ENHYDROSS: A New Mechanistic Model Supports the Trans-Oceanic Dispersal Capability of Terrestrial Vertebrates

Many terrestrial vertebrates, both extinct and extant, have widespread or even global distributions. Although vicariance (e.g., through continental fragmentation, sea-level changes) explains some of these patterns, others seemingly require long-distance trans-oceanic dispersal. A key but underexplored factor in this debate is the biological feasibility of such dispersal based on an organism's physiology and biomechanics. We introduce ENHYDROSS, a new mechanistic energetic model that estimates optimal swimming speed and minimum cost of transport for any vertebrate. These allow us to estimate maximum swimming distances and durations. We tested ENHYDROSS on two mammals (elephant, polar bear) and five reptiles, including the Aldabra giant tortoise, saltwater crocodile, ostrich, and two extinct nonavian dinosaurs (Lambeosaurus and Rapetosaurus). For the extinct dinosaurs, we used a broad range of basal metabolic rates to account for different thermophysiological hypotheses. The model's estimates for extant animals align with observed data, while cases of underestimates can be attributed to the effects of ocean currents, as evidenced by estimated passive drifting distances and times under predominantly mild and intermediate currents. ENHYDROSS generally predicts greater swimming capacity than previously proposed models due to assumptions like null-thermogenesis, resulting in lower minimum cost of transport. Applying our model to test the feasibility of extinct dinosaur dispersal between Africa and Europe during the Cretaceous via the Alboran route (the oceanic corridor separating Iberia from Morocco), we found that both hadrosaurs and titanosaurs could plausibly complete the journey, particularly under favorable conditions such as low sea levels, stepping-stone islands, and higher fat reserves. Hadrosaurs showed slightly better swimming efficiency. Dispersal was especially feasible during the early-middle Albian (112.5-107.5 Ma) and latest Cretaceous (72.5-66 Ma), but was unlikely during periods of high sea levels (97.5-77.5 Ma). These results support the possibility of trans-oceanic dinosaur dispersal across distances of up to ~560 km.