Baby Longnecks Were Jurassic Popcorn
Brachiosaurus was among the largest of the Morrison Formation sauropods, including at Dry Mesa.
This post originally appeared in Riley’s newsletter The Boneyard. To support independent science writing and get stories like this direct to your inbox, subscribe on Buttondown.
If I could travel to any ancient environment, where would I go? The question always stalls me. There are so many to choose from - most of all habitats in the mountains, in the deep seas, and other places that did not create fossils. But I know my heart answer, the one I always go to. It has to be the Morrison Formation floodplains of the Late Jurassic.
Morrison Formation habitats were weird. Winding streams and ponds spread across lowlands dotted with ginkgoes and conifers, horsetails reaching up from the water’s edge along the fringes of ancient clearings full of ferns and cycads. There were no grasses, and perhaps no angiosperms of any kind. And in this place, dinosaurs. Not just a few. But an incredible abundance. The lush plant life fed Camptosaurus, Stegosaurus, Apatosaurus, Diplodocus, Camarasaurus, Brachiosaurus, and more, in turn preyed upon by carnivores that ranged from pipsqueak tyrannosaurs like Stokesosaurus to hulking, multi-ton meat-eaters such as Allosaurus and Torvosaurus. If you were to travel to ancient Utah circa 150 million years ago, the world would look fundamentally different.
How on Earth did such an ecology work?
The sheer productivity of the Morrison Formation environments, preserved across western North America from the Dakotas down to Texas, has long astonished paleontologists. Experts have run multiple studies on how digestible and nutritious Jurassic plants were, for example, and found that supposedly archaic, hard-to-digest plants actually could have supported the colossal bodies of multiple sauropod species. Now a new study from University College London paleontologist Cassius Morrison has taken a broader view, focused on how the Jurassic classics of Colorado’s Dry Mesa Quarry interacted with each other.
A simplified diagram of a Morrison Formation food web, arrows indicating who was eating whom 150 million years ago. From Morrison et al. 2026.
Even if you haven’t heard of Dry Mesa Quarry before, you’ve almost certainly heard of the dinosaurs found there. The fossil beds yielded the first-described remains of the huge carnivore Torvosaurus, as well as the slender Supersaurus and a dinosaur, once called "Ultrasaurus,” that was later recognized as Brachiosaurus. Along with these relative rarities, widespread Morrison dinosaurs such as Allosaurus and Camarasaurus have been found in the quarry as well, in addition to microfossils from crocodiles, lungfish, lizards, turtles, small mammals, and other creatures. Even better, all of these animals were likely buried and preserved within a short timeframe - not a jumble of bones from multiple seasons but a reflection of the actual fauna.
“Dry Mesa has one of the highest taxonomic diversity of dinosaurs in a single quarry within the Morrison Formation,” an assemblage of animals brought together by drought that were then buried soon after death, Morrison says. By pairing these occurrences with what’s known about the growth, diets, and habits of these animals, Morrison and coauthors fed the data to a program called cheddar that generates approximate food webs. The abundance of Jurassic plants, the researchers found, fed an incredible number of young and small sauropod species that in turn supported an array of carnivores, the largest of which were feeding upon virtually everyone save for the very largest sauropods.
The little long necks converted plant food into flesh, which in turn filled many carnivorous stomachs. “What was surprising was how the size of the sauropods made the young sauropods a prime option for the predators,” Morrison says. All the sauropod dinosaurs hatched out of very small eggs that were roughly about the size of a softball. The herbivores were vulnerable for years afterwards, especially given that no evidence of sauropod parental care has yet been found, and so the little long necks fed voraciously to fuel growth spurts that would hopefully make them too large to be harassed or attacked. But very few sauropods were able to reach such sizes. With the largest sauropods like adult, 40-ton Brachiosaurus inaccessible, carnivores focused on the smaller individuals.
Study author Cassius Morrison and the Morrison Formation in the background. Credit: Cassius Morrison
Paleontologists had previously hypothesized about such interactions among the Morrison Formation dinosaurs, but the new study provides the analytical evidence that the details of dinosaur reproduction, growth, and feeding really did shape the Jurassic garden. Plant life grew from ground level to tall trees. Large adult herbivores fed high, or broadly, while younger sauropods fed lower down. Adults and juveniles could coexist as a result of this partitioning, acting like ecosystem engineers, Morrison says. But it’s the young sauropods that allowed Torvosaurus, Allosaurus, Ceratosaurus, and other carnivores to thrive, not only as prey but as multi-ton carcasses that were food for many different organisms. In this way, a greater variety of species were able to live in the same place.
The smaller sauropods - whether young or just small species - were so numerous that the larger carnivores may not have carved out particular prey preferences or meat-eating niches. “The abundance of sauropods, especially the young ones, were found in the study to offer a lot of food options to all three large, predatory theropods,” Morrison says. The carnivores may have had different home habitats, and each meeting of predator and prey played out uniquely, but it wasn’t as if Torvosaurus was a Brachiosaurus specialist while Allosaurus fed on young Diplodocus. The presence of Torvosaurus, Allosaurus, and Ceratosaurus together speaks to the incredible volume of fleshy food rather than specific dietary differences between them.
I have to wonder how this magnificent menagerie came together in the first place. The Dry Mesa Quarry gives us one snapshot, while Cleveland-Lloyd Dinosaur Quarry, the Mother’s Day Quarry, Hanksville-Burpee, the Carnegie Quarry, Mygatt-Moore, and many others offer their own views. All present varying collections of species and settings, but all rife with Late Jurassic herbivores and their predators. Did carnivores such as Allosaurus evolve because of the sauropod lifecycle, a result of abundant juvenile prey? Or were such carnivorous dinosaurs already present before the long necks diversified and pushed their biological limits, perhaps nudging the sauropods to reach larger sizes? Maybe the story is altogether different, something we cannot perceive until we find the right fossil layers. The great reptiles had formed an intimate, complicated relationship through millions of years, underwritten by plants and within boundaries unfamiliar to us mammals. Paleontologists have known the Morrison Formation and sought its incredible dinosaurs for over a century and a half. We’re only just now beginning to understand how such a habitat, overflowing with great reptiles, came to be.