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Amniotes
Amniotes are a clade of tetrapod vertebrates that comprises sauropsids (including all reptiles and birds, and extinct parareptiles and non-avian dinosaurs) and synapsids (including pelycosaurs and therapsids such as mammals). They are distinguished from the other tetrapod clade — the amphibians — by the development of three extraembryonic membranes ( amnion for embryoic protection, chorion for gas exchange, and allantois for metabolic waste disposal or storage), thicker and more keratinized skin, and costal respiration (breathing by expanding/constricting the rib cage). All three main features listed above, namely the presence of an amniotic buffer, water-impermeable cutes and a robust respiratory system, are very important for amniotes to live on land as true terrestrial animals – the ability to reproduce in locations away from water bodies, better homeostasis in drier environments, and more efficient air respiration to power terrestrial locomotions, although ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pennsylvanian (geology)
The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain by a few hundred thousand years. The Pennsylvanian is named after the U.S. state of Pennsylvania, where the coal-productive beds of this age are widespread. The division between Pennsylvanian and Mississippian comes from North American stratigraphy. In North America, where the early Carboniferous beds are primarily marine limestones, the Pennsylvanian was in the past treated as a full-fledged geologic period between the Mississippian and the Permian. In parts of Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tetrapod
Tetrapods (; ) are four-limb (anatomy), limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant taxon, extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct therapsids and all extant mammals). Tetrapods evolved from a clade of primitive semiaquatic animals known as the Tetrapodomorpha which, in turn, evolved from ancient lobe-finned fish (sarcopterygians) around 390 million years ago in the Middle Devonian, Middle Devonian period; their forms were transitional between lobe-finned fishes and true four-limbed tetrapods. Limbed vertebrates (tetrapods in the broad sense of the word) are first known from Middle Devonian trackways, and body fossils became common near the end of the Late Devonian but these were all aquatic. The first crown group, crown-tetrapods (last common ancestors of extant tetrapods capable of terrestrial locomotion) appeared by the very early Mississippian ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Varanopidae
Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an ''Archaeothyris''-like synapsid in the Late Carboniferous. However, some recent studies have recovered them being taxonomically closer to diapsid reptiles. A varanopid from the latest Middle Permian ''Pristerognathus'' Assemblage Zone is the youngest known varanopid and the last member of the "pelycosaur" group of synapsids. Description No known varanopids developed a sail like ''Dimetrodon''. The length of known varanopids, including the tail, varies from . Varanopids already showed some advanced characteristics of true pelycosaurs such as their deep, narrow, elongated skulls. Their jaws were long and their teeth were sharp. However, they were still primitive by mammalian standards. They had long tails, lizard-like bodies, and thin legs. The varanopids were mostly carnivorous, but as they w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sauropsid
Sauropsida ("lizard faces") is a clade of amniotes, broadly equivalent to the class Reptilia. Sauropsida is the sister taxon to Synapsida, the other clade of amniotes which includes mammals as its only modern representatives. Although early synapsids have historically been referred to as "mammal-like reptiles", all synapsids are more closely related to mammals than to any modern reptile. Sauropsids, on the other hand, include all amniotes more closely related to modern reptiles than to mammals. This includes Aves (birds), which are now recognized as a subgroup of archosaurian reptiles despite originally being named as a separate class in Linnaean taxonomy. The base of Sauropsida forks into two main groups of "reptiles": Eureptilia ("true reptiles") and Parareptilia ("next to reptiles"). Eureptilia encompasses all living reptiles (including birds), as well as various extinct groups. Parareptilia is typically considered to be an entirely extinct group, though a few hypotheses ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kraterokheirodon
''Kraterokheirodon'' ("cupped hand tooth") is an extinct genus of enigmatic tetrapod, that was possibly an amniote, from the Late Triassic Chinle Formation of Arizona. The type and only species is ''K. colberti''. Although it is known only from two large teeth, their shape is so unlike those of any other animal that ''Kraterokheirodon'' cannot definitively be classified under any known group of tetrapods. Its discovery also indicates that our understanding of Late Triassic tetrapod diversity is still incomplete, with ''Kraterokheirodon'' representing an otherwise unknown lineage of large tetrapod in western North America. Description The teeth of ''Kraterokheirodon'' are broad and relatively large—27.7 mm across at their base and approximately 19 mm high—with an arched ridge across its crown. Without associated jaws, even the orientation of the teeth are unknown, but the ridge has been interpreted as running transversely across the tooth from side-to-side, rather t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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