page_title: Rhynchonkos
section_title: Relationship to caecilians
hierarchical_section_title: Rhynchonkos / Classification / Relationship to caecilians
caption_attribution_description: Eocaecilia micropodia, an early caecilian from the Lower Jurassic of Arizona, pencil drawing
context_page_description: Rhynchonkos is an extinct genus of microsaur. It is the only known member of the family Rhynchonkidae. Originally known as Goniorhynchus, it was renamed in 1981 because the name had already been given to another genus; the family, likewise, was originally named Goniorhynchidae but renamed in 1988. The type and only known species is R. stovalli, found from the Early Permian Fairmont Shale in Cleveland County, Oklahoma. Rhynchonkos shares many similarities with Eocaecilia, an early caecilian from the Early Jurassic of Arizona. Similarities between Rhynchonkos and Eocaecilia have been taken as evidence that caecilians are descendants of microsaurs. However, such a relationship is no longer widely accepted.
context_section_description: Rhynchonkos shares many features with the early caecilian Eocaecilia, including an elongated snout, small limbs, and a similar skull. Based on these features, it has been suggested that caecilians 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 is 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. Carroll 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.
caption: Eocaecilia micropodia, an early caecilian that shares many similarities with Rhynchonkos
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