I am familiar with the human Ventricular system that circulates Cerebrospinal fluid. This is needed among other reasons, to suspend the heavy human brain, and for injury protection. Do all mammals have a need a Ventricular system?
Maybe some did not have as strong of an evolutionary need for cerebrospinal fluid?
Do all animals...as in your title ordo all mammals...as in your post. Note that after askingdo all mammals...in your post you are askingFor example don't woodpeckers..., while woodpeckers are obviously not mammals. Note that many animals don't have a circulatory system nor a brain (such as jellyfish for example) and so the answer to the question in the title isno. – Remi.b Sep 14 '15 at 00:23