Two partial actinopterygian neocrania (occipital ossifications) from Blue Beach, Nova Scotia

The earliest Carboniferous period (Tournaisian stage) is a crucial interval in actinopterygian evolution, but the actinopterygian fossil record for this stage is dominated by flattened specimens referred to inconsistently defined summary taxa. The locality of Blue Beach in Nova Scotia preserves Tournaisian-aged strata of the Horton Bluff Formation and offers a critical window into the actinopterygian fauna. Significantly, actinopterygian specimens from this locality are often preserved in three dimensions, so even partially complete or fragmentary material provides valuable data on actinopterygian morphology and evolutionary dynamics. Here, we describe two partial actinopterygian neocrania from Blue Beach. We review actinopterygian neocranium morphology and the dorsal arterial system to provide a comparative basis identifying these new specimens. We find one neocranium (NSM 017.GF.017.007) is most like early-diverging actinopterygians from the Devonian period; the other (NSM 017.GF.017.004) is most similar to later-diverging Carboniferous actinopterygians. This result underscores the diversity of the actinopterygian fauna preserved in the Horton Bluff Formation and suggests that this fauna was mosaic in composition and non-continuous with derived European actinopterygian faunas. Furthermore, this result contributes to an emerging picture of a gradual transition between Devonian and Carboniferous actinopterygian faunas.