When it comes down to it, basically, in a roundabout way, Canada definitely invented birds so you’re welcome.
Read morePandas Disprove Intelligent Design
Pandas are working on becoming wholly specifically herbivorous, but there is some serious room for improvement.
Read moreMilk Sweat Since 110MYA
“Q: could you explain a bit of the what-the-fuckery that is monotremes? how did they evolve, and how have they survived for so long? they separated from the rest of mammals so long ago, and everything else that separated there is extinct, but not monotremes. is there a reason for that, some kind of adaptation?”
ALRIGHT MY FRIENDS hold on to your egg-laying horses because this will be a convoluted and likely uncomfortable ride.
Photo from Pinterest
Monotremes, represented these days by platypuses and echidnas, are super goddamn weird mammals. They’re an ungodly patchwork of highly specialized, definitively mammalian traits mixed with some equally primitive reptilian-esque ones, which result in a hot mess that gives me a headache.
For example, monotremes:
Lay eggs, but produce milk from mammary glands to feed their young. Not in a normal way, but in a “leaking out of your pores” kind of way.
Their X chromosomes resemble those of birds more than they do ours, and they have a cloaca. Why
Have tribosphenic molars and inner ear bones incorporated into the skull, both incontrovertible traits of therian mammals. Finally, proof that they are-
JUST KIDDING it turns out both of those things could have convergently evolved!! haha! HILARIOUS
Their gait is closer to the sprawling synapsid gait than the erect therian one, I can only assume because they are going for a cool and retro look
Though platypus venom is derived from proteins also found in the immune systems of therian mammals, guess who else uses those proteins in venom?
REPTILES.
AUGH
Photo from Understanding Evolution
To add insult to injury here, the fossil record for monotremes is fairly garbage, with the absolute earliest examples (Teinolophus and Steropodon - shown below) already being recognizably similar to extant monotremes. These two species are dated to the Early Cretaceous, but based on genetic and molecular data it is thought that monotremes diverged from all other mammals at the very least in the Early Jurassic, and potentially as early as the Late Triassic.
Photo from Australian Museum
Of course, it is almost impossible that we’ll ever stumble across the fossil remains of an actual direct ancestor to extant taxa, due to the rarity of fossilization in general. The fossil monotremes that we do have are from a period of highly successful radiation - not only have they been found in several locales across Australia and New Guinea, but a single ancestral platypus tooth was found in South America, proving that monotremes were once fairly widespread across the Gondwana supercontinent.
So, we have no proof of how and when monotremes came to be, and a lot of their evolutionary history is just straight up missing. The ones that have made it this far likely did so because they managed to grab a hyper-specific niche that live-bearing mammals couldn’t steal from them. Until more fossils are found, the rest is just conjecture.
tl;dr: monotremes are the ultimate wannabe-Triassic mammalian hipsters and nobody knows why we still put up with them
SOURCES YO
The evidence lines up in early mammal evolution (2011)
Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas (2009)
Genome analysis of the platypus reveals unique signatures of evolution (2008)
Independent Origins of Middle Ear Bones in Monotremes and Therians (2005)
Review of the monotreme fossil record and comparison of palaeontological and molecular data (2003)
Phylogenetics Is Yikes
“what are human’s closest living relatives that live in north america, since there are no primates in north america”
As with all specific phylogenetic questions, allow me to preface this answer with
Genetics never has and never will be my strong suit, so I’m always cautious talking about it. Not to mention that it seems like these days anybody with electricity and some agarose is publishing new and conflicting phylogenetic trees. And yes, I am looking directly at you, bat geneticists. But I digress.
Just to clarify, there are primates in North America - all kinds of monkeys cavort about in Mexico and Central America, but I’m assuming you specifically mean the US and Canada. Excluding the smaller sister taxa that also aren’t found in North America*, the closest relatives of primates in the US and Canada are Rodentia and Lagomorpha - meaning rodents and rabbits/hares/pikas.
*treeshrew phylogenetic placement is pretty wonky in and of itself, so I’m not even gonna GO there. Just know that they are in the vicinity of primates