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PALAEONTOLOGY
The last of them? A new relic karaurid stem salamander from the Lower Cretaceous of Western Siberia, Russia
Pavel Skutschas1, Veniamin Kolchanov1, Ekaterina Anpilogova1, Igor Parakhin1, Alexander Averianov2, and Marc Jones345
1Saint Petersburg State University, Universitetskaya nab., 7-9, Saint Petersburg, 199034, Russian Federation
2Zoological Institute, Russian Academy of Sciences, Universitetskaya nab., 1, Saint Petersburg, 199034, Russian Federation 3Natural History Museum, Cromwell Road, SW7 5BD, London, UK 4University College London, Gower Street, WCIE 6BT, London, UK 5University of Adelaide, Adelaide, South Australia, SA 5005, Australia
Address correspondence and requests for materials to Pavel Skutschas, p.skutschas@spbu.ru
Abstract
Citation: Skutschas, P., Kolchanov, V., Anpilogova, E., Parakhin, I., Averianov, A., and Jones, M. 2023. The last of them? A new relic karaurid stem salamander from the Lower Cretaceous of Western Siberia, Russia. Bio. Comm. 68(4): 219-226. https:// doi.org/10.21638/spbu03.2023.402
Authors' information: Pavel Skutschas, Dr. of Sci. in Biology, Professor, orcid. org/0000-0001-8093-2905; Veniamin Kolchanov, MSc, Assistant Professor, orcid. org/0000-0001-6644-3486; Ekaterina Anpilogova, Student, orcid.org/0009-0004-3735-0458; Igor Parakhin, MSc, PhD Student, orcid.org/0000-0002-7306-9565; Alexander Averianov, Dr. of Sci. in Biology, RAS Professor, Chief Researcher, orcid.org/0000-0001-5948-0799; Marc Jones, PhD, Curator, orcid.org/0000-0002-0146-9623
Manuscript Editor: Nikita Zelenkov, Cabineth of Palaeoornithology, Borissiak Palaeontological Institute, Russian Academy of Sciences, Moscow, Russia
Received: August 31, 2023;
Revised: October 17, 2023;
Accepted: October 17, 2023.
Copyright: © 2023 Skutschas et al. This is an open-access article distributed under the terms of the License Agreement with Saint Petersburg State University, which permits to the authors unrestricted distribution, and self-archiving free of charge.
Funding: The laboratory work was supported by the Russian Science Foundation Grant No. 23-24-00098.
Ethics statement: This paper does not contain any studies involving human participants or animals performed by any of the authors.
Competing interests: The authors have declared that no competing interests exist.
A new karaurid stem salamander, Kuzbassia sola gen. et sp. nov., from the Lower Cretaceous (Aptian) Ilek Formation of Shestakovo 1 locality in Western Siberia, Russia, is described on the basis of isolated vertebrae, including incomplete atlantal and trunk vertebral centra. The new taxon is diagnosed by the following unique combination of vertebral characters: the presence of a shallow dorsolateral depression and low ridges (longitudinal, vertical and oblique ridges) flanking this depression on the lateral surface of the atlantal centrum; the absence of deep lateral grooves or depressions on the lateral surfaces and ventral depression on the ventral surface of the atlantal centrum; the absence of ventro-lateral ridges, transverse processes and alar processes associated with the transverse processes on the atlantal centrum; anterior cotyles with elliptical anterior outline, located at an angle of approximately 150-160 degrees to each other; and the presence of a pair of rugose surfaces with low tubercles (= ?anterior basapophyses) on the ventral surface of the anterior portion of the trunk vertebral centrum. Kuzbassia sola gen. et sp. nov. is the last karaurid salamander in the fossil record to date.
Keywords: Caudata, stem salamanders, Karauridae, Early Cretaceous, Western Siberia, Russia, Shestakovo 1 locality
Introduction
The Lower Cretaceous (Aptian) temperate-latitude Shestakovo vertebrate assemblage (paleolatitude estimate N 49°-52° in paleolatitude.org; http://paleolatitude. org/; van Hinsbergen et al., 2015) derives from several localities of the Ilek Formation in Western Siberia, Kemerovo-Kuzbass oblast, Russia. Among vertebrate localities of the Ilek Formation, the Shestakovo 3 locality in Kemerovo Province is famous due to the discovery of articulated skeletons of the basal ceratopsian Psit-tacosaurus sibiricus (Averianov, Voronkevich, Leshchinskiy, and Fayngertz, 2006; Lopatin et al., 2015), whereas the Shestakovo 1 locality is known for numerous microvertebrates including salamanders (Skutschas, 2013, 2014).
The Shestakovo assemblage is similar in composition to that of the Lower Cretaceous high-latitude Teete locality (paleolatitude estimate of N 62° in Averianov et al., 2019b; N 66.5° in Fossilworks, http://fossilworks.org; N 63°-65° in paleolatitude.org, http://paleolatitude.org/, van Hinsbergen et al., 2015) of the Batylykh Formation in southwestern Yakutia (Eastern Siberia, Russia) (Averianov et al., 2018, 2019a; Skutschas et al., 2018, 2021). Both the Teete and Shestakovo assemblages include taxa with Jurassic affinities (namely stem karaurid
salamanders, primitive choristoderes, paramacellodid lizards, stegosaurs, tritylodont mammaliamorphs, and docodont mammaliaforms) that survived as relics into the Early Cretaceous of present-day Siberia (e. g., Ave-rianov et al., 2018; Skutschas et al., 2018). The similarity of the high-latitude assemblage of Teete and the mid-latitude vertebrate assemblage of Shestakovo suggests that the territory of a geographically vast "Great Siberian re-fugium" (sensu Skutschas et al., 2021) for Jurassic vertebrate relicts covered the northeastern part of the Asiatic continent during the Early Cretaceous (Averianov et al., 2018; Skutschas et al., 2018).
The Shestakovo 1 locality has produced remains of two salamander taxa. In 2002, A. O. Averianov and A. V. Voronkevich described a possible crown-group salamander Kiyatriton leshchinskiyi based on a fragmentary atlas and femoral fragments (Averianov, Voronkevich, 2002). Later, P. P. Skutschas provided a detailed redescription of type and newly collected material on Kiyatriton leshchinskiyi, consisting of isolated and incomplete cranial and postcranial bones and suggested that Kiyatriton leshchinskiyi is a crown group salamander with possible cryptobranchoid affinities (Skutschas, 2014). The finding of the second species of Kiyatriton (K. krasnolutskii) in the Middle Jurassic (Bathonian) Itat Formation of the Berezovsk Quarry locality in Western Siberia, Russia extended the stratigraphic range of the genus Kiyatri-ton backward some 40 million years and indicated that K. leshchinskiyi from the Shestakovo 1 locality survived as a relic into the Early Cretaceous of present-day Western Siberia (Skutschas, 2016a). In 2016, an incomplete trunk
KAZAKHSTAN J V MONGOLIA
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vertebra of a relic stem salamander from the Shestakovo 1 locality was described (Skutschas, 2016b). Later, the two additional specimens (incomplete atlantal centra) of a stem salamander from the Shestakovo 1 locality were recognized among microvertebrate remains collected by several expeditions with participants from Tomsk and Saint Petersburg state universities and from Paleontological and Zoological institutes of the Russian Academy of Sciences at Shestakovo localities. Here we formally describe the stem karaurid salamander taxon from the Shestakovo 1 locality and discuss some aspects of the evolution of karaurid salamanders. This new taxon is the most recent karaurid salamander in the fossil record known to date.
Institutional abbreviations. The material used in this study is deposited in following institutional collections: ZIN PH, Paleoherpetological collection, Zoological Institute of the Russian Academy of Sciences, Saint Petersburg, Russia; LMCCE, Laboratory of Mesozoic and Cenozoic Continental Ecosystems, Tomsk State University, Western Siberia, Tomsk, Russia.
Material and methods
The fossil material derives from the Shestakovo 1 locality which is situated in Western Siberia, near Shestakovo village in Chebula district of Kemerovo-Kuzbass oblast, Russia (GPS coordinates: N 55°54.60', E 87°56.90'; Fig. 1). The fossiliferous level is confined to the upper part of the Ilek Formation with a currently estimated Early Cretaceous age (Aptian) based on spore-pollen spectra, see Bugdaeva, Markevich, and Volynets (2017); the geologi-
100 km
Fig. 1. Geographic setting of Shestakovo 1 locality.
cal settings of the Shestakovo localities and discussion of their age are given in Averianov et al. (this issue).
The study material comprises two incomplete at-lantal centra (ZIN PH 18-19/173). To prepare accurate figures and to gain microanatomical information, all at-lantal specimens of Kuzbassia sola gen. et sp. nov. were X-ray microCT scanned at the Saint Petersburg State University Research Centre for X-ray Diffraction Studies (Saint Petersburg, Russia) using a microtomography scanner Skyscan 1172. Settings comprised: voltage = 71 kV; current = 0.13mA; pixel size = 2.7 ^m; and output = 1500 x 1500 pixels per slice.
The atlases of Egoria, Kokartus and Kulgeriherpe-ton (used for comparisons) were CT-scanned (at 70 kV and 139 ^A, generating a nominal resolution of 2.97 ^m, with cubic voxels and an output of2472 x 2472 pixels per slice for Egoria and Kokartus and at 100 kV and 100^A, generating a nominal resolution of 4.48 ^m, with cubic voxels and an output of 4000 x 4000 pixels per slice for Kulgeriherpeton) at the Saint Petersburg State University Research Centre for X-ray Diffraction Studies (Saint Petersburg, Russia) using a Skyscan 1172.
Segmentation of the CT scan data and 3D model reconstructions were made with Amira 6.3.0 (FEIVSG Company). The CT scans of incomplete atlantal centra of Kuzbassia sola gen. et sp. nov. were used to create surface models of these centra. The surface models were imported in Blender 3.6.4, where they were duplicated, mirrored and adjoined to each other based on the structure of preserved parts, to create the reconstruction of the centrum shown in this paper.
The CT data are deposited in the Department of Vertebrate Zoology of the Saint Petersburg State University, Saint Petersburg, Russia, and can be made available by the corresponding author for the purpose of scientific study.
Systematic paleontology
Amphibia Linnaeus, 1758 Caudata Scopoli, 1777 Karauridae Ivakhnenko, 1978 Genus Kuzbassia nov.
Type species: Kuzbassia sola sp. nov., monotypic; see below.
Etymology: From Kemerovo-Kuzbass oblast, Russia. Kuzbassia sola sp. nov. Figs. 2, 3, 4A-E.
Etymology: From Latin solum, single, lonely; in reference that it is the last karaurid salamander in the fossil record to date. Holotype: ZIN PH 18/173, fragmentary atlantal centrum.
Referred material: ZIN PH 19/173, fragmentary atlantal centrum; LMCCE 1/4, fragmentary trunk vertebral centrum.
Type locality: Shestakovo 1, Western Siberia, Kemerovo-
Kuzbass oblast, Russia. Type horizon: Ilek Formation, Aptian, Lower Cretaceous.
Diagnosis. — Referred to karaurid 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 the level of anterior cotyles, the atlantal cotyle larger than the neural canal, and its relatively large size (the estimated maximum anterior width is about 4-5 mm and the ventral mid-line length, excluding the intercotylar tubercle is about 3-3.5 mm). Differs from all other karaurid 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 England and Scotland, Urupia and Egoria from the Middle Jurassic (Batho-nian) and Kulgeriherpeton from the Lower Cretaceous (Berriasian-Barremian) of Siberian Russia) by following combination of characters: the presence of a shallow elliptical dorsolateral depression flanked by three low ridges (a longitudinal lateral ridge flanking its ventral border, a vertical ridge flanking its anterior border, and an oblique ridge, flanking its posterior border); the lack of lateral grooves or depressions on the lateral surfaces of the atlantal centrum (there is such a lack also in Marmorerpeton wakei); the lack of a ventral depression on the ventral surface of the atlantal centrum (lack also in Egoria, Marmorerpeton wakei); the lack of ventro-lat-eral ridges (lacks also in Kulgeriherpeton, Egoria, Kokartus, Marmorerpeton wakei and M. kermacki); anterior cotyles with elliptical anterior outline, located at an angle of approximately 150-160 degrees to each other (similar outline of anterior cotyles is present in Kokartus, see Fig. 4); the lack of transverse processes and alar processes associated with the transverse processes (lack also in Marmorerpeton wakei).
Differs from all other stem salamanders for which the morphology of the trunk vertebral centra is known (namely Urupia, Egoria, Kokartus, Marmorerpeton, and Kulgeriherpeton) in having a pair of rugose surfaces with low tubercles (= ?anterior basapophyses) on the ventral surface of the anterior portion of the trunk vertebral centrum.
Description. The atlas is known from two fragmentary centra of different sizes (the estimated maximum anterior width (i. e., between the lateral rims of the anterior cotyles) 4-5 mm). The atlantal centrum (Fig. 2, 4 A-E) is wider than long. The anterior cotyles (Fig. 2A, I, 4A) are large, elliptical in anterior outline (ratio of maximum height: width is about 0.87) and they are located at an angle of approximately 150-160 degrees to each other. The articular surfaces of the anterior cotyles are
Fig. 2. Kuzbassia sola gen. et sp. nov., photo and tomographic reconstructions of specimens ZIN PH 18-19/173. A-D — photo of holotype ZIN PH 18/173 in anterior (A), lateral (B), ventral (C) and posterior (D) views; E-H — tomographic reconstruction of holotype ZIN PH 18/173 in anterior (E), lateral (F), ventral (G) and posterior (H) views; I-L — photo of centrum fragment ZIN PH 19/173 in anterior (I), lateral (J), ventral (K) and posterior (L) views; M-P — tomographic reconstruction of centrum fragment ZIN PH 19/173 in anterior (M), lateral (N), ventral (O) and posterior (P) views. Abbreviations: dld — dorsolateral depression, lg — longitudinal groove, lr — longitudinal ridge, nc — notochordal canal, obr — oblique ridge, tub — tubercle, vr — vertical ridge.
moderately dorsoventrally concave. The posterior cot-yle is circular in posterior outline (Fig. 4B). The inner surface of the posterior cotyle is deeply concave and bears a notochordal canal in its central part (Fig. 2D, H, L, P).
The ventral surface of the centrum is flat with no ventral (= median) depression. Ventrolateral ridges are absent.
The lateral surface of the larger centrum (specimen ZIN PH 18/173, holotype, Fig. 2A-H) has a shal-
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Fig. 3. Kuzbassia sola gen. et sp. nov., virtual sections showing microanatomy of the holotype ZIN PH 18/173. A — tomographic reconstruction in lateral view showing the level of virtual sections, B-D — virtual sections. Abbreviations: cor — cortex, eb — endochondral bone, vas — vascular canals.
low elliptical dorsolateral depression. This depression is flanked by low ridges: a longitudinal lateral ridge flanking its ventral border, a vertical ridge flanking its anterior border, and an oblique ridge, running from the base of neural arch to lateral surface of the rim of the posterior condyle, flanking its posterior border. A low tubercle is present at the fusion of longitudinal and vertical ridges. A small longitudinal groove is present in the anterior part of the dorsolateral depression, approximately at mid height of the centrum. The transverse processes, distinct alar processes associated with the transverse processes, and lateral grooves or depressions are absent.
The lateral surface of the smaller centrum (specimen ZIN PH 19/173, Fig. 2I-P) has less prominent ridges, flanking the dorsolateral depression, and the longitudinal groove is positioned slightly higher, close to the base of the neural arch (Fig. 2N, P).
The pedicels of the neural arch are anteroposteri-orly short, massive and its anterior borders are situated behind the level of the anterior cotyle. The spinal nerve foramen is absent.
The internal microanatomical organization (Fig. 3) of the centrum is characterized by the presence of a thick compact periosteal cortex and an inner cancellous endo-chondral bone. The periosteal cortex is heavily vascular-ized by a network of short vascular canals. These canals exit on the ventral and lateral surfaces of the centrum through large rounded foramina, forming a characteristic pitted sculpture. The endochondral bone is formed by numerous trabeculae of varying thickness. Internally, the vascular canals of the cortex are connected with erosion bays of the inner cancellous endochondral bone.
The structure of the trunk vertebral centrum was described and figured by Skutschas (2016b: fig. 1). A unique feature of the trunk vertebral centrum is the presence of paired rugose surfaces that bear distinct tubercles located in the approximate position of (and
perhaps homologous with) the anterior basapophyses (Skutschas, 2016b: fig. 1).
Comparisons and discussion
Kuzbassia sola gen. et sp. nov. can be assigned to stem karaurid salamanders on the basis of the following characteristic combination of features: the absence of spinal nerve foramina in the atlas; the presence of pitted ventral and lateral surfaces of the atlas; and an antero-pos-teriorly short neural arch with its anterior border situated behind the level of the anterior cotyles (Skutschas, 2016b; Skutschas et al., 2020; Jones et al., 2022).
Among karaurid salamanders, the atlas of Kuzbassia sola gen. et sp. nov. most closely resembles that of Marmorerpeton wakei from the Middle Jurassic (Ba-thonian) of Scotland in the presence of slight dorsoven-tral compressions at the anterior cotyles, in the absence of transverse processes and associated alar processes, in the absence of the lateral grooves or depressions on the lateral surfaces and the ventral depression on the ventral surface of the atlantal centrum (Jones et al., 2022: fig. 2A-D). The trunk vertebral centrum referred to Kuzbassia sola gen. et sp. nov. is similar to those of other karaurid salamanders in having ventral and lateral surfaces roughened and indented by scattered, small, rounded and oval pits, but differs in having paired rugose surfaces with distinct tubercles located in the approximate position of (and perhaps homologous with) the anterior basapophyses seen in some crown-group salamanders (Skutschas, 2014).
Karaurids are robustly built neotenous stem salamanders that are characterized by several synapomor-phies (an interorbital distance greater than the width of the orbit, a posterolateral process of the prefrontal, heavy sculpture on the skull roofing bones, and vertebral cotyles that are greater in diameter than the neural
Fig. 4. Atlantal centrum of Kuzbassia sola gen. et sp. nov., and atlases of karaurid salamanders used for comparison: A-E — Kuzbassia sola gen. et sp. nov., reconstruction based on specimens ZIN PH 18-19/173; F-J — Kokartus honorarius, ZIN PH 3/47 (referred specimen) mirrored for comparison; K-O — Kulgeriherpeton ultimum, ZIN PH 3/246 (holotype); P-T — Egoria malashichevi, ZIN PH 40/144 (holotype).
canal; Jones et al., 2022), and a suite of features of uncertain polarity (e. g., atlas and other vertebrae sculptured and lacking spinal nerve foramina; the presence of an anteroposteriorly short neural arch with an anterior bor-
der that is situated far from the level of anterior cotyles; amphicoelous post-atlantal vertebrae lacking basapophyses; ribs bicapitate; Skutschas and Martin, 2011; Skutschas et al., 2018).
Karaurids first appear in the fossil record in the Middle Jurassic (Bathonian). The oldest karaurids are represented by Kokartus honorarius from Kyrgyzstan, Marmorerpeton spp. (three species) from the United Kingdom, and Urupia monstrosa and Egoria malashichevi from Siberian Russia (Evans, Milner, and Mussett, 1988, Nesov, 1988; Evans and Milner, 1994; Skutschas and Kras-nolutskii, 2011; Skutschas and Martin, 2011; Skutschas, 2013; Skutschas et al., 2020; Jones et al., 2022). Karaurids were the dominant salamander component in the Bathonian vertebrate assemblages of present-day Great Britain, Kyrgyzstan and Western Siberia.
The next youngest karaurid salamanders date from the Late Jurassic. These include two Kimmeridgian occurrences, namely Karaurus sharovi from the Karabas-tau Formation in Kazakhstan and "cf. Marmorerpeton" (sensu Wiechmann, 2000) from Portugal (Ivakhnenko, 1978; Milner, 2000; Wiechmann, 2000). Karaurus sharo-vi is known by a well-preserved, nearly complete and articulated skeleton (Ivakhnenko, 1978). The salamander remains from Portugal identified as "cf. Marmorerpeton" have never been described and figured and their karau-rid affinities should be tested in the future. We know very little about Late Jurassic karaurids, especially about their abundance and role in ecosystems.
The Early Cretaceous record of karaurids is restricted to Kulgeriherpeton ultimum from the Berria-sian-Barremian of Yakutia, Eastern Siberia (Skutschas et al., 2018) and the new salamander Kuzbassia sola gen. et sp. nov. from the Aptian of Kemerovo-Kuzbass oblast, Western Siberia, Russia. Kulgeriherpeton ultimum is the dominant salamander component in the vertebrate assemblage of Yakutian Teete locality and the largest (the estimated body length of Kulgeriherpeton, based on the proportions of the stem salamander Karaurus, is about 35 cm) aquatic predator of the local ecosystem (PPS, VVK, pers. obs.). The remains of the new salamander Kuzbassia sola gen. et sp. nov. are extremely rare in the Siberian Shestakovo 1 locality and its dominant salamander component is a possible crown group salamander Kiyatriton leshchinskiyi. Karaurids are not known from the post-Aptian deposits, so Kuzbassia sola gen. et sp. nov. is the last karaurid salamander in the fossil record to date survived as a relic in the "Great Siberian re-fugium". The absence of karaurids in the younger deposits suggests karaurids became extinct after the Aptian.
Acknowledgements
We thank all the members of expeditions in Western Siberia for their help.
References
Averianov, A.O., Martin, T., Lopatin, A.V., Skutschas, P.P.,
Schellhorn, R., Kolosov, P.N., and Vitenko, D.D. 2018.
A high latitude fauna of mid-Mesozoic mammals from
Yakutia, Russia. PLoS ONE 13:e0199983. https://doi. org/10.1371/journal.pone.0199983 Averianov, A.O., Martin, T., Lopatin, A.V., Skutschas, P.P., Schellhorn, R., Kolosov, P., Markova, V.D., Kolcha-nov, V.V., Grigoriev, D. V., Kuzmin, I. T., and Vitenko, D. D. 2019a. A new euharamiyidan mammaliaform from the Lower Cretaceous of Yakutia, Russia. Journal of Vertebrate Paleontology 39(6):e1762089. https://doi.org/10.1371/ journal.pone.0248163 Averianov, A. O., Skutschas, P. P., Schellhorn, R., Lopatin, A.V., Kolosov, P.N., Kolchanov, V.V., Vitenko, D.D., Grigoriev, D.V., and Martin, T. 2019b. The northernmost sauropod record in the Northern Hemisphere. Lethaia 53(2):362-368. https://doi.org/10.1111/let.12362 Averianov, A.O. and Voronkevich, A.V. 2002. A new crown-group salamander from the Early Cretaceous of Western Siberia. Russian Journal of Herpetology 9:209-214. Averianov, A.O., Voronkevich, A.V., Leshchinskiy, S.V., and Fayngertz, A.V. 2006. A ceratopsian dinosaur Psittaco-saurus sibiricus from the Early Cretaceous of West Siberia, Russia and its phylogenetic relationships. Journal of Systematic Palaeontology 4(4):359-395. https://doi. org/10.1017/S1477201906001933 Bugdaeva, E.V., Markevich, V. S., and Volynets, E. B. 2017. Pa-laeoenvironmental and palaeoclimatic reconstruction of the Early Cretaceous psittacosaur localities, Asia, pp.3134 in Cheong, D., Lee, Y.-L., Kim, D. (eds.). Proceedings and Field Guidebokk for the Fifth International Symposium of International Geoscience Programme IGCP Project 608. October 22-28, 2017. Jeju Island, Korea. Evans, S.E., Milner, A.R., and Mussett, F. 1988. The earliest known salamanders (Amphibia, Caudata): a record from the Middle Jurassic of England. Geobios 21(5):539-552. https://doi.org/10.1016/S0016-6995(88)80069-X Evans, S. E. and Milner, A. R. 1994. Middle Jurassic microverte-brate assemblages from the British Isles; pp. 303-321 in In the Shadow of the Dinosaurs: Early Mesozoic Tetra-pods. Cambridge, H.-D.Sues, N.C.Fraser (eds.). Cambridge University Press. Ivakhnenko, M. F. 1978. Urodelans from the Triassic and Jurassic of Soviet Central Asia. Paleontologiceskij Zurnal 1978 (3):362-368. Jones, M.E.H., Benson, R.B., Skutschas, P., Hill, L., Panciro-li, E., Schmitt, A.D., Walsh, S.A., and Evans, S.E. 2022. Middle Jurassic fossils document an early stage in salamander evolution. Proceedings of the National Academy of Sciences 119(30):e2114100119. https://doi.org/10.1073/ pnas.2114100119 Linnaeus, C. 1758. Systema Naturae, Ed. X.(Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synony-mis, locis. Tomus I. Editio decima, reformata). Holmiae. https://doi.org/10.5962/bhl.title.542 Lopatin, A.V., Maschenko, E.N., Tarasenko, K.K., Podles-nov, A.V., Demidenko, N.V., and Kuzmina, E.A. 2015. A unique burial site of Early Cretaceous vertebrates in Western Siberia (the Shestakovo 3 locality, Kemerovo Province, Russia). Doklady Biological Sciences 462(1):148-151. https://doi.org/10.1134/S0012496615030102 Milner, A. R. 2000. Mesozoic and Tertiary Caudata and Al-banerpetontidae;pp. 1412-1444 in H.Heatwole and R. L. Carroll (eds.). Amphibian Biology. Vol. 4. Palaeontology: The Evolutionary History of Amphibians. Chipping Norton, Surrey Beatty and Sons. Nesov, L.A. 1988. Late Mesozoic amphibians and lizards of Soviet Middle Asia. Acta Zoologica Cracoviensa 31:475-486. Scopoli, G.A. 1777. Introductio ad historiam naturalem, sistens genera lapidum, plantarum et animalium hac-
tenus detecta, caracteribus essentialibus donata, in tribus divisa, subinde ad leges naturae. Wolfgang Gerle, Prague. https://doi.org/10.5962/bhl.title.10827 Skutschas, P. P. 2013. Mesozoic salamanders and albanerpe-tontids of Middle Asia, Kazakhstan, and Siberia. Palaeo-biodiversity and Palaeoenvironments 93:441-457. https:// doi.org/10.1007/s12549-013-0126-8 Skutschas, P.P. 2014. Kiyatriton leshchinskiyi Averianov et Voronkevich, 2001, a crown-group salamander from the Lower Cretaceous of Western Siberia, Russia. Cretaceous Research 51:88-94. https://doi.org/10.1016Zj.cre-tres.2014.05.014 Skutschas, P. P. 2016a. A new crown-group salamander from the Middle Jurassic of Western Siberia, Russia. Palaeo-biodiversity and Palaeoenvironments 96:41-48. https:// doi.org/10.1007/s12549-015-0216-x Skutschas, P.P. 2016b. A relict stem salamander: Evidence from the Early Cretaceous of Siberia. Acta Palaeonto-logica Polonica 61(1 ):119-1 23. https://doi.org/10.4202/ app.00124.2014 Skutschas, P. P., Averianov, A. O., Schellhorn, R., Kolosov, P. N., Kolchanov, V.V., and Martin, T. 2021. Amphibians from the high latitude Early Cretaceous Teete locality, Yakutia, Russia. Abstracts of the 92 Annual Meeting of the Paläontologische Gesellschaft 142:84. Skutschas, P. P., Kolchanov, V. V., Averianov, A. O., Martin, T., Schellhorn, R., Kolosov, P.N., and Vitenko, D.D. 2018.
A new relict stem salamander from the Early Cretaceous of Yakutia, Siberian Russia. Acta Palaeontologica Polonica 63:519-525. https://doi.org/10.4202/app.00498.2018 Skutschas, P.P., Kolchanov, V.V., Krasnolutskii, S.A., Averianov, A.O., Schellhorn, R., Schultz, J., and Martin, T. 2020. A new small-sized stem salamander from the Middle Jurassic of Western Siberia, Russia. PLoS ONE 15(2):e0228610. https://doi.org/10.1371/journal.pone.0228610 Skutschas, P. P., and Krasnolutskii, S.A. 2011. A new genus and species of basal salamanders from the Middle Jurassic of Western Siberia, Russia. Proceedings of the Zoological Institute RAS 315072:167-175. Skutschas, P. P., and Martin, T. 2011. Cranial anatomy of the stem salamander Kokartus honorarius (Amphibia: Cau-data) from the Middle Jurassic of Kyrgyzstan. Zoological Journal of the Linnean Society 161(4):816-838. https://doi. org/10.1111/j.1096-3642.2010.00663.x van Hinsbergen, D.J.J., de Groot, L.V., van Schaik, S.J., Spak-man, W., Bijl, P. K., Sluijs, A., Langereis, C. G., Brinkhuis, H. 2015. A paleolatitude calculator for paleoclimate studies. PLoS ONE 10(6):e0126946. https://doi.org/10.1371/ journal.pone.0126946 Wiechmann, M. F. 2000. The albanerpetontids from the Gui-marota mine; pp. 51-54 in T. Martin and B. Krebs (eds.). Guimarota: A Jurassic Ecosystem. Munich, Verlag Dr. Friedrich, Pfeil.
