Artwork of a herd of titanosaurs and some dromaeosaurids. The titanosaurs were a diverse group of sauropod (long-tailed, long-necked) dinosaurs that lived throughout the Mesozoic era. They were the last surviving sauropods, before being wiped out in the mass extinction at the end of the Cretaceous period. The group includes the largest animals ever known to have walked the Earth, with lengths of 30-40 metres and weights up to several dozen tonnes. The largest known among these animals are argentinosaurus and dreadnoughtus, from what is now Argentina, although their remains are very sparse. The dromaeosaurids were a family of feathered theropod dinosaurs (often called raptors) that flourished particulalry in the Cretaceous period. They most likely hunted in packs.