Albertonykus borealis
Albertonykus (Longrich and Currie, 2009) was one of those serendipitous discoveries. Albertonykus is a member of the Alvarezsauridae a group of dinosaurs characterized by long, lanky hindlimbs, slender jaws like a pair of needle-nose pliers, and stubby forelimbs with a pick-like claw on the forelimb. Following the discovery of the alvarezsaur Mononykus in Mongolia, it was realized that similar animals were present in North America, but only isolated bones were known.
Alvarezsaurs have always fascinated me because of their bizarre morphology, and so when I was studying fossils from the late Campanian Dinosaur Park in Alberta, I kept a careful look out for them. Without any luck- despite looking at hundreds if not thousands of bones, there wasn't a single one that could be identified as an alvarezsaur. Apparently, they simply didn't live in Alberta at this time, and so I eventually gave up looking.
Years later, I was studying some claws from a new species of ostrich dinosaur (unfortunately, far too fragmentary to name). I needed to compare the claws to tyrannosaur claws to rule out the possibility that they came from a tyrannosaur. So I opened up some cabinets containing tyrannosaurs from Dry Island Provincial Park, Alberta and started rifling through drawers. This collection, as it happened, came from a place called Dry Island Buffalo Jump (a buffalo jump being a place where Indians would drive bison off the cliff to kill them), in a deep valley along the Red Deer River. The site contains the remains of over 20 tyrannosaurs at last count, but also has a number of other animals mixed in, including fish and small vertebrates.
In the process of rummaging through the material, I chanced on a small claw, less than an inch long, and had a sudden flash of recognition. I'd seen the same thing before- but in fossils from Mongolia. In Mononykus.
After rifling through more drawers, I struck upon other bones- a tibia, an ulna, some bones from the feet and toes. Hardly enough to make a skeleton, but enough to get an impression of the animal and to compare it to relatives from South America and Mongolia. As it turns out, the animal combines features seen in its South American relatives with features seen in Asian relatives. One possibility is that the animals migrated from South America, into Asia. Another possibility is that Albertonykus is coming from Asia.
At the time, Albertonykus was the smallest dinosaur known from North America; it remains one of the smallest. Small dinosaurs were probably a lot more common than we realized, but skeletons of small terrestrial animals are virtually absent from the Cretaceous of North America, so they tend to get overlooked.
Alvarezsaurs are really, really bizarre animals. I think of them as being sort of Suessian- more like something from a Dr. Suess book than anything real. The odd combination of long hindlimbs and short forelimbs and the delicate jaws with their tiny teeth, it's all really quite bizarre. The forelimbs are perhaps the weirdest part of the package. They are short but massively constructed, with large processes for muscle attachment, giving the muscles a lot of leverage. The thumb is large and has a hooked claw, but the other fingers are reduced almost to nothing. It looks like a digging apparatus, but obviously it wouldn't have been very well-equipped to burrow. The hindlimbs are too long, and the forelimbs can't even reach past the nose. The thumb wouldn't be very useful for moving earth, either- it's more like a pick than a shovel (unlike, say, a mole) so it's probably used to break through something hard, rather than to move soft dirt. What I found rather illuminating is that other animals do have similar hands- notably, anteaters and pangolins, both of which use their claws to rip into the nests of ants and termites.
My guess was that Albertonykus and other alvarezsaurs were insect predators. But what sort of insects? Ants were present in the Cretaceous, but they were rare and probably didn't form the huge colonies that modern ants do. Termites were around, but mound-building termites, the sort that build the towering nests in Africa, hadn't evolved yet. That left wood-dwelling termites. After sorting through the drawers, I came across some wood from the same formation, which was riddled with insect burrows. It suggests that wood-dwelling termites were around at the time. Another possibility, I suppose, is that alvarezsaurs ripped into logs for beetle larvae. It's my opinion that the traces in the wood were more like termite burrows. The beetle idea isn't impossible, but given that the Asian alvarezsaurs inhabited deserts (where termites are abundant, but wood-boring beetle larvae tend to be scarce) and given that the South American ones were quite large (requiring a very high biomass of insects) the termite-eater idea makes the most sense.
You can find the paper here: http://www.sciencedirect.com/science/article/pii/S0195667108000943