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Placoderms Of North America
Placodermi (from Greek πλάξ 'plate' and δέρμα 'skin', literally 'plate-skinned') is a class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first of their gill arches. Placoderms are thought to be paraphyletic, consisting of several distinct outgroups or sister taxa to all living jawed vertebrates, which originated among their ranks. In contrast, one 2016 analysis concluded that placodermi are likely monophyletic, though these analyses have been further dismissed with more transitional taxa between placoderms and modern gnathosthomes, solidifying their paraphyletic status. Placoderms were also the first fish to develop pelvic fins, the precursor to hindlimbs in tetrapods, as well as true t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entelognathus
''Entelognathus primordialis'' (“primordial complete jaw”) is a maxillate placoderm from the late Silurian (Ludlow epoch) of Qujing, Yunnan, 419 million years ago. A team led by Min Zhu of the Academy of Sciences' Institute of Vertebrate Paleontology and Paleoanthropology in Beijing discovered the intact, articulated fossil in rock formations at Xiaoxiang reservoir. Specimen and taxonomy The holotype of ''E. primordialis'' is the uncrushed and mostly intact anterior half of an individual with the articulating head and trunk armor preserved in three dimensions. The holotype is about long, and the live animal is estimated to have been over long. In overall form, the animal resembles primitive arthrodires, but the anatomy of the jaws strongly suggests the anatomies of bony fish and tetrapods. Specifically, this is the first stem gnathostome with dermal marginal jaw bones. These bones are the premaxilla, maxilla, and dentary. Most known placoderms had simple beak-like jaw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thorax
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the creature's body, each of which is in turn composed of multiple segments. The human thorax includes the thoracic cavity and the thoracic wall. It contains organs including the heart, lungs, and thymus gland, as well as muscles and various other internal structures. Many diseases may affect the chest, and one of the most common symptoms is chest pain. Etymology The word thorax comes from the Greek θώραξ ''thorax'' "breastplate, cuirass, corslet" via la, thorax. Plural: ''thoraces'' or ''thoraxes''. Human thorax Structure In humans and other hominids, the thorax is the chest region of the body between the neck and the abdomen, along with its internal organs and other contents. It is mostly protected and supported by the rib cage, spi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Head
A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple animals may not have a head, but many bilaterally symmetric forms do, regardless of size. Heads develop in animals by an evolutionary trend known as cephalization. In bilaterally symmetrical animals, nervous tissue concentrate at the anterior region, forming structures responsible for information processing. Through biological evolution, sense organs and feeding structures also concentrate into the anterior region; these collectively form the head. Human head The human head is an anatomical unit that consists of the Human skull, skull, hyoid bone and cervical vertebrae. The term "skull" collectively denotes the mandible (lower jaw bone) and the cranium (upper portion of the skull that houses the brain). Sculptures of human heads are general ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozoic Era. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by a few million years. The base of the Silurian is set at a series of major Ordovician–Silurian extinction events when up to 60% of marine genera were wiped out. One important event in this period was the initial establishment of terrestrial life in what is known as the Silurian-Devonian Terrestrial Revolution: vascular plants emerged from more primitive land plants, dikaryan fungi started expanding and diversifying along with glomeromycotan fungi, and three groups of arthropods (myriapods, arachnids and hexapods) became fully terrestrialized. A significant evolutionary milestone during ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the ''fossil record''. Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years old to 4.1 billion years old. Early edition, published online before print. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prehistoric Fish
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish. Early examples include ''Haikouichthys''. During the late Cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. Most jawless fish are now extinct; but the extant lampreys may approximate ancient pre-jawed fish. Lampreys belong to the Cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans. The earliest Gnathostomata, jawed vertebrates probably developed during the late Ordovician period. They are first represented in the fossil record from the Silurian by two groups of fish: the armoured fish known as Placodermi, placoderms, which evolved from the ostracoderms; and the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Class (biology)
In biological classification, class ( la, classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order. History The class as a distinct rank of biological classification having its own distinctive name (and not just called a ''top-level genus'' ''(genus summum)'') was first introduced by the French botanist Joseph Pitton de Tournefort in his classification of plants that appeared in his ''Eléments de botanique'', 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine a distinct ''grade'' of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with a distinct ''type'' of construction, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plate (animal Anatomy)
A plate in animal anatomy may refer to several things: Flat bones (examples: bony plates, dermal plates) of vertebrates * an appendage of the Stegosauria group of dinosaurs * articulated armoured plates covering the head of thorax of Placodermi (literally "plate-skinned"), an extinct class of prehistoric fish (including skull, thoracic and tooth plates) * bony shields of the Ostracoderms (armored jawless fishes) such as the dermal head armour of members of the class Pteraspidomorphi that include dorsal, ventral, rostral and pineal plates * plates of a carapace, such as the dermal plates of the shell of a turtle * dermal plates partly or completely covering the body of the fish in the order Gasterosteiformes that includes the sticklebacks and relatives * plates of dermal bones of the armadillo * Zygomatic plate, a bony plate derived from the flattened front part of the zygomatic arch (cheekbone) in rodent anatomy Other flat structures * hairy plate-like keratin scales of the pan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stensioella
''Stensioella heintzi'' is an enigmatic placoderm of arcane affinity. It is only known from the Lower Devonian Hunsrück slate of Germany. Anatomy ''Stensioella heintzi'' has an elongated body, a whip-like tail, and long, wing-like pectoral fins. In life, the animal would have looked vaguely like an elongated ratfish. Like the sympatric ''Gemuendina'', ''S. heintzi'' had armor made up of a complex mosaic of small, scale-like tubercles. Taxonomy ''Stensioella'' is tentatively placed within Placodermi as being among the most basal of all placoderms, as from what can be discerned from the only whole specimen found, the shoulder joints of its armor appear to be very similar to other placoderms. Despite this detail, coupled with superficial similarities in skull plates, and gross, superficial similarities between its tubercles, and the tubercles of the rhenanids, some paleontologists believe that there are very few concrete reasons for ''S. heintzis placement in Placodermi. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pseudopetalichthyida
Pseudopetalichthyida is an extinct order of lightly armored placoderms known only from rare fossils in Lower Devonian strata in Hunsrück, Germany. Like ''Stensioella heintzi'', and the Rhenanida, the Pseudopetalichthids had armor made up of a mosaic of tubercles. Like ''Stensioella heintzi'', the Pseudopetalichthids' placement within Placodermi is suspect. However, due to a gross lack of whole, uncrushed, articulated specimens, there are no other groups that the Pseudopetalichthids could be, for a lack of a better word, pigeonholed into. On the other hand, according to anatomical studies done on the crushed specimens that have been found, those experts who do regard the Pseudopetalichthyida as placoderms consider them to be a group more advanced than the Ptyctodonts. And as such, pro-placoderm experts consider Pseudopetalichthyida to be the sister group of the Arthrodires + Phyllolepida + Antiarchi trichotomy and the Acanthothoraci + Rhenanida dichotomy. The best known s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brindabellaspis
''Brindabellaspis stensioi'' ("Erik Stensiö's Brindabella Ranges Shield") is a placoderm with a flat, platypus-like snout from the Early Devonian of the Taemas-Wee Jasper reef in Australia. When it was first discovered in 1980, it was originally regarded as a Weejasperaspidae, Weejasperaspid acanthothoracid due to anatomical similarities with the other species found at the reef. According to Philippe Janvier, anatomical similarities of ''B. stensiois brain and braincase with those of jawless fish, such as the Osteostraci and the Galeaspida, strongly suggest that ''B. stensioi'', and also Antiarchi, the antiarchs, are basal placoderms closest to the ancestral placoderm. References *Gavin Young, Young, Gavin C. 1980, A new Early Devonian placoderm from New South Wales, Australia, with a discussion of placoderm phylogeny: ''Palaeontographica'' 167A pp. 10–76. 2 pl., 27 fig. * Philippe Janvier, Janvier, Philippe. Early Vertebrates Oxford, New York: Oxford University Press, 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
