ScienceDaily has an item on research into the control of consciousness by M Devor (here).

…discovery of an area of the brain that participates in the control of “alert status.”

Loss of response to painful stimuli and loss of consciousness are the most striking characteristics of surgical anesthesia and anesthesia-like states, such as concussion, reversible coma, and syncope (fainting). These states also exhibit behavioral suppression, loss of muscle tone, a shift to the sleep-like “delta-wave” EEG pattern, and depressed brain metabolism.

It has been widely presumed that this constellation of dramatic functional changes reflects widely distributed suppression of neuronal activity in the brain due to dispersed drug action, or to global oxygen or nutrient starvation.

However, new results revealed by the Hebrew University scientists suggest a radically different architecture — that a small group of neurons near the base of the brain, in the mesopontine tegmentum, has executive control over the alert status of the entire cerebrum and spinal cord, and can generate loss of pain sensation, postural collapse and loss of consciousness through specific neural circuitry.

…this knowledge could contribute to the ability of medical science to treat disorders of consciousness and its loss, such as insomnia, excessive sleepiness and even coma. …

the discovery of a specific cluster of neurons that control the brain’s state of consciousness can be expected to lead to the beginnings of an understanding of the actual wiring diagram that permits a biological machine, the brain, to be conscious.

This seems to imply that at least some aspects of consciousness are extremely ancient and at least shared with all vertibrates.