Final answer:
In the somatosensory cortex of a newly discovered vertebrate, a larger area devoted to body part A indicates that it has more sensory neurons compared to body part B. This cortical representation is not based on the physical size, motor control, or evolutionary age of the body part, but rather the concentration of sensory neurons and tactile sensitivity.
Step-by-step explanation:
In reference to the question, 'In a newly discovered vertebrate, the somatosensory cortex devoted to body part A is larger than the area devoted to body part B,' it implies that body part A has more sensory neurons. The somatosensory cortex is an area of the brain which processes tactile and sensory information such as touch, temperature, and pain, and the size of the cortical area dedicated to a particular body part reflects the density of sensory neurons and sensory acuity in that area. This is evident from the concept of the sensory homunculus, which is a visual representation of the body's sensitivity mapped onto the somatosensory cortex. Parts of the body with higher tactile acuity, such as the fingers and face, are represented by larger regions in the somatosensory cortex, compared to areas like the back or legs which have a lesser degree of sensitivity and a smaller cortical representation.
It is also important to clear up a common misconception that a larger area of the cortex represents a physically larger body part. While it might be intuitive to think that bigger body parts have larger cortical areas, it's the concentration of sensory neurons that matters more for the cortical representation size, not the physical size of the body part itself. Additionally, the degree of motor control or the evolutionary age of the body part are not directly correlated to the size of the somatosensory cortical area; the sensory neuron density is the predominant factor influencing the size of cortical representation.