Why bigger is not better in the long run: investigating mammal lineage
survivorship using Neogene mammals of Eurasia

Lee Hsiang Liow1, Mikael Fortelius2, Ella Bingham3, Kari Lintulaakso2,
Heikki Mannila3,4, Larry Flynn5, Nils Chr. Stenseth1

1 Center for Ecological & Evolutionary Synthesis, Department of Biology,
University of Oslo, Oslo, Norway, 
2 Department of Geology, University of
Helsinki, Helsinki, Finland, 
3 HIIT, Department of Computer Science, University of Helsinki, Helsinki, 
Finland, 
4 HIIT, Department of Computer and Information Science, Helsinki University 
of Technology, Helsinki,Finland 
5 Peabody Museum, Harvard University, Cambridge, MA, USA.

It is commonly postulated that body size is an overarching factor
intimately linked with many other biological traits such as fecundity,
geographic range and metabolic rates. However, does body size matter for
lineage longevity or survivorship and why should it matter?  We use a
densely sampled Neogene Old Word mammal dataset (NOW) to investigate these
questions. Using multiple approaches to correct for sampling biases, we
calculated longevity, survivorship and turnover rates for mammals grouped
into two body size classes.  Large mammal genera and species have shorter
durations than small mammal genera and species as a result of higher rates
of both origination and extinction.  This result is robust to treatments of
the data using approaches with vastly different assumptions.  We also
discuss preliminary results from testing a related hypothesis, namely, that
it is not body size per se that influences survivorship, but the ability to
hide from adverse conditions. This ability seems more common among smaller
mammals.