Unknown Mammal? Teeth

In early 2009 I found a really odd looking tooth along the Maryland side of the Potomac River.  At first I thought it was a "modern" tooth from some sort of mammal that died along the river, but it passed the fossil test "sound" when I tapped it against my rake.  I didn't think much of it at the time and still wasn't 100% sure it was a fossil, but I kept it anyway.  I showed it to one of the geologists/paleontologists that attends one of my club meetings, and he thought it was a significant "fossil find" and that it could belong to some sort of land mammal.  He said to forward him some pics of it and he would forward them on to a colleague for further ID.  Well, after I took the tooth home, I was so excited that I might have something important, that I wrapped it up carefully, before taking any pics however, and put it away amidst the rest of my collection, which was in boxes, shoe boxes, etc.  Bottom line, I knew I had it, but couldn't find it...until recently.  A trip back to the same spot along the Potomac earlier this Spring yielded another such "weird" looking tooth.  However, this second odd tooth looked a lot like a porpoise tooth of some sort.  I recognized the coloring and worn occlusal surface of the tip and thought it might be similar to the first odd tooth I found last year.  Sure enough, it superficially resembles the other tooth in size, and enamel style, and also has a worn crown/occlusal surface.  So, now I have two of these teeth and am planning on submitting the pics to this paleontologist for further ID help.  I'll post back later if I get any ID info.  If anyone else has an idea as to what these teeth might have belonged to, let me know.

The pics are in their original "large" file size, so give them about 20 seconds to load.