The Rybinskian Gorizont ("Rybinskian Horizon") is a Lower Triassic biostratigraphic unit in Western Russia. It is a part of the Vetlugian Supergorizont and corresponds to the earliest part of the Olenekian stage, lying above the late Induan-age Zaplavnian Horizon[1] and below the Sludkian Gorizont. The Rybinskian Gorizont is sometimes known as the Benthosuchus fauna, due to abundant fossils of Benthosuchus, a temnospondyl amphibian index fossil. Related amphibians such as Thoosuchus also increase in abundance, and the interval additionally hosts the oldest fossils of procolophonines and putative true archosaurs in the region.[2][3]
The Rybinskian is exposed in several svitas (equivalent to geological formations) spread out over a wide area: the type assemblage is the Rybinskaya Svita in the Moscow Syncline, and another is the Staritskya Svita in the Southern Urals area.[2][3][4]