Alopias subexigua is an extinct species of thresher shark, that lived in the Eocene to Miocene. It is known only from teeth. Alopias subexigua was discovered in North America, in California, Asia, Portugal, and Africa.
The classification of A. subexigua are in debate, also is the case of most sharks. A. subexigua is a related species to the extinct Small or Modest Thresher shark (Alopias exigua), that your fossils are very similar to genus Isurus. A. subexigua is placed in Alopiidae family.