A fluffy, 91-centimetre-long killer found in Wyoming is the oldest known relative of Velociraptor discovered in North America, palaeontologists announced today. Named Hesperornithoides miessleri, the ancient animal is also the smallest dinosaur yet found in the state, which until now has been known for fossils of celebrity behemoths such as Brachiosaurus, Diplodocus, and Stegosaurus.
The newly described dinosaur, reported today in the journal PeerJ, specifically comes from a layer of roughly 150-million-year-old rocks called the Morrison Formation, which covers a vast swath of the western U.S. centred on Wyoming and Colorado.
“When you’re working in the Morrison, you’re expecting to only find big stuff—even an isolated vertebra of Diplodocus is almost as big as this entire skeleton,” says study coauthor Dean Lomax, a palaeontologist at the University of Manchester in the U.K. This diminutive fossil, he says, “demonstrates that the Morrison Formation was more diverse than previously known … and shows that there were little dinosaurs around.”
Over a thousand dinosaur species once roamed the Earth. Learn which ones were the largest and the smallest, what dinosaurs ate and how they behaved, as well as surprising facts about their extinction.
But the description of Hesperornithoides may ruffle some feathers among palaeontologists, as the study authors argue that it hints the first flying ancestors of birds evolved among ground-dwelling dinosaurs, rather than tree-dwelling dinosaurs that could climb and glide.
Fluffy little murderbird
Wyoming’s smallest known dinosaur was found by accident during a 2001 fossil dig to uncover the bones of its largest, a 34-metre-long sauropod called Supersaurus. A shovel went through Hesperornithoides’ snout, unfortunately destroying part of it, as surface layers of soil were removed to reach the larger bones of Supersaurus.
These fossils belong to "Lori," now known to science as Hesperornithoides miessleri. The Jurassic animal is the smallest dinosaur yet found in the state of Wyoming.
PHOTOGRAPH BY LEVI SHINKLE
When the dig crew first uncovered the fossil, they thought it might be a pterosaur, a flying reptilian contemporary of the dinosaurs, based on the minute size of the bones. It was only after careful preparation that they realised the find’s full significance.
The specimen is currently held in a public collection at the Wyoming Dinosaur Center in Thermopolis and has long been known among palaeontologists as “Lori,” after volunteer Lori Hockemeyer, who was involved in the 2001 dig.
After initial preparation and analysis, Lori languished unstudied for many years. But Bill Wahl, preparation laboratory manager at the dinosaur centre, showed Lomax the specimen in 2008, and he was enthralled by it.
Lomax didn’t forget about Lori, and in 2015 he brought together the team of researchers who would publish the description, using crowdfunding to get them and the specimen to the University of Wisconsin-Madison for a week of intense study in 2016.
The team found that Hesperornithoides was a type of dinosaur known as a troodontid, and it lived during the late Jurassic period. Its great age places it as a very early member of the wider group of dinosaurs that includes speedy, predatory dromaeosaurs such as Velociraptor, which lived in the Cretaceous period, about 75 million years ago.
Similar to that infamous Jurassic Park predator, Hesperornithoides had a large sickle-shaped claw on each foot, possibly useful for disemboweling prey. It also had many bird-like features, but was clearly terrestrial, seemingly supporting the idea that birds evolved on the ground from running dinosaurs, Lomax says. (Find out how some scientists think birds survived the dino-killing asteroid.)
The experts believe Hesperornithoides would have been covered with feathers, including long feathers on its forelimbs, effectively forming small wings. But the proportion of its limbs in relation to its body suggests that it was unable to fly. It likely lived in wetland and lakeside environments and hunted small animals including mammals, lizards, and other dinosaurs.
“It was a stereotypical raptor-like dinosaur. It would have behaved very much like a bird, and was about the size of a chicken with a long tail,” Lomax says.
A skeletal reconstruction shows what Hesperornithoides miessleri would have looked like as it moved through what is now Wyoming. The scientists who described the fossil think it would have been covered in feathers, including long feathers on its forelimbs, effectively forming small wings.
ILLUSTRATION BY SCOTT HARTMAN
Messy origin story
The tiny dinosaur “is an exceptionally rare find and the best of its kind in 150 years of fossil collecting in the Morrison,” says David Varricchio, a palaeontologist at Montana State University in Bozeman who studies troodontid dinosaurs but was not involved in this research.
Based on similar fossil finds in China, experts suspected that small, bird-like dinosaurs should be found in these rocks in the U.S. But more than a century of collecting “has produced very little in the way of specimens,” Varricchio says. “It’s amazing how little we know about them from this time in North America.”
Hesperornithoides is by far the region’s most complete small dinosaur fossil, with about 44 percent of its skeleton uncovered—others are only known from isolated teeth. This helped the study authors create a freshly detailed family tree of the dinosaurs most closely related to birds.
Based on their work, “most of the things we associate with birds—wings, feathers, etcetera—seem to evolve in a terrestrial context prior to the origin of bird flight,” says study leader Scott Hartman of the University of Wisconsin-Madison. He argues that likely tree-dwelling Chinese dinosaurs, which have been thought of as possible transitional steps in the evolution of bird flight, may be dinosaurs that evolved flight separately from the direct ancestors of birds.
This detailed view shows the hunk of rock that contains the fossilised skull of Hesperornithoides miessleri.
PHOTOGRAPH BY LEVI SHINKLE
“It’s a cool specimen for sure and adds to the very fragmentary number of [dinosaurs closely related to birds] known from this time,” says Jingmai O’Connor, a palaeontologist at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. “It’s pretty clear that flight evolved in dinosaurs more than once, and this new dataset supports that.”
However, she cautions that the findings related to bird origins are speculative, and that we shouldn’t read too much into them until we have more fossils to clarify relationships.
“We have more to learn before we can … discuss how and when flight and birds evolved,” Varricchio agrees. “I think it will probably be messy for a while.”
Lead Image: A pair of Hesperornithoides miessleriis hunt along the forest floor in what is now Wyoming in an illustration. The newly described species is a relative of Velociraptor and may offer new clues to how birds evolved to fly.
ILLUSTRATION BY GABRIEL UGUETO