from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. In the middle of the rostrum (beak)
from The Century Dictionary and Cyclopedia
- Pertaining to or situated upon the median line of the beak: specifically, referring to the beak or prolongation of the head of such a cetacean as a dolphin.
meso- + rostral (Wiktionary)
It’s clearly a rorqual skull, and the pointed, narrow rostrum and posterior widening of the mesorostral gutter indicates that it’s a minke whale skull.