Is This a JRT?

by Cyndi Glass
(Indiana, USA)

I have just adopted this little guy from our local shelter. They said he is a Jack Russell, the vet called him a "terri-poo" (?), the lady I got him from thought he was part beagle (I disagree due to his delicate bone structure), and meanwhile everyone else I've shown him to says he's not a JRT at all but a rat terrier. I tend to agree with this, but now I have seen pictures of smooth-haired JRT's and don't know what to think.

I also think maybe a bit of Chihuahua due to the facial structure.

He is 13 lb and they said he is about a year old. He hardly ever barks unless a stranger approaches. He fetches. He howls if a baby cries on TV. He loves to burrow under the covers.