The giant mammal bones on display at New York City's American Museum of Natural History are impressive approximations of creatures that once walked the earth (and in some cases, those that still do). But equally if not more amazing? How those displays were actually assembled.

We recently ran across a collection of rare, archival photos from the museum's archive—dating all the way back to the early 1900s—and they give us a glimpse of a gruesome but fascinating world. What's more, while these images might date back many moons, most of the techniques used to prepare displays at the Museum haven't changed much.

A museum worker assembles a mastodon for display, using wire and supports, below. The year is unknown.

This 1934 photo of a graceful elephant-shaped frame shows the first step in mounting an elephant's hide.

Speaking of elephants, here's a female elephant getting her head attached in 1926.

This is a brontosaurus—or part of one. This image shows the front limbs being modeled in 1904.

Here we see museum staff moving a brontosaurus skeleton (though it's unclear whether it's the same brontosaurus) in 1938.

But what's a brontosaurus without its skull? Below, workers move the dino's heavy head.

Below, a clay model of a hippo from 1909. More than 100 years later, the process hasn't changed.

This is the framework used for a model of a Sulphur Bottom Whale, in 1906.

And in 1916, workers mount a duck-billed dinosaur.

In 1927, the AMNH restored the jaw of this fossil Shark.

All photos via the American Museum of Natural History (©AMNH)