LIOW, Lee Hsiang; University of Chicago: Lineage longevity: Luck and a Little Flexibility Go a Long Way

Some lineages are more persistent through geologic time than their relatives, so much so they are sometimes called �living fossils� and conjure up images of freaks of nature. Are persistent taxa really distinct ecologically or morphologically from their less persistent relatives? Using a database of well-fossilized and well-documented microfossils, the trachyleberidid ostracodes, I ask if longer-ranging genera and species are distinct in their morphology from shorter-ranging ones. I also ask if longer-ranging species and genera are ecologically more versatile, as measured here by depth distribution, than shorter-ranging ones. I show that longer-ranging genera cannot be distinguished from shorter-ranging genera with respect to their morphological distance from the mean of the family. However, there is evidence that species that are morphologically more variable at the population level tend to persist for longer intervals in the fossil record. The number of depth zones that a species occupies is positively correlated with its longevity, but not significantly so. The duration distribution of genera that are both shallowly and deeply distributed is significantly different from those that are bathymetrically more restricted. However, the mean number of depth zones occupied by the species constituting a genus, shows no relationship to its longevity I conclude that persistent trachyleberidid taxa are in general not much different from their relatives in terms of morphological distance from the family mean or ecological versatility, as measured by the number of depth zones they occupy. However, some ecological flexibility and morphological variability, combined with what can be termed luck, could contribute to prolonged persistence through time.