Abstract

Phylogenetic relationships within the neogastropod family Nassariidae are poorly understood as are relationships between the Nassariidae and other fossil and extant buccinid taxa. The poor resolution of nassariid and buccinoidean relationships is due to: 1) the complex distribution among these gastropods of characters commonly used in classification; 2) a number of Mesozoic and Paleogene genera whose relationships to extant buccinoidean lineages are poorly constrained; and 3) a lack of previous efforts to address these problems on a rigorous, phylogenetic basis.

The results of a phylogenetic analysis of nassariid genera did not decisively support the monophyly of the family. The buccinid subfamily Photinae was an extant sister group to the Nassariinae in a phylogenetic analysis of extant taxa and on many cladograms from an analysis combining fossil and extant taxa. In addition, Buccitriton (representing the Paleogene Tritiaria group) was a sister taxon to the Nassariinae in all analyses in which it was included, regardless of the identity of the extant nassariine sister group. This suggests that the photines, which likely arose from a Tritiaria ancestor, are the closest living relatives to the Nassariinae. Many Paleogene fossil “buccinoid” taxa appear to be more distantly related to the Nassariinae and possibly to the rest of the nassariids as well. Stratigraphic range data combined with the results of this study suggest that the Nassariinae diversified rapidly in the early Miocene and achieved a cosmopolitan distribution early in their history. A largely Indo-Pacific subclade was consistently deeply-nested within the Nassariinae, suggesting that nassariines invaded the Indo-Pacific region most recently. The timing of this invasion is difficult to estimate but had occurred by the end of the Miocene. Further analyses using molecular sequence data, relative stratigraphic position, or focusing in more detail on the Paleogene taxa are required to resolve the identity of the sister group to the Nassariinae with greater confidence.

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