taxon_rank hallopus
Lizards are a widespread ___MASK59___ of squamate reptiles , with over 6 , 000 ___MASK76___ , ranging across all continents except Antarctica , as well as most oceanic island chains . The ___MASK59___ , traditionally recognized as the suborder Lacertilia , is defined as all extant members of the Lepidosauria ( reptiles with overlapping scales ) that are neither sphenodonts ( i . e ., tuatara ) nor snakes  they form an evolutionary grade . While the snakes are recognized as falling phylogenetically within the Toxicofera clade from which they evolved , the sphenodonts are the sister ___MASK59___ to the squamates , the larger monophyletic ___MASK59___ , which includes both the lizards and the snakes . Amphisbaenia ( called amphisbaenians or worm lizards ) is a ___MASK59___ of usually legless squamates , comprising over 180 extant ___MASK76___ . Amphisbaenians are characterized by their long bodies , the reduction or loss of the limbs , and rudimentary eyes . As many ___MASK76___ have a pink body and scales arranged in rings , they have a superficial resemblance to earthworms . While the genus " Bipes " retains forelimbs , all other genera are limbless . Although superficially similar to the snakes and Dibamidae , recent phylogenetic studies suggest that they are most closely related to the Lacertidae . Amphisbaenians are widely distributed , occurring in North America , Europe , Africa , South America , and the Caribbean . Most ___MASK76___ are less than long . Little is known of them outside of their anatomy , and even that is difficult to study due to the mechanics of dissecting such small animals . The Triassic  Jurassic extinction event marks the boundary between the Triassic and Jurassic periods , , and is one of the major extinction events of the Phanerozoic eon , profoundly affecting life on land and in the oceans . In the seas , a whole ___MASK81___ ( conodonts ) and 34 % of marine genera disappeared . On land , all pseudosuchians ( non - ornithodiran archosaurs ) other than crocodylomorphs ( Sphenosuchia and Crocodyliformes ), some remaining therapsids , and many of the large amphibians became extinct . The ___MASK85___ Tetrapoda ( Ancient Greek s tetrapods , " four - footed "), or the tetrapods , comprises the first four - limbed vertebrates and their descendants , including the living and extinct amphibians , birds , mammals , reptiles and some ancient , exclusively aquatic creatures such as the Acanthostega . Tetrapods evolved from the lobe - finned fishes around 390 million years ago in the middle Devonian Period , with modern tetrapod groups having appeared by the late Devonian , 367 . 5 million years ago . The specific aquatic ancestors of the tetrapods , and the process by which land colonization occurred , remain unclear , and are areas of active research and debate among palaeontologists at present . Sphenosuchia is a ___MASK69___ of basal crocodylomorphs that first appeared in the Triassic and occurred into the Middle Jurassic . Most were small , gracile animals with an erect limb posture . They are now thought to be ancestral to crocodyliforms , a ___MASK59___ which includes all living crocodilians . Dinosaurs are a diverse ___MASK59___ of animals of the clade Dinosauria that first appeared during the Triassic . Although the exact origin and timing of the evolution of dinosaurs is the subject of active research , the current scientific consensus places their origin between 231 and 243 million years ago . They became the dominant terrestrial vertebrates after the Triassic  Jurassic extinction event 201 million years ago . Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous  Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago . In zoological nomenclature , a type ___MASK76___ (" ___MASK76___ typica ") is the ___MASK76___ name with which the name of a genus or subgenus is considered to be permanently taxonomically associated , i . e ., the ___MASK76___ that contains the biological type specimen ( s ). A similar concept is used for suprageneric groups called a type genus . In biology and ecology , extinction is the end of an organism or of a ___MASK59___ of organisms ( taxon ), normally a ___MASK76___ . The moment of extinction is generally considered to be the death of the last individual of the ___MASK76___ , although the capacity to breed and recover may have been lost before this point . Because a ___MASK76___ ' potential range may be very large , determining this moment is difficult , and is usually done retrospectively . This difficulty leads to phenomena such as Lazarus taxa , where a ___MASK76___ presumed extinct abruptly " reappears " ( typically in the fossil record ) after a period of apparent absence . Herpetology ( from Greek "" herpein "" meaning " to creep ") is the ___MASK47___ of zoology concerned with the study of amphibians ( including frogs , toads , salamanders , newts , and caecilians ( gymnophiona )) and reptiles ( including snakes , lizards , amphisbaenids , turtles , terrapins , tortoises , crocodilians , and the tuataras ). Batrachology is a further subdiscipline of herpetology concerned with the study of amphibians alone . The Triassic is a geologic period and system which spans 50 . 9 million years from the end of the Permian Period million years ago ( Mya ), to the beginning of the Jurassic Period Mya . The Triassic is the first period of the Mesozoic Era . Both the start and end of the period are marked by major extinction events . The Triassic was named in 1834 by Friedrich von Alberti , after the three distinct rock layers (" tri " meaning " three ") that are found throughout Germany and northwestern Europe  red beds , capped by marine limestone , followed by a ___MASK91___ of terrestrial mud - and sandstones  called the " Trias ". Snakes are elongated , legless , carnivorous reptiles of the ___MASK69___ Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears . Like all squamates , snakes are ectothermic , amniote vertebrates covered in overlapping scales . Many ___MASK76___ of snakes have skulls with several more joints than their lizard ancestors , enabling them to swallow prey much larger than their heads with their highly mobile jaws . To accommodate their narrow bodies , snakes ' paired organs ( such as kidneys ) appear one in front of the other instead of side by side , and most have only one functional lung . Some ___MASK76___ retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca . A clade ( from , " klados ", " ___MASK47___ ") is a ___MASK59___ of organisms that consists of a common ancestor and all its lineal descendants , and represents a single " ___MASK47___ " on the " tree of life ". Amphibians are ectothermic , tetrapod vertebrates of the ___MASK81___ Amphibia . Modern amphibians are all Lissamphibia . They inhabit a wide ___MASK62___ of habitats , with most ___MASK76___ living within terrestrial , fossorial , arboreal or freshwater aquatic ecosystems . Thus amphibians typically start out as larvae living in water , but some ___MASK76___ have developed behavioural adaptations to bypass this . The young generally undergo metamorphosis from larva with gills to an adult air - breathing form with lungs . Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin . They are superficially similar to lizards but , along with mammals and birds , reptiles are amniotes and do not require water bodies in which to breed . With their complex reproductive needs and permeable skins , amphibians are often ecological indicators ; in recent decades there has been a dramatic decline in amphibian populations for many ___MASK76___ around the globe . Tuatara are reptiles endemic to New Zealand . Although resembling most lizards , they are part of a distinct lineage , the ___MASK35___ Rhynchocephalia . Their name derives from the Mori language , and means " peaks on the back ". The single ___MASK76___ of tuatara is the only surviving member of its ___MASK35___ , which flourished around 200 million years ago . Their most recent common ancestor with any other extant group is with the squamates ( lizards and snakes ). For this reason , tuatara are of great interest in the study of the evolution of lizards and snakes , and for the reconstruction of the appearance and habits of the earliest diapsids , a group of amniote tetrapods that also includes dinosaurs , birds , and crocodilians . Reptiles are tetrapod ( four - limbed vertebrate ) animals in the ___MASK81___ Reptilia , comprising today ' s turtles , crocodilians , snakes , amphisbaenians , lizards , tuatara , and their extinct relatives . The study of these traditional reptile orders , historically combined with that of modern amphibians , is called herpetology . A ___MASK98___ ( genera ) is a taxonomic rank used in the biological classification of living and fossil organisms in biology . In the hierarchy of biological classification , ___MASK98___ comes above ___MASK76___ and below family . In binomial nomenclature , the ___MASK98___ name forms the first part of the binomial ___MASK76___ name for each ___MASK76___ within the ___MASK98___ . The Paleogene ( or ; also spelled Palaeogene or Palæogene ; informally Lower Tertiary ) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago ( Mya ) to the beginning of the Neogene Period Mya . It is the beginning of the Cenozoic Era of the present Phanerozoic Eon . The Paleogene is most notable for being the time during which mammals diversified from relatively small , simple forms into a large ___MASK59___ of diverse animals in the wake of the Cretaceous  Paleogene extinction event that ended the preceding Cretaceous Period . The Crocodilia ( or Crocodylia ) are an ___MASK35___ of mostly large , predatory , semiaquatic reptiles . They appeared 83 . 5 million years ago in the Late Cretaceous period ( Campanian stage ) and are the closest living relatives of birds , as the two groups are the only known survivors of the Archosauria . Members of the ___MASK35___ ' s total ___MASK59___ , the clade Pseudosuchia , appeared about 250 million years ago in the Early Triassic period , and diversified during the Mesozoic era . The ___MASK35___ Crocodilia includes the true crocodiles ( ___MASK44___ Crocodylidae ), the alligators and caimans ( ___MASK44___ Alligatoridae ), and the gharial and false gharial ( ___MASK44___ Gavialidae ). Although the term ' crocodiles ' is sometimes used to refer to all of these , a less ambiguous vernacular term for this ___MASK59___ is crocodilians . Hallopus was a prehistoric reptile , classified by O . C . Marsh in 1881 as a dinosaur . It was probably a crocodilian or possibly a more primitive crurotarsan , and may be closely related to Junggarsuchus . It was a quite small animal , reaching a length of 1 m ( 3 . 3 ft ) . Junggarsuchus is an extinct ___MASK98___ of sphenosuchian crocodylomorph from the Middle Jurassic of China . The type ___MASK76___ is " J . sloani ".