One species of dolphin, specifically the long-finned pilot whale: https://en.wikipedia.org/wiki/Long-finned_pilot_whale#Physiology https://en.wikipedia.org/wiki

One species of dolphin, specifically the long-finned pilot whale: https://en.wikipedia.org/wiki/Long-finned_pilot_whale#Physiology https://en.wikipedia.org/wiki/Long-finned_pilot_whale#Physio... It adds a wrinkle, but appears to be larger due to brain volume rather than density: However, as neuron density in long-finned pilot whales is lower than that in humans, their higher cell number appears to be due to their larger brain. .... Our results underscore that correlations between cognitive performance and absolute neocortical neuron numbers across animal orders or classes are of limited value - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4244864/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4244864/ Which I take to mean we shouldn't rely on one indicator to explain the emergence of consciousness. It used to be thought that brain size dictated intelligence. Corvid tool is one challenge to that assumption. We shouldn't replace brain size with neuron size. It looks like evolution fleshed out multiple paths to achieving certain reasoning behaviors.