There are lots of cool things about this critter:
1) Small size. Specimens of Fruitadens have a maximum body length of about 75 cm, making it the smallest known ornithischian. Histological work was done to determine the relative age of the specimens. It is estimated that the largest individual was about 4-5 years old at death, but had already slowed down its growth as is seen in sub-adult and adult non-avian dinosaurs.
2) Age. The specimen is Late Jurassic, making it one of the youngest known heterodontosaurids. Only Echinodon from the Early Cretaceous of England is younger. Interestingly both Echinodon and Fruitadens have small adult sizes, but it is possible to differentiate the two.
3) Plesiomorphic dentition. Fruitadens differs from older heterodontosaurs in possessing less sophisticated craniodental adaptations, thus was probably more of a generalist feeder. The authors believe that this adaptation, as well as small size, allowed the group to survive into the Late Triassic and Early Cretaceous. Also cool is that it seems to have regularly undergone tooth replacement, which is unknown in most other heterodontosaurs.
4) Theropod-like femur. One feature of Fruitadens that I find interesting is that the femur closely resembles that of theropods like Dilophosaurus and is very unlike that of ornithischians. Richard Butler assures me that the material represents a single taxon so this is an interesting characteristic. I often like to play devil's advocate and claim that there are no Triassic ornithischians (not even Pisanosaurus) despite a wealth of saurischians, and although I've been assured over and over by dinosaur workers that the saurischian line could not have given rise to the ornithischians, I always find synapomorphies like this (basal ornithischian with saurischian-like characters) of great interest. Hey, someones got to keep stirring the pot or we'll get too complacent.
4) Biogeography. Fruitadens is from the Upper Jurassic Morrison Formation of Colorado. This is the first described heterodontosaurid from North America. As it is from the Brushy Basin Member it was a contemporary of the classic dinosaurs such as Allosaurus, Camarasaurus, Stegosaurus, and Diplodocus.
Overall another great find. They just keep coming. Read more here and here.
Butler, R. J., Galton, P. M., Porro, L. B., Chiappe, L. M., Henderson, D. M., and G. M. Erickson. 2009. Lower limits of ornithischian dinosaur body size inferred from a new Upper Jurassic heterodontosaurid from North America. Proceedings of the Royal Society B. doi:10.1098/rspb.2009.1494.
Abstract-The extremes of dinosaur body size have long fascinated scientists. The smallest (<1>Fruitadens haagarorum, from the Late Jurassic of western North America that rivals the smallest theropods in size. The largest specimens of Fruitadens represent young adults in their fifth year of development and are estimated at just 65–75 cm in total body length and 0.5–0.75 kg body mass. They are thus the smallest known ornithischians. Fruitadens is a late-surviving member of the basal dinosaur clade Heterodontosauridae, and is the first member of this clade to be described from North America. The craniodental anatomy and diminutive body size of Fruitadens suggest that this taxon was an ecological generalist with an omnivorous diet, thus providing new insights into morphological and palaeoecological diversity within Dinosauria. Late-surviving (Late Jurassic and Early Cretaceous) heterodontosaurids are smaller and less ecologically specialized than Early (Late Triassic and Early Jurassic) heterodontosaurids, and this ecological generalization may account in part for the remarkable 100-million-year-long longevity of the clade.