Fifty years ago, the Beach Boys released the milestone album Pet Sounds, a collection of groundbreaking songs that redefined what pop music could be. In the decades since, critics and fans have scrutinized and analyzed every aspect of the album’s 13 tracks.

But the recording’s genius was hardly represented by its incongruous sleeve art, which features only a snapshot of the band -- Mike Love, Al Jardine and the Wilson brothers (Brian, Carl and Dennis) -- standing in a San Diego petting zoo. Feeding goats.

It's Thursday, Feb. 10, 1966. The goats awake before dawn. The air is cool and still over San Diego, and the sky is cloudy. In Los Angeles, 150 miles to the north, the Beach Boys arise and prepare for a journey. For on this day, the greatest band in America will meet seven goats in a petting zoo. It’s everything. It’s nothing. It’s a moment in history.

“I don't remember who thought of going to the zoo,” says Brian Wilson, “but when we got there we got some apples and we cut 'em in little pieces and we fed 'em to the goats, and they took a few pictures, and we decided to put that as our cover for Pet Sounds. We all looked so good, you know, we were so young and happy and smilin' and great, you know?"

He’s right. Take a look at that cover. In February 1966, they were still young and happy and smilin' and great. We know what happened to the Beach Boys. But what happened to those goats?

“Who would know?” Wilson asks me. “Peter, who would know?”

Somebody knows. But before we get there, let’s stay with that Thursday in 1966.

“I remember I drove my new yellow XKE convertible down to the shoot,” front man Mike Love recalls. “Driving down Highway 1, 'cause you take the coast route if you know what you’re doing, you don't go down the 5, you take the beach route, right? So we cruised by Trestle's and Swami's and all the good places and went to the zoo.”

But for guitarist and singer Al Jardine, that day in the petting zoo still holds dark memories. Specifically of a large white goat that Jardine will be forever feeding on the album’s cover.

“I hated that sucker, it kept getting in my face,” he says. “And they took us all the way to the San Diego Zoo, not the L.A. Zoo. To this day I can’t even believe it. At that time, we were just young and naive, and if that's what they want us to do, we'll do it. And of course when they heard the title Pet Sounds they thought we had to go to a zoo and take a picture with a bunch of animals. But I guess they may not have heard the material to realize we were really referring to Brian's two dogs, Louie and Banana.”

The sounds of the pets close the final cut on the album, “Caroline No,” serenading the roar of a passing train.

“We put my dogs Banana and Louie -- my beagle and my Weimaraner -- we put them barking right at the end,” confirms Wilson. “And a few minutes later, Mike goes, 'Why don't we call this album Pet Sounds?' you know, because of the dogs."

“Mike made a joke,” Al Jardine says. “ ‘Brian, you're making music that only dogs can hear,’ which at the time was meant to be funny because of the amazing harmonies and ideas Brian was coming up with. That was Mike's way of saying, ‘I don't understand it, but the dogs do.’ ”

So that was it. People loved the name. Not everybody loved the cover.

“McCartney literally said, 'Mike, I think you really ought to take more care with your album covers,' because what was Pet Sounds? It was a big white goat’s butt on it taken at the San Diego Petting Zoo,” offers Love. “I don't think we were as fixated or focused on the covers as we could have been. We were focused on the music.”

The core of that focus was songwriter Brian, who said at the time he wanted to create “the greatest rock album ever made.” By many accounts he did, thanks perhaps to a somewhat cosmic connection. The goat is one of the 12 zodiac animals, and it represents introversion, creativity, shyness and being a perfectionist.

“Really?!” asks Wilson when confronted with this news. Does it sound like him?

“Well, perfectionist. The other parts didn't. My dad taught me how to be a perfectionist. He said, 'When you mow the lawn, mow it twice!' So that stuck in my mind when I did Pet Sounds. I said to myself, I'm going to mow the lawn twice with this album.”

He did. And though over the years the quality of the Pet Sounds cover has been questioned against the transcendent music inside, the composer has no such issue.

“The cover was beautiful, it was beautiful,” Wilson says. “Can’t explain the mood, we were all just young kids feeding goats apples, ya know?"

Which brings us back to the fate of the goats. San Diego Zoo public relations representative Christine Simmons provided the answer in a brief note: “Thank you for your inquiry. I regret that the goats in the photo have all passed away, and, as this is not a breeding group, they did not produce offspring.”

So, while there may still be Hemingway cats, there are no Pet Sounds goats. These simple cloven beasts -- petted by countless tiny hands of 1960s children -- lived out their years and died. But they are not forgotten. As the humble goat once stood by at the birth of Jesus himself, these goats will be forever linked to the birth of Brian Wilson and the Beach Boys’ masterpiece.