a common ancestor but have the same function of clinging to whatever support is available.
Flowering plants (Delphinium, Aerangis, Tropaeolum and others) from different regions form tube-like spurs that contain nectar. This is why insects from one place sometimes can feed on plants from another place that have a structure like the flower, which is the traditional source of food for the animal.
Some dicots (Anemone) and monocots (Trillium) in inhospitable environments are able to form underground organs such as corms, bulbs and rhizomes for reserving of nutrition and water until the conditions become better.
C4 photosynthesis is estimated to have evolved over 60 times within plants, via multiple different sequences of evolutionary events. C4 plants use a different metabolic pathway to capture carbon dioxide but also have differences in leaf anatomy and cell biology compared to most other plants.
Bilateral flowers, with distinct up-down orientation, came about independently in a number of different plants like: violets, orchids and peas.
United petals, petals that unite into a single bell shape came about independently in blueberries, Ericaceae and other plants.
Hummingbird flowers are scentless tubular flowers that have independently came about in at least four plant families. They attract nectar-feeding birds like: hummingbirds, honey eaters, sunbirds. Remote Hawaii also has Hummingbird flowers.
Fruit that develops underground, after the upper part is pollinated the flower stalk elongates, arches downward and pushes into the ground, this has independently came about in :peanut, legume, Florida's endangered burrowing four o’clock and Africa's Cucumis humifructus.
The protein prestin that drives the cochlea amplifier and confers high auditory sensitivity in mammals, shows numerous convergent amino acid replacements in bats and dolphins, both of which have independently evolved high frequency hearing for echolocation. This same signature of convergence has also been found in other genes expressed in the mammalian cochlea
The myoglobin from the abalone Sulculus diversicolor has a different structure from normal myoglobin but serves a similar function — binding oxygen reversibly. "The molecular weight of Sulculus myoglobin is 41kD, 2.5 times larger than other myoglobins." Moreover, its amino acid sequence has no homology with other invertebrate myoglobins or with hemoglobins, but is 35% homologous with human indoleamine dioxygenase (IDO), a vertebrate tryptophan-degrading enzyme. It does not share similar function with IDO. "The IDO-like myoglobin is unexpectedly widely distributed among gastropodic molluscs, such as Sulculus, Nordotis, Battilus, Omphalius and Chlorostoma."
The hemocyanin from arthropods and molluscs evolved from different ancestors, tyrosinase and insect storage proteins, respectively. They have different molecular weight and structure. However, the proteins both use copper binding sites to transport oxygen.
The hexokinase, ribokinase, and galactokinase families of sugar kinases have similar enzymatic functions of sugar phosphorylation, but they evolved from three distinct nonhomologous families since they all have distinct three-dimensional folding and their conserved sequence patterns are strikingly different.
Hemoglobins in jawed vertebrates and jawless fish evolved independently. The oxygen-binding hemoglobins of jawless fish evolved from an ancestor of cytoglobin which has no oxygen transport function and is expressed in fibroblast cells.
Toxic agent, serine protease BLTX, in the venom produced by two distinct species, the North American short-tailed shrewBlarina brevicauda and the Mexican beaded lizard, undergo convergent evolution. Although their structures are similar, it turns out that they increased the enzyme activity and toxicity through different way of structure changes. These changes are not found in the other non-venomous reptiles or mammals.
Antifreeze proteins are a perfect example of convergent evolution. Different small proteins with a flat surface which is rich in threonine from different organisms are selected to bind to the surface of ice crystals. "These include two proteins from fish, the ocean pout and the winter flounder, and three very active proteins from insects, the yellow mealworm beetle, the spruce budworm moth, and the snow flea."
RNA-binding proteins which contain RNA-binding domain (RBD) and the cold-shock domain (CSD) protein family are also an example of convergent evolution. Except that they both have conserved RNP motifs, other protein sequence are totally different. However, they have a similar function.
Blue-light-receptive cryptochrome expressed in the sponge eyes likely evolved convergently in the absence of opsins and nervous systems. The fully sequenced genome of Amphimedon queenslandica, a demosponge larvae, lacks one vital visual component: opsin-a gene for a light-sensitive opsin pigment which is essential for vision in other animals.
The structure of immunoglobulin G-binding bacterial proteins A and H do not contain any sequences homologous to the constant repeats of IgG antibodies, but they have similar functions. Both protein G, A, H are inhibited in the interactions with IgG antibodies (IgGFc) by a synthetic peptide corresponding to an 11-amino-acid-long sequence in the COOH-terminal region of the repeats.
Here is a list of examples in which unrelated proteins have similar tertiary structures but different functions. Whole protein structural convergence is not thought to occur but some convergence of pockets and secondary structural elements have been documented.
Some secondary structure convergence occurs due to some residues favouring being in α-helix (helical propensity) and for hydrophobic patches or pocket to be formed at the ends of the parallel sheets.
ABAC is a database of convergently evolved protein interaction interfaces. Examples comprise fibronectin/long chain cytokines, NEF/SH2, cyclophilin/capsid proteins.
McGhee, G.R. (2011) Convergent Evolution: Limited Forms Most Beautiful. Vienna Series in Theoretical Biology: Massachusetts Institute of Technology Press, Cambridge (MA). 322 pp.
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^Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,Winter 2011 Appendix.
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^"The illustration of the swim bladder in fishes is a good one, because it shows us clearly the highly important fact that an organ originally constructed for one purpose, namely, flotation, may be converted into one for a widely different purpose, namely, respiration. The swim bladder has, also, been worked in as an accessory to the auditory organs of certain fishes. All physiologists admit that the swimbladder is homologous, or "ideally similar" in position and structure with the lungs of the higher vertebrate animals: hence there is no reason to doubt that the swim bladder has actually been converted into lungs, or an organ used exclusively for respiration. According to this view it may be inferred that all vertebrate animals with true lungs are descended by ordinary generation from an ancient and unknown prototype, which was furnished with a floating apparatus or swim bladder." Darwin, Origin of Species.
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^Advanced Biology Principles, p296, fig 14.16—Diagram detailing the re-absorption of substrates within the hypha.
^Advanced biology principles, p 296—states the purpose of saprotrophs and their internal nutrition, as well as the main two types of fungi that are most often referred to, as well as describes, visually, the process of saprotrophic nutrition through a diagram of hyphae, referring to the Rhizobium on damp, stale whole-meal bread or rotting fruit.
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The evolution of mammals has passed through many stages since the first appearance of their synapsid ancestors in the Pennsylvanian sub-period of the late Carboniferous period. By the mid-Triassic, there were many synapsid species that looked like mammals. The lineage leading to today's mammals split up in the Jurassic; synapsids from this period include Dryolestes, more closely related to extant placentals and marsupials than to monotremes, as well as Ambondro, more closely related to monotremes. Later on, the eutherian and metatherian lineages separated; the metatherians are the animals more closely related to the marsupials, while the eutherians are those more closely related to the placentals. Since Juramaia, the earliest known eutherian, lived 160 million years ago in the Jurassic, this divergence must have occurred in the same period.
After the Cretaceous–Paleogene extinction event wiped out the non-avian dinosaurs (birds being the only surviving dinosaurs) and several mammalian groups, placental and marsupial mammals diversified into many new forms and ecological niches throughout the Paleogene and Neogene, by the end of which all modern orders had appeared.
Mammals are the only living synapsids. The synapsid lineage became distinct from the sauropsid lineage in the late Carboniferous period, between 320 and 315 million years ago. The sauropsids are today's reptiles and birds along with all the extinct animals more closely related to them than to mammals. This does not include the mammal-like reptiles, a group more closely related to the mammals.
Throughout the Permian period, the synapsids included the dominant carnivores and several important herbivores. In the subsequent Triassic period, however, a previously obscure group of sauropsids, the archosaurs, became the dominant vertebrates. The mammaliaforms appeared during this period; their superior sense of smell, backed up by a large brain, facilitated entry into nocturnal niches with less exposure to archosaur predation. The nocturnal lifestyle may have contributed greatly to the development of mammalian traits such as endothermy and hair. Later in the Mesozoic, after theropod dinosaurs replaced rauisuchians as the dominant carnivores, mammals spread into other ecological niches. For example, some became aquatic, some were gliders, and some even fed on juvenile dinosaurs.
Most of the evidence consists of fossils. For many years, fossils of Mesozoic mammals and their immediate ancestors were very rare and fragmentary; but, since the mid-1990s, there have been many important new finds, especially in China. The relatively new techniques of molecular phylogenetics have also shed light on some aspects of mammalian evolution by estimating the timing of important divergence points for modern species. When used carefully, these techniques often, but not always, agree with the fossil record.
Although mammary glands are a signature feature of modern mammals, little is known about the evolution of lactation as these soft tissues are not often preserved in the fossil record. Most research concerning the evolution of mammals centers on the shapes of the teeth, the hardest parts of the tetrapod body. Other important research characteristics include the evolution of the middle ear bones, erect limb posture, a bony secondary palate, fur, hair, and warm-bloodedness.
The following outline is provided as an overview of and topical guide to evolution:
Evolution – change in heritable traits of biological organisms over generations due to natural selection, mutation, gene flow, and genetic drift. Also known as descent with modification. Over time these evolutionary processes lead to formation of new species (speciation), changes within lineages (anagenesis), and loss of species (extinction). "Evolution" is also another name for evolutionary biology, the subfield of biology concerned with studying evolutionary processes that produced the diversity of life on Earth.
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