Echidna and Platypus, the monotremes.
Confusing creatures, these. The fossil history of monotremes in Australia is only ~2 mil years old, and depicts species that are largely the same as current species. Unlike marsupials, which evolved separately in both in the Pacific Islands and North America simultaneously, there was no convergent evolution of egg-laying mammals in other parts of the world. At least none that we’ve discovered thus far.
Using molecular genetics, we can understand the relations of monotremes to other classes by finding when they diverged and the differences between the species, but it doesn’t tell us the steps that they followed to become the creatures they are today.
By the way, don’t mess with platypods. The males venomous spikes on their back heels and aren’t afraid to use them.