Undorosaurus

In 1878, paleontologist and geologist German Trautschold discovered anterior left fins, skull fragments and ribs of an unknown genus of ichthyosaurs in the green earth sands of the Tithonian layer near the village of Mnevniki (now a residential area of Moscow ). Unfortunately, these remains were severely deformed under the influence of weathering , and only the fins remained until the 21st century ^[3] .

In 1999, Vladimir Efimov described a new genus of ichthyosaurs, Undorosaurus , identified by him in the Undorosauridae family from the discovered remains in the Tithonian sediments of the Ulyanovsk and Moscow regions ^[4] . In the genus, the researcher identified species U. gorodischensis and U. nessovi from the Ulyanovsk region, as well as U. khorlovensis from the Voskresensky district of the Moscow region. The last two species were recognized as synonyms of the first ^[2] .

In 2000, Michael W. Maisch and Andreas T. Matzke synonymized Undorosaurus and Paraophthalmosaurus with the genus Ophthalmosaurus ^[5] , but in the same year Glenn Storrs, Maxim Arkhangelsky and Nikolai Zverkov substantiated the difference between Undorosaurus and Ophthalmosaurus with larger and more massive teeth ^[6] . In 2003, Chris McGowan and Ryosuke Motani also identified Undorosaurus as an independent genus ^[7] . In 2010, the validity of Undorosaurus was also confirmed by Maisch, who initially spoke out for synonymization ^[8] .

In 2014, Arkhangelsk and Zverkov assigned Undorosaurus and Paraophthalmosaurus to the subfamily Ophthalmosaurinae of the family Ophthalmosauridae ^[3] .

Based on the close relationship of Undorosaurus with Paraophthalmosaurus and Cryopterygius discovered on Svalbard , in 2015 Zverkov, Arkhangelsk and Stenshin conditionally combined these three genera in the clade (tribe) of Paraophthalmosaurini, and Ophthalmosaurus and Acamptonectes in the clade Ophalosaurini ninethiini thiini thini ^] .

In 2019, Zverkov and Efimov identified the genus Cryopterygius as a synonym for the genus Undorosaurus, and the species Cryopterygius kristiansenae as a species for Undorosaurus gorodischensis . The second species of the genus Cryopterygius , C. kielanae, is previously supported by the authors as an independent species within the genus Undorosaurus ^[10] .

• Undorosaurus gorodischensis is a typical species from the Tithonian stage, named after the village of Gorodishchi in the Ulyanovsk region, where it was first discovered ^[2] . This is a large ichthyosaur, 4-6 m long ^[6] , with a massive spine and 60 mm teeth ^[3] .
• Undorosaurus trautscholdi - described by a partial front left fins (holotype GSM 1503) by Arkhangelsk and Zverkov in 2014 from the Upper Tonian deposits Mnevnikov and named after Herman Trautshold, who found him in 1878 ^{[2] [3]} .

At the end of the Jurassic period, the European part of Russia was covered by the waters of the northern part of the Tethys Ocean, in which, in addition to Undorosaurus , other ichthyosaurs were found, including Ophthalmosaurus , Paraophthalmosaurus and Grendelius . These animals were likely prey for large predatory pliosaurs , and their own diet included small fish and cephalopods, which ichthyosaurs caught, including at great depths, as evidenced by the pathological consequences on their bones caused by a change in water pressure ^[11] .