Allonautilus: A new genus of living nautiloid cephalopod and its bearing on phylogeny of the Nautilida

Journal of Paleontology, Nov 1997 by Ward, Peter D, Saunders, W Bruce

We examine two problems in this paper. First, we address the question of whether soft-, as well as hard-part anatomy differs in the currently defined species of Nautilus. We attempt to answer this by presenting preliminary observations on the soft-part anatomy of N. scrobiculatus and by comparing these anatomical features to homologous structures in three other extant Nautilus species. Secondly, we inquire whether this newly recovered information can shed new light on the phylogeny of extant and selected extinct nautilacean taxa, through the use of cladistic analysis using morphological as opposed to genetic characters for all extant species (and several extinct taxa) currently placed in Nautilus. Our goal is to arrive at a phylogenetic classification of extant nautiloid species based on cladistic rather than phenetic philosophy.

MATERIAL AND METHODS

Frozen specimens of two male and one female A. scrobiculatus trapped in 1984 at Ndrova Island, Manus Province, Papua New Guinea, as well as specimens of N. pompilius from the Philippines and N. belauensis from Palau were used for comparisons. Dissected material is reposited in the United States Natural History Museum, (USNM 816504, 816505). Live-caught shells of A. scrobiculatus include USNM 885685-885688.

Observations on gross anatomy included counts of tentacle number, examination of hood and tentacle anatomy, and measurements of gill and radular morphology. Anatomy of the male reproductive system was determined through observation of external anatomy, and by dissection via the ventral body surface. The buccal masses of both species were examined. Gross shell morphology and shell ultrastructural differences of the various species are already well known (Saunders, 1981; 1987; Ward, 1987). We obtained information about shell characters from those sources and from new observations on recent and fossil material.

Our cladistic analysis includes both ingroup (species currently assigned to Nautilus), as well as outgroup nautilacean taxa. The fossil material examined for our study consisted of two specimens of Nautilus cookanum Whitfield, from the Cowlitz Formation of Washington State; five Hercoglossa danica, from the Republic of Georgia; one Cenoceras ornatus (Pia) from an unknown locality in Europe, two H. peruviana Berry from an unknown locality in Peru; and twenty Aturia angustata (Conrad) from various Oligocene localities in Washington State. All of these specimens are housed in the Thomas Burke Museum, University of Washington. We were also able to make observations on a single Nautilus praepompilius Shimansky from the Paleontological Institute, Moscow, recently described by Saunders et al., 1996. Data for Aturia alabamensis (Morton) and Cenoceras trechmanni Kummel came from literature sources (Kummel, 1956; Dzik, 1984; Dzik and Korn, 1992). Since variation in nautilacean morphological characters species is always small (Miller, 1947; Kummel, 1956; Dzik, 1984, Saunders, 1987; Ward, 1987), we believe that relatively few numbers of individuals can be used to typify characters for any species.