The hybrid issue sparked up some interest in taxonomic definitions. I have found that many people disagree on the definition of what should define a species. Here are some different examples:
1. species - a distinct describable type.
2. species- distinct types that can not interbreed.
3. species- distinct types that can breed and produce offspring that themselves could go on as adults to breed.
4. species - A group that, in natural surroundings, breeds exclusively within the group.
Number 1 doesn't work because it is too broad and even individuals could be considered distinct species.
Number 2 doesn't work because of the hybrid definition. Like Lester said when platyrhinos and coronatum reproduce they produce sterile offspring incapable of carrying on the existence of the species therefore they are distinct species.
Number 3 works.
Number 4 doesn't work. I would think when defining a species the rule would have to apply to all organisms. How could you apply a rule to one group but not another. For instance if you apply number 4 to humans that would mean native American Indians would be of a different species than Native Spaniards because of natural bodies of water. The people of Mexico would than be hybrids incapable of reproducing which is not the case.
Hybrid- crosses between species that can produce offspring but they grow up to be sterile adults. (such as horses and donkeys producing mules)
Intergrade- crosses between sub species that can produce offspring that grow up to be fertile adults.
sub species- A population restricted to a geographical area that differs from others of the same species, but not to the extent of being classified as a separate species.
forms or pattern classes- sub species populations within a geographic area distinguished by some common characteristic or quality.
Following these definitions and the work of Baur p. coronatum would actually be a subspecies p. cornutum coronatum and the current sub species would be forms or pattern classes.
