| Ptomacanthus Temporal range: Early Devonian (Lochkovian) | |
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| Genus: | Ptomacanthus |
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Ptomacanthus (meaning thorny corpse) is an extinct genus of spiny shark, [1] an early relative of living cartilaginous fishes (sharks, rays, and chimaeras). [2]
Ptomacanthus is known mainly from the Old Red Sandstone of the United Kingdom. [1] The most completely known species, P. anglicus is known from several articulated fossils from Wayne Herbert Quarry, Herefordshire, United Kingdom. [1] Two indeterminate species are known from shoulder-girdles recovered from Castle Mattock Quarry, Herefordshire and Zaleszychi, Ukraine. [1]
The only species known in any detail, P. anglicus was a fish about 25 cm long. [3] Like other acanthodians it had small, shark like scales, and a suite of fin-spines in front of its dorsal, pectoral, and pelvic fins. [1]
P. anglicus is important to our understanding of early vertebrate evolution as it preserves part of the braincase, a scientifically informative part of the skeleton. [2] Because of the cartilaginous makeup of the acanthodian internal skeleton, it is very rarely preserved, and the braincase of Ptomacanthus is only the second acanthodian braincase known to science (the first being that of Acanthodes ). [4] The description of this braincase reignited debate over the relationships of acanthodians as well as those of early vertebrates more generally. [2] [4]
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.
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.
Anders Erik Vilhelm Jarvik was a Swedish paleontologist who worked extensively on the sarcopterygian fish Eusthenopteron. In a career that spanned some 60 years, Jarvik produced some of the most detailed anatomical work on this fish, making it arguably the best known fossil vertebrate.
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.
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.
Cladoselache is an extinct genus of shark-like chondrichthyan from the Late Devonian (Famennian) of North America. It was similar in body shape to modern lamnid sharks, but was not closely related to lamnids or to any other modern (selachian) shark. As an early chondrichthyan, it had yet to evolve traits of modern sharks such as accelerated tooth replacement, a loose jaw suspension, enameloid teeth, and possibly claspers.
Bothriolepis 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, averaging around 30 centimetres (12 in) in length. However, the largest species, B. rex, had an estimated bodylength of 170 centimetres (67 in). Although expansive with over 60 species found worldwide, comparatively Bothriolepis is not unusually more diverse than most modern bottom dwelling species around today.
Acanthodes is an extinct genus of acanthodian fish. Species have been found in Europe, North America, and Asia, spanning the Early Carboniferous to the Early Permian, making it one of the youngest known acanthodian genera.
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 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.
Brochoadmones is an extinct genus of acanthodian from the Devonian of what is now Canada. It is the only genus in the suborder Brochoadmonoidei, whose relationship to other acanthodian orders remains currently in flux.
Entelognathus primordialis is an early placoderm from the late Silurian of Qujing, Yunnan, 419 million years ago.
This list of fossil fishes described in 2015 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fishes, bony fishes and other fishes of every kind that have been described during the year 2015, as well as other significant discoveries and events related to paleontology of fishes that occurred in the year 2015. The list only includes taxa at the level of genus or species.
This list of fossil fishes described in 2017 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fishes, bony fishes and other fishes of every kind that are scheduled to be described during the year 2017, as well as other significant discoveries and events related to paleontology of fishes that are scheduled to occur in the year 2017. The list only includes taxa at the level of genus or species.
This list of fossil fish described in 2018 is a list of new taxa of jawless vertebrates, placoderms, acanthodians, fossil cartilaginous fish, bony fish, and other fish of every kind that are scheduled to be described during the year 2018, as well as other significant discoveries and events related to paleontology of fish that are scheduled to occur in 2018.
Sam Giles is a palaeobiologist at the University of Birmingham. Her research combines modern imaging with fossils to understand the evolution of life, in particular that of early fish, and in 2015 "rewrote" the vertebrate family tree. She was a 2017 L'Oréal-UNESCO Rising Star and won the 2019 Geological Society of London Lyell Fund.
Qianodus is a jawed vertebrate genus that is based on disarticulated teeth from the lower Silurian of China. The type and only species of Qianodus, Q. duplicis, is known from compound dental elements called tooth whorls, each consisting of multiple tooth generations carried by a spiral-shaped base. The tooth whorls of Qianodus represent the oldest unequivocal remains of a toothed vertebrate, predating previously recorded occurrences by about 14 million years. The specimens attributed to the genus come from limestone conglomerate beds of the Rongxi Formation exposed near the village of Leijiatun, Guizhou Province, China. These horizons have been interpreted as tidal deposits1 that form part of the shallow marine sequences of the Rongxi Formation.
The evolution of fishes took place over a timeline which spans the Cambrian to the Cenozoic, including during that time in particular the Devonian, which has been dubbed the "age of fishes" for the many changes during that period.
