Bird-like Dinosaur is Smallest Known to North America
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A newly discovered alvarezsaur from near Red Deer, Alberta, Canada provides insight into dinosaur evolution and biogeography.
The smallest dinosaur known from North America was found by Nick Longrich, a research associate at the University of Calgary. He stumbled upon the chicken-sized fossils while conducting an unrelated study at the Royal Tyrrell Museum in Alberta, Canada.
“These animals were previously unknown from North America,” says Dr. Francois Therrien, an expert in dinosaur paleoecology at the Royal Tyrrell Museum. “We suspected they were here but we just hadn’t discovered their remains until now.”
Until now, Longrich says, only two alvarezsaur bones have been discovered, and neither in Canada. Dubbed Albertonykus borealis, Longrich was able to isolate and analyze about a dozen bones from two animals. Although the skeletons are incomplete, Longrich says that some of these bones, “like the ulna and the thumb claw, are really critical to figuring out what the animal is related to.”
Bird-Like Characteristics of Small Dinosaur Albertonykus borealis
The alvarezsaurs were closely related to birds, Longrich says in his paper published in the August 2008 issue of Cretaceous Research. Its long, slender hind legs resembled a bird’s, standing on two feet, supported by three toes.
“Bones of the arms, legs, and mouth can tell you a lot about lifestyle,” says Therrien, “because animals use those for daily activity.”
“While birds were off flitting around, becoming specialized for flight, alvarezsaurs were looking earthward, becoming specialized for digging things up,” Longrich says. Based on an evaluation of ground and log-dwelling insects abundant 70 million years ago, the most likely victims of the Albertonykus were prehistoric termites, he reports.
However, bird legs and bug-eating are not the only things that the dinosaurs had in common with their evolutionary counterparts. Previously, relatives of the Albertonykus borealis were known only from South America and Asia and one of these well-preserved specimens from Mongolia, shows evidence of feathers or a downy covering, Longrich says. This alvarezsaur, “would have been furry or feathery in appearance, not scaly, and almost certainly warm-blooded,” he says.
Because feathers are used for insulation, cold-blooded animals would have had no use for them, Therrien says. “If you are cold-blooded, you don’t need to stay warm.”
Origination and Migration of Alvarezsaurids
Longrich and his colleague, Dr. Philip Currie from the University of Alberta, who originally collected the fossils in 2002 from the Dry Island Buffalo Jump Provincial Park in Alberta, believe that this family of dinosaurs originated in South America and migrated to Asia, through North America.
“The most primitive and ancient alvarezsaurids are found in South America and the most ‘highly evolved’ and most recent alvarezsaurids are from Asia, it suggests that the group originated in South America and found their way to Asia at a later time,” Therrien agrees. “The ‘degree of evolution’ of the Alberta alvarezsaurid falls in between the South American and Asian animals, so it suggests that alvarezsaurids moved through here on their way to Asia.”
Finding More Alvarezsaurs
The chances of finding more undiscovered treasures in museum collections are relatively good. “When specimens are collected, if they are not easily recognizable they are usually assigned a ‘best guess’ until further study,” says Therrien. “Depending on the scientific interest for the material, it may be studied right away or may just be stored until someone looks at it.”
These cat-sized dinosaurs were found in a Cretaceous layer abundant with albertosaurs, not known for having these alvarezsaur fossils, and Longrich says, he probably won’t go hunting for more.
“It’s an extremely tough site to work,” he says. “The fossils are preserved in ironstone, which lives up to its name.” Instead, Longrich says he will stick to museum collections where he’s had his best luck.
