When scientists discover new organisms, they classify the organisms according to their traits into the taxonomic tree of life. They place both living and extinct organisms into this tree, so all known species are classified together. As a result, scientists can see which living species resembles an extinct species the most and then can specify that living organism as the nearest living relative of the extinct organism. Based on information about the nearest living relative, scientists can make reasonable assumptions about the extinct organism's lifestyle. By enabling us to gain an understanding of the extinct species' favored habitat, this method allows us to obtain a reasonable estimate for the climate in the region and during the time in which the extinct species lived.

Luckily, studies using different types of organisms often provide overlapping information. Combining the data from various studies allows scientists to gain a better understanding of the past climate and provides a method of checking studies' results and of ensuring that the estimate for the climate is more accurate. Only using information about one species would make the climate estimate less likely to be correct because the organism used for the study could in fact have had different traits than its nearest living relative.

One reason that nearest living relative analysis is so useful for estimating the past climate is that temperature greatly affects the ability of an organism to survive in an area. Based on this fact, scientists can use fossil distributions to determine estimates for past temperatures in regions in which organisms' fossils are found. Click on the links below to learn more about this topic.