AcknowledgementsG.E.B. acknowledges support from the Swedish Scientific Research Council (VR), and
S.J. acknowledges support from the National Science Foundation (grant EAR-0074021 to
M.L.Droser). We would like to thank Mary L.Droser, James G. Gehling, Philip
Donoghue, and Mats Björklund for valuable discussion, and Andrew B.Smith and an
anonymous reviewer for constructive and thoughtful criticisms that considerably
improved the manuscript.
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