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Stegocephali
Stegocephali (often spelled Stegocephalia, from Greek , lit. "roofed head") is a clade of vertebrate animals containing all fully limbed tetrapodomorphs. It is equivalent to a broad definition of the superclass Tetrapoda: under this broad definition, the term "tetrapod" applies to any animal descended from the first vertebrate with four limbs each with digits in the extremity (pentadactyly), rather than fins of their sarcopterygian relatives. Stegocephalians include both the modern lineage of limbed vertebrates (the crown group tetrapods, including modern amphibians, reptiles, birds and mammals) as well as a portion of the stem group, the earliest limbed tetrapodomorphs such as ''Ichthyostega'' and ''Acanthostega'', which evolved in the Devonian period long before the origin of the crown group. Many paleontologists prefer a stricter definition of Tetrapoda which applies solely to the crown group, excluding earlier types of limbed tetrapodomorphs. Stegocephali was re-estab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrapod
A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetrapoda (). Tetrapods include all Neontology#Extant taxa versus extinct taxa, extant and Extinction, extinct amphibians and amniotes, with the latter in turn Evolution, evolving into two major clades, the Sauropsida, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (extinct pelycosaur, "pelycosaurs", therapsids and all extant mammals, including Homo sapiens, humans). Hox gene mutations have resulted in some tetrapods becoming Limbless vertebrate, limbless (snakes, legless lizards, and caecilians) or two-limbed (cetaceans, sirenians, Bipedidae, some lizards, kiwi (bird), kiwis, and the extinct moa and elephant birds). Nevertheless, they still qualify as tetrapods through their ancestry, and some retain a pair of ves ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Michel Laurin
Michel Laurin is a Canadian-born French vertebrate paleontologist whose specialities include the emergence of a land-based lifestyle among vertebrates, the evolution of body size and the origin and phylogeny of lissamphibians. He has also made important contributions to the literature on phylogenetic nomenclature. As an undergraduate, he worked in the laboratory of Robert L. Carroll and earned his Ph.D. at the University of Toronto under the direction of Robert R. Reisz; his thesis concerned the osteology of Seymouriamorpha, seymouriamorphs. His 1991 review of diapsid phylogeny provided the broadest review of the subject up to that date. In 1995, Laurin and Reisz coauthored a widely cited article providing evidence that the synapsids are the sister group of all other amniotes. He later worked on untangling the phylogeny of the Stegocephalia, a group with a notoriously difficult phylogeny. He later moved to France; since 1998, he has been a CNRS researcher at the Muséum National d'H ... [...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] |
Tetrapodomorph
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 hum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amphibian
Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excluding the amniotes (tetrapods with an amniotic membrane, such as modern reptiles, birds and mammals). All extant taxon, extant (living) amphibians belong to the monophyletic subclass (biology), subclass Lissamphibia, with three living order (biology), orders: Anura (frogs and toads), Urodela (salamanders), and Gymnophiona (caecilians). Evolved to be mostly semiaquatic, amphibians have adapted to inhabit a wide variety of habitats, with most species living in freshwater ecosystem, freshwater, wetland or terrestrial ecosystems (such as riparian woodland, fossorial and even arboreal habitats). Their biological life cycle, life cycle typically starts out as aquatic animal, aquatic larvae with gills known as tadpoles, but some species have devel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sarcopterygian
Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a 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 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 bony spines supporting the fins. The tetrapods, a mostly terrestrial clade of vertebrates, are now recognized as having evolved from sarcopterygian ancestors and are most closely related to lungfishes. Their paired pectoral and pelvic fins evolved into limbs, and their foregut diverticulum eventually evolved into air-breathing lungs. Cladistically, this would make the tetrapods a subgroup within Sarcopterygii and thus sarcopterygians themselves. As a result, the phrase "lobe-finned fish" normally re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acanthostega Gunnari
''Acanthostega'', from Ancient Greek ἄκανθα (''ákantha''), meaning "spine", and στέγη (''stégē''), meaning "roof", is an extinct genus of stem-tetrapod, among the first vertebrate animals to have recognizable 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'' 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 walking on land. It also had a remarkably fish-like shoulder and forel ... [...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] |
Devonian Period
The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding Carboniferous period at Ma. It is the fourth period of both the Paleozoic and the Phanerozoic. It is named after Devon, South West England, where rocks from this period were first studied. The first significant evolutionary radiation of life on land occurred during the Devonian, as free- sporing land plants (pteridophytes) began to spread across dry land, forming extensive coal forests which covered the continents. By the middle of the Devonian, several groups of vascular plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants ( pteridospermatophytes) appeared. This rapid evolution and colonization process, which had begun during the Silurian, is known as the Silurian-Devonian Terrestrial Revo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fish Fin
Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only by muscles. Fish fins are distinctive anatomical features with varying structures among different clades: in ray-finned fish (Actinopterygii), fins are mainly composed of bony spines or rays covered by a thin stretch of scaleless skin; in lobe-finned fish ( Sarcopterygii) such as coelacanths and lungfish, fins are short rays based around a muscular central bud supported by jointed bones; in cartilaginous fish ( Chondrichthyes) and jawless fish ( Agnatha), fins are fleshy " flippers" supported by a cartilaginous skeleton. Fins at different locations of the fish body serve different purposes, and are divided into two groups: the midsagittal ''unpaired fins'' and the more laterally located ''paired fins''. Unpaired fins are p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three Evolution of mammalian auditory ossicles, middle ear bones. These characteristics distinguish them from reptiles and birds, from which their ancestors Genetic divergence, diverged in the Carboniferous Period over 300 million years ago. Around 6,640 Neontology#Extant taxon, extant species of mammals have been described and divided into 27 Order (biology), orders. The study of mammals is called mammalogy. The largest orders of mammals, by number of species, are the rodents, bats, and eulipotyphlans (including hedgehogs, Mole (animal), moles and shrews). The next three are the primates (including humans, monkeys and lemurs), the Artiodactyl, even-toed ungulates (including pigs, camels, and whales), and the Carnivora (including Felidae, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bird
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a four-chambered heart, and a strong yet lightweight Bird skeleton, skeleton. Birds live worldwide and range in size from the bee hummingbird to the common ostrich. There are over 11,000 living species and they are split into 44 Order (biology), orders. More than half are passerine or "perching" birds. Birds have Bird wing, wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which are modified forelimbs, gave birds the ability to fly, although further evolution has led to the Flightless bird, loss of flight in some birds, including ratites, penguins, and diverse endemism, endemic island species. The digestive and respiratory systems of birds are also uniquely a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
