There were three species of thylacoleo, all extinct now. They were:
1. Thylacoleo carnifex
2. Thylacoleo crassidentatus
3. Thylacoleo hilli
T. carnifex was the largest and latest of these animals. T. crassidentatus and T. hilli lived during the Pliocene epoch and were only about the size of a large and small dog, respectively.