These didnt actually evolve at all since those days, they lived along modern armadillos, but the later just did not get extinctinct. But the answer to your question is that being "badass" is sometimes just not the best option. Sometimes smaller, slower and dumber is actually more efficient if it saves you from needing a few extra calories that the enviroment might sometimes not be able to provide.
che, como andas?...tengo un paleontologo conocido, quiere poner laburos tuyos en un museo...y quiere hablar con vos por el tema del permiso para usar las imagenes...si te interesa mandame tu mail y se lo paso...
yes, by the way, sence you know alot about paleobiology i have a question, t-rex and dromesaurs are closely related to birds, but there never shown to have beaks, or any other therapod for that matter.
the platypus does not have a beak, the "bill" is not like a beak at all, it is soft, sensitive, and filled with sense organs. It's like calling a foot a hand, or something like that. If anything on a playypus is more like a beak, it has teeth that are actually made of keratin, pads in the mouth, that is more analogous to a beak in my opinion, the "bill" is really more like the sensitive snout of any mammal.
True I was aware of that, I must be conditioned to think of "beak" and "bill" as synonyms since we only have one word for them in Spanish.. but yea, I guess I could have used a better convergent structure as an example. Still itīs quite an unusual structure between mammals, convergent evolution is never really the same. Wings in birds and insects work nothing alike and they are still considered convergent in their function.