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Kotlassia prima skull, occipital and otic views
Occipital and otic views of the skull of Kotlassic prima (after 5 )
Kotlassia prima
was a late Permian amphibian found on the North Dvina River in Russia.
It was dicovered by Amalitsky in 1898 at the site of Sokolki near
Kotlas, the town for which the genus is named.
Kotlassia is a reptiliomorph, or amphibian with some reptilian traits. Given its similarities to the Early Permian amphibian Seymouria, Kotlassia is grouped in the order Seymouriamorpha. A collection of various specimens found on the North Dvina River permit a nearly complete description (Bystrow 1944).
Kotlassia has many amphibian characters. Immature individuals have external gills. As an adult it became a terrestrial form, in contrast to the contemporary Dvinosaurus. The skull length ranges from about 6 mm in the smallest juveniles (Ivakhnenko 1981) to 15 cm in presumably mature individuals (Laurin 1998). Seymouriamorphs had a relatively short trunk (24 to 28 presacral vertebrae) and stout limbs, with a shape somewhat like that of a salamander.
Their sharp, conical teeth and palatal fangs suggest that seymouriamorphs were predators. All seymouriamorphs had a slender stapes (see fig.) that may have been involved in hearing. As such, this is a reptilian trait. The stapes, used as an ossicle in the middle ear by reptiles, had evolved from the hyomandibular bone of lobe-finned fish and primitive tetrapods. Interestingly, this character appeared convergently in temnospondyls ("cut vertebra", a group of primitive amphibians originally thought to be reptiles) and in several groups of tetrapods (Laurin 1998).
References:
Bystrow, A. P. 1944.
Ivakhnenko, M. F. 1981. Discosauriscidae from the Permian of Tadzhikistan. Paleontological Journal 1981: 90-102.
Laurin, M. 1998.
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