To dream of a brachiosaurus represents a fear that a person or situation is making you insignificant. Fearing yourself being too unimportant. Feeling stupid that someone doesn't need you at all. Feeling impotent to make yourself relevant. Unbearable feelings of a positive situation that you don't like witnessing.
Negatively, a brachiosaurus may reflect your jealousy of not having to be needed by someone or not being unable to control someone who doesn't need to be controlled anymore. A sign that you are having control issues, issues with letting go, or in adjusting to role changes. It may also reflect a fear that someone will get ahead of you or have more power than you and become impossible to stop.
*Please See Dinosaur