The phrase "a relatively large brain" is correct and usable in written English.
You can use it when discussing the size of a brain in comparison to others, often in a scientific or descriptive context.
Example: "In many species, having a relatively large brain is associated with higher cognitive abilities."
Alternatives: "a notably large brain" or "an unusually large brain".
It's also a relatively large brain, at least for a dinosaur, which hints that T. rex was fairly intelligent.
To feed on fish and shrimp, it has as many as 90 small tentacles — and, like all cephalopods, a relatively large brain and eyes.
The small size of human guts (combined with our having the same basal metabolic rate as any other primate, relative to body mass) means that we have some spare energy, which contributes to explaining how we can afford a relatively large brain.
It had a relatively large brain and long flat face.
It stood tall and had a relatively large brain and slender hips.
Little is known about H. rudolfensis except that it had a relatively large brain and large teeth compared to H. habilis and that it overlapped in time and space with other early Homo.
Because the results were inconclusive for males in that study, we here use a more ecologically relevant test of male cognitive ability to investigate whether or not a relatively larger brain increases cognitive ability also in males.
Because the anadromous males in our study were still immature we can not disentangle whether it is the maturation process per se or the need for coordinating the complex behaviours associated with sneaking tactic that leads to a relatively larger brain in ad lib fed early maturing males and a larger telencephalon in early maturing fish of both feeding groups.
Konrad Lorenz argued that infantile features serve as a Kindchenschema (infant schema) [2] with "innate releasing mechanisms" for affection and nurturing in adult humans and that most of these features are evident in the face including a relatively large head, predominance of the brain capsule, large and low lying eyes and bulging cheek region [3].
In recent years, sheep (Ovis aries) have emerged as a useful animal model for neurological research due to their relatively large brain and blood vessel size, their cortical architecture, and their docile temperament.
The relatively large brain of Psittacosaurus leads scientists to suspect it may have been a relatively smart dinosaur, with complex behaviours.
