Age-frequency profiles of micromammals and population dynamics of Proheteromys floridanus (Rodentia) from the early Miocene Thomas Farm site, Florida (U.S.A.)

Abstract

The rich early Miocene (Hemingfordian, ca.18 Ma) Thomas Farm microfauna provides an excellent opportunity to study the population dynamics of a fossil rodent population. A sample of 113 upper fourth premolars (P 4's) of Proheteromys floridanus (minimum number of individuals [ MNI]=63 ) was analysed for discrete age classes (cohorts) to compare the life statistics of modern and fossil heteromyids. Univariate and principal components analyses were inconclusive, but showed that wear characters are highly correlated and that interpretation of attritional vs. catastrophic accumulations using age-frequency profiles of micromammals may be misleading. Cluster analysis of age-dependent tooth wear characters indicates the presence of two distinct clusters interpreted as cohorts. The first cluster ( MNI = 59 ) are those individuals interpreted to have died in their first year; the second cluster ( MNI = 4 ) represents survivors into the next breeding season. First year survival rate is 6%. Estimated average longevity is 6.7 months; estimated maximum annual productivity is 8.5 young per female. Comparison with modern heteromyids indicates no difference in longevity, first year survivorship, or annual productivity between modern and fossil populations. This study demonstrates that population dynamics of small, brachyodont, short-lived micromammals can be estimated with sufficiently large samples.