Mesozoic Mammals Fight Back

The Mesozoic was a dangerous time to be a mammal, and a new study by Hurum et al. (2006) show that they just didn't yield to becoming simply Dinosaur snacks. Using a spur on the ankle, Mesozoic mammals, such as multituberculate Catopsbaatar fought back against dinosaur predators by secreted poison from a gland and imbedding it into the skin of a predators.

Amazingly living monotremes, such as the platypus still retain this ankle spur.
The ankle spur is composed of three parts, the os calcaris (the base), the ossified cornu calcaris (the core), and the cornu calcaris, the keratinous covering. All marsupials and placental mammals have lost this structure.

Hurum, J.H., Luo, Z−X., and Kielan−Jaworowska, Z. 2006. Were mammals originally venomous? Acta Palaeontologica Polonica 51 (1): 1–11.