M. rex may refer to: Megalopanax rex, a flowering plant species endemic to Cuba Melanocharacidium rex, a species of South American darter Meriones rex, the king jird, a rodent species found in Saudi Arabia and Yemen Mormula rex, a species of sea snail Mylomys rex, the Ethiopian mylomys, a rodent species found only in Ethiopia Myodes rex, the Hokkaido red-backed vole, a rodent species found only in Japan M. Rex, a comic book series that inspired Generator Rex.
See also Rex (disambiguation)