由于个体种化石的的数量统计随着时间的推移而变化，研究生物灭绝的古生物学家们更倾向于对称为类的有相互联系的整个物种种群进行统计研究。
Rather than counting individual species of fossils,which vary over time, palaeontologists who study extinction usually countentire groups of related species, called genera.
当时的人数甚至不及现在濒临灭绝的黑猩猩（21000头）和大猩猩（25000头）的有效种群大小（即能生育的个体数量）。
That number is smaller than current figures for the effective population size (or number of breeding individuals) for endangered species such as chimpanzees (21, 000) and gorillas (25, 000).
个体被发现的时间、地点已经建立模式用于预测种群生存和数量规模。
Patterns of when and where individual animals have been observed are used to estimate survival and population size.
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