Plicatostylidae is a family of extinct large-sized epifaunal marine to brackish bivalves that inhabited Europe, Asia, Africa and America during the Jurassic, though they survived until the Eocene.[1] These groups are informally known as "Lithiotids" or "Lithiotid Bivalves".[2][3] They represent large reef builders, analogues to the younger Rudists and modern Crassostrea, and less extent to Tridacna.[2][4]
Plicatostylid bivalves were large sized, with the spoon-shaped Lithiotis reaching heights of 25-30 cm and a thickness of up to 1.5-3 cm, with the largest as high as 50 cm and some specimens of Lithioperna reaching 70 cm and 4 cm thick.[4][5] They developed in large reef systems like modern Crassostrea, but in warm, shallow seas, with some bioherms attaining lengths over 60 m and thicknesses of 3-5 m.[2][4] They were rapid growers, with their shells often made of aragonite, leading to massive shell accumulations that shaped the sea floor, known as the "Lithiotis Facies".[2][6] These bivalves were major players in their marine ecosystems, contributing to the geological structure of carbonate platforms.[4] Plicatosylids were notably widespread in the Lower Jurassic, specially within the Sinemurian-Pliensbachian, with significant occurrences in Tethyan and Panthalassan margins, from areas in Italy (Rotzo Formation of the Trento Platform, Apennine Carbonate Platform), Slovenia (Podpeč Limestone), Montenegro (Budoš Limestone) and parts of North America (e.g., Oregon).[4] In High Atlas of Morocco (ex. Aganane Formation & Tafraout Group) they are found in association with Corals, suggesting a different ecological context during their later survival.[4][7] Most of these bivalves met their end during a significant environmental upheaval known as the Toarcian Oceanic Anoxic Event, which altered ocean chemistry and made survival challenging. Yet, in some areas like Morocco or the Apennine Mountains, they persisted, showing some adaptability.[8]Gervilleioperna survived until at least the Aalenian in Chile, likely due to having a small shell.[1][9] The genus Pachyperna is know from the Eocene (Bartonian-Priabonian?), revelating the group also survived the Cretaceous–Paleogene extinction event.[10]
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