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.
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.
Sarcopterygii — sometimes considered synonymous with Crossopterygii — is a clade of bony fish commonly referred to as lobe-finned fish. They are characterised by prominent muscular limb buds (lobes) within their fins, which are supported by articulated appendicular skeletons. This is in contrast to the other clade of bony fish, the Actinopterygii, which have only skin-covered bony spines supporting the fins.
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.
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.
The Mackenzie Mountains are a Canadian mountain range forming part of the Yukon-Northwest Territories boundary between the Liard and Peel rivers. The range is named in honour of Canada's second prime minister, Alexander Mackenzie. Nahanni National Park Reserve and Nááts'ihch'oh National Park Reserve are in the Mackenzie Mountains.
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".
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.
Nerepisacanthus is an extinct genus of acanthodian, probably acritolepid, from Middle Silurian deposits of New Brunswick, Canada. Nerepisacanthus is known from many incomplete but articulated specimens. It was collected from the Cunningham Creek Formation, near Nerepis, southern New Brunswick. It was first named by Carole J. Burrow in 2011 and the type species is Nerepisacanthus denisoni. Additional specimen is known from Bertie Formation, making that species the oldest near-complete acanthodian.
Gracianella is a genus of fossil brachiopods. It was described by Johnson and Coucot in 1967, and existed from the Silurian to the Devonian of Australia, Austria, Canada, China, the Czech Republic, Italy, Tajikistan, and the United States. A new species, G. paulula, was described by Andrzej Baliński in 2012, from the early Devonian of Ukraine.
Tetanopsyrus is a genus of Acanthodii. There are two species of this genus that lived through the lower Devonian (Lochkovian), some 416 to 359 million years ago.
The Wood Bay Series is a geologic formation found on the island of Spitsbergen, Svalbard in Norway. It preserves fossils dating back to the Pragian–Emsian stages of the Devonian period.
The Frænkelryggen Formation is a geologic formation in Svalbard, Norway. The fluvial sandstones and green shales preserve flora and early fish fossils dating back to the Lochkovian stage of the Early Devonian period.
Anglaspis is an extinct genus of cyathaspidiform heterostracan agnathan. Fossils are found in marine strata of Europe, from the late Silurian period until the genus' extinction during the Early Devonian. As with other cyathaspidiforms, individuals of Anglaspis had dorsal and ventral plates covering the forebody, gill pouches, and nasal openings that lay on the roof of the oral cavity.
Archipelepis is a genus of extinct thelodont agnathans, and are the most primitive recognized thelodonts of which whole body fossils are known. Fossils of bodies and scales are currently known from Late Telychian to Wenlock-aged marine strata of northern Canada.
The Bertie Group or Bertie Limestone, also referred to as the Bertie Dolomite and the Bertie Formation, is an upper Silurian geologic group and Lagerstätte in southern Ontario, Canada, and western New York State, United States. Details of the type locality and of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line at the National Geologic Map Database. The formation comprises dolomites, limestones and shales and reaches a thickness of 495 feet (151 m) in the subsurface, while in outcrop the group can be 60 feet (18 m) thick.
Tiiu Märss is an Estonian geologist and palaeoichthyologist.
Dudleyaspis is an extinct genus of Lower to Middle Devonian odontopleurid trilobites that lived in a shallow sea that lay between Euramerica and Gondwana. It was named in 1949 by Prantl & Pribyl.
