October 6, 2008
About 70 million years ago, in what is now Alberta, Canada, a chicken-sized dinosaur scampered through the undergrowth of an ancient forest. Covered in a light coat of wispy feathers, this slender dinosaur was one of the theropods, yet it possessed a rather perplexing feature.
Many theropod dinosaurs had small arms for their body size (the massive predator Tyrannosaurus rex is often ridiculed for its diminutive forelimbs), but this dinosaur had little more than stumps tipped with a massive thumb claw. Dubbed Albertonykus borealis, this theropod was one of the Alvarezsaurids, a group containing some of the strangest dinosaurs.
Up until the 1990s, no one had any idea that dinosaurs like Albertonykus existed. Fragments of their skeletons had been recovered before, but without more complete material for comparison the small fragments paleontologists collected were sometimes referred to more familiar animals with similar bones. A succession of discoveries made in South America and Asia revealed the existence of these previously unknown theropod dinosaurs, but the arms perplexed paleontologists.
The talons seemed superficially similar to the huge claws of living anteaters and pangolins, mammals that use their powerful claws to rip open the nests of ants and termites. Could it have been possible that the Alvarezsaurids were doing the same thing?
An article soon to be published in the journal Cretaceous Research begins to answer that question. Paleontologists Nicholas Longrich and Philip Currie not only described the first North American alvarezsaurid known so far, forming a crucial link between similar dinosaurs from South America and Asia, but they also provided evidence for the insect-eating hypothesis by studying the environment of Albertonykus.
Large dinosaurs like the hadrosaur Edmontosaurus, horned dinosaurs like Anchiceratops, and the predator Albertosaurus, would have dominated the ecosystem of Albertonykus. But Currie and Longrich were more concerned with more inconspicuous animals. If Albertonykus was eating ants or termites, then some traces of those animals should be preserved in the fossil record. Of ants the researchers found few traces, and certainly not any evidence of large colonies that would have fed a population of Albertonykus. Likewise, there were no body fossils of termites found from the area — but the traces termites left behind are abundant.
Today some species of termites build huge mounds in tropical areas of the world, and these mounds are ripped open by anteaters that lap the insects up with their long, sticky tongues. Given that the habitat of Albertonykus was cool and no fossil termite mounds have been found, it is unlikely that mound-building termites lived in the same habitat. What the researchers did find, however, were traces of termites that lived in and fed on wood. Pieces of wood from the same era as Albertonykus are full of just the type of burrows wood-eating termites make.
The arms of Albertonykus were too weak to dig into living trees, but instead these dinosaurs probably made their living by ripping upon the softer, decaying logs on the forest floor. The rotting trees would have been favorable habitat for termites and other insects, providing the small dinosaurs with a juicy insect feast. While it does not settle the debate over the arms of these dinosaurs once and for all, the study is strong evidence that the tiny theropod slurped up wood-munching insects.
We often think of dinosaurs as massive beasts that shook their earth with their footsteps and their roars, but under the feet of those giants were smaller, stranger dinosaurs that no one ever expected to find. There are still many questions about the Alvarezsaurids to be addressed, but Albertonykus has provided several key pieces of information that help to what the lost world of Cretaceous Alberta was like.
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