The Avashishta bacharamensis is dated to about 72 to 66 million years ago. It is known from a single tooth from Late Cretaceous India, Avashishta may represent a late-surviving haramiyidan, a non-mammalian mammaliaform near the mammal line. Its classification is debated, so this is best marked as a tentative “possible last known” entry.

For sure, non-mammal mammaliaforms lived to about 150 million years ago. For example, the Late Jurassic docodont mammaliaform from Portugal. It had many mammal-like traits, including complex teeth and mammaliaform-style tooth replacement, but belonged to a side branch outside the living mammal line.

The Brasilodon is an early mammal/mammaliaform threshold at 225 million years ago. The more conservative textbook marker is the Morganucodon at 205 million years ago. The Natural History Museum notes that Brasilodon dates to 225 million years ago and predates Morganucodon, which is usually considered the first mammal, by about 20 million years.