Abstract
AbstractTwoCaudicriodusspecies from lowermost Devonian strata in southern Laurentia (Texas–Oklahoma–Western Tennessee),C. anitaesp. nov. andC. murphyisp. nov., are endemic forms that appeared during the positive δ13C excursion associated with the Klonk Event. The otherCaudicriodusspecies that occur during the Klonk Event and that are often used to recognize the base of the Devonian,C. hesperiusandC. woschmidti, differ in that the I elements of the southern Laurentia species possess a middle row of nodes on the transverse ridges of the spindle. The apparatus ofC. murphyisp. nov. possesses three groups of elements in addition to the I element: F elements (short wide coniforms); D elements (denticles on the posterior margin) and C elements (slender coniforms with basally flaring costae). Strong provinciality in slightly younger LochkovianCaudicriodusspecies was demonstrated earlier, and we propose thatCaudicriodusspecies radiated independently into endemic species in different geographic regions just before or during the Klonk Event. A form originally described asC. woschmidti hesperiusby Simpson (1998) is reinterpreted as a late Ludlow–Pridoli species ofPraeicriodus, P. simpsonisp. nov., with an I element and apparatus structure probably ancestral toCaudicriodus.
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