A SPECIES ACCUMULATION CURVE FOR TRILOBITA

Tabulation of the date of publication of 20,928 trilobite species currently considered valid results in a time series depicting trilobite species accumulation from 1781 to the present. Due to edge effects in tabulating the very recent literature, analysis was based on all publications prior to the end of 2005. A second tabulation documented 5,958 scientific publications whose primary subject was trilobites (or which contained a section primarily concerned with trilobites).

The species accumulation curve begins a slow, nearly rate-constant increase around 1838. Rate of species description increased only slightly from then through 1933, with an average of 42 new species a year added during this interval. In 1934, the species accumulation rate began a sustained acceleration, disrupted somewhat by World War Two, with maximum rates of increase seen in the 1970s and 1980s. The curve begins to level off with a clear inflection point after 1983, and species accumulation in recent years (through 2005) reflects a gradually slowing trend (the first period of slowing growth in the systematic history of the group) with the present rate similar to that seen in the 1940s. The curve clearly suggests an asymptote is being approached. One obvious potential explanation for this pattern is the possibility that the pool of easily accessible new trilobite species in the world is approaching saturation.

Comparison with the trilobite publication curve, however, suggests a second explanation. The publication accumulation curve agrees well with the species accumulation curve through 1983. After that, the marked rate decline in the species curve is not reflected in the publication curve: trilobite publications have been added at a reasonably steady rate of just under 90 per year since the late 1960s. This suggests that changes in the discipline of paleontology, including shifts away from fundamental systematic research beginning in the 1980s, could be at least partly responsible for the slowing rate of species accumulation. This shift in focus could be due to the declining availability of new species, or possibly to diminishing professional rewards and decreased funding sources for systematic research.