Sometimes paleontologists want to compare commonness of two animals obtained from different levels at a fossil site, but often the time represented by each level is unknown. Having 20 sabertooth cats from one level and two from the other level is meaningless without knowing how long it took to deposit each level. After all, if it took 100 years to deposit the level with 20 and 10 years for the level with two, then the two levels were collecting sabertooths at the same rate. But if each took 100 years to deposit, the results are 20 per 100 years in the first level versus only two per 100 years in the second.
One way around this is to look at percentages of each in relation to
other animals preserved. If 100 of the cats make up 50% of the total number of animals
in level one and two make up 50% of the animals in level 2, then you can hypothesize
that sabertooths were equally common at the two sites, and that's better than a
wild guess any day!
Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.