Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes. Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads. To accommodate their narrow bodies, snakes' paired organs appear one in front of the other instead of side by side, and most have only one functional lung. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca. Lizards have independently evolved elongate bodies without limbs or with greatly reduced limbs at least twenty-five times via convergent evolution, leading to many lineages of legless lizards. These resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal.
Ophidia is a group of squamate reptiles including modern snakes and reptiles more closely related to snakes than to other living groups of lizards.
Many vertebrates are limbless, limb-reduced, or apodous, with a body plan consisting of a head and vertebral column, but no adjoining limbs such as legs or fins. Jawless fish are limbless but may have preceded the evolution of vertebrate limbs, whereas numerous reptile and amphibian lineages – and some eels and eel-like fish – independently lost their limbs. Larval amphibians, tadpoles, are also often limbless. No mammals or birds are limbless, but some feature partial limb-loss or limb reduction.
Petrolacosaurus is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, 40-centimetre (16 in) long reptile, and one of the earliest known reptile with two temporal fenestrae. This means that it was at the base of Diapsida, the largest and most successful radiation of reptiles that would eventually include all modern reptile groups, as well as dinosaurs and other famous extinct reptiles such as plesiosaurs, ichthyosaurs, and pterosaurs. However, Petrolacosaurus itself was part of Araeoscelida, a short-lived early branch of the diapsid family tree which went extinct in the mid-Permian.
Najash is an extinct genus of basal snake from the Late Cretaceous Candeleros Formation of Patagonia. Like a number of other Cretaceous and living snakes it retained hindlimbs, but Najash is unusual in having well-developed legs that extend outside the rib cage, and a pelvis connected to the spine.
Haasiophis, consisting of the sole species Haasiophis terrasanctus, is an extinct genus of snakes with hind limbs. It is one of three genera of Cenomanian snakes known to have possessed hindlimbs.
Pachyrhachis is an extinct genus of snake with well developed hind legs known from fossils discovered in Ein Yabrud, near Ramallah, in the central West Bank. It is a relatively small snake, measuring more than 1.5 metres (4.9 ft) long at maximum. Pachyrhachis appears to have been an ancient marine snake; the fossils occur in a marine limestone deposit, and the thickened bone of the ribs and vertebrae would have functioned as ballast to decrease the buoyancy of the animal, allowing it to dive beneath the ancient Cretaceous seas that it once inhabited.
Pelvic spurs are external protrusions found around the cloaca in certain superfamilies of snakes belonging to the greater infraorder Alethinophidia. These spurs are made up of the remnants of the femur bone, which is then covered by a corneal spur, or claw-like structure. This femur derives from ancestral hind limbs found in the most recent common ancestor of modern snakes and the other reptiles of the clade Toxicofera, many of which have fully functional front and hind limbs. Due to the fact that the spurs derive from the ancestral state of functional legs, but are no longer functional for locomotion specifically, these structures do meet the criteria for being considered vestigial. Nonetheless, uses for the structures have been thoroughly documented. Species that have external spurs have corresponding muscles, neurological structures, and vascularization to allow for independent movement. The spurs are more pronounced and visible in male specimens and have been observed in use during courtship behavior. The spurs are specifically used in the clasping and stimulation of females by males during courtship and mating. In certain species, males will also use their spurs to engage in combat with one another.
Adriosaurus is an extinct genus of squamate which lived in what is now Slovenia and other parts of Europe during the Late Cretaceous. It was small, snake-like reptile, with type species measuring up to 30 cm (12 in) in length. This is the first fossil record of vestigial limbs in lizards. It lost its manus and forearm completely in order to elongate its axial skeleton. These unique anatomical features led to discussions of the evolutionary patterns of limb reduction in Squamata.
Kaganaias is an extinct genus of basal and oldest dolichosaur that lived in what is now Japan during the Early Cretaceous. Kaganaias was semi-aquatic and is the only known aquatic squamate known from before the Cenomanian stage of the Cretaceous. It is also the first to be found in an inland area, instead of on the coast where aquatic squamates are commonly found. Its generic name is derived from Kaga Province, the old name for the Ishikawa Prefecture where the specimens were found, while the species name hakusanensis comes from the mountain that gives its name to Hakusan the city near its find site. The geological formation in which the specimens were found, the Kuwajima Formation, stands alongside the Tetori River and has been the site of numerous other finds including molluscs, dinosaurs, fish, and pterosaurs.
Polycotylus is a genus of plesiosaur within the family Polycotylidae. The type species is P. latippinis and was named by American paleontologist Edward Drinker Cope in 1869. Eleven other species have been identified. The name means 'much-cupped vertebrae', referring to the shape of the vertebrae. It lived in the Western Interior Seaway of North America toward the end of the Cretaceous. One fossil preserves an adult with a single large fetus inside of it, indicating that Polycotylus gave live birth, an unusual adaptation among reptiles.
Carsosaurus is a genus of extinct amphibious reptiles, in the mosasaur superfamily, containing only the species Carsosaurus marchesetti. It is known from a single individual that lived during the Upper Cretaceous in what is now Slovenia. The specimen is well-preserved, containing many different bones as well as some skin impressions and sternal cartilage. While more remains are needed to be certain, it is generally thought to belong to the Aigialosauridae. In life, it was an amphibious creature that spent most of its time on land, although its later relatives would become fully aquatic.
Fruitadens is a genus of heterodontosaurid dinosaur. The name means "Fruita teeth", in reference to Fruita, Colorado (USA), where its fossils were first found. It is known from partial skulls and skeletons from at least four individuals of differing biological ages, found in Tithonian rocks of the Morrison Formation in Colorado. Fruitadens is one of the smallest known ornithischian dinosaur, with young adults estimated at 65 to 75 cm in length and 0.5 to 0.75 kg in weight. It is interpreted as an omnivore and represents one of the latest-surviving heterodontosaurids.
Acteosaurus is an extinct genus of aquatic lizard that lived in the upper Cretaceous period. Its species, A. tommasinii and A. crassicostatus, were described in 1860 and 1993. Though A. crassicostatus is probably a junior synonym for Adriosaurus suessi, A. tommasinii was found to be similar to coniasaurs, mosasauroids, and a sister taxon to modern snakes in 2010.
Antlerpeton is an extinct genus of early tetrapod from the Early Carboniferous of Nevada. It is known from a single poorly preserved skeleton from the Diamond Peak Formation of Eureka County. A mix of features in its compound vertebrae suggest that Antlerpeton is a primitive stem tetrapod that has affinities with later, more advanced forms. Its robust pelvis and hind limbs allowed for effective locomotion on land, but the animal was likely still tied to a semiaquatic lifestyle near the coast.
Vivian de Buffrénil is a French histologist and paleobiologist who has worked at the Muséum National d'Histoire Naturelle in Paris from 1982 to 2021. His doctorate (1980) and his doctorat d'état (1990), a diploma now replaced by the habilitation, were supervised by Armand de Ricqlès. His main fields of interest include basic histological descriptions, growth dynamics as recorded in bone growth marks, and adaptation of the tetrapod skeleton to a secondarily aquatic lifestyle. He is also interested in life history and population dynamics of exploited or threatened reptile taxa, especially among Varanidae and Crocodilia. He has published at least 92 papers, including 76 research papers, 10 reports on exploited or threatened species, and six popular papers.
Tetrapodophis is an extinct genus of lizard from the Early Cretaceous (Aptian) aged Crato Formation of Brazil. It has an elongate snake-like body, with four limbs. Tetrapodophis has been considered by some authors to be one of the oldest members of Ophidia. However, this classification has been disputed by some other authors, who identify Tetrapodophis as a dolichosaurid much less closely related to snakes.
Pachyophis is an extinct genus of Simoliophiidae snakes that were extant during the Cenomanian stage of the Late Cretaceous period. More specifically, it was found to be from the Cenomanian Age about 93.9-100.5 million years ago in the suburb area of Bileca, Herzegovina.
Serikornis is a genus of small, feathered anchiornithid dinosaur from the Upper Jurassic Tiaojishan Formation of Liaoning, China. It is represented by the type species Serikornis sungei.
Dolichosauridae is a family of Cretaceous aquatic lizards. They are widely considered to be the earliest and most primitive members of Mosasauria, though some researchers have recovered them as more closely related to snakes.
