A few months ago I wrote a post about ‘What Makes a Species‘. However, I only talked about the biological species concept which states that a species must be able to interbreed and produce viable offspring. Like I mentioned before, nature doesn’t like to follow the rules that we establish for it.
As genetic techniques have improved in the last few decades, they have been used more and more to identify new species. Genetic species share a common gene pool and are more genetically similar to each other than to anything else. For example, traditionally there were two species of elephants: African elephants (Loxodonta africana) and Asian elephants (Elephas maximus). Recent genetic evidence suggests that African bush elephants (L. africana) and African forest elephants (L. cyclotis) are separate species. To many, genetic species identification is the gold standard. Unfortunately, that’s not always possible.
Paleontologists have to deal with a unique set of problems when it comes to species. How can you identify species when you have never seen these creatures and have few clues as to how they behaved? The primary method is morphology, or what the organism looked like. Paleontologists assume that organisms that are more closely related will look more similar than organisms that are more distantly related. Unfortunately, fossil remains are typically restricted to bones, while soft tissues such as cartilage, fur and feathers generally don’t preserve (with some impressive exceptions). However, morphology can be misleading. Just think about those elephants; even though African bush and forest elephants look the same, they are genetically different. Regardless, scientists often use comparative collections of modern species to identify fossil specimens.
So what happens after paleontologists compare fossils to modern specimens? Depending on the age of the fossil, things could get complicated. More recent specimens may have modern relatives that are similar in appearance, which makes comparison easier. But what about more ancient fossils without obvious modern relatives? Historically, fossils have been dramatically misinterpreted. When the Greeks found the fossils of ancestral elephants, they thought the bones were the remains of the giant cyclops. Victorian scientists studying dinosaurs drastically misunderstood the creatures’ morphology. It takes time, experience and quality comparative collections to identify a taxon’s place in the taxonomic hierarchy.
Finally, how long can a single species exist? After millions of years, can taxa be considered the same species even if they look the same? Dr. Benjamin Burger presented on the topic of mammal species durations in the fossil record at the GSA 125th Annual Meeting. According to his talk, the insectivore Centetodon magnus survived for about 25 million years, while the proboscidean Gomphotherium angustidens persisted for about 23 million years. Often, scientists will name new species or genera because it seems unlikely that a single species could persist that long. However, that is a problem for another day.
The moral of the story is that taxonomic methods are human constructs. We are the ones who decided to classify all life on Earth. The more we learn, the more obvious it becomes that our current methods are frequently insufficient. Don’t let that discourage you! That’s the beauty of science; the more you learn, the more there is to learn.
To learn more about even more species concepts, check out this list.