The Ancestry of the Genus Nautilus

Abstract

The genus Nautilus is known to be represented by at least six extant species that inhabit a well-circumscribed large area in the southwestern Pacific Ocean, the Philippines, Indonesia, and the tropical seas of Australia [see Saunders (1981b) and Part III of this volume]. The most puzzling aspect of these occurrences is that Nautilus seems to have no ancestors in the immediately preceding pre-Holocene rocks; i.e., no representatives of Nautilus, indeed no nautilids of any kind, have ever been authentically recorded from rocks of Pliocene and Pleistocene age. The only published mention of a Pliocene occurrence is that of a single specimen of a "true Nautilus" from the coast of Oregon (Dall, 1909, p. 21), but the specimen and its stratigraphie position were never described, and Miller (1947, p. 9) was inclined to discount this record. At most, it is obscure and undocumented. Also, the definition of a "true Nautilus" in 1909 differed from that of today. Since marine Pliocene and Pleistocene rocks are widely exposed in the area of distribution of living Nautilus, the fact that no documented records of any nautilids of those ages exist suggests that the immediate ancestors of living Nautilus must have been so rare that up until now they have escaped detection and not only because nobody "has taken the trouble to look for them" (Ward, 1984).