T135 Cephalopods Present and Past: Insights into Evolution, Paleobiology, and Links to Paleoenvironmental Change

Wednesday, 28 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

THE FOSSIL AND EXTANT SPECIES OF NAUTILUS AND ALLONAUTILUS: SYSTEMATICS, BIOGEOGRAPHY AND A NEW PHYLOGENY OF THE POST TRIASSIC NAUTILOID CEPHALOPODS USING CHARACTER WEIGHTING DICTATED BY NEW UNDERSTANDING OF THE EXTANT SPECIES

Paper number: T135-2
Program: Technical Sessions
Time: 1:45 PM – 2:00 PM

Authors

Abstract

New genetic and morphological analyses demonstrate that the extant species of Nautilus are more diverse than currently accepted: along with the previously accepted Nautilus pompilius (the type species), N. macromphalus, N. stenomphalus, and N. belauensis we are part of a larger group (from Harvard and the American Museum of Natural History) that recognize new species from Vanuatu, Fiji, and American Samoa; the formal definitions are in press. From the extensive new work, as well as the recognition that the genus Allonautilus contains both smooth shelled, but also heavily ribbed species, we propose that shell ribbing in post-Triassic genera, currently used as a single character for genetic definition (such as the genera Cymatoceras, Procymatoceras, and others), is invalid. Here we report on the new discoveries of a diverse assemblage of Late Cretaceous nautilids that are currently placed in Cymatoceras but which, in fact, have shell shapes, sutural morphology, and the important pre-and post-hatchling morphology of extant Nautilus and Allonautilus that correctly place them in Nautilus and Allonautilus. We recognize three new ornamented species of Nautilus from the Santonian and Campanian Stages, and two new species of Allonautilus from the same deposits of the Late Cretaceous Nanaimo Group of Vancouver island region. These are the first reported Allonautilus fossils. To date the complete extinction of all ribbed, Late Cretaceous species in the K/Pg mass extinction remains an unsolved mystery, as smooth species passed through the mass extinction unscathed. We attribute this to the ribbed forms having been shallower water in habitat, with deeper water forms surviving, and then re-radiating back into shallow water habitats in the Paleogene. By the Neogene, only the deep water Aturia, Nautilus, and Allonautilus survived. We conclude by showing that open water distances of more than 200km completely isolate extant Nautilus and Allonautilus species, and this has led to their extraordinary and diverse tradition to the present day of probably a dozen species combined.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-358188

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