parent_taxon microsauria
Metamorphosis is a biological process by which an ___MASK13___ physically develops after birth or hatching , involving a conspicuous and relatively abrupt change in the ___MASK13___ ' s body structure through cell growth and differentiation . Some ___MASK78___ , fishes , amphibians , mollusks , crustaceans , cnidarians , echinoderms and tunicates undergo metamorphosis , which is often accompanied by a change of nutrition source or behavior . Animals that goes through metamorphosis are called metamorphoses . Animals can be divided into species that undergo complete metamorphosis (" holometaboly "), incomplete metamorphosis (" hemimetaboly "), or no metamorphosis (" ametaboly "). The Carboniferous is a geologic period and system that spans 60 million years from the end of the Devonian Period million years ago ( ___MASK34___ ), to the beginning of the Permian Period , ___MASK34___ . The name " Carboniferous " means " coal - bearing " and derives from the Latin words " carb " (" coal ") and " fer " (" I bear , I carry "), and was coined by geologists William Conybeare and William Phillips in 1822 . Based on a study of the British rock succession , it was the first of the modern ' system ' names to be employed , and reflects the fact that many coal beds were formed globally during that time . The Carboniferous is often treated in North America as two geological periods , the earlier Mississippian and the later Pennsylvanian . The ___MASK56___ salamander or eastern ___MASK56___ salamander (" Ambystoma tigrinum ") is a North American species of mole salamander . A walking fish , or ambulatory fish , is a fish that is able to travel over land for extended periods of time . Some other modes of non - standard fish locomotion include " walking " along the sea floor , for example , in ___MASK36___ or frogfish . Amphibians are ectothermic , tetrapod vertebrates of the class ___MASK67___ . Modern amphibians are all Lissamphibia . They inhabit a wide variety of habitats , with most species living within terrestrial , fossorial , arboreal or freshwater aquatic ecosystems . Thus amphibians typically start out as larvae living in water , but some species 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 species around the globe . A fish is any member of a group of organisms that consist of all gill - bearing aquatic craniate animals that lack limbs with digits . They form a sister group to the tunicates , together forming the ___MASK22___ . Included in this definition are the living ___MASK54___ , lampreys , and cartilaginous and bony fish as well as various extinct related groups . Tetrapods emerged within lobe - finned fishes , so cladistically they are fish as well . However , traditionally fish are rendered obsolete or paraphyletic by excluding the tetrapods ( i . e ., the amphibians , reptiles , birds and mammals which all descended from within the same ancestry ). Because in this manner the term " fish " is defined negatively as a paraphyletic group , it is not considered a formal taxonomic grouping in systematic biology . The traditional term pisces ( also ichthyes ) is considered a typological , but not a phylogenetic classification . Salamanders are a group of amphibians typically characterized by a ___MASK72___ - like appearance , with slender bodies , blunt snouts , short limbs projecting at right angles to the body , and the presence of a tail in both larvae and adults . All present - day salamander families are grouped together under the scientific name Urodela . Salamander diversity is most abundant in the Northern Hemisphere and most species are found in the Holarctic ecozone , with some species present in the Neotropical zone . Snakes are elongated , legless , carnivorous reptiles of the suborder 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 species of snakes have skulls with several more joints than their ___MASK72___ 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 species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca . ___MASK79___ is a diverse taxon of Paleozoic tetrapods ( four - limbed vertebrates ). It , along with its presumed daughter clade ___MASK11___ , and ___MASK67___ proper , are the primary taxa that make up the vertebrate group Batrachomorpha . With the exception of one late - surviving lepospondyl from the Late Permian of Morocco (" Diplocaulus minumus "), lepospondyls lived from the Early Carboniferous ( Mississippian ) to the Early Permian and were geographically restricted to what is now Europe and North America . Five major groups of lepospondyls are known : Adelospondyli ; Aïstopoda ; Lysorophia ; Microsauria ; and Nectridea . Lepospondyls have a diverse range of body forms and include species with newt - like , eel - or snake - like , and ___MASK72___ - like forms . Various species were aquatic , semiaquatic , or terrestrial . None were large ( the biggest genus , the diplocaulid " Diplocaulus ", reached a meter in length , but most were much smaller ), and they are assumed to have lived in specialized ecological niches not taken by the more numerous temnospondyl amphibians that coexisted with them in the Paleozoic . ___MASK79___ was named in 1888 by Karl Alfred von Zittel , who coined the name to include some tetrapods from the Paleozoic , that shared some specific characteristics in the notochord and teeth . Mexico (, modern Nahuatl ), officially the United Mexican States , is a federal republic in the southern half of North America . It is bordered to the north by the United States ; to the south and west by the Pacific Ocean ; to the southeast by Guatemala , Belize , and the Caribbean Sea ; and to the east by the Gulf of Mexico . Covering almost two million square kilometers ( over 760 , 000 sq mi ), Mexico is the sixth largest country in the Americas by total ___MASK21___ and the 13th largest independent nation in the world . With an estimated population of over 120 million , it is the eleventh most populous country and the most populous Spanish - speaking country in the world while being the second most populous country in Latin America . Mexico is a federation comprising 31 states and a federal district that is also its capital and most populous city . Other metropolises include Guadalajara , Monterrey , Puebla , Toluca , Tijuana and León . The axolotl ( from ] ) also known as a Mexican salamander (" ___MASK58___ mexicanum ") or a Mexican walking fish , is a neotenic salamander , closely related to the ___MASK56___ salamander . Although the axolotl is colloquially known as a " walking fish ", it is not a fish , but an amphibian . The species originates from numerous lakes , such as Lake Xochimilco underlying Mexico City . Axolotls are unusual among amphibians in that they reach adulthood without undergoing metamorphosis . Instead of developing lungs and taking to land , the adults remain aquatic and gilled . The Devonian is a geologic period and system of the Paleozoic , spanning 60 million years from the end of the Silurian , million years ago ( ___MASK34___ ), to the beginning of the Carboniferous , ___MASK34___ . It is named after Devon , England , where rocks from this period were first studied . The first significant adaptive radiation of life on dry land occurred during the Devonian . Free - sporing vascular plants began to spread across dry land , forming extensive forests which covered the continents . By the middle of the Devonian , several groups of plants had evolved leaves and true roots , and by the end of the period the first seed - bearing plants appeared . Various terrestrial arthropods also became well - established . Fish reached substantial diversity during this time , leading the Devonian to often be dubbed the " Age of Fish ". The first ray - finned and lobe - finned bony fish appeared , while the placodermi began dominating almost every known aquatic environment . ___MASK100___ is an order of aquatic Carboniferous and Permian amphibians within the extinct subclass ___MASK79___ . Lysorophians resembled small snakes , as their bodies are extremely elongate . There is a single family , the Cocytinidae ( previously known as Lysorophidae ). Currently there are around five genera included within ___MASK100___ . ___MASK42___ ( `` small lizards '' ) is an extinct order of lepospondyl amphibians from the late Carboniferous and early Permian periods . It is the most diverse and species - rich group of lepospondyls . Recently , ___MASK42___ has been considered paraphyletic , as several other non - microsaur lepospondyl groups such as ___MASK100___ seem to be nested in it . ___MASK42___ is now commonly used as a collective term for the grade of lepospondyls that were originally classified as members of ___MASK42___ . The microsaurs all had short tails and small legs , but were otherwise quite varied in form . The group included ___MASK72___ - like animals that were relatively well - adapted to living on dry land , burrowing forms , and others that , like the modern axolotl , retained their gills into adult life , and so presumably never left the water . They are possible ancestors of the newts and salamanders , if that group did not arise from the temnospondyls along with the frogs and toads . Devon ( archaically known as Devonshire ) is a county of England , reaching from the Bristol Channel in the north to the English Channel in the south . It is part of South West England , bounded by Cornwall to the west , Somerset to the northeast , and Dorset to the east . The City of Exeter is the county town ; seven other districts of East Devon , Mid Devon , North Devon , South Hams , Teignbridge , Torridge , and West Devon are under the jurisdiction of Devon County Council ; Plymouth and Torbay are each a part of Devon but administered as unitary authorities . Combined as a ceremonial county , Devon ' s ___MASK21___ is and its population is about 1 . 1 million . Coal is a combustible black or brownish - black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams . The harder forms , such as anthracite coal , can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure . Coal is composed primarily of carbon , along with variable quantities of other elements , chiefly hydrogen , sulfur , oxygen , and nitrogen . A fossil fuel , coal forms when dead ___MASK98___ matter is converted into peat , which in turn is converted into lignite , then sub - bituminous coal , after that bituminous coal , and lastly anthracite . This involves biological and geological processes that take place over time . The Triassic is a geologic period and system which spans 50 . 9 million years from the end of the Permian Period million years ago ( ___MASK34___ ), to the beginning of the Jurassic Period ___MASK34___ . 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 series of terrestrial mud - and sandstones  called the " Trias ". The Permian is a geologic period and system which spans 46 . 7 million years from the end of the Carboniferous Period million years ago ( ___MASK34___ ), to the beginning of the Triassic Period 252 . 2 ___MASK34___ . It is the last period of the Paleozoic Era ; the following Triassic Period belongs to the Mesozoic Era . The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison , who named it after the city of Perm .