SHELL MICROSTRUCTURE OF A TRIASSIC PATELLOGASTROPOD LIMPET

The Sr. Cassian formation of northern Italy contains an unsurpassed di versity of Triassic organisms, often with original or only slightly re crystallized shells. The shell microstructure of Patella costulata Mun ster, 1869, is examined and compared with the shell microstructures of 14 extant gastropod limpet taxa. The distribution of shell structure characters supports the assignment of P. costulata to the patellogastr opod taxon Patellidae. St. Cassian facies also include near-shore envi ronments that are consistent with the habitat of extant Patella specie s. The corroboration of Patella costulata as a member of the Patelloga stropoda reduces the hiatus between estimated origination and the prev ious unequivocal first occurrence by a minimum of 116 Ma.