35: Apatosaurus
I write to you from Arapahoe, Ute, and Cheyenne land. I am interested in learning about the different animals that live in the place where I was born. I want to mention that biological classification as taught by western science has its roots in racism, sexism, and transphobia – here’s a good explainer about why.
Ok I lied. This is not “tomorrow” from the last newsletter and we are also not going to discuss our state mammal until TOMORROW. Instead today we’ll talk about an extinct animal that used to live in this place we call Colorado, 152 million years ago in the Late Jurassic: Apatosaurus (A. ajax and A. louisae).
152 million years is not really that long ago. It seems like the universe is 13.77 billion years old, so almost everything in the past had already happened by the Late Jurassic. The Ancestral Rocky Mountains had risen to great heights between 320 and 270 million years ago, but had been eroding for many more millions of years since and the Late Jurassic saw their remains covered by a profusion of lakes, rivers, and marshes. The verdant landscape supported some of the most massive animals to have ever existed: sauropods, including Apatosaurus.
Apatosaurus was around 20-35 tons of quadruped, with a generally robust bone structure and hollow vertebrae that allowed the animal to keep its head up and its tail extended like a whip. It had a small head relative to its body and would have foraged on a variety of plant matter, perhaps along riverbanks eating submerged plants. It also had a single claw on each of its forelimbs which may have been used to grasp tree trunks when it reared up.
Here’s my dog Nori and myself beside a model of an Apatosaurus shoulder blade.

I bring up Apatosaurus because this past weekend I hiked with a friend and the two best dogs to see the largest dinosaur trackway in North America, located in Picketwire Canyon in southeastern Colorado. This Late Jurassic Period trackway has preserved the footprints of Apatosaurus and Allosaurus, among others.
Here’s Yofi drinking out of an Apatosaurus footprint:

The trackway is truly massive; none of my photos convey just how big it is. Tracks of many individual dinosaurs sunk deep into the now-fossilized mud reveal a palimpsest of activity: herds of the massive sauropods moving together, raising their young, while the more solitary Allosaurus predators moved on their own, circling, hunting.
Here’s some dog paws in comparison to an Allosaurus paw:

One of the things people learned about Apatosaurus from this trackway and others is that, as Dr. Alan Grant says in Jurassic Park (1993), “They do move in herds.” This was a relatively novel concept in the late 1980s/early 1990s, and little Jamie made an illustrated book about Apatosaurus herds raising their babies after reading a National Geographic article on the topic of dinosaur eggs sometime in the mid-1990s. It’s amazing to think how much our understanding of dinosaurs has changed in a relatively short time – from lumbering lizards to proto-birds. At least to me, the theropods like Tyrannosaurus Rex have become much more relatable because of the comparison to modern birds, but sauropods like Apatosaurus remain more mysterious because they are so very extinct. What did one of the largest land animals to ever exist think about? Were they smart, like elephants? How much did they teach their young? What did they smell like?
After the Late Jurassic, millions more years passed, and the thick layers of sandstone and mudstone that herds of Apatosaurus walked over solidified into stone. Then the earth buckled and shook, and the new Rocky Mountains arose in the Laramide Orogeny, and a lot of the now ancient lake and river beds got shoved up like crooked teeth lining the vast jawlines of the eastern and western borders of the Rockies. In 1877, near Morrison, Colorado, a British clergyman and professor, Arthur Lakes, excavated the fossilized remains of Apatosaurus in those uplifted, fossilized river beds – the Morrison Formation. He also discovered Stegosaurus, Camptosaurus, and Allosaurus, all Apatosaurus contemporaries in the Late Jurassic, and Tyrannosaurus Rex, who lived in the Late Cretaceous, closer in time to us today than she did to Apatosaurus.
Time is a funny thing.
By the way, there was some controversy about whether or not Brontosaurus was actually just another Apatosaurus, but a 2015 study has restored the “thunder lizard” to its rightful place as another species. Maybe some day there will be justice for Pluto too.