Supplementary material from "The largest extinct volant bird Pelagornis could not meet the energetic demands of skimming"

The fossil record is one of our only direct insights into the lives of extinct species. In recent years, the development of biomechanical and aerodynamic models has allowed us to ask specific questions that the fossil records alone cannot answer. Pelagornis was a Paleocene marine bird characterised by a large bill with pseudo-teeth, which has generated debate about the way it may have fed. Here we assess the idea that Pelagornis could have fed by skimming, a feeding behaviour seen almost exclusively in modern Skimmers, Rynchops (Aves). Using biomechanical models and morphological measurements of the bills of two Pelagornis species, P. chilensis and P. sandersi, we show that Pelagornis could not have met the energetic requirements of skim-feeding. Additionally, we show that Pelagornis could not have overcome the drag induced by picking prey from the surface of the water, shedding doubt on the possibility that Pelagornis could have fed from the water's surface. Our results refute the hypothesis that Pelagornis could skim-feed and illustrate how biomechanical models can be used to infer ecological interactions of extinct species.