USE OF ARCHAEOLOGICAL SERIATION CURVES IN PALEONTOLOGY

Paleontologists have traditionally used spindle diagrams to show changes in number of taxa within groups (genera, families, phyla, etc.) over time or through intervals of rock. These diagrams plot numbers of taxa by means of bar length (e.g., 5 mm = 1 taxon; 5 taxa = 25 mm). Numbers of taxa may be real, estimated, or, in some cases, hypothetical.

Such trends can also be shown in a quantitative manner using archaeological seriation curves, a methodology commonly used by archaeologists and anthropologists to depict change over time (time series). Archaeologists have used the technique for depicting changes in pottery over time and such graphs have also been used by anthropologists and geologists to show changes in stone used for gravestones and other cultural items over time. In this method bar length is determined by proportions of items (relative percentages) per time interval, not by raw numbers of items. Gravestones are dated and so it is straight forward to plot stone type used for gravestones versus intervals of years. The gravestone usage is easily adapted to paleontological use.

Graphs obtained using spindle diagrams and those using archaeological seriation curves are strikingly different, and both have their advantages and disadvantages. Seriation curves have the advantage of eliminating the large expansion of taxa bar-lengths seen on spindle diagrams that include both prehistoric and extant taxa.