Silurian-Devonian vertebrates from the Northern hemisphere

Sammanfattning: Microscopic remains of early vertebrates such as scales and dermal hone fragments are common in Silurian andDevonian rocks world wide. Although they only represent a small part of the whole animal they still provideimportant information about the organism and its evolution, ecology and distribution. Moreover, such remainsoften occur in rock units where other more complete vertebrate fossils are lacking. This thesis investigatemicroscopic vertebrate remains from several remote areas in the Northern Hemisphere to expand the knowledgeof early vertebrates and their distribution.Remains of thelodonts, acanthodians, heterostracans, osteostracans, anaspids and chondrichthyans aredescribed from Silurian - Lower Devonian rocks of the North Greenland segment of the Franklinian Basin.Isolated thelodont scales from the Lower Silurian are compared with Eurasian forms. Samples containing a widerange of vertebrate remains from the Chester Bjerg Formation, Hall Land, suggest that the Silurian-Devonianboundary may occur between the two vertebrate-bearing beds of the formation.Dermal skeletons of well-preserved articulated specimens of birkeniid anaspids from Scotland and Norwayshow a characteristic sculpture for each species. The sculpture of scales and platelets is used to clarify theposition of scales previously left in open nomenclature. Description of a large collection of disarticulated scalesand platelets from the Northern Hemisphere allows development of a new anaspid taxonomy presented thatincludes both articulated and disarticulated material, and traces changes in histology and sculpture of the scalesand platelets through time.Scales of ten thelodont taxa, of which three are new, are described from the Red Bay Group of Spitsbergen.Different assemblages of Nikolivia, Canonia, Turinia and Apalolepis scales characterise five thelodont bearinghorizons from the Fraenkelryggen and Ben Nevis formations. Comparison with similar faunas from other partsof the Northern Hemisphere suggests a early-middle Lochkovian age for the Fraenkelryggen Formation and amiddle-late Lochkovian age for the Ben Nevis Formation.