...we have never been gone from your fifth dimension

[Silk]

'The remaining part of the cycle, we have never been gone from your fifth dimension'

I'm pretty convinced they're the blue avians.

Corey Goode much? Careful whence thou treadeth

How does the above Ra quote convince thee of "blue avians"? Is it the "remaining part of the cycle" part, or "never been gone from your fifth dimension"? Where does it spell out "blue avians"?
Thou art convinced, yet One would'st perhaps fail to see this connection

I feel like they are the ascended, of the reptilian race.
What did avians evolve from?

Just therapods (think "raptor" types). Most definitely not all or any reptile type. Reptiles get a lot of bad rep (eg. "reptilian vs mammalian brain"). Also, to assume late-2D evolution in other worlds includes all the same branching paths as on Earth would be rather folly.

The fact that there are so many hi-D ET reptilian races out there would be a fair indication that they need not become a bird to "ascend" into 4D and beyond.

Evolution is far more varied than a backwater Earth experience would suggest.

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PS: Also, positive 6D entities (and to some extent 5D) would typically adopt the appearance of the 3D race they'd be interacting with. They'd appear no different than those "Venusian Space Brothers" from the 50's