paleontologists have found bite marks on fossilised skull of a juvenile daspletosaurus , which lived around 75 million years ago .
scientists believe that another daspletosaurus , which could grow to nine metres -lrb- 30ft -rrb- as adults and weigh up to four tons , fed on the youngster 's body .
tyrannosaurus rex and its relatives were more intelligent than previously thought and hunted in gangs which included young and older members , researchers have claimed .