Apsisaurus
| Apsisaurus | ||||||||||||
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Head reconstruction by A. witteri |
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| Temporal occurrence | ||||||||||||
| lower lower perm | ||||||||||||
| 299 to 290 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Apsisaurus | ||||||||||||
| Laurin , 1991 | ||||||||||||
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Apsisaurus is an extinct genus of early synapsids (" pelycosaurs ") from the Early Permian of North America. Recently, Apsisaurus has been classified as a basic ("primitive") representative of the Varanopidae . The type species and the only representative of the genus is Apsisaurus witteri , which was originally assigned to the early Diapsids ( Eosuchia )due to the poor state of preservation of the holotype. Apsisaurus is only with the holotype known which consists of a obtained in parts of the skeleton including incomplete obtained skull and the mandible, as well as remnants of the postcranial skeleton with vertebrae, ribs, and proximal ( proximal exists) parts of the front and rear limbs.
The fossil comes from the Archer City Formation of the Wichita Group near Archer City , Texas .
description
Apsisaurus was an early, small representative of the Varanopidae whose characteristics included elongated and high spinous processes of the vertebrae . The genus was also characterized by very slender humerus bones and clearly differed from other, more derived forms of the Varanopids such as Mesenosaurus , Mycterosaurus , Aerosaurus and Varanodon due to the lack of a strong curvature of the lateral teeth .
The original interpretation of the fossil as an early diapsis is due to the erroneous identification of a further opening below the eye socket (suborbital window), as this is considered to be the synapomorphism of this subclass of reptiles . A comparison with the palate of Mesenosaurus and Archaeovenator , in which this part of the skull is particularly well preserved, suggests that the area inadvertently identified as the opening of the skull in Apsisaurus is merely damaged. In particular, the proposed position of the opening - in the middle of the wing bone and laterally adjacent to the palate and the ectopterygoid - differs from that in the early diapsids, in which the skull opening is laterally bordered by the upper jaw or zygomatic bone.
Apsisaurus had relatively large, pointed teeth. A small hump on the zygomatic bone of the animal is another typical feature of the Varanopidae. Mycterosaurine Varanopids also have a small lateral protrusion on the zygomatic bone, directly on the ventral edge of the orbit . This characteristic is not known from any other clade of early Permian amniotes .
The post- cranial skeleton of Apsisaurus also shows surprising similarities to that of Archaeovenator .
classification
| Position of Apsisaurus within the Varanopidae | |||||||||||||||||||||||||||||||||||||||||||||
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| according to Reisz et al. 2010 |
Initially, Apsisaurus was placed in the first description of the Diapsids. Reisz et al. but have shown that Apsisaurus witteri can be classified as a basal varanopid due to the similarities described. According to the authors, on the one hand this leads to an increase in the diversity of the known varanopids, on the other hand it also leads to a reduction in the taxonomic diversity of the early diapsids, so that the fossil record for these reptiles in the Paleozoic is extremely low. This is all the more astonishing if one keeps in mind that the Diapsids were the dominant subclass of the Amniotes during the Mesozoic Era.
Individual evidence
- ↑ a b c d e f Robert R. Reisz, Michel Laurin and David Marjanović: Apsisaurus witteri from the Lower Permian of Texas: yet another small varanopid synapsid, not a diapsid . In: Journal of Vertebrate Paleontology . 30, No. 5, 2010, pp. 1628-1631. doi : 10.1080 / 02724634.2010.501441 .
- ^ A b Michel Laurin: The osteology of a Lower Permian eosuchian from Texas and a review of diapsid phylogeny . In: Zoological Journal of the Linnean Society . 101, No. 1, 1991, pp. 59-95. doi : 10.1111 / j.1096-3642.1991.tb00886.x .