Before the prehistoric fauna of the southern hemisphere became relatively well-studied, pieces of small, fragmentary fossils started turning up in South America that looked suspiciously like the large carnivores of the northern hemisphere. While palaeontologists there were quick to label these finds as southern tyrannosaurs, a series of finds in 1985 by Argentine palaeontologist José Bonaparte brought to light what these finds really represented. They were massive theropods defined by stunted, wrinkled skulls and miniscule arms.
To date, more than 20 types of these strange carnivores, known as abelisaurids, have been found. They range from the strange scavenger Rugops, a mid-sized animal with a wrinkly, roughly-textured sheath covering its face, to the larger Majungasaurus, a stumpy-legged predator with an odd, blunted, unicorn-like spike. The Late Cretaceous Carnotaurus was particularly strange; it boasted a pair of bull-like horns over its eye sockets as well as rows of bony scales lining its body, and was able to run at a terrifying top speed of 56 kilometers per hour (35 miles per hour). All of these animals are united in this family by forwardly-compressed skulls with strange decorations, and miniscule arms that T. rex could have made bad jokes about.
Today, these abelisaurids are found in 4 continents, and seem to have replaced the larger allosauroids and more specialized spinosaurids as the dominant carnivores of Gondwana. Interestingly enough, it seems that this trans-continental distribution happened rather suddenly, and one particular creature may explain just why they were able to spread so far.