| Elpistostegalia Temporal range: 385–374 Ma Late Devonian |
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| Panderichthys | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Subphylum: | Vertebrata |
| Superclass: | Osteichthyes |
| Class: | Sarcopterygii |
| Superorder: | Osteolepiformes |
| Order: | †Elpistostegalia Camp & Allison, 1961 |
| Familia | |
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Elpistostegalia or Panderichthyida is an order of prehistoric lobe-finned fishes which lived during the Late Devonian period (about 385 to 374 million years ago).[1] They represent the advanced tetrapodomorph stock, the fishes more closely related to tetrapods than the osteolepiform fishes. The elpistostegalians, combining fishlike and tetrapod-like characters, are sometimes called fishapods, a phrase coined for the advanced elpistostegalian Tiktaalik.
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The elpistostegalids were shallow-water fishes. Many of the basic adaptions that later allowed the tetrapods to become terrestrial animals took place in the group. The most important ones were the shift of main propulsion apparatus from the tailfin to the pectoral and pelvic fins, and a shift to reliance on lungs rather than gills as the main means of obtaining oxygen.[2] Both of these appear to be a direct result of moving to an inland freshwater mode of living.[3]
A rise in global oxygen content allowed for the evolution of large, predatory fish that were able to exploit the shallow tidal areas and swamplands as top predators.[4] Such environments would have had periodic oxygen deficiency.[5] In comparable modern aquatic environments like shallow eutrophic lakes and swampland, modern lungfish and some genera of catfish also rely on the more stable, atmospheric source of oxygen.[6][7]
The elpistostegalids gave rise to the labyrinthodonts in the Eifelian (early middle Devonian) around 395 million years ago. While the early tetrapods flourished and diversified over the next 30 million years, the elpistostegalians disappear from the fossil record fairly quickly in the early Frasnean around 380 million years ago, leaving the labyrinthodonts the sole survivors of their line.[8]
Professor Per Ahlberg has identified the following traits as synapomorphic for Elpistostegalia (and thus Tetrapoda):[9]
The name, originally coined around the genus Elpistostege has become a synonym for Panderichthyida.[2] In most analysis the group is an evolutionary grade, the last "fishes" of the tetrapod stem line, though Chang and Yu (1997) treat them as the sister clade to Tetrapoda.[9][10]
The elpistostegalians encompasses a number of well known transitional fossils such as Tiktaalik, Panderichthys and Elginerpeton.
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