Comparative Trophic Levels of Phragmocone-Bearing Cephalopods (Nautiloids, Ammonoids, and Sepiids).

This article focuses on the ecological roles and trophic positions of phragmocone-bearing cephalopods, particularly extant nautiloids (Nautilus and Allonautilus) and their comparison to other cephalopods such as sepiids and extinct ammonoids. Using stable isotope analyses of carbon and nitrogen from both soft tissues and hard parts, combined with gut content studies and baited remote underwater video system (BRUVS) observations, the study reveals that extant nautiloids occupy a distinct isotopic niche characterized by decreasing nitrogen isotope values through ontogeny, suggesting obligate scavenging behavior rather than active predation. The findings also highlight physiological and ecological differences between nautiloids and coleoids, with nautiloids adapted to low-energy lifestyles in low-oxygen environments, subsisting on energy-poor food sources like crustacean molts and carrion. Comparisons with extinct ammonoids support the view that ammonoids were ecologically closer to coleoids than to nautiloids, reflecting divergent evolutionary strategies among phragmocone-bearing cephalopods.