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The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 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.
Placoderms are members of the class Placodermi 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.
Pterygotus is a genus of giant predatory eurypterid, a group of extinct aquatic arthropods. Fossils of Pterygotus have been discovered in deposits ranging in age from Middle Silurian to Late Devonian, and have been referred to several different species. Fossils have been recovered from four continents; Australia, Europe, North America and South America, which indicates that Pterygotus might have had a nearly cosmopolitan (worldwide) distribution. The type species, P. anglicus, was described by Swiss naturalist Louis Agassiz in 1839, who gave it the name Pterygotus, meaning "winged one". Agassiz mistakenly believed the remains were of a giant fish; he would only realize the mistake five years later in 1844.
Galeaspida 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 shallow, fresh water and marine environments during the Silurian and Devonian times in what is now Southern China, Tibet and Vietnam. Superficially, their morphology appears more similar to that of Heterostraci than Osteostraci, there being currently no evidence that the galeaspids had paired fins. A galeaspid Tujiaaspis vividus from the Silurian period of China was described in 2022 as having a precursor condition to the form of paired fins seen in Osteostraci and gnathostomes. Earlier than this, Galeaspida were already in fact regarded as being more closely related to Osteostraci, based on the closer similarity of the morphology of the braincase.
Erettopterus is a genus of large predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Erettopterus have been discovered in deposits ranging from Early Silurian to the Early Devonian, and have been referred to several different species. Fossils have been recovered from two continents; Europe and North America. The genus name is composed by the Ancient Greek words ἐρέττω (eréttō), which means "rower", and πτερόν (pterón), which means "wing", and therefore, "rower wing".
Rhinocarcinosoma is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Rhinocarcinosoma have been discovered in deposits ranging of Late Silurian age in the United States, Canada and Vietnam. The genus contains three species, the American R. cicerops and R. vaningeni and the Vietnamese R. dosonensis. The generic name is derived from the related genus Carcinosoma, and the Greek ῥινός, referring to the unusual shovel-shaped protrusion on the front of the carapace of Rhinocarcinosoma, its most distinctive feature.
The Paleozoological Museum of China is a museum in Beijing, China. The same building also houses the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences. The museum contains exhibition halls with specimens aimed at the public, while the rest of the building is used for research purposes.
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.
The Xiushan Formation is a palaeontological formation located in China. It dates to the Lower Silurian period. Studies of conodonts found in the formation suggests the lower member and main part of the upper member correspond to the Pterospathodus eopennatus Superbiozone, whereas the top of the upper member likely correlates with the Pterospathodus celloni Superbiozone.
Tonganosaurus is a genus of mamenchisaurid sauropod dinosaur, similar to Omeisaurus. It is known from one specimen consisting of twenty vertebrae, a front limb and pectoral girdle, and a complete hind limb with partial hip. It was discovered in the Yimen Formation, China. The horizon of the specimen and the age of the Yimen Formation is controversial. The formation has been divided into three levels, and Tonganosaurus appears to be of late Early Jurassic (Pliensbachian) age. Tonganosaurus is the oldest known member of the mamenchisaurids, being almost 15 million years older than the next-oldest members of the group. It was first named by Li Kui, Yang Chun-Yan, Liu Jian and Wang Zheng-Xin in 2010 and the type species is Tonganosaurus hei.
Shuyu is an extinct genus of early jawless vertebrate from the Early or Middle Silurian period. It is the basalmost known eugaleaspidiform galeaspid and it lived in what is now northwestern Zhejiang Province, Southeast China. It is known from more than 20 headshields and at least 20 of them include three-dimensionally preserved neurocrania. The specimens of Shuyu were collected from the lower part of Maoshan Formation, located in Changxing District. Shuyu zhejianensis was first assigned by Pan, 1986 to a species of Sinogaleaspis. The genus was first named by Zhikun Gai, Philip C. J. Donoghue, Min Zhu, Philippe Janvier and Marco Stampanoni in 2011 and the type species is Shuyu zhejianensis.
Dunyu is an extinct genus of eugaleaspidiform galeaspid known from the Silurian of Yunnan, southwestern China. Two species are known: D longiforus, the type species and D. xiushanensis, which was initially named as a species of Eugaleaspis. The type specimen of D. longiforus is IVPP V 17681, a complete cephalic shield prepared by C. H. Xiong, and the holotype of D. xiushanensis is IVPP V 6793.1, another complete cephalic shield.
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.
Homostiidae is a family of flattened arthrodire placoderms from the Early to Middle Devonian. Fossils appear in various strata in Europe, Russia, Morocco, Australia, Canada and Greenland.
Entelognathus primordialis is an early placoderm from the late Silurian of Qujing, Yunnan, 419 million years ago.
Megamastax is a genus of lobe-finned fish which lived during the late Silurian period, about 423 million years ago, in China. Before the discovery of Megamastax, it was thought that jawed vertebrates (gnathostomes) were limited in size and variation before the Devonian period. Megamastax is known only from jaw bones and it is estimated that it reached about 1 metre long.
Apteryx littoralis is an extinct species of kiwi from New Zealand's North Island. The species was first described in 2021 based on the holotype, a complete left tarsometatarsus that was found in the Pleistocene (Calabrian)-aged Rangitikei Formation.
This list of fossil fish research presented in 2022 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fishes, bony fishes, and other fishes that were described during the year, as well as other significant discoveries and events related to paleoichthyology that occurred in 2022.
Bashanosaurus is an extinct genus of stegosaurian dinosaur from the Middle Jurassic Shaximiao Formation of Yunyang County, China. The genus contains a single species, Bashanosaurus primitivus, known from incomplete skeletons belonging to three individuals. It is one of the basalmost stegosaurs, as well as one of the oldest known stegosaurs, along with Adratiklit and Isaberrysaura.
Yuzhoulong is a genus of macronarian sauropod dinosaur from the Middle Jurassic Shaximiao Formation of Chongqing, China. The type and only species is Yuzhoulong qurenensis.
References
- ↑ "Over 400-mln-yr-old fossil of fish found in China - China.org.cn". www.china.org.cn.
- 1 2 "They find remains of a fish that lived 400 million years ago". March 4, 2022.
- 1 2 3 Chen, Yang; Gai, Zhikun; Li, Qiang; Wang, Jianhua; Peng, Lijian; Wei, Guangbiao; Zhu, Min (April 2022). "A New Family of Galeaspids (Jawless Stem‐Gnathostomata) from the Early Silurian of Chongqing, Southwestern China". Acta Geologica Sinica - English Edition. 96 (2): 430–439. doi:10.1111/1755-6724.14909. S2CID 247063430.
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