Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyians, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opecula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
Gnathostomata are the jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. In addition to opposing jaws, living gnathostomes have true teeth, paired appendages, the elastomeric protein of elastin, and a horizontal semicircular canal of the inner ear, along with physiological and cellular anatomical characters such as the myelin sheaths of neurons, and an adaptive immune system that has the discrete lymphoid organs of 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.
Acanthodii or acanthodians is an extinct class of gnathostomes. They are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes, which includes living sharks, rays, and chimaeras. Acanthodians possess a mosaic of features shared with both osteichthyans and chondrichthyans. In general body shape, they were similar to modern sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteians.
Placodermi 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.
Mizia is a genus of primitive antiarch placoderm found in Emsian-aged marine strata of Early Devonian China.
Arthrodira is an order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine ecological niches. Arthrodires were the largest and most diverse of all groups of placoderms.
Meemannia is a genus of extinct bony fish from the early Devonian period. It was initially classified as a lobe-finned fish; however, a restudy conducted by Lu et al. (2016) indicates that it was actually an early-diverging ray-finned fish. It was found in Yunnan, China. As preserved, it consists mainly of skull roofing bones and a partial otic region of the braincase. Its anatomy is unique in a number of features that resemble ray-finned fishes (Actinopterygii), and more generalized jawed vertebrates.
Psarolepis is a genus of extinct bony fish which lived around 397 to 418 million years ago. Fossils of Psarolepis have been found mainly in South China and described by paleontologist Xiaobo Yu in 1998. It is not known certainly in which group Psarolepis belongs, but paleontologists agree that it probably is a basal genus and seems to be close to the common ancestor of lobe-finned and ray-finned fishes. In 2001, paleontologist John A. Long compared Psarolepis with onychodontiform fishes and refer to their relationships.
Youngolepis is a genus of prehistoric coelocanth which lived during the Early Devonian period. Fossils of Y. praecursor have been found in the Xitun Formation of China & the Bac Bun Formation of Trang Xa, Vietnam. Some additional fossil specimens from the Xishancun Formation of China have been referred to Youngolepis sp. & represent the oldest known occurrence of the genus. In addition, Y. praecursor is also found in the Xujiachong formation
Minicrania is an extinct genus of tiny antiarch fish, with armor averaging up to about 2 centimetres (0.79 in) long, which lived during the Lochkovian epoch in Early Devonian Yunnan Province, China and northern Vietnam.
Gavinaspis is a phyllolepid placoderm which lived during the Early Devonian period, of Qujing, Yunnan province, south China.
Achoania is an extinct genus of primitive bony fish which lived during the Early Devonian period. It is known from a skull discovered in the Xitun Formation of Yunnan, China. While originally originally considered to be a lobe-finned fish, later studies suggested that it may be a stem-group Osteichthyes instead.
Guiyu oneiros is one of the earliest articulated bony fish discovered. Fossils of Guiyu have been found in what is now Qujing, Yunnan, China, in late Silurian marine strata, about 425 million years old.
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.
Entelognathus primordialis is a early placoderm from the late Silurian of Qujing, Yunnan, 419 million years ago.
Parayunnanolepis xitunensis is an extinct, primitive antiarch placoderm. The fossil specimens, including a marvelously preserved, intact specimen, are known from the Lochkovian Epoch-aged Xitun Formation of Early Devonian Yunnan. The armor is very similar to that of Yunnanolepis, but is distinguished by being comparatively more flattened.
Meemann Chang also known as Zhang Miman, is a Chinese paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP). She completed her undergraduate studies at Moscow University and completed her PhD thesis entitled 'The braincase of Youngolepis, a Lower Devonian crossopterygian from Yunnan, south-western China' at Stockholm University. She was the first woman to become head of IVPP in 1983. For her many career achievements, she received an honorary degree from the University of Chicago in 2011 and the Romer-Simpson Medal from the Society of Vertebrate Paleontology in 2016.
Phymolepis is an extinct genus of yunnanolepidid placoderm from the Early Devonian of China. The type species, P. cuifengshanensis, was named by Zhang Goroui in 1978 and was re-evaluated in 2018, while a second species, P. guoruii, was named and described in 1996.
Houia is an extinct genus of dekatriatan, a clade of chelicerate arthropods. Fossils of Houia have been discovered in deposits of the Early Devonian period in Guangxi and Yunnan, both in China. The genus contains two species: H. guangxiensis, from the Pragian to Emsian epoch of Guangxi; and H. yueya, the type species, from the Lochkovian epoch of Yunnan. The name of the genus is derived from the Chinese character 鲎 (hòu), meaning "horseshoe crab".
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