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Tristichopteridae

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Tristichopteridae
Temporal range: 392–359 Ma Middle - Late Devonian
Teeth of Platycephalichthys, in CosmoCaixa Barcelona
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Sarcopterygii
Clade: Tetrapodomorpha
Clade: Eotetrapodiformes
Family: †Tristichopteridae
Cope, 1889
Genera
Synonyms
  • Eusthenopteridae Berg, 1955

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 (Hyneria and Eusthenodon).

Some tristichopterids share some of the features of the elpistostegalians, a diverse clade of tetrapodomorphs close to the origin of (and including) tetrapods.[1][better source needed] 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 was able to crawl onto land using its fins. However, there is no evidence actually supporting this idea.[2] All tristichopterids had become extinct by the end of the Late Devonian.

Description

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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.[3] Tristichopterids had a strongly developed fin skeleton. In the skeleton of the front fins, which were deeply attached, the elements of the forelimb of the later tetrapodomorphs, such as the humerus, ulna and radius, can already be recognized.

Comparisons of the skulls of three members of the Tristichopteridae: A, B, C, Edenopteron; D, Eusthenodon, E. Cabonnichthys; F, Mandageria.

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 lacked the cosmine 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.[4] The earliest-known fossilised evidence of bone marrow has been found in Eusthenopteron, which may be the origin of bone marrow in tetrapods.[5]

The ontogeny of the Tristichopteridae is relatively well-known, and can be somewhat reliably inferred through Eusthenopteron.[6] Eusthenopteron differs significantly from some later Carboniferous tetrapods in the apparent absence of a recognized larval stage and a definitive metamorphosis. In even the smallest known specimen of Eusthenopteron foordi (at 29 mm), the lepidotrichia 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.[7]

Taxonomy

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The family Tristichopteridae was named by Edward Drinker Cope in 1889, who established it as the sole family of the order Rhipidistia. In turn, Cope deemed Rhipidistia and Actinistia as the two orders forming a superorder he named Rhipidopterygia.[8] In 1955, Lev Berg erected a family named Eusthenopteridae to include the genera Tristichopterus and Eusthenopteron, and placed this family within the order Rhizodontiformes.[9] More genera would later be placed in Eusthenopteridae, with Vorobyeva and Obruchev (1964) stating Eusthenodon and possibly Platycephalichthys are members of this family, while Carroll (1988) added Hyneria and tentatively assigned Devonosteus and Litoptychus to the group.[10][11] Currently, Eusthenopteridae is deemed a junior synonym of Tristichopteridae.[12]

In the past, Tristichopteridae was assigned to the order Osteolepiformes, a group of tetrapodomorphs that is now considered paraphyletic.

The following phylogeny is modified from Schwartz (2012). Here, Platycephalichthys is not considered a member of the Tristichopteridae:[1]

Tristichopteridae

References

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  1. ^ a b Swartz, B. (2012). "A marine stem-tetrapod from the Devonian of Western North America". PLOS ONE. 7 (3): e33683. Bibcode:2012PLoSO...733683S. doi:10.1371/journal.pone.0033683. PMC 3308997. PMID 22448265.
  2. ^ 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.
  3. ^ Thomson, K. S. (1968). "A new Devonian fish (Crossopterygii: Rhipidistia) considered in relation to the origin of the Amphibia". Postilla. 124.
  4. ^ Zylberberg, L., Meunier, F. J. and Laurin, M. 2010. A microanatomical and histological study of the postcranial dermal skeleton in the Devonian sarcopterygian Eusthenopteron foordi. Acta Palaeontologica Polonica 55: 459–470.
  5. ^ Sanchez S, Tafforeau P and Ahlberg P E (2014) "The humerus of Eusthenopteron: a puzzling organization presaging the establishment of tetrapod limb bone marrow" Proceedings of the Royal Society B: Biological Sciences, 281 (1782): 20140299. doi:10.1098/rspb.2014.0299
  6. ^ Schultze, H.-P. 1984. Juvenile specimens of Eusthenopteron foordi Whiteaves, 1881 (Osteolepiform rhipidistian, Pisces) from the Late Devonian of Miguasha, Quebec, Canada. Journal of Vertebrate Paleontology 4: 1-16.
  7. ^ S. Cote; R. Carroll; R. Cloutier; L. Bar-Sagi (September 2002). "Vertebral development in the Devonian Sarcopterygian fish Eusthenopteron foordi and the polarity of vertebral evolution in non-amniote tetrapods". Journal of Vertebrate Paleontology. 22 (3): 487–502. doi:10.1671/0272-4634(2002)022[0487:VDITDS]2.0.CO;2. ISSN 0272-4634.
  8. ^ Cope, E. D. (1889). "Synopsis of the Families of Vertebrata". The American Naturalist. 23 (274): 849–877. ISSN 0003-0147. JSTOR 2451539.
  9. ^ Berg, L.S. (1955). "Classification of fish-like vertebrates, living and fossil. 2., corrected and enlarg". Trudy Zoologicheskogo Instituta (in Russian). 20: 1–286.
  10. ^ Vorobyeva, E.I.; Obruchev, D.V. (1964). Osnovy Paleontologii [Fundamentals of Paleontology] (in Russian). Vol. XI. Agnatha, Pisces. Moscow. pp. 268–322.{{cite book}}: CS1 maint: location missing publisher (link)
  11. ^ Carroll, Robert Lynn (1988). Vertebrate paleontology and evolution. New York, N.Y: Freeman. ISBN 978-0-7167-1822-2.
  12. ^ Schultze, Hans-Peter; Cloutier, Richard (1996). "Taxonomic review of Eusthenopteron foordi". Devonian Fishes and Plants of Miguasha, Quebec, Canada. F. Pfeil. pp. 271–284. ISBN 978-3-931516-03-1.
  • 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.
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