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Statistical methods for paleodemography on fossil assemblages having small numbers of specimens: an investigation of dinosaur survival rates

Published online by Cambridge University Press:  08 April 2016

David Steinsaltz  and
Steven Hecht Orzack
David Steinsaltz
Affiliation:
Department of Statistics, Oxford University, One South Parks Road, Oxford, England OX1 3TG
Steven Hecht Orzack*
Affiliation:
Fresh Pond Research Institute, Cambridge, Massachusetts 02140. E-mail: orzack@freshpond.org
*
∗Corresponding author
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Abstract

We describe statistical methods to formulate and validate statements about survival rates given a small number of individuals. These methods allow one to estimate the age-specific survival rate and assess its uncertainty, to assess whether the survival rates during some age range differ from the survival rates during another age range, and to assess whether the survivorship curve has a particular shape. We illustrate these methods by applying them to a sample of 22 Albertosaurus sarcophagus individuals. We show that this sample is too small to provide any confidence in the claim that this species had a “convex” survivorship curve arising from age-specific survival rates that decreased monotonically with age. However, we show that a sample of 50 to 100 individuals has reasonable statistical power to support such a claim. There is evidence for the much weaker claim that average survival rates for ages 2 to 15 were higher than survival rates for later ages. Finally, we describe one way to account for size-dependent fossilization rates and show that a plausible positively-size-dependent fossilization rate results in a substantially non-convex survivorship curve for A. sarcophagus.

Type
Articles
Information
Paleobiology , Volume 37 , Issue 1 , Winter 2011 , pp. 113 - 125
Copyright
Copyright © The Paleontological Society 

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