Arbrosaurs are a family of primarily tree-dwelling maniraptoran coelurosaurs in the alternate timeline of the Cenozoic era in The New Dinosaurs: An Alternative Evolution. One of the most widespread developments in the dinosaurs after the end of the Cretaceous period was the evolution of the arbrosaurs. These evolved from small, primitive coelurosaurs. In Jurassic times the coelurosaurs gave rise to the birds, and the development of the arbrosaurs from the same stock was brought about by similar evolutionary processes. Perhaps the most typical of the modern arbrosaurs is the genus Arbrosaurus itself from the tropical rainforests of Africa. Various species of this animal appear in almost all the zoogeographical realms.