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 ''
''. This might indicate that ''Eusthenopteron'' developed directly, with the hatchling already attaining the general body form of the adult.