Elpistostegalia

Life image of Panderichthys

• Basalste representative: Eastern Europe, Canada
• Including tetrapods: worldwide

The Elpistostegalia ( = Panderichthyida ) are a group of meat -finned fishes ( Sarcopterygii ). The term is traditionally used for fish-like representatives of the late Devonian in use, but excludes, according to recent opinion, the land vertebrates ( Tetrapoda ) with a.

Features

Skull and dentition of fishy Elpistostegalier resemble those of the earliest land vertebrates (eg, Acanthostega, Ichthyostega ). The skull is flat, in plan view, a parabolic shape and relatively large. It accounts for almost a quarter of the total body length. The eye openings (orbit ) are far above near the center seam on the skull. The trailing edge of the skull has the typical for many early land vertebrates ear slot. This may have indeed had a function for the auditory apparatus, but he stressed, in view of the designed solid columella ( stapes ), most likely none of the representatives that represent the transition from fish to land vertebrates ever a drum on. The tooth crowns are characterized in cross section by complex folded Dentinstrukuren from what in a similar way but also in many fishy Muskelflossern and early land vertebrates ( labyrinthodonts ) occurs.

The dorsal skull roof of fishy Elpistostegalier has three large paired bones: Frontal, Parietal and Postparietale. For all other teleosts occurs no paired Frontale. The front part of the dorsal skull roof as in primitive representatives (eg the Tristichopteriden ), from a large number of smaller bone elements ( Postrostralia, nasals ) is, however, composed. A great paired nasals occurs only at the earliest land vertebrates.

Another feature of the early Elpistostegalier and one of the most important indications of a very close relationship with the land vertebrates is the absence of unpaired fins ( dorsal and anal fin), and the apparently unverknöcherte opercular skeleton, by no osseous connection more between the rest of the skull and the shoulder belt is. The elements of the fin base skeleton of the pectoral fins, humerus, ulna and radius ( homologous to the humerus or the forearm bones ulna and the people ) are largely ossified. The pectoral fins are longer than the pelvic fins and the humerus is longer than any other fishy Fleischflossern. The caudal fin is diphyzerk. The body is covered with rhombic bony scales without Cosmi layer.

The Devonian vertebrates with a combination of typical features of earlier land vertebrates and fish typical features are in English informally as " fishapods " (composed of fish = " fish " and tetrapod = "land vertebrate " ) referred.

System

In the classical system, the Elpistostegalia or Panderichthyidae are a small, purely fossil group tetrapodenähnlicher meat -finned fishes. Carroll (1988 ) attributed them to three genera: Panderichthys, Elpistostege and Obruchevichthys. The latter was assigned to the Elginerpetontiden, a small group of early "real" tetrapods, but later ( 1995).

Cladistic analysis, in which both " remaining" Elpistostegalier genera were included, also gave rise to doubts about the monophyly of the group. While once Panderichthys and Elpistostege appeared as be sister, and their common clade in turn formed the sister group of tetrapods, Elpistostege was more closely related to tetrapods than Panderichthys in another analysis.

After the discovery of Tiktaalik, a clearly identified by its combination of features in a traditional sense as Elpisostegalier representatives, the hypothesis of the paraphyletic Elpistostegaliern confirmed. Although Elpistostege and Tiktaalik be sister, their common clade but is more closely related to tetrapods than with Panderichthys. Therefore, a new concept of the group has developed, according to which Elpistostegalia are defined as monophyletic, highly diverse group that includes both Panderichthys, Elpistostege and Tiktaalik and all land vertebrates.