It doesn't have to explain Typhlosion, just it's basic form, Cyndaquil.
Cyndaquil is based of the sechidna, am echidna is a rodent, Cyndaquil known as the fire rodent, the rat is a rodent.
soooooo.
1st gen. Charmander-Dragon
2nd gen. Cyndaquil- Rat
3rd gen. Torchic- Rooster
4th...