In biology and paleontology, species is everything. It’s a point of pride to have named a new species, just like I feel about naming Fractinus palmorem.
In your middle-school science class, you probably learned that a species is defined as organisms that can reproduce, yielding living and fertile offspring, and that do so naturally. This is the biological species concept. It works great, but for fossils, this idea doesn’t work so well. We can’t observe behavior or reproductive success in the fossil record.
Though we have this strict definition, for practical purposes we recognize different species because members of a species look similar to each other. With fossils, comparing overall ‘looks’ or morphology. Using this method, we can consider fossil species as morphological species.
One of the challenges that arises with the use of morphological species is that not all members of a single species do look alike. In some cases there is sexual dimorphism, meaning that males and females look very different. Without prior knowledge that the different looking animals are members of the same species, we can easily mistake males and females from one species as being two independent species.
Likewise, juveniles and adults can look very different and have, in more than one instance, been mistaken for different species. The Triceratops – Torosaurus controversy is on good example of this.
Furthermore, there is a lot of debate about how different is different enough. Some authors name lots of new species that have only subtle differences between them. Such authors are called splitters. Other authors name only a few new species, each having a broad range of morphology. These authors are lumpers. Most scientists lay in the middle somewhere between splitter and lumper, but in all cases new species have to be named and defined in the same way.
A great deal of scientific effort goes into naming new species and convincing other scientists that the new species is legitimate. To do this, a technical paper must be published that describes and defines the new species. This paper must include some important components.
The classification of the animal:
This uses the Linnaean classification scheme from Kingdom to genus and species.
A holotype (and maybe some paratypes):
The holotype is a single specimen that is most representative of the new species is selected. This is the standard to which everything that might also be that species should be compared.
Sometimes there are other really great specimens that should also be used for comparison. These are called paratypes.
The new species was given a name. This is where the origin of that name is explained. Was it named after someone or something? There’s not too many rules, except that a person may not name a new species after themselves. That’s tacky.
Here the new species is described. This includes measurments and comparisons to similar-looking species.
This is a list of characteristics that when all found together are unique to this new species.
This paper must be reviewed by other professionals in a similar area of study then published in a technical journal in order for the species to be considered valid. Species described in Master’s theses or Doctoral dissertations are not considered valid.
But then this thing happens. Sometimes a new species is named and is later found out to be the same thing as something that had be named before. So what do you do?
This is a matter of seniority. The species that was named first is the name that will apply to all members of the species. The species that was named later becomes a junior synonym.
When I was growing up, there was a fossil horse called Eohippus, the dawn horse. By the time I was in college, it have been discovered that what was called Eohippus had actually been named Hyracotherium sometime earlier, so we all got into the habit of calling it Hyracotherium. From then on, Eohippus was considered a junior synonym for Hyracotherium. More recently, like in the last few years, it was discovered that what we call Hyracotherium was named by an even earlier author as Sifrhippus. So now all the books have to be changed again and both Hyracotherium and Eohippus are junior synonyms for Sifrhippus.
When we name new species, we do so hoping that our new species does not later become a junior synonym, but it happens. As long as we’re clear in defining our species, we can work with it.