Tsylmosuchus
Tsylmosuchus is an extinct genus of potentially dubious ctenosauriscid archosauriform reptile known from Western Russia. Fossils referred to "Tsylmosuchus" occurred over a wide area in sediments corresponding to the Induan and Olenekian stages of the Early Triassic. Most of these fossils are fragmentary neck vertebrae which were originally reported as sharing similarities with crocodile-line archosaurs (pseudosuchians) such as "Mandasuchus". As a result, "Tsylmosuchus" was first described as part of the family Rauisuchidae, making it supposedly one of the oldest known archosaurs. However, its fragmentary remains do not show any of the distinguishing features of rauisuchids or even pseudosuchians  in general, so "Tsylmosuchus" has more recently been interpreted as an indeterminate archosauriform. Although three species of "Tsylmosuchus" have been named, they lack diagnostic traits and are probably not distinct from each other. Discovery. The genus is named after the Tsilma River, near where fossils have been found. Three species were named along with the original genus in 1990. Each species was originally based on a single cervical (neck) vertebra. The original specimen of the type species "T. jakovlevi" was found near Ust'-Tsylma in the Komi Republic. This specimen and other referred material (such as ilia) come from the Mezen ' and Pechora river basins, which preserve sediments of the Sludkian and Ustmylian gorizonts (early Olenekian). Some material once referred to the proterosuchid "Chasmatosuchus magnus" has since been referred to this species. "T. samariensis" comes from a single site in Borskoi (Samara Oblast, along the Obshchy Syrt) from the Rybinskian Gorizont (Induan). "T. donensis" comes from the Donskaya Luka site in Volgograd Oblast, which preserves the Lipovskaya Formation of the Yarenskain Gorizont (Upper Olenekian). The three species of "Tsylmosuchus" were only tentatively differentiated based on their ages. Description. "Tsylmosuchus" is known primarily from vertebrae. These vertebrae have been compared to "rauisuchid  vertebrae, from the Manda Beds of Tanzania, which are now referred to Mandasuchus". Like several contemporary "rauisuchians" ("Energosuchus" and "Vytshegdosuchus"), "Tsylmosuchus" has elongated cervical vertebrae. This would have given it a relatively long neck. Nesbitt (2009) suggested that elongated cervical vertebrae were present in numerous archosauriform clades, and that the length of the cervical vertebrae depended on the position in the presacral column, as seen in the poposauroid "Arizonasaurus" and the non-archosaurian archosauriform "Guchengosuchus". The holotypes of each of the three species consist of a single cervical vertebra, which does not bear any other clear autapomorphies. Furthermore, the material  referred to these species cannot be shown to belong to the same taxa as the holotypes. Thus, Nesbitt (2009) considered all three species to represent invalid archosauriforms. Sennikov (2022) interpreted "Tsylmosuchus" as a member of the Ctenosauriscidae and also suggested that "Scythosuchus" may have been the same animal as "Tsylmosuchus". Paleobiology. Along with small proterosuchids such as "Chasmatosuchus", "Tsylmosuchus" and other large archosauriforms were the top predators in Early Triassic European Russia. "Tsylmosuchus" was part of what are referred to as the "Benthosuchus"-"Wetlugasaurus" fauna (a.k.a. the Ustmylian and Rybinskian gorizonts) and the "Parotosuchus" fauna (a.k.a. the Yarenskian Gorizont). These  faunas extend through the early and late Olenekian stage. They are known from hundreds of sites throughout eastern Europe and preserve a wide array of temnospondyls (primarily trematosaurids), procolophonids, and early archosauriforms. They correspond to a massive river basin, which likely experienced a trend of increasing humidity during the later part of the Olenekian.