ABSTRACT
Stratigraphic zones in the Tertiary generally represent lapses of time long enough to make the genus usable in correlation, although of course the use of species will give greater precision and an increasing emphasis on that taxonomic level is highly desirable. The Quaternary divisions of time are much shorter than the average in the Tertiary and far shorter than the length of life of most mammalian genera. This makes the species, and even in some cases the subspecies, the basic unit for correlation in the Quaternary and people has to concentrate on this category to a much greater extent than tradition has prescribed for the study of fossil mammals in general. The main difference between neontology and palaeontology is the introduction of the time dimension and the fact that species change in time. The species of neozoology are 'transient species', practically frozen into immobility by their restriction to a single plane in time.
