Vertebrate remains from Upper Silurian – Lower Devonian beds of Hall Land, North Greenland

Abstract

Vertebrate microscopic remains of twenty-six taxa of thelodonts, heterostracans, osteostracans, anaspids, acanthodians and chondrichthyans are described from limestone beds in two localities of Late Silurian - Early Devonian age of the Chester Bjerg Formation, Hall Land, North Greenland. The limestone beds form a minor part of a monotonous calcareous sandstone-siltstone-mudstone sequence at the top of the Franklinian Basin succession.
Stratigraphical recognition using several thelodont and acanthodian taxa, supported by regional geological and structural trends, suggests a Silurian-Devonian boundary interval between beds of the Halls Grav and Monument localities. This possible resolution of the previous problematic correlation between the two distant sections of monotonous nature demonstrates the potential biostratigraphic utility of thelodonts in Silurian -Devonian marine successions.
The Chester Bjerg Formation thelodont assemblage is unique with several new endemic taxa, but Loganellia cf. L. tuvaensis is very similar to the type material of the Tuva region south of Siberia, Russia and indicates a Late Silurian age for the beds of the Halls Grav locality. Canonia cf. C. grossi suggests an Early Devonian age for the Monument locality, since Canonia is so far only found in Lower Devonian marine strata of Arctic Canada and Russia. Fragments of cosmopolitan acanthodian genera such as Poracanthodes, Gomphonchus and Nostolepis are found together with heterostracans, osteostracans, anaspids and chondrichthyans at both localities but do not give a more exact age determination than Late Silurian - Early Devonian. New thelodont taxa are Loganellia almgreeni sp. nov., Paralogania foliala sp. nov., Praetrilogania grabion gen. et sp. nov. and Thulolepis striaspina gen. et sp. nov. Nostolepis halli sp. nov. is a new acanthodian species.