Anzu: Lion with wings (and cells)

Anzû (Sumerian: AN.IM.DUGUDMUŠEN), also known as dZû and Imdugud, is a lesser divinity or monster in several Mesopotamian religions. He was conceived by the pure waters of the Apsu and the wide Earth, or as son of Siris.[1] Anzû was depicted as a massive bird who can breathe fire and water, although Anzû is alternately depicted as a lion-headed eagle. Source

How could a monster like that exist? ?

I don’t know but I think they had cells, like we do;)