Morphology and paleogeography of the Ordovician conodont Paracordylodus gracilis Lindström, 1955: comparison of two populations

Populations of the widely distributed Early Ordovician conodont Paracordylodus gracilis Lindström, 1955, have been measured and studied in detail. Natural clusters and rich collections of isolated elements allowed calculations of size frequency distributions and construction of survivorship curves. Small morphological differences, as well as dissimilarities in population structure between collections from separate areas, were observed. This led to the recognition of Type A populations from Kazakhstan and other Arenigian warm water, low latitude regions and Type B populations from Baltica and other areas with cool water, mainly located at high latitudes in the Arenigian.