TetrapodA tetrapod (; from Ancient Greek (tetra)'four' and (poús)'foot') is any vertebrateanimal of the cladeTetrapoda (). The main diagnostic and defining trait (synapomorphy) of tetrapods is having four limbs, connected to the shoulder- and pelvic girdles, for which the group is named. As a clade, Tetrapoda is defined such that it includes every organism which descended from four-limbed ancestors, including those which have lost some or all of these limbs, e.g. snakes.
AmnioteAmniotes are tetrapod vertebrate animals belonging to the clade Amniota, a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates. Amniotes evolved from amphibious stem tetrapod ancestors during the Carboniferous period. Amniota is defined as the smallest crown clade (the group including all descendants of the last common ancestor) containing humans, the Greek tortoise, and the Nile crocodile.
ReptileClass of animalsReptiles, as commonly defined, are tetrapodvertebrateanimals with an ectothermic metabolism and amniotic development. Reptiles traditionally comprise four orders: Testudines (turtles), Crocodilia (crocodiles, alligators and gharials), Squamata (lizards and snakes) and Rhynchocephalia (tuatara), with about 12,000 extant species listed in the Reptile Database.
AmphibianAmphibians are ectothermic, anamniotic, four-limbedvertebrateanimals that constitute the classAmphibia. In its broadest sense, it is a paraphyletic group encompassing all tetrapods, but excluding the amniotes (tetrapods with an amniotic membrane, such as modern reptiles, birds and mammals). All extant (living) amphibians belong to the monophyleticsubclassLissamphibia, with three living orders: Anura (frogs and toads), Urodela (salamanders), and Gymnophiona (caecilians).
Evolutionary gradeA grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. PhylogeneticsThe concept of evolutionary grades arises in the context of phylogenetics: the study of the evolutionary history and relationships among or within groups of organisms.
LissamphibiaThe Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs and their extinct relatives), the Caudata (salamanders and their extinct relatives), and the Gymnophiona (the limbless caecilians and their extinct relatives).
MammalClass of animals with milk-producing glandsA mammal (from Latin mamma 'breast') is a vertebrate animal of the classMammalia (). Mammals are characterized by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which their ancestors diverged in the Carboniferous period over 300 million years ago.PaleozoicThe Paleozoic ( PAL-ee-ə-ZOH-ik, -ee-oh-, PAY-; or Palaeozoic) Era is the first of three geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.902 Ma at the start of the Mesozoic Era. The Paleozoic is subdivided into six geologic periods, (from oldest to youngest) Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.
Ancient GreekAncient Greek (Ἑλληνική, Hellēnikḗ [hellɛːnikɛ̌ː]) includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (c. 1400 – c. 1200 BC), Dark Ages (c. 1200 – c. 800 BC), the Archaic or Homeric period (c. 800 – c. 500 BC), and the Classical period (c. 500 – c. 300 BC).
CladeIn biology, a clade () (from Ancient Greekκλάδος (kládos)'branch'), also known as a monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population, or a species (extinct or extant).MesozoicThe Mesozoic Era is an era of Earth's geological history, lasting from about 252 to 66 million years ago, comprising the Triassic, Jurassic and Cretaceous Periods. It is characterized by the dominance of archosaurian reptiles such as the dinosaurs, and of gymnosperms such as cycads, ginkgoaceae and araucarian conifers; a hot greenhouse climate; and the tectonic break-up of Pangaea.
ExtinctionTermination of a species' lineageThe thylacine (Thylacinus cynocephalus) is an example of a recently extinct species.Palaeotherium is an example of an extinct genus that is only recorded from fossil records before the existence of hominids.Extinction is the termination of a species via the death of its last member. A taxon may become functionally extinct before the death of its last member if it loses the capacity to reproduce and recover.
ParaphylyParaphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic with respect to the excluded subgroups. In contrast, a monophyletic grouping (a clade) includes a common ancestor and all of its descendants. The terms are commonly used in phylogenetics (a subfield of biology) and in the tree model of historical linguistics.*As an Amazon Associate I earn from qualifying purchases.