Sarcopterygii — sometimes considered synonymous with Crossopterygii — is a clade of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates 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.
Acanthostega is an extinct genus of stem-tetrapod, among the first vertebrate animals to have recognizable limbs. It appeared in the late Devonian period about 365 million years ago, and was anatomically intermediate between lobe-finned fishes and those that were fully capable of coming onto land.
Eusthenopteron is a genus of prehistoric sarcopterygian fish known from several species that lived during the Late Devonian period, about 385 million years ago. It has attained an iconic status from its close relationship to tetrapods. Early depictions of animals of this genus show them emerging onto land, but paleontologists now think that eusthenopteron species were strictly aquatic animals, though this is not completely known.
Panderichthys is a genus of extinct sarcopterygian from the late Devonian period, about 380 Mya. Panderichthys, which was recovered from Frasnian deposits in Latvia, is represented by two species. P. stolbovi is known only from some snout fragments and an incomplete lower jaw. P. rhombolepis is known from several more complete specimens. Although it probably belongs to a sister group of the earliest tetrapods, Panderichthys exhibits a range of features transitional between tristichopterid lobe-fin fishes and early tetrapods. It is named after the German-Baltic paleontologist Christian Heinrich Pander. Possible tetrapod tracks dating back to before the appearance of Panderichthys in the fossil record were reported in 2010, which suggests that Panderichthys is not a direct ancestor of tetrapods, but nonetheless shows the traits that evolved during the fish-tetrapod evolution
Hynerpeton is an extinct genus of early four-limbed vertebrate that lived in the rivers and ponds of Pennsylvania during the Late Devonian period, around 365 to 363 million years ago. The only known species of Hynerpeton is H. bassetti, named after the describer's grandfather, city planner Edward Bassett. Hynerpeton is known for being the first Devonian four-limbed vertebrate discovered in the United States, as well as possibly being one of the first to have lost internal (fish-like) gills.
Tiktaalik is a monospecific genus of extinct sarcopterygian from the Late Devonian Period, about 375 Mya, having many features akin to those of tetrapods. Tiktaalik is estimated to have had a total length of 1.25–2.75 metres (4.1–9.0 ft) based on various specimens.
Holoptychius is an extinct genus of porolepiform lobe-finned fish from the Middle Devonian to Carboniferous (Mississippian) periods. It is known from fossils worldwide. The genus was first described by Louis Agassiz in 1839.
The Fram Formation is an Upper Devonian (Frasnian) sequence of rock strata on Ellesmere Island that came into prominence in 2006 with the discovery in its rocks of examples of the transitional fossil, Tiktaalik, a sarcopterygian or lobe-finned fish showing many tetrapod characteristics. Fossils of Laccognathus embryi, a porolepiform lobe-finned fish, and Qikiqtania, a close relative of Tiktaalik, were also found in the formation. The Fram Formation is a Middle to Upper Devonian clastic wedge forming an extensive continental facies consisting of sediments derived from deposits laid down in braided stream systems that formed some 375 million years ago, at a time when the North American craton ("Laurentia") was straddling the equator.
A walking fish, or ambulatory fish, is a fish that is able to travel over land for extended periods of time. Some other modes of non-standard fish locomotion include "walking" along the sea floor, for example, in handfish or frogfish.
Edward B. 'Ted' Daeschler is an American vertebrate paleontologist and Associate Curator and Chair of Vertebrate Biology at the Academy of Natural Sciences in Philadelphia. He is a specialist in fish paleontology, especially in the Late Devonian, and in the development of the first limbed vertebrates. He is the discoverer of the transitional fossil tetrapod Hynerpeton bassetti, and a Devonian fish-like specimen of Sauripterus taylori with fingerlike appendages, and was also part of a team of researchers that discovered the transitional fossil Tiktaalik.
Elpistostegalia is a clade containing Panderichthys and all more derived tetrapodomorph taxa. The earliest elpistostegalians, combining fishlike and tetrapod-like characters, such as Tiktaalik, are sometimes called fishapods. Although historically Elpistostegalia was considered an order of prehistoric lobe-finned fishes, it was cladistically redefined to include tetrapods.
Laccognathus is an extinct genus of amphibious lobe-finned fish from Europe and North America. They existed from the Middle Devonian to the Late Devonian. The name comes from Greek for 'pitted jaw'.
Ichthyostegalia is an order of extinct Tetrapodomorphs, representing the earliest landliving vertebrates. The group is thus an evolutionary grade rather than a clade. While the group are recognized as having feet rather than fins, most, if not all, had internal gills in adulthood and lived primarily as shallow water fish and spent minimal time on land.
Antlerpeton is an extinct genus of early tetrapod from the Early Carboniferous of Nevada. It is known from a single poorly preserved skeleton from the Diamond Peak Formation of Eureka County. A mix of features in its compound vertebrae suggest that Antlerpeton is a primitive stem tetrapod that has affinities with later, more advanced forms. Its robust pelvis and hind limbs allowed for effective locomotion on land, but the animal was likely still tied to a semiaquatic lifestyle near the coast.
Laccognathus embryi is an extinct species of porolepiform lobe-finned fish recovered from Ellesmere Island, Canada. It existed during the Frasnian age of the Late Devonian epoch.
Tinirau is an extinct genus of sarcopterygian fish from the Middle Devonian of Nevada. Although it spent its entire life in the ocean, Tinirau is a stem tetrapod close to the ancestry of land-living vertebrates in the crown group Tetrapoda. Relative to more well-known stem tetrapods, Tinirau is more closely related to Tetrapoda than is Eusthenopteron, but farther from Tetrapoda than is Panderichthys. The type and only species of Tinirau is T. clackae, named in 2012.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. Tetrapods are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals. While most species today are terrestrial, little evidence supports the idea that any of the earliest tetrapods could move about on land, as their limbs could not have held their midsections off the ground and the known trackways do not indicate they dragged their bellies around. Presumably, the tracks were made by animals walking along the bottoms of shallow bodies of water. The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear. They are areas of active research and debate among palaeontologists at present.
Innovations conventionally associated with terrestrially first appeared in aquatic elpistostegalians such as Panderichthys rhombolepis, Elpistostege watsoni, and Tiktaalik roseae. Phylogenetic analyses distribute the features that developed along the tetrapod stem and display a stepwise process of character acquisition, rather than abrupt. The complete transition occurred over a period of 30 million years beginning with the tetrapodomorph diversification in the Middle Devonian.
The Zachelmie trackways are a series of Middle Devonian-age trace fossils in Poland, purportedly the oldest evidence of terrestrial vertebrates (tetrapods) in the fossil record. These trackways were discovered in the Wojciechowice Formation, an Eifelian-age carbonate unit exposed in the Zachełmie Quarry of the Świętokrzyskie Mountains. The discovery of these tracks has complicated the study of tetrapod evolution. Morphological studies suggest that four-limbed vertebrates are descended from a specialized type of tetrapodomorph fish, the epistostegalians. This hypothesis was supported further by the discovery and 2006 description of Tiktaalik, a well-preserved epistostegalian from the Frasnian of Nunavut. Crucial to this idea is the assumption that tetrapods originated in the Late Devonian, after elpistostegalians appear in the fossil record near the start of the Frasnian. The Zachelmie trackways, however, appear to demonstrate that tetrapods were present prior to the Late Devonian. The implications of this find has led to several different perspectives on the sequence of events involved in tetrapod evolution.
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.
