Category: Anatomy
[Skip to list of Topics for this Category →]
In some ways, animals are like machines, with skeletons, pumps, lungs, blood systems and yes, penises. Is it so surprising that the number of ways in which these organs work is actually rather limited, so that again and again the same solution is arrived at? Now this matters not only because of these providing splendid examples of convergence, but also because it has an immediate bearing on such features as walking, swimming, and picking up objects. Did you know the flexible tentacle of an octopus actually works just like our arm? Or that the way a cockroach walks is very similar to how mammals do it, despite insect legs and mammalian limbs being very different indeed? Or that the adhesive pads, which allow geckos to run so effortlessly across the ceiling, are employed by many other groups of animals too? In fact we invite you to think of any biological structure that has only evolved once. Any offers?
Even curious structures such as love darts that are used to stab the partner during courtship (which is likely to facilitate sperm transfer and fertilisation) have evolved several times independently. Not only can they be found in slugs and snails but an equivalent is also present in some earthworms (that are hermaphrodites, too).
Gliding has evolved repeatedly in various animal groups, such as mammals, reptiles (even snakes!), frogs and even ants and bristle-tails. To generate the necessary aerodynamic forces, different groups rely on different mechanisms and structures. For example, many mammals use gliding membranes or patagia, which extend from fore- to hindlimbs. In some reptiles and amphibians, the patagia stretch between fingers, whereas gliding tree snakes rely on a flattened body shape (with the ribs splayed outwards during descent) in combination with stereotypic lateral undulations. With a similar function, gliding ants (e.g. Cephalotes atratus) possess lateral flaps, or flanges, on their bodies.
Teeth are a rich source of insight into evolutionary convergence, having evolved (and subsequently been lost) a number of times. In terms of structure and function, several groups of snakes have independently invented hinged teeth that can fold down to deal with hard-bodied prey, crustacean-trapping teeth are found in the extinct mesosaurs as well as in crabeater seals, and dental batteries at the back of the mouth evolved in some groups of dinosaurs (especially hadrosaurs and ceratopsians) and also elephants to shear and slice vegetation. Teeth are, of course, subject to wear and the various strategies to deal with this inevitability, such as the incorporation of zinc to harden them, are exceedingly convergent, too. On the more curious side, several groups of frogs have independently evolved fangs, which could allow them to tackle larger prey or make males more attractive to females.
In plants, xylem, a transport tissue conducting water and nutrients from the plant's roots up to the leaves, is characteristic of the angiosperms and yet has evolved independently in several other groups of plants (probably at least seven times). Wood (or secondary xylem) characterises the angiosperms, gymnosperms and pteridosperms, and yet it also evolved in a few lycophytes (Isoetes and the extinct Lepidodendron) and the giant Carboniferous swamp plant Calamites (a monilophyte). While the conifers developed torus-margo pits to rival the water conduction efficiency of angiosperm xylem 'vessels', several angiosperms independently reverted from vessels to 'tracheids' in order to cope with frequent freeze-thaw cycles.
| Topic title | Teaser text | Availability |
|---|---|---|
| Mammal-like locomotion in chameleons | n/a | Unavailable |
| Echolocation in bats | How can bats navigate in total darkness amongst trees and branches, but still locate a tiny, fluttering insect with extraordinary acuity? All made possible through echolocation, an astonishing sensory mechanism… | Available |
| Endothermy ("warm-bloodedness") | n/a | Unavailable |
| Filter-feeding rotifer anatomy | n/a | Unavailable |
| Ear structural modification in iguanids | n/a | Unavailable |
| Prehensile caudal tails in reptiles and mammals | n/a | Unavailable |
| Marsupials with aye-aye-like digits | n/a | Unavailable |
| Pycnodontid fish dentition | n/a | Unavailable |
| Fin collagen in tuna, dolphins and sharks | n/a | Unavailable |
| Agriculture in dugongs | When you think of grazing mammals, you might envisage large herds of antelopes roaming African savannahs. Did you know that there is an equivalent in the ocean, feeding on seagrass? | Available |
| Pressure sensitivity and the tactile sense (excluding the lateral line) | The star-nosed mole is famous for, well, its nose, but do you have any idea what these peculiar 'tentacles' are for? The answer is rather touching and, of course, convergent... | Available |
| Foam nests in animals | Nests crop up everywhere, but one made out of foam? Might not sound like a great idea, but it is. And no surprise, it has evolved several times... | Available |
| Hydrogenosomes and mitosomes | n/a | Unavailable |
| Trabeculae (skeletons) | n/a | Unavailable |
| Pufferfish (and inflation) | Pufferfish are some of the most extraordinary fish to have evolved, especially because of their capacity to swallow water and inflate themselves to something like a football. Not only that but some representatives can be deadly to the unwary diner... | Available |
| Lunglessness | n/a | Unavailable |
| Bacterial cell shapes | A fascinating example of convergence in bacterial cell shape is the independent evolution of multicellularity in magnetotactic bacteria, with striking similarities to the arrangement seen in eukaryotic green algae. | Unavailable |
| "Broken jaw" - mandibular and maxillary jaw joints | At first sight having a jaw with a joint seems a contradiction in terms, but such exist and not only are obviously functional, but needless to say convergent. | Available |
| Myelinated nerves in vertebrates, annelids and crustaceans | Myelinated nerves are an excellent biological solution and needless to say have evolved independently in several groups other than vertebrates. In each case myelination is associated with very rapid nervous conduction and often escape reactions. | Available |
| Eel-like ("anguilliform") fish | Within the African catfish, eel-like forms have evolved four times independently, and other expmales include the Neotropical swamp eel, the true eels (which include the morays) and the lamprey. | Unavailable |
| Explosive discharge in fungi and plants | The very rapid release of reproductive bodies is perhaps most famous in the fungi, where several methods of flinging spores at high velocity have evolved independently. | Available |
| Moray eels | Eels masquerading as snakes sounds interesting, and that is before they go hunting with their friends the groupers... | Available |
| Feathers and similar integumentary structures | n/a | Unavailable |
| Suction feeding in fish, amphibians, reptiles and aquatic mammals | Probably everyone is familiar with the walrus, but did you know that it generates a vacuum in its mouth to suck clams out of their shells? And this is just one example of suction feeding, the feeding mode typically used by bony fish… | Available |
| Thermal sensing in mammals and insects | Insects and mammals have a group of ion channels (known as TRPs or Transient Receptor Potential channels) that are very similar and assumed to have a single origin. | Unavailable |
| Beak structures in reptiles and birds | Among reptile taxa with beak structures, we find several cases of convergent evolution, for example between turtles, Uromastyx lizards, a number of herbivorous dinosaurs and the tuatara (Sphenodon) of New Zealand. | Available |
| Desert plants with succulent stems | Fleshy, succulent stems have evolved in several distantly related desert plant families, including cacti, certain species of Euphorbia and two genera of the family Asclepiadaceae, Hoodia and Stapelia. | Available |
| Desert plants with succulent leaves | Perhaps the most striking case of convergence among leaf succulents occurs between Agave and its relatives Yucca and Hesperaloe in the Americas and Aloe and its relatives (e.g. Haworthia and Gasteria) in Africa. | Available |
| Crabs: insights into convergence | You might think of crabs mainly as food, but this group is also highly instructive in terms of convergence… | Available |
| Limblessness in lizards | What's that slithering towards you? A snake? Look more closely, look convergently... | Available |
| Independent eye movement in fish, chameleons and frogmouths | One of the most surprising convergences amongst animals is that seen between a small fish that lives in coral sands, known as the sandlance, and the lizards known as chameleons. | Available |
| SNARE protein receptors and the evolution of multicellularity | There is an intriguing correlation with larger numbers of SNAREs and multicellularity, at least in plants and animals. | Unavailable |
| Bats: Insights into convergence | Bats show a fascinating array of convergences, from echolocation to flight to nectar feeding. Vampire bats can even detect infrared radiation, while others might be able to see into the ultraviolet end of the spectrum. | Available |
| Echolocation in toothed whales and ground-dwelling mammals | Given the extraordinary powers of echolocation in bats, it is not surprising that this group has received the most attention. However, they are not the only mammals to have evolved echolocation. Who invented sonar millions of years before the Navy? | Available |
| Membranes and vesicle formation in bacteria | Examples include endoplasmic membranes with a capacity to attach ribosomes in E. coli, and in the hyperthermophile Archaea what are evidently vesicles that are believed to have budded from a cytoplasmic membrane. | Unavailable |
| Pharyngeal jaws in teleost fish | One of the great evolutionary breakthroughs in the teleost fish was the conversion of some of the elements that supported the gill bars into a second set of pharyngeal teeth that complemented the oral teeth. See how a fish becomes a snake! | Available |
| Durophagy (hard prey-eating) in fish | Plenty of animals have an extraordinary capacity to crush hard prey and this has evolved independently many times in the vertebrates. If you suspect it is a durophage, watch your fingers! | Available |
| Dinoflagellate "nematocysts" | Examples of convergence within the dinoflagellates range from the evolution of a camera-like eye to stinging 'nematocysts' reminiscent of those in jellyfish. | Available |
| Sodium voltage-gated ion channels | Sodium voltage-gated ion channels are vital to electric signal transmission, but it is less widely appreciated that they are convergent and have evolved at least twice in groups outside the animals. | Unavailable |
| Gliding lizards, frogs and ants | Tree-dwelling (‘arboreal’) ants capable of controlled gliding do so when dislodged or threatened by predation. Gliding species include members of three disparate families: Myrmicinae, Pseudomyrmecinae and Formicinae. | Available |
| Gliding in feathered reptiles | A number of reptile species have been discovered in the Mesozoic fossil record, bearing feathers that were apparently used to support gliding locomotion, rather than true, powered flight as we see in present day birds. | Available |
| Gliding in Draco lizards and tree snakes | “The agamid lizard genus Draco (consisting of the so-called ‘flying dragons’) exhibits an array of morphological traits associated with gliding.” – A.P. Russell & L.D. Dijkstra (2001) Journal of the Zoological Society of London, vol. 253, page 457 | Available |
| Gliding mammals | Gliding mammals rely primarily on extensive skin membranes or ‘patagia’ that stretch between fore- and hind-limbs, creating a wing-like structure. | Available |
| Sand-dwelling (psammophilous) lizard ecomorphs | Desert sand dunes represent an extreme environmental setting in which selective forces have apparently generated dune ‘ecomorphs’ in six lizard families. – Lamb et al. (2003) Biological Journal of the Linnean Society, vol. 73, p. 253 | Available |
| Ecological adaptations in Moloch and Phrynosoma lizards | Lizards of the genera Phrynosoma and Moloch have been considered a classic example of convergent evolution J. J. Meyers & A. Herrel (2005) The Journal of Experimental Biology, vol. 208, p. 114 | Available |
| Drinking adaptations in desert lizards | Both Moloch horridus and [...] Phrynosoma cornutum have the remarkable ability to transport water over their skin’s surface to the mouth where drinking occurs. Sherbrooke et al. (2007) Zoomorphology, vol. 126, p. 89 | Available |
| Mammal-like placentation in skinks (and fish) | “Only two types of vertebrates [have] evolved a reproductive pattern in which the chorioallantoic placenta provides the nutrients for fetal development. One is [...] the eutherian mammals […], and the other, a few lineages of the family Scincidae.” A.F. Flemming (2003) J Exp Zool 299A 33-47 | Available |
| Viviparity in mosasaurs | An exceptionally preserved gravid female of the aigalosaur Carsosaurus contains at least at least four advanced embryos […] Their orientation suggests that they were born tail-first […] to reduce the possibility of drowning, an adaptation shared with other other highly aquatic amniotes” M.W. Caldwell & M.S.Y. Lee (2001) Proceedings of the Royal Society of London B, vol. 268, p.2397 | Available |
| Viviparity in lizards, snakes and mammals | “In over 100 lineages of […] squamates, the oviduct has been recruited for viviparous gestation of the embryos, representing a degree of evolutionary convergence that is unparalleled in vertebrate history.” D. G. Blackburn (1998) Journal of Experimental Zoology, vol.282, p.560 | Available |
| Infrared detection in snakes | Warm-blooded rodents watch out! There are heat-sensing predators on the prowl... | Available |
| Mitochondrial lens formation in flatworms | In some of the flatworms (platyhelminthes) the lens is formed from mitochondria, and it is intriguing to speculate whether a mitochondrial enzyme has been co-opted to provide a crystallin. | Available |
| Defensive spines in animals | Sea-urchins, porcupines (and porcupine fish), lizards and many other animals bristle with defensive spines. | Unavailable |
| Hearts in cephalopods and vertebrates | There is a striking convergence between the aorta of the cephalopod and vertebrate heart, notably in its structure and the employment of elastic proteins. | Available |
| Corneal nipple arrays in insect eyes | Anti-reflection coating? Not only on mobile phone displays, but also on insect eyes... | Available |
| Milk production in tsetse flies and cockroaches | In at least some cases the cycle of milk secretory activity in tsetse flies and coackroaches is strikingly similar to that found in the mammary glands of mammals. | Unavailable |
| Wire plants, moas and elephant birds | Madagascar and New Zealand were once home to giant herbivorous birds. And the plants have not forgotten... | Available |
| Compound eyes in ark clams | Read on if you want to know more about bivalves with burglar alarms… | Available |
| Camera eyes in gastropod molluscs | The fast-moving cephalopod molluscs are famous for their camera eyes, but why on earth have gastropod snails, which are not exactly known for their speed, evolved this superb visual organ at least four times? | Available |
| Scanning eyes in molluscs and arthropods | Some sea snails have a linear retina. What a hopeless arrangement, to see the world through just a narrow slit! Not quite, because they have come up with a rather intriguing trick to extend their visual field - and it's a trick too good to use only once. | Available |
| Telephoto eyes in animals | Pursued by the paparazzi? Watch out for those animals equipped with telephoto lenses... | Available |
| Camera-like eyes in arthropods | Arthropods are famous for their compound eyes, but some groups have had a fair crack at evolving the optically superior camera eye… | Available |
| Adhesive pads: from geckos to spiders | In terms of adhesive pads we find they have a remarkably wide distribution evolving in at least four distinct groups, including members of the reptiles, amphibians, arthropods and mammals, with tentative parallels in sea urchins. | Available |
| Pollen harvesting adaptations in bees (and honey-wasps) | n/a | Unavailable |
| Mussel attachment and the Pinna byssus | It is clear that the Pinna byssus has unusual properties in comparison to its equivalent in the bivalve mussel, and is conspicuously different in terms of crystallinity. | Available |
| Bacterial carboxysomes (and other microcompartments) | It is now clear that the cellular construction of at least the eubacteria is more complex than realized, and includes organelle-like structures known as microcompartments, of which the best known are the carboxysomes. | Available |
| Filter feeding in whales, birds and reptiles | Filter feeding is most familiar in the baleen whales , but closely analogous arrangements have appeared at least twice in the birds, first the flamingos and second the sub-antarctic broad-billed prions. | Unavailable |
| Birds: insights into convergence | Intriguing ecological and morphological parallels can be found among the Neoaves. Many of these forms were initially believed to be each other's closest relatives, but are now widely recognised as classic examples of convergence. Think how similar swifts and swallows are, but they are only distantly related. | Available |
| Gut fermentation in herbivorous animals | Ever tried eating a newspaper? Don't. Plant cell walls contain cellulose, which is notoriously difficult to digest. Considering that all vertebrates lack the enzymes to attack this polysaccharide, how do so many of them manage to survive on a plant diet? | Available |
| Baculum (penile bone) in mammals | Ouch!! Gentlemen, fancy a bone in your penis? Seems a bit risky, given it could fracture during copulation. Even our near ancestors had such a bone. It has probably evolved several times, but what is its function? | Available |
| Bacterial flagellar motors | The bacterial flagellum has proved to be a cause celebre because of its high-jacking by the “intelligent design” movement who argue that it is “irreducibly complex” and therefore could not have evolved by Darwinian processes. | Unavailable |
| Sabre-toothed cats and marsupials | Marsupials with giant fangs? Yes, not all of the extinct sabre-toothed cats were actually cats… | Available |
| Viverrid ecomorphs: from linsangs to Binturongs | The viverrids or civets are a highly successful group of carnivores, fairly closely related to the cats and showing several striking examples of convergence. | Unavailable |
| Cavitation: bubble formation in plants, reptiles and shrimps | The formation of bubbles in a fluid is known as cavitation. Typically this occurs at low pressures, and is perhaps best known in the xylem of plants where embolisms can be destructive to the surrounding tissues. | Available |
| Halteres in flies, strepsipterans and beetles | Halteres are balancing organs found in flies (dipterans) where the hind-wings are modified as balancing structures, and are convergent with the arrangement in the strepsipteran insects. | Unavailable |
| Electric fish: insights into convergence | Ever seen an electric eel in an aquarium? Don’t dare putting your hand in the tank... | Available |
| Chloroplast and mitochondrial plastid origins | Not only are there intriguing parallels in the story of gene loss in chloroplasts and mitochondria, but there is also the re-invention of bacterial pathways, such as oxidation of quinols. | Available |
| Raptorial appendages in mantids and other arthropods | The praying mantises exercise a peculiar fascination, not only because of their lunging predatory habits, but also because on occasion the process of copulation ends with a decapitated male being chewed to pieces by the female while the reproductive movements continue. | Unavailable |
| Strepsipterans: convergent halteres and eyes | Strepsipteran females spend their whole life inside a wasp. The males are rather more exciting, particularly in terms of convergence… | Available |
| Beetles: insights into convergence | The beetles are probably the most diverse animal group on earth, so it is not at all surprising that they provide many fascinating insights into convergence. | Available |
| Woodpeckers and woodpecker-like birds and mammals | You think woodpeckers are unique? Consider the ovenbirds. Or even the curious aye-aye. | Available |
| Trap-jaws in ants | Remarkable trap-jaw structures have evolved independently in various ants. | Unavailable |
| Sharks and rays (elasmobranchs): insights into convergence | In terms of sensory evolution the elasmobranchs are of particular interest, because independently of other fish and even some mammals (e.g. duck-billed platypus) they have evolved electrosensory systems. | Unavailable |
| Swimming and thermoregulation in sharks and tuna | Thunniform swimming depends on a large, lunate tail that is joined to the rest of the body via a narrow peduncle. Whilst the tail flicks backwards and forwards, so propelling the animal, the rest of the body hardly moves sideways. | Available |
| Vultures: insights into convergence | Vultures are not only charistmatic birds in the popular imagination, but are strikingly convergent, as the Old World and New World vultures are not closely related. | Unavailable |
| Developmental genetic pathways to convergence | At first sight there is a fairly simple dichotomy between convergent features that have effectively the same genetic basis, and those where the same feature emerges but the underlying genetics are different. The former, however, is somewhat more complicated... | Available |
| Locomotion in insects: walking and flying | It is now realized that the locomotory action of the walking legs in an insect such as a cockroach is strikingly similar to that found in mammals whereby the posterior legs are primarily propulsive whereas the anterior set have a more complex function that includes braking. | Unavailable |
| Crustaceans: insights into convergence | Whilst predominantly marine, quite a number of crustaceans have invaded freshwater habitats and even more interestingly a few demonstrate terrestrialization, effectively freeing themselves from their aquatic ancestry. | Available |
| Elephants: senses, intelligence and social structure | There is evidence that elephants are sensitive to seismic communication, with the large pads of the feet and the trunk tip capable of picking up vibrations transmitted through the ground. | Unavailable |
| Bivalve molluscs: convergent shells and symbioses | Despite their range of shell types, there is evidence of extensive convergence, notably amongst the fresh water swan-mussels (unionids), mytilids and anomalodesmatans. | Unavailable |
| Molluscan radulas and boring organs | Most likely the radula is primitive to the molluscs, but not surprisingly the various functional and feeding requirements have led to significant convergence. | Unavailable |
| Gastropod molluscs: snail shell anatomy | Snail shells typically form a helical spiral, but within this geometry there is a considerable degree of convergence. | Unavailable |
| Transparent tissues: eyes, bodies and reflective surfaces | Read on if you want to know about the numerous animal equivalents to the invisible man... | Available |
| Love darts in slugs, snails and annelid worms | The curious habit of stabbing their partners with sharp calcareous (or chitinous) darts during courtship and prior to actual copulation has understandably attracted considerable attention. | Available |
| Penis form in mammals, turtles, birds and octopus | The specific case of a penis with a hydrostatic structure, as well as an array of collagen fibres that allows both expansion and guards against aneurysms, has evolved in a strikingly convergent fashion in mammals and turtles. | Available |
| Statoliths and balance in animals | An almost universal, but convergent, method to detect changes in orientation is for small grains (statoliths) to be attached to fine hairs, whose movement triggers nervous impulses. | Unavailable |
| Hearing and ears in animals | Hearing has evolved independently in a number of groups, notably in the insects and vertebrates. | Unavailable |
| Worm-like body form | Man is but a worm, but so are many other vertebrates... | Available |
| Tongues of chameleons and amphibians | Convergence in tongue function represents repeated morphological exploration within different lineages made possible by loss of an ancestral functional constraint | Available |
| Burrowing: from worms to vertebrates | Quite a few adaptations are useful for burrowing into the soil. So it is not exactly surprising that they have evolved several times... | Available |
| Swim bladders of fish and the octopus Ocythoe | Swim bladders have evolved independently in fish and in Ocythoe octopus females. | Unavailable |
| Moulting in arthopods, annelids and other animals | Moulting has, however, evolved independently in other groups, including the annelids where some polychaetes shed their jaws. | Unavailable |
| Octopus arm function | If you want to see a truly remarkable example of convergence, then present an octopus with a piece of food and have a high-speed camera ready… | Available |
| Sexual mimicry in mammals and cephalopods | Sexual mimicry is widespread, and the most famous example is probably the male-like genitalia in the females of the hyaena. | Unavailable |
| Ammonoids: fossil insights into convergence | Ammonoids, perhaps most familiar from the Mesozoic ammonites, are abundant as fossils and typically occur as planispiral forms. They show extensive homeomorphy, that is the same shapes repeatedly evolve. | Unavailable |
| Camera eyes of cephalopods | The remarkable similarity between the camera eyes of cephalopods and vertebrates is one of the best-known examples of evolutionary convergence. | Available |
| Reflective tissues | Other cephalopods achieve reflectivity by employing collagen fibrils, of which the deep-sea Vampyroteuthis is perhaps the most striking example. | Unavailable |
| Octopus and other cephalopods: convergence with vertebrates | What could be more different from us than the alien-like octopus? Hold on. Look it in the eye and think again. | Available |
| Camera eyes in vertebrates, cephalopods and other animals | Camera eyes are superb optical devices, so it is not surprising that they have evolved several times. But why, of all animals, in the brainless jellyfish? Or for that matter in a slow-moving snail? | Available |
