Exceptionally well-preserved trochospirally coiled Involutinina have been found in Late Triassic (Wallowa Mountains, Oregon, U.S.A.) and Early Jurassic (northern Calcareous Alps, Austria) carbonate rocks. Their remarkable preservation, related to impregnation of the test prior to recrystallization, allowed us to observe features usually obliterated by diagenetic and metamorphic processes. This paper provides a revision of the morphology, structure, systematic position, phylogeny, and stratigraphic range of the family Trocholinidae Kristan-Tollmann. New criteria permitting the distinction between trocholinid genera, even in cases of intense recrystallization, are presented. An identification key and a new, monophyletic tree are proposed for the whole family. The main outcomes of this work are that 1) Neotrocholina Reichel is definitively excluded from the Involutinina; 2) the genera Andersenolina Neagu, Hottingerella Piller, and Septatrocholina BouDagher-Fadel and Banner are placed in synonymy with Coscinoconus Leupold; 3) the genus Ornatoconus di Bari is considered a synonym of Trocholina Schlumberger; 4) the distinction between the genera Auloconus Piller and Lamelliconus Piller is abandoned; 5) five new genera (Coronaserra n. gen., Frentzenella n. gen., Kristantollmanna n. gen., Papillaconus n. gen., and Wallowaconus n. gen.) and three new species (Frentzenella frentzeni n. gen., n. sp., Frentzenella perforata n. gen., n. sp., and Wallowaconus oregonensis n. gen., n. sp.) are introduced; 6) the species “Trocholina intermedia” Henson is reinstituted; 7) “Trocholina gigantea” Pelissié and Peybernès, and “Semiinvoluta verrucosa” Tollmann and Kristan-Tollmann are renamed Coscinoconus limognensis nom. nov. and Papillaconus kristani nom. nov., respectively; and 8) new combinations for several species of Trocholinidae are provided.
The recognition of two subfamilies (Lamelliconinae and Trocholininae) and twelve genera within the Trocholinidae underlines the high diversity of the family. The rapid diversification and widespread distribution characterizing the group suggest that the potential of trochospirally coiled Involutinina in stratigraphic and paleoenvironmental studies is greatly undervalued.