"Stenopterygius" is known from the lectotype GPIT 43/0219-1, articulated complete skeleton which preserved a very large embryo. The animal is about in length. It was collected from the "Harpoceras elegantulum-exaratum" ammonoid subzones (more specifically Lias ε II3-4), "Harpoceras falcifer" zone, of the famous Posidonien-Schiefer lagerstätte (Posidonia Shale) of Holzmaden, dating to the early Toarcian stage of the Early Jurassic, about 182 million years ago. Maisch referred to the type species 30 additional specimens, all came from Dobbertin of Mecklenburg-Vorpommern and Holzmaden, Germany and Dudelange, Luxembourg. They were collected from the "Harpoceras palum" to "H. falciferum" ammonoid subzones (Lias ε I2-II11, lower-middle early Toarcian), "Harpoceras tenuicostatum-falcifer" zones, of the Posidonia Shale. "S. triscissus" is known from the holotype GPIT 12/0224-2, articulated almost complete skeleton. The animal is a young adult about in length. It was collected from the "Harpoceras exaratum-elegans" ammonoid subzones (more specifically Lias ε II6), "Harpoceras falcifer" zone, of the Posidonia Shale in Ohmden, dating to the middle Early Toarcian stage of the Early Jurassic. Maisch referred to this species 13 additional specimens, all came from various localities in England, France, Germany, Luxembourg and Switzerland. They were collected from the Lias ε II1-III, dating to the middle-late Early Toarcian.