- The Paleontological Society
The functional morphology of septal sutures and modified body-chambers of ammonoids and their inferred life habits have been popular topics for over a hundred years. Such long history includes the repetition of ideas, some rejected long ago, that originated in the last half of the 19th century mainly in Germany and Austria. Recent examples of such recurrences are the papers by Lewy (1996, 2000, 2002). His nude-ammonites-became-octopods thesis goes back to Suess (1865) and Steinmann (1888); Naef (1922) argued that argonautid octopods later grew an epipelagic shell to replace the ammonite shells when they were no longer available as drifting egg and brood chambers. Lewy, extending these hypotheses, supposed that octopods modified the host apertures and the hatchlings lived off the decomposing host.
Lewy (2002) also revived the hypothesis that intricately folded septal lobes served only or mainly to securely attach the animal to the shell (Diener, 1912) in order to withstand the buoyant force between the light shell and the heavier body and, especially, the dragging force produced by arms and tentacles during swimming and predation. He concludes that septal complexity correlated with the ferocity of predatory activity.
We will review the history of these and similar hypotheses relating to ammonite body-chambers, septal sutures and possible octopod relations in order to show the dangers in promoting ideas, which have been long forgotten and rejected, in ignorance of their history.
FUNCTION OF MODIFIED BODY-CHAMBERS
Disparate hypotheses have been proposed for the variously uncoiled or recoiled body-chambers of many Jurassic and Cretaceous “heteromorph” ammonoids (reviewed in Westermann, 1996). Lewy (1996, 2000) proposed that most adult body-chamber modifications “must have resulted in death, rather than providing the mature organism with suitable means for living its prime stage” (1996, p. 627).
His arguments are the following: 1) The terminal body-chamber of many Cretaceous …