KARAURIDAE IVAKHNENKO, 1978

Skutschas, Pavel & Martin, Thomas, 2011, Cranial anatomy of the stem salamander Kokartus honorarius (Amphibia: Caudata) from the Middle Jurassic of Kyrgyzstan, Zoological Journal of the Linnean Society 161 (4), pp. 816-838 : 821-823

KARAURIDAE IVAKHNENKO, 1978

Type genus: Karaurus Ivakhnenko, 1978

Geographical and stratigraphical range: Central Asia , Middle–Late Jurassic .

Included genera: Karaurus Ivakhnenko, 1978 , Kokartus Nesov 1988 .

Diagnosis (revised from Ivakhnenko, 1978; Estes, 1981): [primitive (-), derived (+), and of uncertain polarity (?) for caudate character states]. Stem salamanders characterized by the following combination of characters: skull wide, relatively short, and flattened (?); skull roof heavily sculptured by tubercles and short ridges (+); alary process of premaxilla broad and short (-); nasal strongly overlaps the anterior portion of the frontal (-); prefrontal and frontal form a postorbital projection (+); frontal with no anterolateral extension (-); sculptured dorsal portion of squamosal element extending over the otic capsule and contacting parietal (-); quadratojugal present (-); vomerine tooth rows parallel to the maxillary arcade (-); parasphenoid with rounded anterior incisure owing to large intervomerine fontanelle (+); internal carotid foramen on lateral process of parasphenoid present (-); exoccipital sculptured (?), not fused with the opisthotic (-); occiput not projecting beyond the skull roof (-); teeth monocuspid, nonpedicellate (?); stapes robust and perforate (-); ossified pair of hypobranchials (-) and trident-shaped basibranchial present (+); amphicoelous vertebrae sculptured (-), with no basapophyses and spinal nerve foramina (-); spinal cord supports in the neural canal of the vertebrae (+); ribs bicapitate (-); complex strap-like glenoid and supraglenoid foramen present in scapulocoracoid (-).

Remarks: Marmorerpeton Evans, Milner & Mussett, 1988 from the Middle Jurassic of Great Britain differs from ‘typical’ karaurids ( Karaurus , Kokartus ) in having weak or no sculpture on the premaxilla and maxilla, bicuspid teeth (monocuspid in Karaurus and Kokartus ), a lower number of premaxillary teeth (seven vs. 25 in Karaurus and about 15–20 in Kokartus ). Additionally, Marmorerpeton differs from Kokartus by a circular dentary symphysis (rectangular in Kokartus ). Thus, we exclude Marmorerpeton from the Karauridae .

The ‘Kirtlington salamander A’ is present at the same localities as Marmorerpeton and this large undescribed salamander is characterized by plesiomorphic morphology of the vertebrae similar to that of Kokartus ( Milner, 2000) . Some cranial bones assigned to Marmorerpeton may belong to this form ( Milner, 2000). The attribution of the ‘Kirlington salamander A’ to the Karauridae is not supported by any synapomorphic features.

Isolated salamander atlantes from the Upper Jurassic Morrison Formation, USA, were referred to the Karauridae by Nesov (1993) without further explanation, and this material never has been described or figured. Therefore, the attribution of this material to the Karauridae needs further confirmation.

The robust anterior dentary fragment from the Middle Jurassic Berezovsk Quarry locality, Russia, was presumably referred to the Karauridae because of its coarsely sculptured lateral surface ( Skutschas et al., 2005; Skutschas, 2006). The dentaries of Karaurus and Kokartus differ significantly from the Russian specimen in the following features: weak sculpture formed by thin longitudinal ridges and grooves, and symphyseal region low and lightly built in contrast to the coarse sculpture composed of rounded and oval pits and deep and robust symphyseal region of the Russian specimen, excluding it from the Karauridae . The heavily sculptured dentary fragment from the Berezovsk Quarry may belong to non-lissamphibian temnospondyls, which were a common element of the Middle-Late Jurassic vertebrate assemblages in Asia ( Shishkin, 2000a; Averianov et al., 2008; Skutschas et al., 2009).

According to this re-evaluation, the family Karauridae currently includes only two genera and the geographical and temporal distribution of karaurids is restricted to the Middle–Late Jurassic of Central Asia. The heavily sculptured skull roof of Karauridae was considered to be a primitive character ( Carroll, 2007), similar to that of the non-lissamphibian temnospondyls. However, the sculpture of the skull roof in karaurids is formed by relatively high tubercles and short ridges, sometimes anastomosing with other ridges, in contrast to the honeycombed or pitted sculptural pattern of the most of the nonlissamphibian temnospondyls and the polygonal pitted sculptural pattern of the albanerpetontids (P. Skutschas, pers. observ., 2009). Some nonlissamphibian temnospondyls (e.g. amphibamid Micropholis , plagiosaurid Gerrothorax ) have the tubercular sculpture ( Schoch & Rubidge, 2005; Jenkins et al., 2008; Witzmann et al., 2010), which differs from that of karaurids in several aspects. In contrast to non-lissamphibian temnospondyls with the tubercular sculpture, tubercules in karaurids are considerably smaller and more numerous and short ridges never form a regular radial pattern (P. Skutschas, pers. observ., 2009). The specific sculpture of the skull roof in karaurids could represent a highly modified sculpture of the non-lissamphibian temnospondyls or it could be developed secondarily, like in some salamandrids (e.g. Chelotriton , Tylotriton ). The results of our phylogenetic analysis (see below in ‘Phylogenetic position of Kokartus ’) support a suggestion about the secondarily developed sculpture of the skull roof in karaurids.