A dipterid-grade lungfish from the Tournaisian Horton Group of Nova Scotia, Canada

ABSTRACT Lungfishes achieved high diversity in the Devonian, but most of these lineages went extinct in the late Devonian mass extinctions. Carboniferous lungfish are generally thought to belong to one larger diversification, Phaneropleuriformes, typically associated with freshwater and estuarine environments. We here use μCT to describe a lungfish occiput from the Tournaisian of Blue Beach, Nova Scotia, Canada, the first lungfish occurrence from the Tournaisian of North America. The occiput is short and high with well-developed dorsolateral cristae, two pairs of spinal nerves posterior to the vagus nerve, and a short triangular posterior stem of the parasphenoid. Although this specimen is too incomplete to place into a phylogenetic analysis, we identify characteristics shared with both holodontids and dipterids and absent within Phaneropleuriformes, suggesting the persistence of a wider range of lungfish lineages through the end-Devonian mass extinction events, in line with recent findings from the Tournaisian-aged Ballagan Formation of Scotland. Differences in the faunal composition of the Blue Beach Member of Nova Scotia and the Ballagan Formation of the Scottish Borders may be a consequence of different paleoenvironments in these roughly coeval formations or of palaeobiogeographical barriers to dispersal between Europe and Atlantic Canada. The possible persistence of a marine or estuarine lungfish into the mid-Tournaisian shows turnover of the marine durophage guild across the Hangenberg extinction was not complete, but may have been sufficient to disrupt incumbency in earliest Carboniferous marine trophic guilds.