EARLY PERMIAN CARBONITIDAE (OSTRACODA): PALEOENVIRONMENTS AND EVOLUTIONARY IMPLICATIONS

An assemblage of four species of Carbonitidae was deposited with charophytes, lungfishes, and lysorophids in a lenticular mudstone from an early Permian freshwater pond. Samples contained few adult carbonitids indicating perhaps a stressed and unstable environment that favored either early sexual maturity, other dwarfism, or high juvenile mortality rates. Morphological characters of these carbonitids suggest an affinity to the Healdioidea, marine taxa that are likely ancestral to the Carbonitidae. The muscle-scar patterns of Carbonitidae, which comprise closely grouped circular bundles of secondary muscle scars, resemble closely those of Healdioidea and not those of freshwater Cypridoidea and Cytheroidea, whose muscle scars are fewer and spaced farther apart. The muscle-scar pattern of C. pungens, a circular scar with an ascertainable pattern of secondary scars, is morphologically similar to species of Darwinula, but study of additional specimens of C. pungens with better-preserved muscle scars is essential to determine their evolutionary affinity. Evolutionary affinity of carbonitids to healdioids suggests that the ostracodes invaded freshwater habitats at least four times in their long history.