Complex sentence: The first late saber-tooth instance is aoup of animalestral to mammals but not yet mammnown as synapsids or mammal-like reptiles, they were onf the firs of animals to experience specialization of teeth and had long canines.
Split into simpler sentences: The first late saber-tooth instance is a group of animals ancestral to mammals but not yet mammals. Known as synapsids or mammal-like reptiles, they were one of the first groups of animals to experience specialization of teeth and many had long canines.