|Ramón y Cajal’s drawing of the neurons in a bird’s cerebellum.|
Early 20th Century.
The Nobel Prize committee decided that Ramón y Cajal and [Camillo] Golgi should share the 1906 Nobel Prize for Medicine/Physiology, even though the two scientists held absolutely opposite views about how the nervous system worked. If one of them was right, the other one must certainly be wrong. - Santiago Ramón y Cajal
Small songbirds, which weigh as little as 4.5g, really do have small brains. Their brains can weigh as little as a third of a gram and only contain about 100 million neurons. But the heavier birds can have brains that weigh more than a dozen grams and pack in more than 2 billion neurons. On average, birds have twice as many neurons per unit mass as mammals do. So a bird called the goldcrest, which Wikipedia introduces as "a very small passerine bird," weighs a bit more than 10 percent of your average mouse but has more than double the neurons. - Bird brains are dense—with neurons by John Timmer - June 17, 2016Via Detroit Steve