By Raymond C. Moore
Read Online or Download Treatise on Invertebrate Paleontology - Part O - Trilobitomorpha PDF
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Extra info for Treatise on Invertebrate Paleontology - Part O - Trilobitomorpha
Another important taphonomic effect is selective sorting by transport. In Chapter 1, we discussed the distortions introduced by transport in water and noted that more robust shells or bones tend to be the most often preserved, even if their original abundance in the population was much lower. But transport can work in surprising ways. In one study, a collection of clams from a beach in Trinidad showed a remarkable bias (Martin-Kaye, 1951). The shells on the northern beaches were almost all left valves (from 87% to 89%), those on the southern beaches were almost all right valves (87% at the southernmost sampling site), and those in the middle were about 50:50.
However, Callomon (1963) and Makowski (1963) argued that the smaller forms (“microconchs”) with the long lappets around the aperture are from males, and the larger shells (“macroconchs”) are from females. ) macroconch and has small horns or “lappets” that protrude from the opening. Which conch is male and which is female is still debated. Taphonomic Variability So far, we have discussed the variability of populations due to biological causes. However, the process of fossilization can add even more variability to the specimens that were not present when the organisms were alive and members of a natural population.
If you glance around the room, however, it should be obvious that there are also tremendous variations between individuals in the same population, as in the interbreeding population of Homo sapiens of which you are a part. This is population variation, and it can have enormous effects as well. Both types of variation occur within a single species, yet their effects can be so great that an unwary paleontologist might interpret the differences as representing different species. What is a population?