Global Assessment of Marine Reptiles and Mammals Using a Taxonomic Distinctness Tool: Implications for Their...

Understanding the spatial distribution of marine biodiversity is essential for assessing evolutionary processes and informing conservation priorities. This study investigates global distribution patterns of marine reptiles and mammals-two clades with contrasting evolutionary histories. Marine reptiles, representing lineages with arrested diversification, have undergone extensive extinction events since the Mesozoic, while marine mammals are characterized by recent and rapid diversification, particularly during the Miocene. Using taxonomic distinctness (Δ⁺) and species richness across 15 oceanic regions, we evaluated whether observed distribution patterns deviate from null expectations derived from randomized assemblages. Our results reveal that marine mammals exhibit significantly non-random, patterned distributions, with higher-than-expected taxonomic distinctness in the Arctic and North Pacific, indicating evolutionary radiation and lineage diversification in these regions. Conversely, marine reptiles generally conform to random expectations, with lower-than-expected Δ⁺ values in the Tropical Pacific and Indian Oceans-areas dominated by closely related sea snakes-suggesting phylogenetic clustering and historical lineage loss. These results support our initial hypothesis that diversification dynamics shape current species distributions. Specifically, rapidly diversifying groups lead to phylogenetic clustering (i.e., creating local assemblages of closely related species), while lineages with arrested diversification show overdispersed or clustered patterns. Importantly, we identify key conservation hotspots, highlighting the Indo-Pacific for marine reptiles and the Arctic-North Pacific for marine mammals. These findings underscore the necessity of integrating taxonomic distinctness and species richness to guide the strategic expansion of Marine Protected Areas (MPAs). As ocean warming and anthropogenic pressures continue to reshape the distribution of marine species, understanding macroecological and phylogeographic patterns becomes vital for ensuring the efficient protection of marine biodiversity.