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Newer taxonomy is frequently based on cladistics instead, giving a variable number of major "branches" of the tetrapod family tree. As is the case throughout evolutionary biology today, there is debate over how to properly classify the groups within Tetrapoda.
Family Liolaemidae (iguana relatives, such as swifts) Family Opluridae (Madagascan iguanas) Family Phrynosomatidae (spiny lizards, horn lizards, tree lizards, and more) Family Polychrotidae (anoles) Family Tropiduridae (neotropical ground lizards) Family Gymnophthalmidae (spectacled lizards) Family Lacertidae (wall lizards) Family Teiidae (tegus)
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.
Stegocephali was re-established to replace the broad definition of Tetrapoda, resolving the usage of two conflicting definitions in discussions of tetrapod evolution. Stegocephali was coined in 1868 by the American paleontologist Edward Drinker Cope , who used it as a general category of prehistoric amphibians.
The stem tetrapods may also include one or both of Temnospondyli and Lepospondyli, depending on author. This is due to the uncertain origin of the modern amphibians, whose position in the phylogenetic tree dictates what lineages go in the crown group Tetrapoda.
Like paleontologists, molecular phylogeneticists have differing ideas about various details, but here is a typical family tree according to molecular phylogenetics: [98] [99] Note that the diagram shown here omits extinct groups, as one cannot extract DNA from most fossils. Some finer-level subdivisions are glossed-over.