In Genesis 1:21 the creation narrative names Taninim Gedolim”: Big reptile or lizard. Later in Exodus 4:3 Moses casts his staff on the ground and it becomes a “nahash” which is Hebrew for serpent or snake. Then, before Pharaoh it becomes a ”tannin” which is the singular case for ”taninim” above.
This sense of naming becomes surprising in God’s discussing kashrus in Leviticus 11:19 where He mentions the Hebrew word “Tinshemet” in referring to a bird, and a little later in v30 He uses to same word in referring to a reptile. It takes on special significance in the modern paleontological sense of referencing the relationship of the hip structure of birds to similar structures in the hips of Ornisthician dinosaurs such as the Stegosuars and Hadrosauridae of the Mesozoic era.
Why would God and The Bible have used these terms overall no less than for the latter two? These juxtapositions would form yet another of my ongoing arguments (Israel=struggle) with Him had He something else entirely in mind.