Load the chapter 'Bad Blood'. From the start there is a downed helicopter you have to move to. When you reach this stage there is 10-15 little dinosaurs on the ground for you to kill. Kill 6 or 7 then 'save' and then reload checkpoint. (Always, ALWAYS make sure you save before you reload or it does not count!) If you also need the Turok Defense Force achievement right after you kill all little guys checkpoint will pop and you can then kill the Raptors that come.