As Hungry as a Sauropod: The Morrison’s Giant Conundrum

The presence of one fifteen-meter sauropod species would be difficult for any environment to accommodate.

How about twelve?

The Morrison Formation of North America is a dinosaur goldmine. Stretching from Montana to New Mexico, the Morrison is one of the most productive fossil sites known to science. Since the 1870’s, paleontologists have discovered thousands of specimens that date to the Late Jurassic period, some 150 million years ago. Many famous dinosaurs hail from the Morrison, including Stegosaurus, Allosaurus and Ceratosaurus. Yet the most common dinosaurs found at Morrison (and by far the largest) were the sauropods.

At least twelve different species of sauropod called the Morrison Formation home, making it the most diverse collection of sauropods known to science. Some of these sauropods are household names, including Brontosaurus (yes, it’s still a dinosaur,) Diplodocus and Brachiosaurus. Other species that you may have heard of include Apatosaurus, Camarasaurus and Barosaurus. More obscure species include Haplocanthosaurus, Suuwassea and Supersaurus, dinosaurs that are typically known from either a handful of specimens or have been discovered recently. The smallest of the Morrison sauropods would have been similar in weight to an African Elephant (five tonnes,) while the largest weighed over 35 tonnes. With such an abundance of giant sauropods, how did they manage to survive alongside each other?

The first thing to note is that not all the sauropods lived at the same time and place. The Morrison is a giant area of land and encompasses over 10 million years of time. Some sauropods, like Brachiosaurus, are only found in certain cites that span a very small amount of time (about two million years for Brachiosaurus). Other species can be found throughout the Morrison and Camarasaurus even lived for the duration of the Morrison’s 10 million years. With such a wide distribution, did any of the sauropods live together?

The answer is yes. At various sites, different sauropod species have been found together. Some are so closely linked, including those at Colorado’s Dinosaur National Monument, that the bones of different sauropods are found intermingled with each other. Up to five different sauropod species can be found at any given site, making the Morrison a crowded place for long-necked dinosaurs. Take for example Dinosaur National Monument, where four species – Apatosaurus, Barosaurus, Camarasaurus and Diplodocus – all lived together. On top of this, other herbivores like Stegosaurus, the Iguanodontid Camptosaurus, and the smaller Dryosaurus lived next to the sauropods as well.

So how did they manage? The first thing to consider is the plants of the Morrison. The Morrison’s landscape consisted of large savannas interspersed with Conifer forests, meaning there was plenty of vegetation to go around. Having said this, a high volume of plants doesn’t necessarily explain how so many massive sauropods could coexist with one another. After all, the African Savanna has plenty of vegetation yet only supports one herbivore that weighs more than three tonnes. To solve the mystery, we must look deeper into what the dinosaurs were eating.  

Instead of the amount, it was the diversity of plants that truly fostered the growth of the sauropods. With a broad diversity of plant species, including conifers, cycads, ferns, shrubs, and other extinct plants, sauropods could evolve to eat different foods. For example, the infamously vertical neck of Brachiosaurus allowed it feast on tree-tops, giving it access to food that no other sauropod could reach. Analysis on the peg-like teeth of Diplodocus have revealed that it was best suited for stripping leaves off branches, while the bulky skull and teeth of Camarasaurus could munch through harder materials like branches and tree bark. By adapting to live with each other without competing for resources – a term known as “niche partitioning” – the sauropods were able to thrive.

It wouldn’t have been easy for these sauropods to become so specialized. Adaptations like Brachiosaurus’ vertical neck and elongated forelimbs would have taken millions of years to develop. The niche partitioning of the Morrison sauropods highlights the adaptability of the dinosaurs, which allowed them to exploit even the most competitive environments. Life in the Jurassic certainly would have been difficult, but by learning to live together, the sauropods made it just a bit easier.

References:

I do not take credit for any images that are found in this article.

“A Brachiosaurs’ eye view” Courtesy of Brian Engh, found here.

Sauropods of the Morrison courtesy of Pgrigor on deviantart, found here

Diplodocus carnegii courtesy of John Conway, whose work can be found at his website here

Brachiosaurus courtesy of deskridge on deviantart, found here

Dinosaur National Monument Sauropod wall found here

Apatosaurus courtesy of Mark Witton, found here

Benton, M. J. Dinosaurs Rediscovered: The Scientific Revolution in Paleontology. Thames & Hudson, 2020.

Brusatte, Stephen. The Rise and Fall of the Dinosaurs. Pan Macmillan, 2019.

Pickrell , John. “Sauropods Grew Big by Munching ‘Superfoods’ with Sturdy Beaks.” Science, 17 Oct. 2019, www.science.org/news/2019/10/sauropods-grew-big-munching-superfoods-sturdy-beaks.  

Rees, P. McAllister, et al. “Late Jurassic Climates, Vegetation, and Dinosaur Distributions.” The Journal of Geology, vol. 112, no. 6, 2004, pp. 643–653., https://doi.org/10.1086/424577.

Tang, Carol Marie. “Morrison Formation”. Encyclopedia Britannica, 23 Jan. 2020, https://www.britannica.com/place/Morrison-Formation

“The Dinosaurs of Dinosaur.” National Parks Service, U.S. Department of the Interior, https://www.nps.gov/dino/learn/nature/dinosaurs-of-dinosaur.htm.