Yes, the original GOT dragons were designed with a bird-like sternum in the rough skeletal stage. All subsequent dragon designs are built off this base design/rig (even Caraxes).

"like monkey with night visison"

Stock image sites and reddit are especially bad for labeling highland cattle as yak. I have even seen Muskox and Takin posted as yak.

Not a Yak at all. Doesn't even look like a hybrid Dzo.

I know Gary Gygax put a some of these creatures into his Dungeons & Dragons Monster Manual book and gave them names such as Owlbear, Rust Monster, and Bulette.

They are most commonly known as 'chinasaurs'. Very common and cheap toys I think started appearing in the 1960's and produced for decades after.

It would fit in well with these guys.

Yes it is a Opossum.

A paper I looked at yesterday suggests the Echidna's spur/gland was similarly venomous as the platypus's in the past. As for what came first that would be difficult to determine. Perhaps the two features already existed and converged to create a more potent fighting spur.

Some likely are, but there is a huge variety of mammalian scent glands in many regions of the body that probably have different origins.

It being a modified scent/musk gland seems possible and indeed that is how the Echidna currently uses its gland (its spur is greatly reduced).