Interesting NASA survey described in the Atlantic about the limits of science and technology to detect past civilizations.
Difficult to reconcile:
Part of the above can be explained:
On 1, we assume that communication is human-like using current or near-current technologies. Anything outside that range is something we would miss.
On 2, we assume that space travel is the end objective, not simulation or miniaturization.
I agree that it's doubtful dinosaurs ever evolved to human-like technology levels. But, let’s explore that interesting notion (that anything older than a couple of million years would be almost impossible to detect - fossils, tools, and even the hallmarks of advanced societies like skyscrapers will decay and be buried deep in the crust after a few million years).
So the math says that there’s plenty of time for other advanced specifies to have emerged, died off, and/or remain hidden from our current technological survey systems (radar, LIDAR).
I think that the most plausible features of such a candidate species would be (as many of) the following (as possible):
The above article resituates the locus of our speculation upon the terrestrial and earthly. What about space travel in such a scenario? A smattering of concerns:
In the discussion of space travel, I think we tend to overlook the usefulness of miniaturization. Star Wars depicts massive fleets of gigantic battle cruisers, X-Com's Earth is invaded by city-size motherships, Independence Day is the same, etc. While those are awesome franchises, scientifically-speaking miniaturization has rarely been considered in Science Fiction (Three-Body Problem being the only franchise I'm aware of that employs that directly as a narrative conceit).
Miniaturization is advantageous for many reasons: it makes a spacecraft difficult to detect (and attack), a spacecraft would probably have lower energy needs, and one is able to have a higher density of spacecraft per unit of space improving survivability and redundancy as one spreads across the infinite expanse (of spacetime).
I think that miniaturization would also be an option for such a species. Provided they could achieve miniaturization technologies, I'd think they'd also still have the ability to produce large spaceships, xenomorphs, etc. (For humanity, miniaturization is likely to come in at the tail end of technological development. Even XNA - yes, xeno nucleic acid, has been solved before the so-called "fat fingers problem".)
The presence of miniaturization in some past (yet, futuristic) animal societies might also help explain the absence of various artifacts being discovered.
To create advanced drone technology (and manufacture it) would seem to require fairly strong infrastructure and scientific capabilities that are "off the grid" (so to speak).
I can think of no other set of current/extant organizations/institutions with those capabilities save for the Drug Cartels who have near-complete dominance over several countries in Central America now.
They have far-ranging science, logistics, and infrastructure capacities that extend across continents. They can manufacture advanced and synthetic chemicals with relative ease. Is it possible they dabbled in aerospace and achieved certain breakthroughs? (They certainly don't disclose their chemistry research with the wider scientific community.)