Redescription and revised taxonomy of Early Devonian (Emsian) acanthodians from New Brunswick and the Gaspé Peninsula, Quebec, Canada

Devonian strata in eastern Canada, to the south of the Restigouche River in New Brunswick and north of Baie des Chaleurs in the Gaspé Peninsula, Quebec, are renowned for their vertebrate fossil faunas. Of the stem chondrichthyans, the taxa originally named as Ctenacanthus latispinosus Whiteaves, 1881, Diplodus problematicus Woodward, 1892, Gyracanthus incurvus Traquair, 1890, and Protodus jexi Woodward, 1892 have been reviewed and reassessed recently. In this work, we reassess ? Cheiracanthus costellatus Traquair, 1893 and Acanthodes semistriatus Woodward, 1892, long known from the Atholville beds, and also found in Gaspé. Specimens from the latter sites comprise fin spines and scales, and the material from the Atholville beds comprises the articulated holotypes for each species plus isolated spines and scales. We reassign ? Cheiracanthus costellatus to the diplacanthid Milesacanthus Young and Burrow, 2004 based on the distinctive structure of the fin spines, and scale morphology and histology. This represents the first record of Milesacanthus from the Americas. Acanthodes semistriatus was reassigned to Mesacanthus Traquair, 1888 in the early 1900s. We reaffirm this assignment based on the morphology and histology of dermal elements, and scapulocoracoid shape. We also describe rarer material from “nostolepid” and undetermined acanthodians, and reassess ? Ctenacanthus ? ornatus from Gaspé.