A review of the psammosteid genus Traquairosteus Tarlo, 1964 (Heterostraci: Pteraspidiformes) from the Givetian-Frasnian basins of Laurussia, with new data on the species composition, distribution and paleoecology

The overview of the Mid to Late Devonian psammosteid heterostracan genus Traquairosteus Tarlo, 1964 is provided, which represents derived and late-surviving psammosteids in the fossil record. A new species, which is the oldest currently known for the genus, is described from Givetian deposits of the Mikhailovsky Quarry of the Zheleznogorsk mining and processing plant (Kursk Region) in Central Russia. The diagnoses and stratigraphic distribution of most species within the genus have been updated and clarified. These fossils characterize Frasnian vertebrate assemblages across the East European Platform, Timan, Scotland, Arctic Canada, and probably Severnaya Zemlya Archipelago. The paleoecology of derived psammosteids is discussed, with an attempt to identify a recent ecological analogue. The hydrodynamic function of the cephalothorax of psammosteids is discussed by means of terminology used in fluid dynamics to explain the laws of motion for towed underwater gliders (bathyplans) with depressed hydrofoils. The hypothetical scenario of the exctinction of psammosteids has been proposed.