Genesis 1:24

And God said, Let the earth bring forth the living creature after his kind, cattle, and creeping thing, and beast of the earth after his kind: and it was so.

1. God issued a command that cattle, creeping things and other land-dwelling beasts be introduced upon the earth.
2. These creatures were to reproduce after their own kind - that is, cattle would reproduce cattle, etc.
3. God's commandment was obeyed. How it occurred is not explained.