Elpistostegalia
| Elpistostegalia | ||||||||||||
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Life picture of Panderichthys |
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| Temporal occurrence | ||||||||||||
| Middle to Upper Devonian (including tetrapods to date) |
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| 385 (according to palichnological findings possibly also 395) to 359 (including tetrapods up to 0) million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Elpistostegalia | ||||||||||||
| Camp & Allison , 1961 |
The Elpistostegalia (= Panderichthyida) are a group of the meat-flossers (Sarcopterygii). The term is traditionally in use for fish-like representatives of the late Devonian , but, according to a more recent view, also includes the terrestrial vertebrates (Tetrapoda).
features
The skull and teeth of the fish-like Elpistostegalier resemble those of the earliest terrestrial vertebrates (e.g. Acanthostega , Ichthyostega ). The skull is flat, parabolic in plan view and relatively large. It makes up almost a quarter of the entire body length. The eye openings (orbit) are high up on the skull near the central suture. The rear edge of the roof of the skull has the ear slit typical of many early terrestrial vertebrates. This may have had a function for the auditory apparatus, but in view of the massive columella (stapes) it probably never opened an eardrum in any of the representatives who represent the transition from fish to terrestrial vertebrate . The tooth crowns are characterized in cross-section by complexly folded dentin structures , which, however, also occurs in a similar way in many fish-like muscle fins and early terrestrial vertebrates ( labyrinthodontic animals ).
The dorsal cranial roof of the fish-like Elpistostegalier has three large paired bones: frontal, parietal and post-parietal. In all other bony fish there is no paired frontal. The foremost part of the dorsal roof of the skull, on the other hand, is composed of a large number of smaller bone elements (postrostralia, nasalia) , as in the more original representatives (e.g. the Tristichopteriden ). A large paired nasal does not appear until the earliest terrestrial vertebrates.
Another peculiarity of the early Elpistostegalier and one of the most important indications of a very close relationship with the terrestrial vertebrates is the absence of the unpaired fins ( dorsal and anal fin ), as well as the apparently non-ossified gill cover skeleton , due to which there is no longer any bony connection between the rest of the skull and the Shoulder girdle. The elements of the fin base skeleton of the pectoral fins , humerus, ulna and radius ( homologous to the humerus or the forearm bones of the ulna and radius of humans), are largely ossified. The pectoral fins are longer than the pelvic fins , and the humerus is longer than any other fish-like flesh fin . The caudal fin is diphyzerk . The body is covered by rhombic bone scales without a cosmin layer.
The Devonian vertebrates with a combination of typical characteristics of early land vertebrates and typical fish characteristics are also informally referred to in English as "fishapods" (composed of fish = "fish" and tetrapod = "land vertebrate").
Systematics
In the classical system, the Elpistostegalia or Panderichthyidae are a small, purely fossil group of tetrapod-like meat-fins. Carroll (1988) assigned three genera to them: Panderichthys , Elpistostege and Obruchevichthys . The latter, however, was later (1995) assigned to the Elginerpetontidae, a small group of earlier “real” tetrapods.
Cladistic analyzes, which included both “remaining” Elpistostegalier genera, also raised doubts about the group's monophyly . While Panderichthys and Elpistostege once appeared as sister taxa, and their common clade in turn formed the sister group of the tetrapods, in another analysis Elpistostege was more closely related to the tetrapods than Panderichthys .
After the discovery of Tiktaalik , a representative clearly identified as Elpisostegalier in the traditional sense due to his combination of characteristics, the hypothesis of the paraphyletic Elpistostegalians was confirmed. Although Elpistostege and Tiktaalik are sister taxa, their common clade is more closely related to the tetrapods than to Panderichthys . Therefore, a new concept of the group has developed, according to which the Elpistostegalia are defined as a monophyletic, highly diverse group, which includes Panderichthys , Elpistostege and Tiktaalik as well as all terrestrial vertebrates.
literature
- Jennifer A. Clack: Gaining ground: the origin and evolution of tetrapods. Indiana University Press, Bloomington 2002, ISBN 0-253-34054-3 .
- John A. Long: The Rise of Fishes . Johns Hopkins University Press , 1995, ISBN 0-8018-4992-6 .
- Joseph S. Nelson: Fishes of the World. John Wiley & Sons, 2006, ISBN 0-471-25031-7 .
- Hans-Peter Schultze: Elpistostegalia. In: Wilfried Westheide, Gunde Rieger: Special Zoology Part 2: Vertebrae and Skull Animals. 2nd Edition. Spektrum Akademischer Verlag, Heidelberg 2010, ISBN 978-3-8274-2039-8 , p. 321.
Web links
- Palæos Elpistostegalia
Individual evidence
- ↑ Grzegorz Niedźwiedzki, Piotr Szrek, Katarzyna Narkiewicz, Marek Narkiewicz, Per Erik Ahlberg. Tetrapod trackways from the early Middle Devonian period of Poland. In: Nature. Volume 463, 2010, pp. 43-48. doi: 10.1038 / nature08623
- ^ Robert Lynn Carroll : Vertebrate Paleontology and Evolution. WH Freeman and Co., New York 1988, p. 611.
- ↑ Per Erik Ahlberg: Elginerpeton pancheni and the earliest tetrapod clade. In: Nature. Volume 373, 1995, pp. 420-425. doi: 10.1038 / 373420a0
- ^ Richard Cloutier, Per Erik Ahlberg: Morphology, Characters, and the Interrelationships of Basal Sarcopterygians. In: Melanie LJ Stiassny, Lynne R. Parenti, G. David Johnson (Eds.): Interrelationships of Fishes. Academic Press, 1996, ISBN 0-12-670950-5 , pp. 445-479.
- ↑ Per Erik Ahlberg, Ervīns Lukševičs, Elga Mark-Kurik: A Near-Tetrapod from the Baltic Middle Devonian. In: Palaeontology. Volume 43, No. 3, 2000, pp. 533-548. doi: 10.1111 / j.0031-0239.2000.00138.x
- ^ Edward B. Daeschler, Neil H. Shubin, Farish A. Jenkins Jr .: A Devonian tetrapod-like fish and the evolution of the tetrapod body plan. In: Nature. Volume 440, 2006, pp. 757-763. doi: 10.1038 / nature04639
- ^ A b Brian Swartz: A Marine Stem-Tetrapod from the Devonian of Western North America. In: PLoS ONE. Volume 7, No. 3, 2012, p. E33683. doi: 10.1371 / journal.pone.0033683