What is an Armadillo

At the Texas Roadhouse, this New Years Day my daughter looked at a picture on the wall and said, "Look at the pig". My son and I pointed out to her that is was an armadillo. But then he told her an armadillo is a kind of rodent. I said, actually it is a marsupial. Neither of us were correct at that point, but now that I have investigated, I see that I was the least correct.

To my mind, the armadillo was more like an opossum which is a marsupial. But apparently, I was never meant to be a naturalist. So I broke out the Wikipedia, and this is what I discovered ...

It all starts with class Mamilia or mammals, we are all familiar with that, armadillos, rodents, opossums, pigs, platypuses and people are all mammals.  So Mamilia is a class and that is subdivided into two subclasses Theria (live bearing) and Prototheria (egg laying). So here we say goodbye to our friend the platypus and the echidna which I had not yet mentioned as they are both egg laying mammals. This small band is also grouped under the order Monotremata (Monotremes) and can be visited in Australia and New Guinea.

So getting back to sub-class Theria:  armadillos, rodents, opossums, pigs and people. This is again more finely divided into infra-class Eutheria (placental) and Metatheria (marsupial).  Eutheria includes armadillos, rodents, pigs and people. Metatheria includes opossums and kangaroos. So, now I thought I knew what marsupial meant. I knew that the young embryo like joeys crawl up to a nipple to gestate, but you better read for yourself. Seems the reproductive organs are double barreled. Also, the opossum is the one and only marsupial in North America. OK let's shed the opossum.

We are left with armadillos, rodents, pigs and people. Time to cut to the chase, here's where we can put them into separate roughly equivalent categories:

people = order primates
rodents =  order Rodentia (what else)
pigs = order Artiodactyla
armadillos = order Cingulata

the categories on the left are not equivalent as people are a species (H. sapiens) wherease rodents defines the entire order. However, this gives an idea of the split. Fascinating!