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Article: Evidence for seasonal variation in δ13C and δ18O profiles of Baculites and implications for growth rate

Palaeontology - Vol. 62 Part 4 - Cover Image
Publication: Palaeontology
Volume: 62
Part: 4
Publication Date: July 2019
Page(s): 583 598
Author(s): Nicholas M. Ellis, and Thomas S. Tobin
Addition Information

How to Cite

ELLIS, N.M., TOBIN, T.S. 2019. Evidence for seasonal variation in δ13C and δ18O profiles of Baculites and implications for growth rate . Palaeontology, 62, 4, 583-598. DOI: /doi/10.1111/pala.12416

Author Information

  • Nicholas M. Ellis - Department of Earth & Environmental Sciences New Mexico Institute of Mining & Technology Socorro NM USA
  • Nicholas M. Ellis - Department of Geological Sciences University of Alabama Tuscaloosa AL USA
  • Thomas S. Tobin - Department of Geological Sciences University of Alabama Tuscaloosa AL USA

Publication History

  • Issue published online: 24 June 2019
  • Manuscript Accepted: 26 November 2018
  • Manuscript Received: 21 March 2018

Funded By

The University of Alabama Undergraduate Creativity and Research Academy and the Department of Geological Sciences

Online Version Hosted By

Wiley Online Library
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Abstract

The life histories of ammonites and the life strategies they employed are difficult to assess without robust modern analogues but placing constraints on ammonite growth rates provides a fundamental first step to understanding this abundant, but poorly understood, fossil group. Here we interpret periodic variations in carbon and oxygen stable isotope profiles from Campanian and Maastrichtian ammonites (Baculites) as seasonally driven and use these records to determine their rate of shell precipitation. Several of these samples are housed in museums and were originally prepared using sealants for display and preservation but testing of these sealants indicated no alteration of the isotopic values of treated carbonate. Diagenetic alteration, as determined by shell microstructure, affected the preservation of isotopic signals, resulting in the loss of seasonal variation in less well‐preserved specimens, and the δ13C signal is more robust than δ18O. The periodicity of isotopic profiles from Baculites shells presented here suggest that these organisms grew at rapid rates (c. 340 mm per year), which may imply an r‐type life strategy in which the animals reach maturity quickly, spawn large quantities of progeny, and die at a young age. Because of the potential mobility of Baculites, reconstructing palaeoenvironmental conditions from these isotopic records is challenging and should be conducted cautiously. Unfortunately, well‐preserved Baculites shells much longer than 350 mm are rarely recovered, which complicates the statistical treatment of potential periodicity in isotopic profiles.

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