Presented by Philip Lavretsky - Email: firstname.lastname@example.orgOne challenge facing reintroductions of long-extirpated species is knowledge of past range extent and ecology. The Laysan duck (Anas laysanensis) is one of the few remaining endemic species of Hawaiian waterfowl, and is critically endangered; currently restricted to the low-lying atolls of the Northwestern Hawaiian Islands, it is further at risk from sea-level rise. On the main Hawaiian Islands, Laysan duck-like fossils and subfossils have been excavated from sites spanning a range of elevations and habitats, as have subfossils thought to belong to a related endemic duck, the endangered koloa maoli (Hawaiian duck, Anas wyvilliana). However, the species identities are ambiguous. Here, we couple 3D geometric morphometric modeling of wing and leg bones, radiocarbon dating, and ancient DNA techniques to identify subfossils to species, with the goal of evaluating the paleontological record for evidence of species past ranges and habitats. We used structured light scanning to create 3D models of 28 fossil, subfossil, and archaeological bones excavated from 8 sites across the Hawaiian Islands, and contemporary references from 33 wild Laysan and koloa. We then used a custom bait capture array synthesized from 3,750 Anas duck double-digest RAD-seq (ddRAD-seq) loci to genotype 12 sub fossils. We found that nearly all of the fossils and subfossils clustered with contemporary Laysan ducks, suggesting widespread Laysan presence from sea-level, coastal habitats to higher elevation, dry- and wet-forested locations. Interestingly, modern Laysan ducks had shorter, more robust leg bones than those of the Pleistocene-era fossils, possibly reflecting eco-morphological adaptation to extreme terrestriality in their current habitat. Only 2 subfossils were morphometrically and genetically aligned with the koloa, and both were from archaeological sites; these could have been brought from elsewhere on the island, but both sites were at sea-level. Notably, we also recovered a Laysan duck in the same archeological site (400-500 ybp), suggesting that the two species co-occurred on the Islands well after Polynesian arrival. A total of 6 samples had both molecular and morphometric data. Of these, 5 indicated discord between molecular and a priori expert species designations, emphasizing the importance of genetically-vetting samples. The applied use of ancient DNA to establish a genetically-vetted paleo-ecological record will help inform the current management of the endangered koloa, the possible reintroduction of the endangered Laysan duck to the main Hawaiian Islands, and add to the scant data on the evolution of these two endemic species.