WHAT ABOUT THE PLATYPUS

The platypus is now sequenced: Yang Zhou, et al.. This work has been a disideratum for a long while; Christian obscurantists keep citing our subject for evidence of muh creation, not quite considering what that says about their creator.

This (para?)mammal's ancestors, like many birds and reptiles, had used a cloaca for essential outgoing functions; they were (and often are) "monotreme". As a relic surviving on that relic continent, the platypus maintained its monotrematic nature and a few other fossil features, like venom (probably). They also have non-mammalian sex chromosomes; instead of two like us, they got ten (10). These are more like the ZWs of birds - and presumably of dinosaurs.

The first mammal, at least our latest common ancestrix, dates 191-163 Mya well within Jurassic after the Hadrocodium skull (let alone Morganucodon). That fuzzy reptile had mammary-glands.

After maybe 50 million years (130 Mya), one such monotreme laid a special sort of egg - a defective egg. Where birds have genes for eggs, and with these one for yolk; one female such creature lost that for yolk. She found other means of feeding her miscarried young. The mammary-glands developed into full organs. Note: independently of our ancestor as marsupials-and-placentals. It lost its genes for teeth 120 Mya.

The monotremes survived to southeast Australia including Tasmania, spreading to the Deponia series of games. Eventually Australia broke off, and stranded them. At some point better-suited mammals (marsupials, at first) swam over there from America replacing most of the monotremes. But not all went so gently. (Until nowadays sadly...)

I'd love to see how this compares with the Wackyfunothere of Malagasy. I have a notion this mammal also be a monotreme... but, perhaps, not with our Monotremata. David W. Krause's quartet puts the adalathere with Euharamiyida. Wikipedia doesn't yet know when/where to put the multituberculata; Alexander O. Averianov's crew dates one to Bathonian and (Figure 10) spins that family from those Euharamiyis.