Adelospondyli
Adelospondyls Temporal range:
Late Mississippian , | |
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Life restoration of Adelospondylus | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Sarcopterygii |
Clade: | Tetrapodomorpha |
Clade: | Stegocephali |
Order: | †Adelospondyli Watson , 1930
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Families and genera | |
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Adelospondyli is an
Most adelospondyls belong to the
Description
Adelospondyls share a variety of traits with other lepospondyls, although whether these traits are an example of convergent evolution is a controversial topic. Like the aïstopods and lysorophian "microsaurs", they had very elongated bodies similar to that of snakes and eels. In addition, they lacked limbs (similarly to the aïstopods), although forelimbs were supposedly found in various adelogyrinids in the late 1960s. Andrews & Carroll (1991) found that all cases of forelimb bones in adelogyrinids were actually misinterpretations. For example, putative forelimbs discovered in Adelogyrinus and Palaeomolgophis by Brough & Brough (1967) were re-identified as hyoid bones and ribs, respectively. Carroll (1967) also claimed that forelimbs were present in Adelospondylus, but these later considered to be hyoids as in Adelogyrinus.[1]
Skull
Adelospondyls had somewhat long and low skulls, with large orbits (eye sockets) shifted towards the front of the skull. As a result, the proportions of the skull bones were affected. For example, the nasal bones along the midline of the skull in front of the eyes were much shorter than the frontal bones directly behind them, which extended forwards past the level of the eyes. The frontal bones were omitted from the edge of the orbits (eye holes) due to a contact between the pre- and post-frontals which typically lie in front of and behind the orbits, respectively. Unlike lysorophians and aïstopods, which had snake-like skulls with large openings and reduced bone material, adelospondyl skulls were strongly built and covered with ridges, pits, and grooves, including lateral line sulci. They typically possessed many teeth, although such teeth differ in structure between families. Adelogyrinids, for example, had many numerous "chisel-shaped" teeth,[1] while Acherontiscus had blunt teeth at the back of the mouth and sharp, thin teeth at the front.[5] As is the case in other lepospondyls, the teeth of adelospondyls did not have a maze-like internal structure like those of "labyrinthodonts", nor did adelospondyls possess enlarged fang-like teeth on the roof of the mouth.[1]
Similar to various other lepospondyls, adelospondyls lost several bones in the temporal region of the skull, which is at the back of the skull between the
Postcranial bones
Adelospondyls can also be characterized by their vertebrae compared to other lepospondyls. They were spool-shaped and high in number, with Acherontiscus having an estimated 64 vertebrae
Although adelospondyls lost all trace of their fore- and hind-limbs, they did retain a notable remnant of their presumably limbed ancestors. This remnant is a large bony dermal shoulder girdle, comprising the plate-like
References
- ^ S2CID 84460890.
- ^ S2CID 31298396.
- PMID 30631641.
- S2CID 86479890.
- ^ a b c Carroll, Robert L. (1969). "A new family of Carboniferous amphibians" (PDF). Palaeontology (12). Archived from the original (PDF) on 2010-02-15.
- ISBN 978-0871691262.
- S2CID 128605530.
- ^ Marjanović, David (21 August 2010). "Phylogeny of the limbed vertebrates with special consideration of the origin of the modern amphibians" (PDF). Dissertation.
- ^ Watson, D.M.S. (1929). "The Carboniferous Amphibia of Scotland". Palaeontologia Hungarica. 1: 219–252.
- Carroll, RL (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.
- von Zittel, K.A (1932), Textbook of Paleontology, CR Eastman (transl. and ed), 2nd edition, vol.2, p. 225, Macmillan & Co.