Category: Reptiles

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Traditionally, reptiles are taken to be a paraphyletic group, i.e. a group that does not include all descendants of the last common ancestor. A monophyletic reptile clade would incorporate birds, which are the closest living relatives of crocodiles (and so united with them as Archosauria). Reptiles, birds and mammals are amniotes (characterised by terrestrially adapted eggs with protective extra-embryonic membranes), and reptiles have been described as amniotes without fur or feathers. More than 8000 living species of non-avian reptiles have been described (and once, of course, non-avian dinosaurs roamed the earth). Most familiar are the lizards and snakes (Squamata), turtles and tortoises (Testudines) and crocodiles and alligators (Crocodilia). The ectothermic ('cold-blooded') reptiles share a number of features, the most prominent of which is probably their dry, horny, impermeable skin. In squamates, it consists of scales, overlapping thickenings of the keratinous epidermal layer, whereas turtle and crocodile skin is formed from usually non-overlapping dermal scutes. Reptiles moult, which is most obvious in snakes that shed their skin periodically in one piece. Curiously, some reptiles show temperature-dependent sex determination (TSD), where offspring sex is determined not by chromosomes but by the incubation temperature during a thermosensitive period.

Reptile reproduction is also interesting in terms of evolutionary convergence. While male turtles have evolved an inflatable penis that is strikingly similar to that of mammals, some lizards (e.g. geckos) provide prime examples of parthenogenesis. Parthenogenetic species reproduce asexually and comprise populations consisting entirely of females that produce genetically identical offspring. This reproductive mode is astonishingly common within the 'Australian arid zone', where it has not only evolved in reptiles, but also in insects and plants, probably in response to unusual environmental challenges. In general, reptile reproduction is highly diverse. Although most species lay eggs (oviparity), some lizards and snakes are ovoviviparous, retaining their eggs internally for extended periods of time. This reproductive strategy has evolved many times within this group, but also in other animal groups, such as molluscs and insects. With ovoviviparity, the developing embryo obtains nutrients from the egg yolk, whereas the embryos of truly viviparous (livebearing) animals depend on nutrients from beyond the yolk (i.e. from a placenta). Usually considered the hallmark of placental and marsupial mammals, true viviparity has also arisen in skinks such as Mabuya. Here we find a placenta remarkably similar to that of placental mammals. Fossils of pregnant female sauropterygians, ichthyosaurs and mosasaurs furthermore indicate that live birth also evolved in several disparate lineages of Mesozoic marine reptiles.

Another group of Mesozoic marine reptiles, the placodontids, were aptly nicknamed "Triassic sea cows" (Diedrich 2010, Palaeogeography, Palaeoclimatology, Palaeoecology, vol. 285, p. 293), as they show a number of striking feeding-related anatomical convergences with dugongs. Both groups evolved adaptations to grinding plant material, such as similar canal-like structures in the horny pads or teeth in the upper jaw, possibly to flush out sand and help to expel fluid while crushing food. Reptile dentition offers other intriguing examples of convergence, including the specialised tooth types of aquatic reptiles, the crustacean-trapping teeth of a group of Early Permian marine reptiles known as mesosaurs, the stunningly mammal-like dentition of the skink-like teiids and the Cretaceous Crocodyliformes and the specialised beak structures of turtles and some lizards. Vipers and cobras have independently evolved enlarged, hollow venom fangs in the upper jaw, analogues of which are also found in some lizards and even in a few mammals. On a rather more peaceful note, a Madagascan gecko feeds on honeydew produced by a sap-sucking planthopper, thus showing remarkable parallels with ants that are known for tending honeydew-producing aphids.

Chameleons are famous for capturing insects with their rapidly protrusible tongues. Such ballistic tongue protrusion has also evolved in frogs and plethodontid salamanders. But chameleons are instructive in other ways, too, as their eyes are strikingly similar to those of the sandlance, a small fish that lives in coral sands. Not only can the eyes operate independently in both groups, but they are also equipped with a telephoto arrangement, which allows for fast and highly accurate prey capture.

When it comes to sensory capacities, snakes are particularly intriguing, as some are able to perceive infrared radiation. Thermosensitive pits on the head have evolved at least twice - once in the pit vipers and, given their different arrangement, evidently separately in the more ancient boas and pythons. These pit organs are similar with regard to their ultrastructure and electrophysiological function, but differ in number, location and overall morphology. Even more remarkable is that analogues of these two types of snake infrared receptor are found in two species of beetle that use this sensory modality not for detecting "warm-blooded" prey but forest fires.

Whilst snakes are also well known for their wriggly way of locomotion, a few species do something rather different - they can glide. The ability to glide has evolved repeatedly in a surprising diversity of animals, including not only reptiles, but also mammals, frogs, ants, fish and even some species of squid. These animals employ a range of impressive morphological and behavioural adaptations to generate the required aerodynamic forces. The two species of gliding tree snake possess a uniquely specialised body shape and aerial behaviour, including rib expansion and stereotypic lateral undulations, to produce controlled glides. Several extinct reptile lineages independently evolved feathers for gliding, whereas modern reptiles, for example Draco lizards and some geckos, use different forms of skin membrane (patagia) on various parts of the body. Geckos are, however, more famous for running effortlessly across the ceiling - how do they manage to do this? Their feet are equipped with hairy adhesive pads that are rampantly convergent amongst animals, having evolved several times within the lizards alone.

Reptiles dominate deserts, and several interesting convergences are found amongst desert species. One case involves an Australian agamid, the thorny devil, and the North American horned lizards that have come up with similar solutions to the problems of food scarcity (they eat ants), aridity (they collect and transport drinking water through modified skin structures) and a need for camouflage in their largely open desert habitat. In different parts of the world, members of six lizard families have independently adapted to sand dune habitats, sharing many aspects of morphology and behaviour that allow efficient locomotion and burrowing into loose sand as well as breathing when buried. These different 'morphotypes' are categorised together as unique, sand-dwelling ('psammophilous') ecomorphs. Another example of the recurrent evolution of ecomorphs is found in the anolid lizards inhabiting the Caribbean islands of Cuba, Jamaica, Hispaniola and Puerto Rico. In response to habitat-specific selection pressures, they have independently acquired remarkably similar forms, such as 'twig' anoles and 'trunk-crown' anoles.

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This table lists all the Topics which are part of the Category "Reptiles"
Topic title Teaser text Availability
Snail eating: an asymmetric diet Snails may not be everyone's first choice on the menu but several distinct colubrid snakes have evolved expert techniques for gorging on these nutritious gastropods. Available
Defensive enrolment Curling up into a ball has evolved many times as an excellent anti-predator defence. Unavailable
Mammal-like locomotion in chameleons n/a Unavailable
Ear structural modification in iguanids n/a Unavailable
Prehensile caudal tails in reptiles and mammals n/a Unavailable
Temperate-adapted lizard ecomorphs n/a Unavailable
Rock-dwelling lizard ecomorphs n/a Unavailable
Brain development and complexity in reptiles and mammals n/a Unavailable
Chemosensory food detection in lizards and snakes n/a Unavailable
Diversification patterns in snakes and lizards n/a Unavailable
Ectoparasite load management in reptiles n/a Unavailable
Directionally asymmetric feeding in snakes n/a Unavailable
Secondary palates in crocodiles and tritylodonts n/a Unavailable
Enamel in reptile teeth n/a Unavailable
Ant-eating (myrmecophagy) n/a Unavailable
Ultraviolet (UV) vision in insects and vertebrates 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
Vibrational communication in animals What on earth could an elephant or treehoppers have in common with a seismometer? Available
Evolution of birds from feathered reptiles Birds, in the sense of flying descendants of feathered reptiles (a more expansive group than the "true" birds in today's skies), evolved several times from within the theropods. Available
"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
Dinosaurs and archosaurs "Far from being a mere curiosity, the Triassic instances [of archosaur convergence] affect our whole understanding of the evolutionary origin of important components of the Mesozoic tetrapod faunae" R.E. Molnar, J. Vert. Pal. 28, p. 586 (2008) Unavailable
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
Sea-snakes n/a Unavailable
Crustacean-trapping teeth in mesosaurs and crabeater seals The multi-lobed post-canines of Lobodon carcinophagus are a functional analogue to the long, thin cage-like teeth of Mesosaurus, as both cage and prevent the escape of small crustacean prey. Available
Teeth in aquatic reptiles Aquatic reptiles tend to display one of three dentition types, well adapted to either seize and slice large vertebrate prey, pierce and gouge slippery fish, or entrap small prey such as crustaceans. Available
Dental batteries in ceratopsians, hadrosaurs and elephants The dental batteries or 'pavements' of ceratopsians and hadrosaurs evolved independently, and yet the dentition of several more distantly related animals also converges on their highly adapted tooth form. Available
Teiid lizard dentition: convergence with other reptiles, mammals and fish Teiids are skink-like lizards whose members show a stunning diversity of tooth types, providing rich evidence of convergence within the teiids themselves, in distantly related reptile groups and even in certain mammals and fish. Available
Complex tooth occlusion in notosuchid crocodiles and tritylodonts (proto-mammals) Two unusual Early Cretaceous crocodiles provide a shining example of convergence, as their dentition parallels that observed in a group of advanced proto-mammals called tritylodonts. Available
Reptile dentition: convergence on complex occlusion Some reptiles have transverse chisel-like teeth for slicing, and others have teeth bearing projections ('cusps') that interlock and slice or grind tough food. In each case evolutionary parallels are clear both within and outside the reptiles. Available
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
Venom and venom fangs in snakes, lizards and synapsids Although the evolution of snake fangs itself provides us with a window on convergence, the presence of fang-like teeth in lizards, therapsids and mammals provides an even broader and more remarkable perspective. Available
Feeding in snakes and lizards The Turtle-headed sea snake feeds on small eggs and its feeding shows intriguing similarities to the way lizards forage, and herbivorous mammals graze and browse. Available
Ecological convergence in snakes Whip snakes are elongate, highly alert, move quickly and hunt lizards.� All are very distinctive, but the European and African whip snakes are convergent. Unavailable
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
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
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
Gliding reptiles In the reptiles, different forms of skin membrane (called ‘patagia’) and in some extinct species, primitive feathers, have evolved convergently as adaptations for gliding. 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
Parthenogenesis in Australian lizards and insects “Evidence on the origin and spread of the two best-studied cases of parthenogenesis from the Australian arid zone, the grasshopper Warramaba virgo and the gecko Heteronotia binoei, suggests that they evolved in parallel.” – Kearney et al. (2006) Molecular Ecology vol. 15, p.1743 Available
Anolis lizard ecomorphs “A classic example of convergent evolution is the set of Anolis lizard ecomorphs of the Greater Antilles.” – Langerhans, Knouft & Losos (2006) Evolution, vol. 6, p.362 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 sauropterygians “The [fossilised] embryos are mostly in articulation and their distribution on each side indicates that female Keichousaurus hui had a pair of oviducts as in ichthyosaurs and many extant lizards.” Y. Cheng et al. (2003) Nature vol. 432, p.383 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 ichthyosaurs “For me, the fossil is a transporting piece of evidence. It shows a female ichthyosaur that died late in pregnancy or perhaps while giving birth; the baby was entombed with its mother in the mud.” J. Rennie (2000) Scientific American, vol. 283(6), p.8 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
Nocturnal colour vision in moths, geckos and aye-ayes Nocturnal colour vision is clearly convergent, and found in groups as disparate as the hawkmoths (insects), geckos (reptiles) and aye-aye (mammals). Unavailable
Infrared detection in snakes Warm-blooded rodents watch out! There are heat-sensing predators on the prowl... Available
Infrared detection in animals Some snakes are famous for 'seeing' infrared, but did you know that their heat-sensing abilities are rivalled by some beetles that can detect forest fires over considerable distances? Available
Ancient opsins and vision in extinct animals Spectral tuning of the eye generally depends on key substitutions of amino acid sites in opsin proteins. Available
Defensive spines in animals Sea-urchins, porcupines (and porcupine fish), lizards and many other animals bristle with defensive spines. Unavailable
Telephoto eyes in animals Pursued by the paparazzi? Watch out for those animals equipped with telephoto lenses... 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
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
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
Sap feeding and honey-dew production in insects Interestingly, it has now been shown that the saliva of the aphids has an analogue to the anti-coagulant properties of blood suckers, subverting the wound repair mechanism of the plant. Available
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
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
Worm-like body form Man is but a worm, but so are many other vertebrates... Available
Viviparity (live birth) in animals Viviparity is rampantly convergent, with famous examples in the reptiles, notably the lizards and snakes. Unavailable
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
Defence in frogs: toxins and camouflage The many striking examples of convergence most famously include the case of mimicry, but the question of defence also extends to the use of toxins (and venoms), such as alkaloids, where we also find molecular convergence. Available