Abstract

Study of the relationships of fossil and living billfishes is crucial to understand the ecological drivers that control their biodiversity through time and how distributional patterns of extant populations can be affected by current abiotic events. Here we describe six istiophorids species that lived sympatrically in the central Mediterranean Sea during the Late Miocene based on fossil istiophorids from Italy. Of these, †Pizzikoskerma salentina, †Sicophasma macrocanalata, †Makaira adensa and †Makaira cyclovata are new, while †M. belgica and †M. cf. colonense is previously were described. The taxon Istiophorus is reported here for first time in the Tortonian based on an unidentified species. We reconstructed the evolutionary direction of morphological traits by integrating the earliest known Billfish, †Hemmingwaya sarissa in our phylogenetic analysis as outgroup. The phylogeny shows that bills with circular cross-section, 12 caudal vertebrae, slim bodies and an elongated first dorsal fin are plesiomorphic traits, while 13 caudal vertebrae, fusiform body, a shorter and pointed first dorsal fin, lateral process and quadrangular spines on the vertebral centra are traits associated with larger body sizes. The Makaira species described herein exhibit trabecular bone in the premaxilla forming the rostrum, an unusual pattern backed by phylogenetics interpreted as an adaptation to reduce weight by simultaneously body size increase. The fossil Billfish assemblage suggests sea-surface temperatures between 23–24 ºC, much warmer than the modern central portion of the Mediterranean. The exquisite preservation of one specimen shows a trophic interaction between marlins and barracudas, the first direct evidence of predator-prey relationships in fossil istiophorids.