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Stem-tetrapod
The Stem Tetrapoda are a cladistically defined group, consisting of all animals more closely related to extant four-legged vertebrates than to their closest extant relatives (the lungfish), but excluding the crown group Tetrapoda. They are thus paraphyletic, though acceptable in phylogenetic nomenclature as the group is defined by strict reference to phylogeny rather than to traits as in traditional systematics. Thus, some finned sarcopterygians are considered to be stem tetrapods. Content of the group Stem tetrapods are members of Tetrapodomorpha, the total group and clade that also includes their descendants, the crown tetrapods: The stem Tetrapoda encompass three distinct grades successively closer to crown group Tetrapoda: * Osteolepiformes, a group of lobe-finned fishes that includes the families Tristichopteridae, Canowindridae, Megalichthyidae, and Osteolepidae * Elpistostegalia, the more advanced lobe-finned fishes (Tristichopteridae) and the " fishapods" (gene ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrapods
A tetrapod (; from Ancient Greek τετρα- ''(tetra-)'' 'four' and πούς ''(poús)'' 'foot') is any four- limbed vertebrate animal of the clade Tetrapoda (). Tetrapods include all extant and extinct amphibians and amniotes, with the latter in turn evolving into two major clades, the sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (extinct "pelycosaurs", therapsids and all extant mammals, including humans). Hox gene mutations have resulted in some tetrapods becoming limbless (snakes, legless lizards, and caecilians) or two-limbed (cetaceans, sirenians, some lizards, kiwis, and the extinct moa and elephant birds). Nevertheless, they still qualify as tetrapods through their ancestry, and some retain a pair of vestigial spurs that are remnants of the hindlimbs. Tetrapods evolved from a group of primitive semiaquatic animals known as the tetrapodomorphs which, in turn, evolved from ancient lobe-finned fish ( sarcopterygians) aro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acanthostega
''Acanthostega'', from Ancient Greek ἄκανθα (''ákantha''), meaning "spine", and στέγη (''stégē''), meaning "roof", is an extinct genus of stem tetrapoda, stem-tetrapod, among the first vertebrates, vertebrate animals to have recognizable Limb (anatomy), limbs. It appeared in the late Devonian period (Famennian age) about 365 million years ago, and was anatomically intermediate between lobe-finned fishes and those that were able to come onto land. Discovery The fossilized remains are generally well preserved, with the famous fossil by which the significance of this species was discovered being found by Jennifer A. Clack in East Greenland in 1987, though fragments of the skull had been discovered in 1933 by Gunnar Säve-Söderbergh and Erik Jarvik. Description The ''Acanthostega'' Polydactyly in stem-tetrapods, had eight digits on each hand (the number of digits on the feet is unclear) linked by webbing. It lacked wrists, and was generally poorly adapted for wa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sarcopterygii
Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class (biology), class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates are characterised by prominent muscular limb buds (lobes) within their fish fin, fins, which are supported by articulated appendicular skeletons. This is in contrast to the other clade of bony fish, the Actinopterygii, which have only skin-covered lepidotrichia, bony spines supporting the fins. The tetrapods, a mostly terrestrial animal, terrestrial clade of vertebrates, are now recognized as having evolved from sarcopterygian ancestors and are most closely related to lungfishes. Their paired pectoral fins, pectoral and pelvic fins evolved into limb (anatomy), limbs, and their lung bud, foregut diverticulum eventually evolved into air-breathing lungs. Cladistics, Cladistically, this would make the tetrapods a subgroup within ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ichthyostega
''Ichthyostega'', from Ancient Greek ἰχθύς (''ikthús''), meaning "fish", and στέγη (''stégē''), meaning "roof", is an Extinction, extinct genus of limbed tetrapodomorpha, tetrapodomorphs from the Devonian, Late Devonian of what is now Greenland. It was among the earliest four-limbed vertebrates ever in the fossil record and was one of the first with weight-bearing adaptations for terrestrial locomotion. ''Ichthyostega'' possessed lungs and limbs that helped it navigate through shallow water in swamps. Although ''Ichthyostega'' is often labelled a 'tetrapod' because of its limbs and fingers, it evolved long before true crown group tetrapods and could more accurately be referred to as a stegocephalian or stem tetrapod. Likewise, while undoubtedly of amphibian build and habit, it is not a true member of the group in the narrow sense, as the first modern amphibians (members of the group Lissamphibia) appeared in the Triassic Period. Until finds of other early stegocephal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrapodomorpha
Tetrapodomorpha (also known as Choanata) is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced forms transitional between fish and the early labyrinthodonts, such as '' Tiktaalik'', have been referred to as "fishapods" by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contains the crown group tetrapods (the last common ancestor of living tetrapods and all of its descendants) and several groups of early stem tetrapods, which includes several groups of related lobe-finned fishes, collectively known as the osteolepiforms. The Tetrapodomorpha minus the crown group Tetrapoda are the stem Tetrapoda, a paraphyletic unit encompassing the fish to tetrapod transition. Characteristics Among the characteristics defining tetrapodomorphs are modifications to the fins, notably a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Panderichthys
''Panderichthys'' is a genus of extinction, extinct Sarcopterygii, sarcopterygian (lobe-finned fish) from the late Devonian period, about 380 Myr, Mya. ''Panderichthys'', which was recovered from Frasnian (early Late Devonian) deposits in Latvia, is represented by two species. ''P. stolbovi'' is known only from some snout fragments and an incomplete lower jaw. ''P. rhombolepis'' is known from several more complete specimens. Although it probably belongs to a sister group of the earliest tetrapods, ''Panderichthys'' exhibits a range of features transitional between Tristichopteridae, tristichopterid lobe-fin fishes (e.g., ''Eusthenopteron'') and early tetrapods. It is named after the German-Baltic paleontologist Christian Heinrich Pander. Possible tetrapod tracks dating back to before the appearance of ''Panderichthys'' in the fossil record were reported in 2010, which suggests that ''Panderichthys'' is not a direct ancestor of tetrapods, but nonetheless shows the traits that evolve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tristichopteridae
Tristichopterids (Tristichopteridae) were a diverse and successful group of fish-like tetrapodomorphs living throughout the Middle and Late Devonian. They first appeared in the Eifelian stage of the Middle Devonian. Within the group sizes ranged from a few tens of centimeters (''Tristichopterus'') to several meters (''Hyneria'' and ''Eusthenodon''). Some tristichopterids share some of the features of the elpistostegalians, a diverse clade of tetrapodomorphs close to the origin of (and including) tetrapods. This mainly concerns the shape of the skull and a reduction in size of the posterior fins. An old and persistent notion is that ''Eusthenopteron'' was able to crawl onto land using its fins. However, there is no evidence actually supporting this idea.M. Laurin, F. J. Meunier, D. Germain, and M. Lemoine 2007A microanatomical and histological study of the paired fin skeleton of the Devonian sarcopterygian ''Eusthenopteron foordi'' ''Journal of Paleontology'' 81: 143–153. All t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Osteolepidida
Osteolepiformes, also known as Osteolepidida, is a group of prehistoric lobe-finned fishes which first appeared during the Devonian period. The order contains the families Canowindridae, Megalichthyidae, Osteolepididae and Tristichopteridae, in addition to several monotypic families. The order is generally considered to be paraphyletic because the characters that define it are mainly attributes of stem tetrapodomorphs. The following taxonomy is based on Borgen & Nakrem, 2016: * Order Osteolepiformes ** Suborder Osteolepidoidei *** Family Osteolepididae *** Family Thursiidae *** Family Megalichthyidae ** Suborder Cyclolepidoidei *** Superfamily Eopodoidea **** Family Chrysolepididae **** Family Gyroptychiidae **** Family Panderichthyidae (incl. Elpistostegalia) **** Family Tristichopteridae *** Superfamily Parapodoidea **** Family Canowindridae **** Family Medoevididae *** Superfamily Rhizodontoidea Below is a cladogram A cladogram (from Greek language, Gre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Canowindridae
The Canowindridae are a family of prehistoric tetrapodomorphs which lived during the Devonian period (Famennian stage, about 374 to 359 million years ago). Fossils belonging to this family have been found in Australia, Antarctica, and Europe. Phylogeny Below is a cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ... from Swartz, 2012. References Tetrapodomorpha Tetrapodomorph families Late Devonian first appearances Late Devonian sarcopterygians Late Devonian extinctions {{paleo-tetrapodomorph-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elpistostegalia
Elpistostegalia is a clade containing ''Panderichthys'' and all more derived Tetrapodomorpha, tetrapodomorph taxa. The earliest elpistostegalians, combining fishlike and tetrapod-like characters, such as ''Tiktaalik'', are sometimes called fishapods. Although historically Elpistostegalia (referred to as Panderichthyida) was considered an Order (biology), order of prehistoric Sarcopterygii, lobe-finned fishes, it was Cladistics, cladistically redefined to include tetrapods. Paleobiology A rise in global oxygen content allowed for the evolution of large, predatory fish that were able to exploit the shallow tidal areas and swamplands as top predators. Several groups evolved to fill these niches, the most successful were the elpistiostegalians. In such environments, they would have been challenged by periodic oxygen deficiency. In comparable modern aquatic environments like shallow eutrophic lakes and swampland, modern lungfish and some genera of catfish also rely on the more stable ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loxommatidae
Baphetidae is an extinct family of stem-tetrapods. Baphetids were large labyrinthodont predators of the Late Carboniferous period (Namurian through Westphalian) of Europe. Fragmentary remains from the Early Carboniferous of Canada have been tentatively assigned to the group. The phylogenetic relationships of baphetids is uncertain; while many studies have placed the group as a close relative of Amniota, other analyses have found Baphetidae to be a more basal clade of early stem tetrapods. Baphetids were among the first of the Carboniferous fossil tetrapods to be found and were originally described in 1850 by John William Dawson. The baphetids have been referred to the family Loxommatidae, but this group was later shown to be a junior synonym of Baphetidae, which was named earlier in 1865. Baphetids are known mainly from skulls; very little postcranial material has been found. Palaeobiology The presence of lateral lines and the long rows of needle-like teeth show that most were f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
