says that of modern threatened-but-not-extinct mammal species, we have recorded fossils for 9% of them. For non-threatened extant mammal species, we have recorded fossils for 20% of them. Assuming that's correct, it doesn't seem crazy to imagine that we might not have fossils for a species or it's say 5 ancestors species that existed let's say 10M years ago -- fossils are also subject to being broken or subducted and so we would expect recent species to leave a greater fossil record. And being an intelligent, cultural species may reduce the chance of fossils being formed for high populations, due to death practices.
We do find for example many different fossils for say triceratops. But that shouldn't be taken to mean that we find lots of different fossils for every, or even most, species extant at the time of the triceratops.
Considering an extant species is like picking an arbitrary point in the existence of a past species, and excluding all fossils formed after that point. On average that half the fossils. As for threatened species, just a guess, but I’d expect most of those to be likely have relatively small populations to start with and live in constrained habitats, all factors that would tend to mean they would leave a lot fewer fossils on average anyway.
A advanced technological species would need to exist in huge numbers to support a developed economy. Id expect them to colonise widely. Also I’d expect artefacts to exceed individuals by probably a handful of orders of magnitude.
I think you're dramatically overestimating the likelihood that artifacts would survive in recognizable form for millions of years. I do think we can be reasonably sure that there was no advanced technological society let's say 50,000 years ago. But 20M years ago is another story. 5M years might be another story.
Whether you'd find fossils of an advanced technological species at a point in their history when they might have a population of billions seems incredibly contingent on unknowable things about their culture. But the question of whether you'd find fossils of them from their prehistoric period (in which their population would not necessarily be enormous), or of their evolutionary ancestors seems less contingent, and very plausibly you wouldn't.
says that of modern threatened-but-not-extinct mammal species, we have recorded fossils for 9% of them. For non-threatened extant mammal species, we have recorded fossils for 20% of them. Assuming that's correct, it doesn't seem crazy to imagine that we might not have fossils for a species or it's say 5 ancestors species that existed let's say 10M years ago -- fossils are also subject to being broken or subducted and so we would expect recent species to leave a greater fossil record. And being an intelligent, cultural species may reduce the chance of fossils being formed for high populations, due to death practices.
We do find for example many different fossils for say triceratops. But that shouldn't be taken to mean that we find lots of different fossils for every, or even most, species extant at the time of the triceratops.