T155 Cephalopods Present and Past: Evolution, Paleoecology, and Links to Paleoenvironmental Change (Posters)

Tuesday, 12 October 2021
9:00 AM - 1:00 PM
Exhibit Hall A

REFINING THE HABITAT OF NAUTILUS MACROMPHALUS BASED ON THE ISOTOPIC COMPOSITION AND TEMPERATURE OF THE WATER COLUMN IN NEW CALEDONIA

Paper number: T155-3
Program: Technical Sessions
Time: 9:00 AM – 1:00 PM

Authors

  • Amane Tajika Presenting Author
    American Museum of Natural History, New York, NY
  • Neil Landman
    American Museum of Natural History, New York, NY
  • James Cochran
    Stony Brook UniversityMarine & Atmospheric Scienc, Elko, NV

Abstract

The Nautiloidea is a group of externally shelled cephalopods that originated in the Late Cambrian. The only modern descendants include the genera Nautilus and Allonautilus—sometimes dubbed “living fossils.” Modern nautiloids have often been studied by paleontologists to better understand the anatomy and ecology of fossil relatives. In terms of their habitat and life history, direct observations of these animals are difficult because they live in deep-sea environments. One approach to investigate their habitat and life history is the analysis of light stable isotopes (C, O) preserved in their shell. The value of δ18O provides information on the temperature of the water in which the shell was formed, and thus is a useful tool to reconstruct the habitat of fossil and modern cephalopods. Application of this method requires information on the chemistry and temperature of the water column. However, such information is absent in most studies of extinct and modern forms due to the difficulty of collecting water samples at the same site. In this study, we analyzed oxygen and carbon isotopes (d18O, d13C) in the septa of two specimens of Nautilus macromphalus from New Caledonia. In addition, we analyzed samples of water for oxygen and carbon isotopes, as well as temperature and salinity, as a function of depth at two nearby stations. We also performed a morphometric analysis to examine if morphological and isotopic changes during ontogeny are correlated. Results reveal that the patterns of change of d18O and d13C in the septa of N. macromphalus pre- and post-hatching are consistent with previous studies. Values of d18Owater range from 0.7 to 1.4‰ (VSMOW), with a maximum coincident with a salinity maximum at ~150m. We use the temperature and d18Owater profiles to calculate equilibrium values of d18Oaragonitewith depth. Comparing these values with the measured d18O of the septa shows that the habitat depth of N. macromphalus is ~125 m before hatching and ~350 m after hatching. Our results do not reveal any correlation between morphological changes and isotopic values in either of the two specimens.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-367632

© Copyright 2021 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.