If there’s one group of dinosaurs that needs better PR, it’s alvarezsaurs. They’re among the strangest dinosaurs to have ever evolved, yet outside of dinosaur die-hards, few people have ever heard of them. They’re not one of those classic forms–the sauropods, tyrannosaurs, stegosaurs, or ceratopsids–that have been cherished for the past century. Paleontologists only recently began to uncover their bones. Alvarezsaurus itself was named in 1991, but it and its close relatives didn’t quite get swept up in the same wave of dinomania as their other Mesozoic cousins.
Alvarezsaurs weren’t big, toothy, or menacing. That’s part of makes them so special. Alvarezsaurus, Mononykus and their relatives from Cretaceous Asia, South America and North America were small dinosaurs–these feathered dinos ranged from the size of a pigeon to about the size of a turkey. In fact, these dinosaurs were so avian in nature that there was once a debate about whether alvarezsaurs were non-avian dinosaurs or birds that had lost the ability to fly. Since those early debates, numerous studies have confirmed that they were non-avian dinosaurs that were closely related to the strange therizinosaurs and ostrich-like ornithomimosaurs.
But the strangest thing of all is the mystery of what alvarezsaurs ate.
Despite being short, alvarezsaur arms weren’t wimpy. Not at all. Alvarezsaur forelimbs were very stout and included one robust finger tipped in a big claw. (Among these dinosaurs, the total number and development of the fingers varied, but they’re connected by having one finger that was bigger than the others.) In contrast, these dinos often had a reduced number of very small teeth. Paleontologists thought they saw a connection between these traits and a life feeding on social insects. Mammals such as pangolins and ant-eaters also have stout, heavy-clawed arms and are toothless–a functional pairing that goes with a life of tearing into ant and termite nests to slurp up the scurrying insects in their nests.
Could alvarezsaurs have done the same? So far, it’s the most popular hypothesis for their bizarre nature. In a 2005 paper, paleontologist Phil Senter proposed that Mononykus would have been capable of the kind of scratch-digging needed to rip open social insect nests. Then, in 2008, Nicholas Longrich and Philip Currie described the alvarezsaur Albertonykus in deposits that also contained traces of Cretaceous termites. Alvarezsaurs seemed to have the right equipment and live at the right time to be social insect predators.
But we don’t really know. No one has published any direct evidence that Albertonykus or any other alvarezsaur ate ants or termites. The hypothesis is certainly a reasonable one, but we still need a test of the idea. Fossil feces may eventually hold the answer.
If paleontologists eventually uncover dinosaur dung of appropriate size that contains ants or termites and comes from a habitat shared by alvarezsaurs, that discovery would strengthen the ant-eating hypothesis. A cololite would be even better. While coprolites are petrified feces that have already been excreted, cololites are fossil poop preserved inside the prehistoric creature’s body prior to expulsion. If paleontologists found an alvarezsaur with a cololite containing termites, that would be direct evidence that these dinosaurs truly did snarf down hordes of insects. For now, though, we can only hope that some lucky fossil hunter makes such a discovery.