Monotremes
en.wikipedia.org
en.wikipedia.org
Are these the links between mammals and birds? Or, on a more naive level, between humans and dinosaurs? Why are they some of the only venom-producing mammals? Could we engineer humans to lay eggs one day? And a million other questions that monotremes stir within me.
Surely mammals such as humans have been engineered via evolution to not lay eggs? Which is one reason we are not welcoming our duck-billed platypus overlords.
Still, I think this and other similar questions could be better discussed on more biologically-oriented forums.