[Virginia-American]

...sometimes they keep on doing the same old thing just because it's not harmful to the product....

What was the marsupial prototype that needed an egg tooth? A monotreme? As in the ToE?

So why do mammalian jaw bones migrate to the ears? Wouldn't it be easier to leave the jaw alone and just improve the ear?

[muawiyah]

"Migrate to the ear"?

An engineer would obviously seek to have all the basic scaffolding work for bones done early on. You'll notice ALL the bones are laid out quite early, and then built up as the critter grows. Growth planned for the future takes place at the ends.

It's a process akin to that used to build up an oil painting or build a photo resist.

I'd suggest that the inner ear bones serve as an amplifier for the ear itself, and that function may well have been performed back when they made up 6 bones in the jaw ~

[muawiyah]

A thought for you ~ recent research reveals that mammals and marsupials both developed and lived in Australia. However, the marsupials appear to have been better adapted and outcompeted the mammals leaving Australia without mammals for tens of millions of years.

So, what happened to the wombs in the marsupials?