Kiss of dying: Mammals have been the primary animals to supply venom

The fossil of the Euchambersia therapsid (a pre-mammalian reptile), that lived in South Africa about 260 million years in the past, is the primary proof of the oldest mammal to supply venom. CT scans of fossils of the pre-mammalian reptile exhibits anatomical options, designed for venom manufacturing.
Paleontology News — ScienceDaily