First Not Worst

The first dromaeosaur discovered in South America was Neuquenraptor. The key dromaeosaur characteristic that was evident with the unearthing of Neuquenraptor was its dromaeosaur foot claw, though the other bones that were discovered also possess dromaeosaur characters. Unenlagia possesses many of the characters of other bones, including the pelvis, that are indicative of the familial relationship between Unenlagiinae and other dromaeosaurids. More important than the anatomical connections between these South American "raptors" and North American and Eurasian genera/species is the geographical implications that were made more apparent by the discovery of Neuquenraptor and cemented by subsequent discoveries like Unenlagia. While the geological implications do not, as yet, appear to be concretely established, the presence of dromaeosaurs in South America points to a land connection between the two Americas after Pangaea split apart. North America at the time would have been part of Laurasia and South America would have been part of Gondwanaland. Prior to the presence of dromaeosaurs on both Gondwanaland and Laurasia there has been no evidence, to my knowledge of hypothesized bridges between northern and southern continents during the Mesozoic post-Pangaea (this is something I definitely want to be kept aware of or corrected on if need be!). Alternatively, however, convergent evolution could be proposed for the occurrence of two groups of animals very much alike on vastly separated continents, though I do not know that anyone has proposed such a hypothesis in regards to dromaeosaurs of South America and North America and Eurasia.

Edit: To look at the map in a larger view, right click and choose view image. It works better than just clicking on the map.

Map of fossil sites of Dromaeosauridae taxa reported on the Paleontology Database