Kokartus honorarius, NESOV, 1988
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publication ID |
https://doi.org/ 10.1111/j.1096-3642.2010.00663.x |
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persistent identifier |
https://treatment.plazi.org/id/C55C87E7-FFF2-FF85-51A4-0EBAFD1FFC9E |
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treatment provided by |
Valdenar |
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scientific name |
Kokartus honorarius |
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KOKARTUS HONORARIUS NESOV, 1988
1988 Kokartus honorarius Nesov , pp. 434–435, figure 2.
1993 Kokartus honorarius Nesov ; Milner, p. 675.
1996 Kokartus honorarius Nesov ; Nesov et al. p. 3, figure 1.
2000a Kokartus honorarius Nesov ; Shishkin, p. 305.
2008 Kokartus honorarius Nesov ; Averianov et al. pp. 6–12, figures 4–7.
Diagnosis (revised from Nesov, 1988; Nesov et al., 1996): Karaurid salamander that differs from Karaurus by a long, slender dentate anterior process of the pterygoid; by an internarial fenestra; and by the presence of a separated coronoid.
Remarks: Recently, Skutschas (2009) noted that Kokartus has spinal cord supports in the neural canal of the vertebrae, but did not provide any illustrations. This structure is unique to caudates and absent in other extant vertebrates, including anurans, caecilians ( Wake & Lawson, 1973), and albanerpetontids (P. Skutschas, pers. observ., 2009). Skutschas (2009) proposed that the presence of spinal cord supports is a synapomorphy of Caudata . Although the main scope of this paper is to describe the skull structure of Kokartu s, we provide an illustration showing the presence of the spinal cord supports in this taxon ( Fig. 8C, D View Figure 8 ). We included this character in the phylogenetic analysis, but detailed information about the structure of the neural canal of basal tetrapods, including groups that are possibly closely related to lissamphibians (e.g. lepospondyls, dissorophoid temnospondyls), is lacking.
DESCRIPTION
Dental arcade
The premaxilla is known from three complete or nearly complete specimens (isolated right premaxilla CCMGE 94/12937 and the pair of premaxillae in the disarticulated partial skull CCMGE 1/12937, Figs 2 View Figure 2 , 6A, B View Figure 6 , 7 View Figure 7 ). The premaxilla is slightly convex externally. It has a short maxillary (= posterior) process and a relatively narrow, long, and posteromedially orientated alary process that arises from the anterior part of the bone and overlaps the nasal anteriorly. The alary processes on the paired premaxillae were closely spaced and probably in contact. The anterior portion of each premaxilla has a shallow incisure, where they were weakly sutured to each other and they bordered the internarial fenestra. The internarial fenestra was not described and figured by Nesov et al. (1996). The dorsal edge of the maxillary process and the lateral edge of the alary process border the anteromedial portion of the external nostril. The dorsal surface is weakly sculptured with short ridges. The maxilla is known only from anterior and posterior fragments in the disarticulated partial skull CCMGE 1/12937 ( Figs 2 View Figure 2 , 7 View Figure 7 ); therefore, information on the shape and the structure of this bone is limited. It seems to be a rather large and long bone (contra Nesov et al., 1996, who suggested that the maxilla in Kokartus was shortened), with a well developed supradental shelf.
Skull roof
The paired (but disarticulated) nasals in the partial skull roof CCMGE 2/12937 document the structure of this bone ( Fig. 4 View Figure 4 ). The nasal is flat, pentagonal in shape, and relatively large. The medial edge is curved and the nasals were in contact along their anteriormost and posterior parts, bordering a narrow fontanelle. The presence of a fontanelle is probably an ontogenetic character. The nasal strongly overlaps the anterior portion of the frontal and its ventral surface bears a large triangular facet reaching the centre of the bone. The posterolateral edge is straight and was in contact with the anteromedial portion of the prefrontal. The anterolateral edge is slightly convex and borders an external nostril. The ventral surface near the anterolateral edge is deeply depressed. The ventral surface of the bone bears striations, which diverge radially from the centre. The external sculpture is unknown.
The frontal is known from complete and fragmentary specimens [paired articulated frontals in the partial skull roof CCMGE 2 View Materials /12937, in the posterior part of skull ZIN PH 65/47, and from the fragmentary frontal CCMGE 1 View Materials /11998 (holotype), Figs 3A, B View Figure 3 , 4 View Figure 4 , 6C, D View Figure 6 ]. The frontal is massive and relatively long with its length almost equalling that of the parietals and it has no anterolateral extension. The anterior part of the bone is roughly triangular and anteriorly extends far below the nasal. The frontals are in contact medially along most of their length and have no median fontanalle (contra Nesov et al., 1996). The lateral edge has a broad, almost triangular process. The anterolateral edge of this process is in contact with the prefrontal and formed together with this bone a distinct postorbital projection, which marked the border between the small orbit and temporal part of orbitotemporal opening (like in Karaurus ). The posterolateral edge of the process is thick, depressed, and bordered the anteromedial part of the temporal fenestra. The posterior part of the lateral edge of the bone is parallel to the midline and has a distinct ridge that is continuous and reaches the middle of the lateral process. The posterior edge of the bone is straight and overlaps the parietal. The ventral surface of the bone bears striations, which diverge radially from the centre. The external sculpture is represented by tubercles and short ridges, sometimes anastomosing with other ridges .
The paired parietal in the partial skull roof CCMGE 2/12937, in the posterior part of the skull ZIN PH 65/47, and the isolated almost complete parietal CCMGE 3/12937 document the structure of this bone ( Figs 3A, B View Figure 3 , 4 View Figure 4 ). The parietal is ‘L’-shaped as a result of the presence of a posterolateral extension (= lateral ala), relatively long with a ratio of its maximum posterior width to the midline length of about 0.6, and thick. Anteriorly it is overlapped by the frontal and posterolaterally it is in contact with the dorsal portion of the squamosal. The anterior edge is roughly straight. The parietals contact one another medially along their entire length. Anterior to the posterolateral extension, the lateral edge is straight and parallel to the midline. It is thick and ventrally bordered by a ridge that continues onto the frontal. The posterolateral extension is nearly rectangular. The posterior edge is slightly curved in the anterior direction. The central part of the ventral surface is deeply depressed. The striations on the ventral surface are similar to that of the frontal and consist of ridges that radially diverge from the posterolateral part of the bone. There is no pineal pit on the ventral surface of the frontals (contra Nesov et al., 1996). The external sculpture is also similar to that of the frontals. In some large, and presumably old, individuals, the parietals are fused to one another ( Fig. 3A, B View Figure 3 ) and to the frontals ( Fig. 6E, F View Figure 6 ).
The squamosal is known from several almost complete specimens: the squamosal in the disarticulated partial skull CCMGE 1 View Materials /12937, the partial squamosals in anatomical position in the posterior part of the skull ZIN PH 65/47, squamosal CCMGE 2 View Materials /11998 (type material), and squamosal CCMGE 6 View Materials /12937, Figs 2 View Figure 2 , 3A, B View Figure 3 , 5 View Figure 5 , 7 View Figure 7 ). It consists of two distinct parts: a flat dorsal portion and a thin ventral ramus. The ventral ramus diverges anteroventrally from the dorsal part, close to its lateral edge. The dorsal portion is nearly rectangular in dorsal view and is only slightly longer than wide. This orientation of the ventral ramus suggests that the jaw articulation was situated anterior to the occiput. The medial edge of the dorsal portion contacts the lateral edge of the posterolateral expansion of the parietal. The ventral ramus has an expanded middle part and tapering distal part, and bears a distinct ridge on its lateral surface and a groove on its ventral surface. The external sculpture of the dorsal portion is mostly composed of isolated tubercles .
Palate
The vomer is known only from a small fragment in the disarticulated partial skull CCMGE 1/12937 ( Figs 2 View Figure 2 , 7 View Figure 7 ) and from an isolated vomer in CCMGE 13/12937 (not figured), providing only a partial picture of the shape and detailed structure of this bone. There is a single row of teeth on the vomer. The orientation of the tooth row is unclear.
The pair of pterygoids in the disarticulated partial skull CCMGE 1/12937, the pterygoid in the posterior part of the skull ZIN PH 65/47, and the isolated complete pterygoid CCMGE 5/12937 document the structure of this bone ( Figs 2 View Figure 2 , 3 View Figure 3 , 6G View Figure 6 , 7 View Figure 7 ). The pterygoid is boomerang-shaped and has a prominent medial process (= medial ramus, = basipterygoid ramus). The structure of the pterygoid–parasphenoid contact (basicranial articulation) is unknown but was probably rather loose. The anterior process (= palatine ramus) is long, strongly arcuate, and tapers anteriorly. The anterior portion of the palatine ramus is anteromedially orientated. The ventral surface of the anterior process bears a row of homodont teeth along its entire length. The posterolateral process (= quadrate ramus) is broad and rounded. The dorsal surface of the pterygoid has a prominent ridge, which is almost parallel to the lateral edge of the bone. Medial to this ridge, the posterolateral process is sculptured by several small parallel ridges.
The parasphenoid is known from imprints on the almost complete specimen CCMGE 3 View Materials /11998 (type material) and from the inner structure and outline of the parasphenoid that was made visible by computed tomography (C/ T) scanning of the disarticulated partial skull CCMGE 1 View Materials /12937 ( Figs 6H, I View Figure 6 , 7 View Figure 7 ). The parasphenoid is relatively broad anteriorly and posteriorly and has a constriction in its middle portion. The parasphenoid rostrum (= cultriform processes) is indented and has a rounded incisure (like in Karaurus ). This incisure forms the posterior border of the intervomerine fontanelle. The dorsal and ventral surfaces of the rostrum have a similar sculpture consisting of parallel straight ridges. The lateral processes are relatively short, narrow, and perforated by a small internal carotid foramen opening into a short transversely orientated groove. The posterior portion of the parasphenoid (behind the lateral processes) is nearly rectangular, with parallel-sided lateral edges and a straight posterior edge. The dorsal surface is slightly concave .
Braincase
The structure of the exoccipital was described in detail and figured by Averianov et al. (2008) (see also Fig. 5D, F, G View Figure 5 ). The exoccipital of Kokartus is sculptured, anteroposteriorly short and not fused with the opisthotic. It has a processus lamellosus along the dorsolateral edge and a prominent rugosity along the ventrolateral edge of the bone. The occipital condyle is single, large, and kidney-shaped.
Mandible
No complete mandible is preserved in the collected material; therefore, the precise number of bones composing the lower jaw is unknown. Three bones are consistently present in the material: the dentary, coronoid, and prearticular ( Figs 2 View Figure 2 , 5F–H View Figure 5 , 7 View Figure 7 ). These elements were figured in Nesov et al.’s (1996) reconstruction of the mandible, but were not described. The structure of the dentary was briefly described by Averianov et al. (2008) as tapering anteriorly and with a relatively deep and almost rectangular symphysis, which is corroborated by specimen CCMGE 1/12937 ( Fig. 7 View Figure 7 ). The medial surface has a wide Meckelian groove, which narrows anteriorly, reaches the symphysis, and is bordered dorsally by a shallow dental shelf and ventrally by a thickened bony margin. The lateral surface is strongly convex and sculptured with parallel longitudinal ridges. There is a wide horizontal groove on the posterior portion of the bone.
Medially and just posteriorly to the middle of the dentary is a small, narrow, tooth-bearing bone, which is interpreted as a coronoid ( Fig. 2 View Figure 2 ). Medially to the dentary fragment in CCMGE 2/11998 ( Fig. 5H View Figure 5 ) is a fragment of a dorsoventrally deep, plate-like bone, which is interpreted as the prearticular.
Dentition
Marginal dentition is present in the premaxillae, maxillae, dentaries, and coronoids. The number of teeth on the maxilla is unclear; the estimated premaxillary tooth count is 15–20, the dentary tooth count is more than 40, and the coronoid tooth count is more than ten. All marginal teeth are homodont, nonpedicellate, and have a sharp monocuspid crown. The tops of some crowns are inclined medially. The premaxillary, maxillary, and dentary teeth are almost equal in size; the coronoid teeth are markedly smaller than the dentary teeth. Palatal dentition is present on the vomers and pterygoids, where they are arranged in a single row and have slightly transversely expanded tooth bases; the structure of the crowns in the palatal dentition is unknown. The vomerine and pterygoid teeth are almost the same size as the dentary and maxillary teeth or only slightly smaller.
Hyobranchial skeleton
The elements of the hyobranchial skeleton are represented by hypobranchials 1 and 2 in the disarticulated partial skull CCMGE 1/12937 ( Figs 2 View Figure 2 , 7 View Figure 7 ), which show general similarity with that of Karaurus . Both hypobranchials are relatively short, straight, and have a slender middle part and expanded ends. Hypobranchial 1 is slightly larger than hypobranchial 2.
| ZIN |
Russian Academy of Sciences, Zoological Institute, Zoological Museum |
| T |
Tavera, Department of Geology and Geophysics |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.