Early vertebrate diversity of the Elm Point Formation of Manitoba, Canada, and evidence of fish faunal diversification in the Middle Devonian of North America

The Elm Point Formation is a Middle Devonian (Eifelian) unit deposited in the Elk Point Basin in North America. Specimens recovered from three localities in the interlake region of Manitoba, Canada, comprise skull and thoracic material of fossil early vertebrates, particularly dental elements. They include the arthrodiran placoderms Elmosteus lundarensis (Jobbins, Moysiuk, Durkin & Brink, 2025), Homosteus manitobensis Okulitch, 1944, and Squamatognathus steeprockensis Hanke, Stewart & Lammers, 1996a, ptyctodonts Ptyctodus cf. calceolus Newberry & Worthen, 1866, and Rhynchodus Newberry, 1873, and sarcopterygians including onychodontids and dipnoans. One sarcopterygian specimen exhibiting cosmine has been cautiously identified as the postparietal shield of an ‘osteolepiform’, likely representing the oldest tetrapodomorph from Canada. The overall faunal diversity of the Elm Point Formation is similar to other North American faunas from the Eifelian. Comparisons between North American Middle Devonian stratigraphic units show a slow change in faunal diversity, with the Eifelian rich in ptyctodont diversity and the Givetian exhibiting a diversification of arthrodires.