Research : Big Brains Not Really Proportional to Animal Size

https://scitechdaily.com/brain-size-myth-debunked-with-new-evolutionary-insights/
Researchers have found that brain size does not increase
proportionally with body size in larger animals,
challenging longstanding beliefs.
The study, which analyzed data from 1,500 species, shows
a non-linear relationship and highlights rapid evolutionary
changes in brain size among primates, rodents, and carnivores.
. . .
   Well, just because muscles get larger does not mean
   you need more brain to control them. A mouse brain
   should be able to run a musk ox. Only more finely-
   detailed control - say an elephant trunk - should
   require more brain.
   Brains TEND to get larger in proportion to physical
   size, but clearly don't NEED to by and large. This
   research debunks the size/brain assumption.
   This research also SUGGESTS that sheer brain size
   may only be coincidentally related to higher IQ.
   "Lucy" may have been as smart as modern humans,
   just "used it better". The intelligence of beasties
   like parrots and covids suggests you can get a LOT
   of IQ from a quite small volume of brain.