10 fast-food menu items you didn't know were more than 50 years old

The first McDonald's restaurant, a small barbecue joint owned by Richard and Maurice McDonald, opened on May 15, 1940, in San Bernardino, California.

According to a photo of an early menu, the restaurant sold its "famous" barbecued beef, ham, or pork, as well as simple hamburgers.

In 1948, the McDonald brothers switched the concept, turning their barbecue restaurant into a burger restaurant and adding its now iconic items like hamburgers and cheeseburgers to the menu.

In 1955, Ray Kroc opened the first McDonald's franchise location. Kroc would go on to build McDonald's into the global chain we know now.

Smithsonian Magazine reported that the Filet-o-Fish was created by Lou Groen, a McDonald's franchise owner in Cincinnati, in 1962 after he realized hamburger sales were declining on Fridays during Lent.

To increase sales at his restaurant, he decided to start selling a fish sandwich topped with tartar sauce.

The sandwich was such a hit that three years later, it was made available nationwide and has remained on McDonald's menus ever since.

The Big Mac is arguably McDonald's most famous burger, but it wasn't added to menus until over a decade after franchises opened.

The burger's ingredients then remain largely the same as they do now: a double-stacked bun, two beef patties, shredded lettuce, pickles, and a Thousand-island-style sauce.

However, McDonald's recently tweaked its most iconic burger to have a softer bun, meltier cheese, and more sauce.

According to Encylopedia.com, the Whopper originally cost just 37 cents, compared to Burger King's original burger, which cost 18 cents.

Although the Whopper now costs around $7, prices vary by location. It still comes with sauce, cheese, lettuce, pickles, and tomato piled on top of a larger patty.

According to the chain, Chick-fil-A founder Samuel Truett Cathy tried hundreds of recipes for the original chicken sandwich before finalizing his famous recipe, which featured a fried chicken fillet with two pickles on a toasted butter bun.

Despite Chick-fil-A's significant growth over the years — the company generated $21.6 billion in sales last year — the chicken sandwich has largely stayed unchanged.

In-N-Out started selling the first "animal-style" burgers after customers began requesting extra spread and grilled onions on their burgers. The "secret" recipe is still the same as it was in the 1960s.

The burgers are made with a mustard-cooked beef patty, lettuce, tomato, pickles, extra spread, and grilled onions.

The Double-Double, In-N-Out's version of a double cheeseburger, is now one of the most popular menu items.

It's also available in a variety of different styles, from "protein-style" sandwiched between two lettuce-leaf "buns" to animal-style.

White Castle is often regarded as the first fast-food hamburger chain in America.

Founded in 1921 by Billy Ingram as a family-owned business, the fast-food establishment originally sold 5-cent, small, square hamburgers "by the sack," according to the chain. They would come to be known as "sliders."

In 1962, White Castle began selling cheeseburgers.

According to a vintage photo of the first Taco Bell menu, pictured above, each item cost just 19 cents, and the menu featured traditional Mexican favorites like frijoles, tostadas, burritos, and tacos.

Quite a few of Taco Bell's original menu items, including tacos and burritos, remain on the menu in some form, though the ingredients have likely changed from classic versions to more creative menu items like the Doritos Locos taco or grilled-cheese burrito.