When paleontologists revisited a site at Aysén where seven-year-old Diego Suarez had found some bone fragments in 2004, they thought he had stumbled upon a graveyard containing remnants of three great dinosaur lineages. Hips with a backwards-pointing pubis bone to make room for a large gut as seen in ornithischians, long thin necks, small rounded skulls and broad, four-toed feet akin to sauropodomorphs, and short arms with two clawed fingers as seen in some theropods, were all strewn about the site. But they were wrong.
The big surprise arrived with four complete skeletons that each sported all of those features, prompting stunned workers to compare them, metaphorically, to Platypus — the oddball, egg-laying, duck-billed mammals from Australia. They were Christened Chilesaurus, referring to the country that yielded their remains. But we can't help thinking that the authors missed a trick by not naming them after Chile-con-carne, another creation that has come to be represented by a hotch-potch of weird and wonderful components.
To deduce their true affinities, Novas et al. compared these new remains to those of a broad range of species from each of the three groups that they were suspected of belonging to and totted up the aggregate score of similarities. The best-supported conclusion is that Chilesaurus belongs to Theropoda, the branch of saurischian dinosaurs that are renowned for their fondness for flesh. But long, forward-slanting, leaf-shaped teeth suggest they were vegetarians, perhaps with a beaked snout, and not particularly swift ones judging by the design of the pelvis, legs and feet.
Of course, vegetarian theropods are nothing new. Ornithomimids, oviraptorosaurs, therizinosaurs, and even a ceratosaur, have all dabbled with herbivory, or at least omnivory. What is unusual, however, is that theropods (carnivorous or otherwise) are far outnumbered in most eco-systems by herbivorous ornithischians and sauropodomorphs, but Aysén theropods, in the form of Chilesaurus, had independently evolved a plethora of features in common with both lineages of herbivorous dinosaur, and the quantity of their remains suggest they outnumbered everything else.
The holotype (SNGM 1935) is an almost complete juvenile skeleton, 1.6 meters long. A second specimen (SNGM-1888), presumably a full-grown adult, was around twice this length.