Skip to content Skip to navigation

Article: The fossil record of ichthyosaurs, completeness metrics and sampling biases

Publication: Palaeontology
Volume: 58
Part: 3
Publication Date: May 2015
Page(s): 521 536
Author(s): Terri J. Cleary, Benjamin C. Moon, Alexander M. Dunhill and Michael J. Benton
Addition Information

How to Cite

CLEARY, T.J., MOON, B.C., DUNHILL, A.M., BENTON, M.J. 2015. The fossil record of ichthyosaurs, completeness metrics and sampling biases. Palaeontology, 58, 3, 521-536.

Author Information

  • Terri J. Cleary - School of Earth Sciences, University of Bristol, Bristol, UK (email:
  • Terri J. Cleary - Department of Earth Sciences, Natural History Museum, London
  • Benjamin C. Moon - School of Earth Sciences, University of Bristol, Bristol, UK (email:
  • Alexander M. Dunhill - School of Earth and Environment, University of Leeds, Leeds, UK (email:
  • Michael J. Benton - School of Earth Sciences, University of Bristol, Bristol, UK (email:

Publication History

  • Issue published online: 21 APR 2015
  • Article first published online: 6 MAR 2015
  • Manuscript Accepted: 9 FEB 2015
  • Manuscript Received: 4 NOV 2014

Funded By

Royal Commission for the Exhibition of 1851 research fellowship
NERC. Grant Number: NE/H525111/1

Online Version Hosted By

Wiley Online Library (Open Access)
Get Article: Wiley Online Library [Open Access]


Ichthyosaurs were highly successful marine reptiles with an abundant and well-studied fossil record. However, their occurrences through geological time and space are sporadic, and it is important to understand whether times of apparent species richness and rarity are real or the result of sampling bias. Here, we explore the skeletal completeness of 351 dated and identified ichthyosaur specimens, belonging to all 102 species, the first time that such a study has been carried out on vertebrates from the marine realm. No correlations were found between time series of different skeletal metrics and ichthyosaur diversity. There is a significant geographical variation in completeness, with the well-studied northern hemisphere producing fossils of much higher quality than the southern hemisphere. Medium-sized ichthyosaurs are significantly more complete than small or large taxa: the incompleteness of small specimens was expected, but it was a surprise that larger specimens were also relatively incomplete. Completeness varies greatly between facies, with fine-grained, siliciclastic sediments preserving the most complete specimens. These findings may explain why the ichthyosaur diversity record is low at times, corresponding to facies of poor preservation potential, such as in the Early Cretaceous. Unexpectedly, we find a strong negative correlation between skeletal completeness and sea level, meaning the most complete specimens occurred at times of global low sea level, and vice versa. Completeness metrics, however, do not replicate the sampling signal and have limited use as a global-scale sampling proxy.

PalAss Go! URL: | Twitter: Share on Twitter | Facebook: Share on Facebook | Google+: Share on Google+