Functional morphology, ecology, and evolution of the Scaphitaceae Gill, 1871 (Cephalopoda)

Abstract

Scaphitids are heteromorph ammonites exhibiting morphological trends counter to of those of the other main heteromorph ammonite groups. These trends include the shortening of the body chamber, lateral compression of the whorl, closure of the coil, and more regular, spiral coiling. Scaphitid-like morphologies may have appeared in other heteromorphs, but the Scaphitaceae are monophyletic. The most primitive scaphitids are known from the Albian, but an important radiation occurred in the Western Interior Seaway of North America from the Santonian to Maastrichtian, some of which spread to the Old World. The scaphitid morphology is consistent with improved swimming abilities, but scaphitids remained associated with the seafloor and are best considered to have been nektobenthos similar to modern nautiluses.