If the Ford Mustang had never happened, what would've been the It car of the 1960s?

Cars like the Camaro and Challenger were a response to the Mustang, so I kinda wonder.

Camaros and Firebirds would have never happened - no need. Likely would have been a string of boxy, practical cars through most of the 60s.

Chevy Corvette Stingray - but neither of them held a candle to the AC Cobra

I'm guessing the Pontiac GTO. It first came out in 1964, the same year as the Mustang ( well technically the Mustang was a 1964.5 model year release ).

Although debatable, many will say the GTO was the first muscle car which ignited the muscle car era.

Corvette and Thunderbird, both of which were "it" cars before the Mustang was introduced.

The Ford Mustang, the original "Pony" car, was not the first Pony Car -- the Plymouth Barracuda was.

1964 Shelby Cobra.

Most likely the Europeans or the Japanese would have taken care of it.
The Jaguar XKE could outrun both the Mustang and the Camaro in handling and braking anyway.

Actually, the Plymouth Barracuda was the first "pony car" of the 1960's, introduced on April 1st, 1964. The Mustang showed up 16 days later, on April 17th.