Ammonoids are diverse and widespread fossil shelly cephalopods that flourished in the world ocean during more than 300 million years before their total extinction, 65 million years ago. In spite of two centuries of intensive scientific studies, their mode(s) of life, and most particularly long-distance dispersal abilities remain poorly known. Here we address this question by looking at the latitudinal distribution of Early Triassic (~250 Myr) ammonoids through similarity-distance decay analyses. We examine and compare how rates of similarity-distance decay differ between various systematic, shell geometry and ornamentation groups, during the same ~3.5 myr Early Triassic time interval, in order to untangle phylogenetical, geometrical and ornamental imprints on the observed biogeographical pattern. Our data do not support any phylogenetical and shell ornamentation control on the similarity-distance decay, but rather evidence a significant effect of (sub-)adult shell geometry: most evolute morphs tend to have been more endemic than most involute ones. This result contrasts with the classical hypothesis that long-distance ammonoid dispersal mainly occurred during the earliest planktonic young stages, and thus that (sub-)adult morphological characteristics should not constrain large-scale biogeographical patterns of ammonoids. While a direct control by Sea Surface Temperature can be discarded, this result may indicate that at least some adult Triassic ammonoid morphs were good active swimmers able to achieve long-distance migrations, as observed for some present-day coleoid cephalopods.