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Placoderm Genera
Placoderms (from Ancient Greek πλάξ 'plax'', ''plakos''' plate' and δέρμα 'derma'''skin') are vertebrate animals of the class Placodermi, an extinct group of prehistoric fish known from Paleozoic fossils during the Silurian and the Devonian periods. While their endoskeletons are mainly cartilaginous, their head and thorax were covered by articulated armoured plates (hence the name), 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 pair of gill arches), as well as the first vertebrates to have true teeth. They were also the first fish clade to develop pelvic fins, the second set of paired fins and the homologous precursor to hindlimbs in tetrapods. 380-million-year-old fossils of three other genera, '' Incisoscutum'', '' Materpiscis'' and '' Austroptyctodus'', represent the oldest known examples of live birth. Placoderms are thought to be paraphyletic, cons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rhenanida
Rhenanida ("Rhine (fish)") is an order of scaly placoderms. Unlike most other placoderms, the rhenanids' armor was made up of a mosaic of unfused scales and tubercles. The patterns and components of this "mosaic" correspond to the plates of armor in other, more advanced placoderms, suggesting that the ancestral placoderm had armor made of unfused components, as well. All rhenanids were flattened, ray-like, bottom-dwelling predators that lived in marine environments. Evolution The rhenanids were once presumed to be the most primitive, or at least the closest to the ancestral placoderm, as their armor was made up of a mosaic of tubercles, as opposed to the solidified plates of "advanced" placoderms, such as antiarchs and arthrodires. However, comparing the skull anatomies of ''Jagorina pandora'' with those of antiarchs, the rhenanids are considered to be the sister group of the antiarchs (together with their respective Acanthothoracid relatives). Presence in the fossil record ... [...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#Paleobiology, Stegosauria group of dinosaurs * articulated Armour (anatomy), armoured plates covering the head of thorax of Placodermi (literally "plate-skinned"), an extinct class of prehistoric fish (including skull, thorax, thoracic and tooth plates) * bony shields of the Ostracoderms (armored jawless fishes) such as the dermal head Armour (anatomy), armour of members of the class Pteraspidomorphi that include Dorsum (anatomy), dorsal, Ventrum, ventral, Rostrum (anatomy), rostral and pineal gland, pineal plates * plates of a carapace, such as the dermal plates of the Turtle shell, 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 th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ancient Greek
Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek Dark Ages, Dark Ages (), the Archaic Greece, Archaic or Homeric Greek, Homeric period (), and the Classical Greece, Classical period (). Ancient Greek was the language of Homer and of fifth-century Athens, fifth-century Athenian historians, playwrights, and Ancient Greek philosophy, philosophers. It has contributed many words to English vocabulary and has been a standard subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Homeric Greek, Epic and Classical periods of the language, which are the best-attested periods and considered most typical of Ancient Greek. From the Hellenistic period (), Ancient Greek was followed by Koine Greek, which is regar ... [...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. The genus is named after Erik Stensiö, the species name honours Anatol Heintz. 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 Chimaeridae, 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 believ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pseudopetalichthyida
Pseudopetalichthyida is an 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 spec ... [...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 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 Galeaspida (from Latin, 'Helmet shields') is an extinct taxon of jawless marine and freshwater fish. The name is derived from ''galea'', the Latin word for ''helmet'', and refers to their massive bone shield on the head. Galeaspida lived in shallo ..., strongly suggest that ''B. stensioi'', and also the antiarchs, are basal placoderms closest to the ancestral placoderm. New findings show ''B. stensioi'' may have evolutionary traits which connect its morph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xiushanosteus
''Xiushanosteus'' is a genus of placoderm from the Huixingshao Formation of China. It contains one species, ''Xiushanosteus mirabilis''. It is one of the earliest known jawed vertebrates, at roughly 435 million years old. ''Xiushanosteus'' is known from around 20 specimens, most of which are complete. Description ''Xiushanosteus'' is roughly long. Its body is dorsoventrally compressed with small, diamond-shaped scales covering it. Along its midline are scales or scutes with a linear ornament, alongside two dorsal fins of similar size, both bearing spines. The caudal fin is epicercal with a round ventral lobe. The head has long, posterolaterally directed head spines, alongside its dermoskeleton having an unusual structure with features from numerous placoderm clades. Dermoskeleton The margins of the skull roof are similar to acanthothoracids, however the plate pattern is closer to actinolepidoids with only one pair of postorbital and paranuchal plates. The skull ro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Eugnathostomata
Gnathostomata (; from Ancient Greek: (') 'jaw' + (') 'mouth') are jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all extant vertebrates, including all living bony fishes (both ray-finned and lobe-finned, including their terrestrial tetrapod relatives) and cartilaginous fishes, as well as extinct prehistoric fish such as placoderms and acanthodians. Most gnathostomes have retained ancestral traits like true teeth, a stomach, and paired appendages (pectoral and pelvic fins, limbs, wings, etc.). Other traits are elastin, horizontal semicircular canal of the inner ear, myelinated neurons, and an adaptive immune system which has discrete secondary lymphoid organs (spleen and thymus) and uses V(D)J recombination to create antigen recognition sites, rather than using genetic recombination in the variable lymphocyte receptor gene. It is now assumed that Gnathostomata evolved from ancestors that already possessed two pairs of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Minjinia
''Minjinia turgenensis'' is a species of placoderm from the Devonian of Mongolia. It is known from a single specimen preserving part of the skull, including remains of endochondral bone, which indicates that a mineralised endoskeleton evolved before the split between bony and cartilaginous fish, and that it was lost in the latter group. ''Minjinia'', an ancient armored fish from the Devonian period, helps scientists understand how the shoulder bones of vertebrates first developed. Researchers found evidence that its skull was connected to the shoulder in a way that suggests the shoulder bones may have evolved from parts of the gill skeleton, supporting one of the main ideas about how fish fins and shoulders first appeared.Brazeau, M. D., Castiello, M., El Fassi El Fehri, A., Hamilton, L., Ivanov, A. O., Johanson, Z., & Friedman, M. (2023, November 1). Fossil evidence for a pharyngeal origin of the vertebrate pectoral girdle. Nature News. https://www.nature.com/articles/s41586-023 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bianchengichthys
''Bianchengichthys'' is a genus of maxillate placoderm fish from the late Silurian Period. Its fossils have been recovered from Yunnan Province, China, and it is represented by only one species: ''Bianchengichthys micros''. Description ''Bianchengichthys'' is a small, somewhat dorsoventrally compressed placoderm fish. The mandible (made from dermal bone) of this genus differs from '' Entelognathus'' and ''Qilinyu''—two other maxillate placoderms from late Silurian China−in that the oral lamina is broad and carries a row of tooth-like denticles, though the marginal flange is toothless. The pectoral fin, preceded by two small spines on its thoracic shield, is lobate in shape and situated along by a 'fringe' of scales similar to those of ''Lepidotrichia'' in bony fishes. Similarly to other maxillate placoderms, its eyes are anteriorly orientated and very close to its mouth. Evolutionary significance ''Bianchengichthys mandible bears physical resemblance to both its relatives ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Silurolepis
''Silurolepis platydorsalis'' is a species of Silurian-aged "maxillate" early placoderm that has been described from (mostly) articulated remains. Although it has been known for several years, it was finally described by Zhang et al., in 2010. ''S. platydorsalis'' was previously considered a basal antiarch, but a 2019 study instead recovers it as a maxillate placoderm most closely related to ''Qilinyu ''Qilinyu'' is a genus of early placoderm from the late Silurian (late Ludfordian stage, ~423 Ma) of China. It contains a single species, ''Qilinyu rostrata'', from the Xiaoxiang fauna of the Kuanti Formation. Along with its contemporary ''Entelo ...''. ''S. platydorsalis'' is known from thoracic armor: as the specific name suggests, the dorsal side is very flat. References Placoderms of Asia Silurian fish of Asia Fossil taxa described in 2010 Placoderm genera {{placoderm-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
