Is there any such thing as a gerbil rat?

It's so cold here that the wildlife is literally throwing itself against the windows to try to get inside. I was sitting down in the basement when I heard a thumping noise on the window. I pulled up the shade and right at eye level was some kind of creepy rodent trying to crawl up the screen. I immediately assumed he wanted to come in and eat my flesh and I might have screamed a little bit, but maybe he just wanted to get warm.

I thought it was a rat at first but as it stared me down through the window, I noticed its tail was covered with black fur. It was way too big to be a mouse and it looked more like one of the gerbils we used to have - the one that used to bite me all the time, little bastard. Anyhow, it was a gerbil the size of a rat. Does something like that exist in the wild? Is it some sort of genetically modified lab experiment escaped from the confines of its cruel cell and now on the lam? It probably is. It's probably going to be trying the doors and windows all day, looking for some weakness to exploit. I hope it doesn't get into my bed tonight and eat my face off.