Groenlandaspidid placoderm fishes from the Late Devonian of North America

Abstract

Two new taxa of groenlandaspidid fish (Placodermi: Arthrodira) from non-marine deposits of the Catskill Formation (Upper Devonian) at Red Hill, Clinton County, Pennsylvania, USA, are the first to be described from North America outside of Greenland. Groenlandaspis pennsylvanica n.sp. is known only from isolated trunk elements that are quite similar to Groenlandaspis antarctica Ritchie, 1975. Groenlandaspis pennsylvanica n.sp. is characterized by distinct features of the median dorsal (MD), posterior dorsolateral (PDL), and anterior dorsolateral (ADL) plates. Turrisaspis elektor n.gen. and n.sp. is a smaller form with a high median dorsal plate (MD) and tall, narrow elements of the dorsolateral trunk shield, particularly the PDL, giving this taxon a distinctively short, high trunk shield. The head shield of Turrisaspis elektor has a divided pineal plate and the postmarginal plate makes contact with the postorbital plate, excluding the marginal plate from the lateral margin of the head shield. Groenlandaspis pennsylvanica n.sp. is a rare faunal component at the Red Hill site whereas Turrisaspis elektor is very common. The large sample size of Turrisaspis elektor provides a glimpse at ontogenetic and individual variation within this taxon.