Rhynchonkos — вымерший род микрозавров. Единственный род семейства Goniorhynchidae. Ранее известный как Goniorhynchus получил современное название в 1981 году. Единственный вид — R. stovalli. Обнаружен в формации Хеннеси (округ Кливленд, Оклахома) раннего пермского периода. Rhynchonkos обладает существенным сходством с ранними безногими земноводными раннего юрского периода Eocaecilia, найденными в Аризоне. 

 Считалось, что безногие земноводные произошли от микрозавров, что сейчас оспаривается.

 Rhynchonkos has an elongated body with at least 37 presacral vertebrae. Most vertebrae have ribs. Unlike other microsaurs, the atlas of Rhynchonkos lacks ribs. Both Rhynchonkos and Euryodus have atlases that bear a strong resemblance to those of nectrideans. Like nectrideans, the arch of the atlas is attached to the centrum, although this is likely the result of convergence.

 The skull is triangular in dorsal view. The limbs are very small. It has a pointed, overhanging snout that extends beyond the tooth row. There are five or six premaxillary teeth and sixteen maxillary teeth, all of which are narrow and peg-shaped. The palate also has teeth, with rows on the ectopterygoid, palatine, and vomer. The bones of the skull roof are similar to those of gymnarthrids. There are two rows of teeth adjacent to one another in the lower jaw, with a marginal row on the dentary and an inner row on the coronoid.

 Rhynchonkos shares many features with the early caecilian Eocaecilia, including an elongated trunk, small limbs, and a similar skull. Based on these features, caecilians seemed to have originated from Rhynchonkos or another closely related microsaur. Carroll and Currie (1975), the first to suggest this possible relationship, noted similarities in temporal fenestration, palatal structure, braincase composition, and mandibular dentition. In the temporal region of the skulls of Rhynchonkos and caecilians, the number of bones are reduced. Both Rhynchonkos and caecilians possess a primitive combination of palatal bones, including the ectopterygoid. The two taxa also have rows of teeth on the palate in addition to the marginal rows on the maxilla and premaxilla. Carrol and Currie also mentioned that Rhynchonkos and caecilians have a pleurosphenoid that joins the otic-occipital portion of the braincase with the sphenethmoid, a characteristic which they considered unique among amphibians. The adjacent tooth rows on the coronoid and the dentary of Rhynchonkos were also considered a characteristic that linked it with caecilians.

 Despite these similarities, many of the characteristics that suggested a close relationship between Rhynchonkos and caecilians have since been considered primitive, convergent, or indeterminate. For example, tooth rows on the palate have evolved multiple times independently in early amphibians. The general appearance of Rhynchonkos is similar to that of caecilians, but is also similar to other amphibians that have independently developed elongated bodies. Adelospondyls, lysorophians, aïstopods, and some salamanders all have an increased number of vertebrae that lengthen the body. Reduced limbs are seen in many aquatic or burrowing amphibians, and are not unique to microsaurs and caecilians.

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Tags: Вымершие амфибии, Лабиринтодонты, Лепоспондилы, Пермь

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