Litiotidni školjkaši u donjojurskim karbonatnim naslagama južnog Velebita i južne Like

Two species of Lithiotis-type bivalves were found in the Lower Jurassic carbonate deposits in the areas of Mali Alan and Stikada: Cochlearites loppianus and Lithioperna scutata. Lythiotis-type bivalve species, dimensions and orientations of their shells were determined in the field, as well as limestone texture and bed structures. A lithostratigraphic column was also recorded in the area of Mali Alan. Samples collected from previous studies were used for sedimentological analyses. Environments in which Lithiotis-type bivalves lived were determined from microscopic thin sections. The Mali Alan succession is 207 m thick and encompasses first and last occurrence of the Lithiotis-type bivalves, while the Stikada succession is 45 m thick and includes their youngest part, i.e. it correlates well with the last unit of the Mali Alan. The first to appear is L. scutata in the Late Sinemurian, which preferred lagoonal subtidal environments, while C. loppianus first appears in the Early Pliensbachian. In these deposits, it is possible to observe how the dimensions of the Lithiotis-type bivalves changed from only a few centimetres to over 20 cm, and during the Early Toarcian the decrease of shell dimensions is observed. After Early Toarcian, the Lithiotis-type bivalves become extinct.