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Placoderms
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, consis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bothriolepis
''Bothriolepis'' (from , 'trench' and 'scale') was a widespread, abundant and diverse genus of antiarch placoderms that lived during the Middle to Late Devonian period of the Paleozoic Era. Historically, ''Bothriolepis'' resided in an array of paleo-environments spread across every paleocontinent, including near shore marine and freshwater settings. Most species of ''Bothriolepis'' were characterized as relatively small, benthic, freshwater detritivores (organisms that obtain nutrients by consuming decomposing plant/animal material), averaging around in length. However, the largest species, ''B. rex'', had an estimated bodylength of . Although expansive with over 60 species found worldwide, comparatively ''Bothriolepis'' is not unusually more diverse than most modern bottom dwelling species around today. Classification ''Bothriolepis'' is a genus placed within the placoderm order Antiarchi. The earliest antiarch placoderms first appeared in the Silurian period of the Pal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coccosteus
''Coccosteus'' (from , 'berry' and 'bone') is an extinct genus of arthrodire placoderm from the Devonian period. Its fossils have been found throughout Europe and North America. The majority of these have been found in freshwater sediments, though such a large range suggests that they may have been able to enter saltwater. It was a small placoderm, with ''Coccosteus cuspidatus'' measuring long. Description Like all other arthrodires, ''Coccosteus'' had a joint between the armor of the body and skull. It also had an internal joint between its neck vertebrae and the back of the skull, allowing for the mouth to be opened even wider. Along with the longer jaws, this allowed ''Coccosteus'' to feed on fairly large prey. The up-and-down movement of the skull also allowed for more water to be pumped through the gills. Possibly, the creature supplemented its diet with organic material filtered from mud using the gills. As with all other arthrodires, ''Coccosteus'' had bony dental pla ... [...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] |
Entelognathus
''Entelognathus primordialis'' (“primordial complete jaw”) is an early 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 jaws made o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gnathostomata
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 ... [...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] |
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] |
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] |
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] |
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] |
