Sarcopterygii — sometimes considered synonymous with Crossopterygii — is a clade including both a group of bony fish commonly referred to as lobe-finned fish, and tetrapods. 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.
Ichthyostega is an extinct genus of limbed tetrapodomorphs from the Late Devonian of what is now Greenland. It was among the earliest four-limbed vertebrates ever in the fossil record and was one of the first with weight-bearing adaptations for terrestrial locomotion. Ichthyostega possessed lungs and limbs that helped it navigate through shallow water in swamps. Although Ichthyostega is often labelled a 'tetrapod' because of its limbs and fingers, it evolved long before true crown group tetrapods and could more accurately be referred to as a stegocephalian or stem tetrapod. Likewise, while undoubtedly of amphibian build and habit, it is not a true member of the group in the narrow sense, as the first modern amphibians appeared in the Triassic Period. Until finds of other early stegocephalians and closely related fishes in the late 20th century, Ichthyostega stood alone as a transitional fossil between fish and tetrapods, combining fish and tetrapod features. Newer research has shown that it had an unusual anatomy, functioning more akin to a seal than a salamander, as previously assumed.
Rhipidistia, also known as Dipnotetrapodomorpha, is a clade of lobe-finned fishes which includes the tetrapods and lungfishes. Rhipidistia formerly referred to a subgroup of Sarcopterygii consisting of the Porolepiformes and Osteolepiformes, a definition that is now obsolete. However, as cladistic understanding of the vertebrates has improved over the last few decades, a monophyletic Rhipidistia is now understood to include the whole of Tetrapoda and the lungfishes.
Eusthenopteron is a genus of prehistoric sarcopterygian fishes 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 widely agree that eusthenopteron species were strictly aquatic animals.
Tetrapodomorpha is a clade of vertebrates consisting of tetrapods and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced forms transitional between fish and the early labyrinthodonts, such as Tiktaalik, have been referred to as "fishapods" by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contains the crown group tetrapods and several groups of early stem tetrapods, which includes several groups of related lobe-finned fishes, collectively known as the osteolepiforms. The Tetrapodomorpha minus the crown group Tetrapoda are the stem Tetrapoda, a paraphyletic unit encompassing the fish to tetrapod transition.
Tristichopterids (Tristichopteridae) were a diverse and successful group of fish-like tetrapodomorphs living throughout the Middle and Late Devonian. They first appeared in the Eifelian stage of the Middle Devonian. Within the group sizes ranged from a few tens of centimeters (Tristichopterus) to several meters.
Kenichthys is a genus of sarcopterygian fish from the Devonian period, and a member of the clade Tetrapodomorpha. The only known species of the genus is Kenichthys campbelli, the first remains of which were found in China in 1993. The genus is important to the study of the evolution of tetrapods due to the unique nature of its nostrils, which provide vital evidence regarding the evolutionary transition of fish-like nostrils to the tetrapod choanae.
Rhizodontida is an extinct group of predatory tetrapodomorphs known from many areas of the world from the Givetian through to the Pennsylvanian - the earliest known species is about 377 million years ago (Mya), the latest around 310 Mya. Rhizodonts lived in tropical rivers and freshwater lakes and were the dominant predators of their age. They reached huge sizes - the largest known species, Rhizodus hibberti from Europe and North America, was an estimated 7 m in length, making it the largest freshwater fish known.
Eusthenodon is an extinct genus of tristichopterid tetrapodomorphs from the Late Devonian period, ranging between 383 and 359 million years ago. They are well known for being a cosmopolitan genus with remains being recovered from East Greenland, Australia, Central Russia, South Africa, Pennsylvania, and Belgium. Compared to the other closely related genera of the Tristichopteridae clade, Eusthenodon was one of the largest lobe-finned fishes and among the most derived tristichopterids alongside its close relatives Cabonnichthys and Mandageria.
Tristichopterus, with a maximum length of sixty centimetres, is the smallest genus in the family of prehistoric lobe-finned fish, Tristichopteridae that was believed to have originated in the north and dispersed throughout the course of the Upper Devonian into Gondwana. Tristichopterus currently has only one named species, first described by Egerton in 1861. The Tristichopterus node is thought to have originated during the Givetian part of the Devonian. Tristichopterus was thought by Egerton to be unique for its time period as a fish with ossified vertebral centers, breaking the persistent notochord rule of most Devonian fish but this was later reinspected and shown to be only partial ossification by Dr. R. H. Traquair. Tristichopterus alatus closely resembles Eusthenopteron and this sparked some debate after its discovery as to whether it was a separate taxon.
The Canowindridae are a family of prehistoric tetrapodomorphs which lived during the Devonian period. Fossils belonging to this family have been found in Australia, Antarctica, and Europe.
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.
Osteolepididae is a family of primitive, fish-like tetrapodomorphs that lived during the Devonian period. The family is generally thought to be paraphyletic, with the traits that characterise the family being widely distributed among basal tetrapodomorphs and other osteichthyans. Some of the genera historically placed in Osteolepididae have more recently been assigned to the family Megalichthyidae, which appears to be a monophyletic group.
Chrysolepis is a genus of prehistoric marine lobe-finned fish that lived during the Late Devonian period. It contains a single species, C. orlensis, known from the middle Famennian of Oryol Oblast, Russia. It is the only member of the family Chrysolepididae, erected due to its highly distinct morphology unseen among other osteolepiforms. It may be the sister taxon to the eusthenopterids.
The skull roof or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium.
Marsdenichthys is an extinct genus of Devonian tetrapodomorph. Fossils have been found from Mount Howitt in Victoria, Australia from strata that are Givetian-Frasnian in age. Mount Howitt is an important site that has been the source of many tetrapodomorph fossils, including Beelarongia and Howittichthys, both of which were first described from the locality.
The Stem Tetrapoda are a cladistically defined group, consisting of all animals more closely related to extant four-legged vertebrates than to their closest extant relatives, but excluding the crown group Tetrapoda. They are thus paraphyletic, though acceptable in phylogenetic nomenclature as the group is defined by strict reference to phylogeny rather than to traits as in traditional systematics. Thus, some finned sarcopterygians are considered to be stem tetrapods.
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.
Eotetrapodiformes is a clade of tetrapodomorphs including the four-limbed vertebrates and their closest finned relatives, two groups of stem tetrapods called tristichopterids and elpistostegalids.
The Mandagery Sandstone is a Late Devonian geological formation in New South Wales, Australia. It is one of several famed Australian lagerstätten, with thousands of exceptional fish fossils found at a site near the town of Canowindra.
