this is different...

[Mugwump]

whoops...LOL...looks like Greg and I found the same site/link....cool

[LizStreithorst]

http://www.macroevolution.net/dog-fox-hybrids.html

Thanks for the article, Greg.  Very good.

[BillT]

There must be something that I don't understand or missed.  I was taught that members of the same species could always interbreed although the offspring was often sterile.

The general rule you are probably thinking of is that if organisms can breed and make fertile offspring, then they are members of the same species. It doesn't always work that way.
This is a disputed species definition (one of many) that any animals that can breed are in the same species and if they can't they are not in the same species.
This definition has its problems. For example a group of salamanders in hills around California's central valley. Each can breed with it neighbor in a loop going around the valley except in a place at each end of the loop where the two populations can't breed (successfully) with each other. The definition fails in this case since they can all breed with their neighbors and should be all in the same species except for the two that don't. Its a contradiction.
Another example is in hybridizing sunflower species. Many species can hybridize together and produce fertile offspring, but they can not breed with either of their parents. In a sense, this makes the hybrids a separate species. However, the two original species can breed and might be thought to be in the same species, but their offspring is not. Not making a lot of sense in this case.

The various dog-like species are considered to be in different species, not the same species. Some however put dogs and wolves in the same species (dogs being a sub-species), but some don't. Dogs and wolves can interbreed.

Here is a nice phylogeny (evolutionary tree) of how the various species are thought to be related:
https://en.wikipedia.org/wiki/Canidae (Its about a page down in this link.)
The whole group is a family. It has several sub-divisions down to genus and species.

Generally, the closer together on the tree two species are, the more likely they will be to successfully interbreed, but no guarantees.