I think this is a section of a mouthplate from a ray, quite possibly a
cow-nosed ray.

Go to www.elasmo.com
Select Extant Dentitions
In the "select species" box, scroll down to Rhinoptera bonasus, at the
bottom of the list
That looks to me like what you have.

Also, from the elasmo.com home page, select Myliobatoid Teeth
Scroll through those pictures and you will find some similar things

Paul M.