Kulgeriherpeton ultimum, Skutschas & Kolchanov & Averianov & Martin & Schellhorn & Kolosov & Vitenko, 2018
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publication ID |
https://doi.org/ 10.4202/app.00498.2018 |
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persistent identifier |
https://treatment.plazi.org/id/03EE87BB-FFE8-FFE5-4A74-FA4B08CF2386 |
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treatment provided by |
Felipe |
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scientific name |
Kulgeriherpeton ultimum |
| status |
sp. nov. |
Kulgeriherpeton ultimum sp. nov.
Figs. 2–4 View Fig View Fig View Fig , 5A View Fig .
Etymology: From Latin ultimus, last; in reference to the relict nature of this stem salamander.
Holotype: ZIN PH 3/246, nearly complete atlas partially embedded in matrix.
Type locality: Teete, Suntar Ulus, Yakutia, Eastern Siberia, Russia.
Type horizon: Batylykh Formation, Sangar Series, Berriasian–Barremian, Lower Cretaceous, for geological settings see Kolosov et al. (2009); Averianov et al. (2018).
Diagnosis.—Placed outside the crown group (Urodela) and referred to stem group salamanders based on the absence of spinal nerve foramina in the atlas, the presence of a pitted texture on the ventral and lateral surfaces of the atlas, the presence of an anteroposteriorly short neural arch with an anterior border that is situated far from level of anterior cotyles, and its relatively large size (the maximum anterior width is about 8.8 mm and the ventral midline length, excluding the intercotylar tubercle is about 6.4 mm). Differs from all other stem salamanders for which the morphology of the atlantal centrum is known (namely Kokartus from the Middle Jurassic (Bathonian) of Kyrgyzstan, Marmorerpeton from the Middle Jurassic (Bathonian) of Great Britain, and Urupia and “Berezovsk salamander A” from the Middle Jurassic (Bathonian) of Russia) in the presence of a transversal ridge and a depression on the ventral surface of the posterior portion of the centrum. Differs further from Marmorerpeton , Urupia , and “Berezovsk salamander A” by presence of an intercotylar tubercle on the atlas with ossified dorsal and ventral lips (vs. absence of the intercotylar tubercle and presence of only the notochondral central pit in Urupia , “Berezovsk salamander A” and M. freemani ; and no division of the intercotylar tubercle into dorsal and ventral lips in M. kermacki ). Additionally, Kulgeriherpeton differs from Urupia by the lack of a deep depression on the ventral surface of the anterior portion of the atlantal centrum, by the lack of pronounced ventro-lateral ridges on the atlas, and by less dorso-ventrally compressed atlantal anterior cotyles (ratio of maximum height/width about 0.79 vs. about 0.5 in Urupia ); additionally differs from “Berezovsk salamander A” in the atlantal centrum being relatively longer (ratio of maximum anterior width, i.e., between lateral rims of the anterior cotyles), midline length (excluding intercotylar tubercle) is about 1.37 vs. about 1.75 in “Berezovsk salamander A”; and additionally differs from Karaurus in the absence of a deep incisure on the distal-most end of the atlantal neural spine.
Description.—The atlantal centrum ( Figs. 2A View Fig , 3 View Fig ) is slightly wider than long: the maximum anterior width (i.e., between the lateral rims of the anterior cotyles) is about 8.8 mm and the ventral midline length, excluding the intercotylar tubercle (= odontoid process), is about 6.4 mm (ratio of maximum anterior width/ventral midline length without intercotylar tubercle about 1.38). The anterior cotyles ( Fig. 3K View Fig ) are large and slightly dorso-ventrally compressed (ratio of maximum height/width about 0.8). The articular surfaces of the anterior cotyles are moderately concave. The intercotylar tubercle is not fully ossified and is represented by dorsal and ventral lips that are separated by a narrow strip of the articular surface extending between the anterior cotyles. The posterior cotyle is nearly circular in posterior outline ( Fig. 3G View Fig ). The inner surface of the posterior cotyle is deeply concave ( Fig. 3G, J, L View Fig ).
The ventral surface of the centrum has a shallow median depression ( Fig. 3H View Fig ). The surface of the median depression is perforated by three relatively large subcentral foramina. Antero-lateral to the medial depression, there is a pair of narrow oblique grooves. Ventro-lateral ridges are absent. A distinct transverse ridge and a relatively deep transverse depression, the latter being situated just behind the transverse ridge, extend across the ventral surface of the posterior portion of the centrum.
The lateral surfaces of the centrum ( Fig. 3A–D, F, I, J, L View Fig ) have distinct unipartite transverse processes (the left transverse process is more prominent). The transverse processes are short and do not project far from the lateral wall of the centrum. There are relatively deep lateral depressions on the lateral surfaces of the centrum. There are three ridges on the lateral surface of the centrum; two are short (anterior and posterior alar processes) and are associated with the transverse process and one longitudinal lateral ridge flanks the dorsal border of the lateral depression. Like the transverse processes, the three ridges are more distinct and prominent on the left side. Hypapophyses and basapophyses are absent.
The neural arch is high and antero-posteriorly short, with its anterior border situated far (about one third of the length of the centrum) behind the level of the anterior cotyles ( Fig. 3E, F, L View Fig ). The pedicels of the neural arch are massive. The spinal nerve foramen is absent, but there is a groove for passage of the first spinal nerve on the anterior edge and the antero-lateral part of the pedicel of the neural arch ( Fig. 3A, K View Fig ). The neural canal is broad and low in anterior and posterior view ( Fig. 3G, K View Fig ). The neural arch roof is posteriorly short and extends back only to about the level of the rim of the posterior cotyle ( Fig. 3F, L View Fig ).
The dorso-median surface of the neural arch roof bears a high, posteriorly massive neural spine. The postero-dorsal end of the neural spine terminates in a deeply concave scar indicating that in life the distal-most end of the spine was cartilaginous. The posterior surface of the neural spine has a pair of dorso-ventrally elongated lateral depressions. The postzygapophyseal proceses project postero-laterally (approximately 45° from the midline). The postzygapophyseal facets are relatively wide, oval in outline and face ventrally and slightly laterally ( Fig. 3G, L View Fig ).
The ventral and lateral surfaces of the centrum and the lateral surfaces of the neural arch pedicels are rugouse and indented by scattered, small, rounded and oval pits.
The internal microanatomical organization of the centrum is characterized by the presence of a thick compact periosteal cortex and an inner cancellous endochondral bone with numerous erosion bays that are separated by irregularly arranged trabeculae of varying thickness ( Fig. 4 View Fig ). The periosteal cortex is moderately vascularized by a network of short vertical and subvertical vascular canals. These vascular canals access the external surface of the bone where they are visible as rounded and oval pits forming a characteristic pitted texture. Internally, the vascular canals of the cortex are connected with erosion bays of the inner cancellous endochondral bone. A narrow notochordal canal is present and centrally located. The notochordal canal is partly infilled by a bone. The neural arch has a microanatomical organization similar to that of the centrum, but differs in a lower degree of vascularization of the cortex.
Stratigraphic and geographic range.— Type locality and horizon only.
| ZIN |
Russian Academy of Sciences, Zoological Institute, Zoological Museum |
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.