Tristichopterids
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Tristichopterids (Tristichopteridae) were a diverse and successful group of fish-like
tetrapodomorph Tetrapodomorpha (also known as Choanata) is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced for ...
s living throughout the Middle and Late
Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
. They first appeared in the
Eifelian The Eifelian is the first of two faunal stages in the Middle Devonian Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the Emsian Stage and followed by the Givetian Stage. North American ...
stage of the Middle Devonian. Within the group sizes ranged from a few tens of centimeters (''
Tristichopterus ''Tristichopterus'', with a maximum length of sixty centimetres, is the smallest genus in the family of prehistoric lobe-finned fish,Bishop, P.J. 2012. A second species of Tristichopterus (Sarcopterygii: Tristichopteridae), from the Upper Devonian ...
'') to several meters (''
Hyneria ''Hyneria'' is a genus of large prehistoric predatory lobe-finned fish which lived in fresh water during the Famennian stage of the Devonian period. Etymology The genus name ''Hyneria'' is a reference to the village of Hyner, Pennsylvania, n ...
'' and ''
Eusthenodon ''Eusthenodon'' (Greek for “strong-tooth” – ''eusthenes''- meaning “strong”, -''odon'' meaning “tooth”) is an extinct genus of marine tristichopterid tetrapodomorphs from the Devonian, Late Devonian period, ranging between 365 and 3 ...
''). Some tristichopterids share some of the features of the
elpistostegalia Elpistostegalia is a clade containing ''Panderichthys'' and all more derived Tetrapodomorpha, tetrapodomorph taxa. The earliest elpistostegalians, combining fishlike and tetrapod-like characters, such as ''Tiktaalik'', are sometimes called fisha ...
ns, a diverse clade of tetrapodomorphs close to the origin of (and including) tetrapods. This mainly concerns the shape of the skull and a reduction in size of the posterior fins. An old and persistent notion is that ''
Eusthenopteron ''Eusthenopteron'' (from 'stout', and 'wing' or 'fin') is an extinct genus of prehistoric marine lobe-finned fish known from several species that lived during the Late Devonian period, about 385 million years ago. It has attained an iconic ...
'' was able to crawl onto land using its fins. However, there is no evidence actually supporting this idea.M. Laurin, F. J. Meunier, D. Germain, and M. Lemoine 2007
A microanatomical and histological study of the paired fin skeleton of the Devonian sarcopterygian ''Eusthenopteron foordi''
''Journal of Paleontology'' 81: 143–153. All tristichopterids had become extinct by the end of the Late Devonian.


Description

The Tristichopteridae were medium-sized (''Tristichopterus'', 30 cm) to very large animals. The smallest forms (such as ''Tristichopterus'') attained lengths of 30 cm, and the largest forms (''Hyneria'') could grow several meters long, possessed teeth up to 5 cm long, and were the largest predators in their faunal communities. The parts of the bones directed outward from the body trunk were flattened. The pelvis had long, tapering pubic branches (pubic rami) that possibly met in a cartilaginous symphysis. The ventral fins also contained the major bones of the hind legs, femur, tibia, and fibula. Ankle bones (tarsal bones) and toes cannot yet be identified. The limbs were oriented to the side and could only be moved back and forth about 20 to 25°. The anal fin sat on a basal, fleshy peduncle. The caudal fin possessed three lobes, initially asymmetrical in basal forms and becoming more symmetrical externally in later forms. The
scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number ...
lacked the
cosmine Cosmine is a spongy, bony material that makes up the dentine-like layers in the scales of the lobe-finned fishes of the class Sarcopterygii. Fish scales that include layers of cosmine are known as cosmoid scales. Description As traditionally d ...
layer found in more primitive tetrapodomorphs. Most of the body was covered in round, overlapping elasmoid scales with a median projection on the inner side. Thicker, enlarged scales occurred on the bases of the fins.lepidotrichia In a zoological context, spines are hard, needle-like anatomical structures found in both vertebrate and invertebrate species. The spines of most spiny mammals are modified hairs, with a spongy center covered in a thick, hard layer of keratin and ...
cover all of the fins, which does not happen until after metamorphosis in genera like '' Polyodon''. This might indicate that ''Eusthenopteron'' developed directly, with the hatchling already attaining the general body form of the adult.

Taxonomy

The family Tristichopteridae was named by
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontology, paleontologist, comparative anatomy, comparative anatomist, herpetology, herpetologist, and ichthyology, ichthyologist. Born to a wealthy Quaker fam ...
in 1889, who established it as the sole family of the order
Rhipidistia 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 de ...
. In turn, Cope deemed Rhipidistia and
Actinistia Coelacanths ( ) are an ancient group of lobe-finned fish (Sarcopterygii) in the class Actinistia. As sarcopterygians, they are more closely related to lungfish and tetrapods (the terrestrial vertebrates including living amphibians, reptiles, bi ...
as the two orders forming a superorder he named Rhipidopterygia. In 1955,
Lev Berg Lev Semyonovich Berg, also known as Leo S. Berg (; 14 March 1876 – 24 December 1950) was a leading Russian geographer, biologist and ichthyologist who served as President of the Soviet Geographical Society between 1940 and 1950. He is known f ...
erected a family named Eusthenopteridae to include the genera ''
Tristichopterus ''Tristichopterus'', with a maximum length of sixty centimetres, is the smallest genus in the family of prehistoric lobe-finned fish,Bishop, P.J. 2012. A second species of Tristichopterus (Sarcopterygii: Tristichopteridae), from the Upper Devonian ...
'' and ''Eusthenopteron'', and placed this family within the order Rhizodontiformes. More genera would later be placed in Eusthenopteridae, with Vorobyeva and Obruchev (1964) stating ''
Eusthenodon ''Eusthenodon'' (Greek for “strong-tooth” – ''eusthenes''- meaning “strong”, -''odon'' meaning “tooth”) is an extinct genus of marine tristichopterid tetrapodomorphs from the Devonian, Late Devonian period, ranging between 365 and 3 ...
'' and possibly ''
Platycephalichthys ''Platycephalichthys'' is a genus of tristichopterid lobe-finned fish which lived during the Upper Devonian, Frasnian stage. Phylogeny Below is a cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "ch ...
'' are members of this family, while Carroll (1988) added ''
Hyneria ''Hyneria'' is a genus of large prehistoric predatory lobe-finned fish which lived in fresh water during the Famennian stage of the Devonian period. Etymology The genus name ''Hyneria'' is a reference to the village of Hyner, Pennsylvania, n ...
'' and tentatively assigned '' Devonosteus'' and '' Litoptychus'' to the group. Currently, Eusthenopteridae is deemed a
junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...
of Tristichopteridae. In the past, Tristichopteridae was assigned to the order
Osteolepiformes Osteolepiformes, also known as Osteolepidida, is a group of prehistoric lobe-finned fishes which first appeared during the Devonian Geological period, period. The order (biology), order contains the families Canowindridae, Megalichthyidae, Osteol ...
, a group of tetrapodomorphs that is now considered
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
. The following phylogeny is modified from Schwartz (2012). Here, ''Platycephalichthys'' is not considered a member of the Tristichopteridae:


References

*Ahlberg, PE and Z Johanson (2001). "Second tristichopterid (Sarcopterygii, Osteolepiformes) from the Upper Devonian of Canowindra, New South Wales, Australia, and phylogeny of the Tristichopteridae." in ''Journal of Vertebrate Paleontology'' 17:563-673. *Johanson, Z. and P.E. Ahlberg (1997). "New tristichopterid (Osteolepiformes; Sarcopterygii) from the Mandagery Sandstone (Famennian) near Canowindra, N.S.W., Australia." in ''Transactions of the Royal Society of Edinburgh'' 88:39-53. {{Authority control Tetrapodomorph families Middle Devonian sarcopterygians Middle Devonian first appearances Late Devonian sarcopterygians Late Devonian extinctions Taxa named by Edward Drinker Cope