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Revision of Undorosaurus, a Mysterious Late Jurassic Ichthyosaur of the Boreal Realm

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Revision of Undorosaurus, a Mysterious Late Jurassic Ichthyosaur of the Boreal Realm Journal of Systematic Palaeontology ISSN: 1477-2019 (Print) 1478-0941 (Online) Journal homepage: https://www.tandfonline.com/loi/tjsp20 Revision of Undorosaurus, a mysterious Late Jurassic ichthyosaur of the Boreal Realm Nikolay G. Zverkov & Vladimir M. Efimov To cite this article: Nikolay G. Zverkov & Vladimir M. Efimov (2019) Revision of Undorosaurus, a mysterious Late Jurassic ichthyosaur of the Boreal Realm, Journal of Systematic Palaeontology, 17:14, 963-993, DOI: 10.1080/14772019.2018.1515793 To link to this article: https://doi.org/10.1080/14772019.2018.1515793 View supplementary material Published online: 24 Jan 2019. Submit your article to this journal Article views: 447 View Crossmark data Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=tjsp20 Journal of Systematic Palaeontology, 2019 Vol. 17, No. 14, 963–993, http://dx.doi.org/10.1080/14772019.2018.1515793 Revision of Undorosaurus, a mysterious Late Jurassic ichthyosaur of the Boreal Realm a,b,cà d Nikolay G. Zverkov and Vladimir M. Efimov aGeological Faculty, Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119991, Russia; bGeological Institute of the Russian Academy of Sciences, Pyzhevsky Lane 7, Moscow 119017, Russia; cBorissiak Paleontological Institute of the Russian Academy of Sciences, Profsoyuznaya St., 123, Moscow 117997, Russia; dUndory Paleontological Museum, Village of Undory, Ulyanovsk Region 433312, Russia (Received 2 December 2017; accepted 10 August 2018) Recent study of ophthalmosaurid ichthyosaurs has brought us a number of new taxa; however, the validity of several ophthalmosaurid taxa from the Volgian (Tithonian) of European Russia still remains unclear, complicating comparisons and in some cases affecting taxonomic decisions about new contributions. A revision of the type series of all three species of Undorosaurus, erected by Efimov in 1999, reveals the potential validity of two of them. This contradicts previous research, which concluded that only the type species, U. gorodischensis, is valid. Furthermore, examination of the holotype of Cryopterygius kristiansenae from coeval strata of Svalbard shows that it is synonymous with Undorosaurus gorodischensis, sharing all diagnostic features of the species, especially those related to forelimb morphology: humerus with extensive anteroposteriorly elongate proximal end, poorly pronounced trochanter dorsalis and reduced deltopectoral crest; and ulna proximodistally elongate and not involved in perichondral ossification on its whole posterior edge. This supports the idea of intensive exchange of ichthyosaurs between the Middle Russian Sea and other Boreal seas in the Late Jurassic. In order to resolve the phylogenetic position of Undorosaurus within Ophthalmosauridae as well as relationships of other ophthalmosaurids, a new data set including 33 taxa and 106 characters, 23 of which are new, was compiled. The results of this analysis challenge all previous phylogenetic hypotheses for Ophthalmosauridae in a number of aspects, including the fact that Undorosaurus spp. was recovered deeply nested within Platypterygiinae as a sister group to derived platypterygiines. Keywords: Ichthyosaurs; Ophthalmosauridae; Undorosaurus; Upper Jurassic; Volgian; Tithonian Introduction rarer Brachypterygius and Nannopterygius (Maisch & Matzke 2000). Ophthalmosauridae is a highly derived clade of ichthyo- Since 1997 several ophthalmosaurid taxa (three gen- saurs that appeared in the Middle Jurassic (Fernandez era and 12 species) have been erected, based on materi- 1999, 2003; Druckenmiller & Maxwell 2014) and domi- als from the Upper Jurassic (Volgian/Tithonian) of nated until the extinction of ichthyosaurs in the early European Russia (Arkhangelsky 1997, 1998, 2001b; Late Cretaceous (Fischer et al. 2016). In the last decade, Efimov 1998, 1999a, b). These genera were soon new ophthalmosaurid taxa have been erected from the regarded as subjective junior synonyms of Arctic (Maxwell 2010; Druckenmiller et al. 2012; Ophthalmosaurus and Brachypterygius (Maisch & Roberts et al. 2014; Delsett et al. 2017) and Europe Matzke 2000; McGowan & Motani 2003), although the (Tyborowski 2016; Paparella et al. 2017) that have illu- validity of most of the Russian ichthyosaurs was ques- minated the previously underestimated taxonomic diver- tioned without first-hand examination (Maisch & sity of Late Jurassic ichthyosaurs. This ‘renaissance’ in the study of Late Jurassic ichthyosaurs was preceded by Matzke 2000; Storrs et al. 2000; McGowan & Motani a conservative period when their diversity was consid- 2003; Maisch 2010). The first attempts to reassess some ered to be “on the low side” (Maisch & Matzke 2000, of these taxa have been undertaken only recently p. 90), and when Late Jurassic ichthyosaurs of the (Arkhangelsky & Zverkov 2014; Zverkov et al. 2015a). Northern Hemisphere were considered to be represented However, the type series of Undorosaurus has been by only three genera: Ophthalmosaurus, and the much awaiting a thorough required revision. à Corresponding author. Email: [email protected] # The Trustees of the Natural History Museum, London 2019. All rights reserved. Published online 24 Jan 2019 964 N. G. Zverkov and V. M. Efimov Despite all of the debates on its validity and poorly Province; Upper Jurassic, upper Volgian (Tithonian), understood osteology (see Maisch & Matzke 2000; Garniericeras catenulatum Ammonite Biozone. McGowan & Motani 2003; Maisch 2010), UPM EP-II-21(1075) is an incomplete skeleton com- Undorosaurus has frequently been used for comparative prising fragments of the premaxilla and nasal, basiocci- purposes when other Late Jurassic ophthalmosaurids are pital, mandibular fragments, atlas-axis and 17 presacral discussed (e.g. Maxwell 2010; Druckenmiller et al. vertebrae, fragments of the coracoids and scapulae, 2012; Roberts et al. 2014; Delsett et al. 2017; Paparella incomplete left forelimb and fragments of right fore- et al. 2017). The phylogenetic position of Undorosaurus limb. It was collected from the bank of the Volga River is no less controversial. First attempts to include near Gorodischi village, Ulyanovsk Province; Upper Undorosaurus in a phylogenetic context were under- Jurassic, middle Volgian (Tithonian), Epivirgatites niki- taken only 15 years after the taxon was described tini Ammonite Biozone. (Arkhangelsky & Zverkov 2014; Roberts et al. 2014). UPM EP-II-22(1073), an incomplete skeleton, com- The position of Undorosaurus varied sufficiently in prises: fragmentary left nasal, left prefrontal, basioccipi- recovered phylogenies that the need for a redescription tal, opisthotic, and stapes; complete left and partial right of the type material is clear. Therefore, some researchers quadrates; mandibular fragments; hyoids; atlas-axis and have preferred to avoid including Undorosaurus in 17 vertebrae; rib fragments; right coracoid and scapular phylogenetic analyses (Fischer et al. 2016;Jiet al. fragments; incomplete humerus, radius and ulna; and 2016), whereas others have continued to consider this autopodial elements. It was collected from the bank of taxon, despite the absence of adequate data on its the Volga River near Gorodischi village, Ulyanovsk morphology (Maxwell et al. 2016; Delsett et al. 2017; Province; Upper Jurassic, middle Volgian (Tithonian), Moon 2017; Paparella et al. 2017). Epivirgatites nikitini Ammonite Biozone. This paper is a part of an ongoing project on the tax- UPM EP-II-24(785), the holotype of U. nessovi, com- onomy and phylogeny of the Late Jurassic ichthyosaurs prises a disarticulated skeleton, including basisphenoid, of the Boreal Realm. The goals of this contribution are basioccipital (severely eroded), right stapes, quadrates, to redescribe the type material of Undorosaurus, and to articular and surangular, hyoid, atlas-axis and 15 verte- assess the position of this genus in a modern taxonomic brae, rib fragments, coracoid, scapulae, and nearly com- and phylogenetic framework. plete right and fragmentary left forelimbs. It was collected from the bank of the Volga River near Slantsevy Rudnik village, Ulyanovsk Province; Upper Material and methods Jurassic, middle Volgian (Tithonian), Virgatites virgatus Ammonite Biozone. The principal focus of this paper is the type material of UPM EP-II-27(870), the holotype of U. khorlovensis, Undorosaurus gorodischensis, U. nessovi and U. khorlo- comprises fragments of the snout, three vertebrae, vensis, stored in the Undory Palaeontological Museum, incomplete scapulae, humeri, radius, and a femur frag- Ulyanovsk Region, Russia (UPM). Additionally, one of ment. It was collected at a phosphate mine near us (NGZ) has personally examined the holotype of Khorlovo village, Voskresensk District, Moscow Cryopterygius kristiansenae (PMO 214.578), which is Province; Upper Jurassic, middle Volgian (Tithonian), on display in the Natural History Museum, University Virgatites virgatus Ammonite Biozone. of Oslo, Norway. YKM 44028-7 is an articulated left forelimb in Specimen UPM EP-II-20(572), the holotype of matrix, collected from the bank of the Volga River near Undorosaurus gorodischensis, is a relatively complete, ‘Detskiy sanatorium’ Ulyanovsk Province; Upper disarticulated skeleton, including most of the skull, 27 Jurassic, middle Volgian (Tithonian), Epivirgatites niki- vertebrae, ribs, pectoral and pelvic girdles and limbs. It tini Ammonite Biozone. was collected from the bank of the Volga River near PMO 214.578,
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