Are you asking specifically to the Australian examples or examples in general? History is replete with many of the latter, in part because the custom was to keep certain artisans/state technologies secret. Before openly disclosed patents were the norm, technologies like greek fire, damascus steel, or Leeuwenhoek's lens often died with those who knew how to make them.
I was curious about specifically Australian examples as the comment implied they had examples in mind such as losing the use of the bow and arrow or somesuch.
The story there is more complex and there's a faction in Austalia that would insist that Australian aboriginals were on the decline when Europeans arrived.
The entire city of Petra was lost to western society (rediscovered in early 1800s) despite it being a part of the Roman Empire at one point and major trading hub for hundreds of years.
One of the problems of reading digital books (at least for me) is near-completely forgetting where a fact came from, and just remembering the fact. The source was a book on the future actually being likely to be good/improving from where we are now.
My memory on the specifics is vague. I remember him saying they had lost fish hooks (maybe just some fishing technique in general?). And that further losses occurred in the migration to Tasmania, leaving the settlers there even further behind.
Some people that replied to this comment were saying Damascus steel was "lost", which is mostly a meme.
If we're talking about modern times, Damascus steel can be easily forged and replicated by modern hobbyist smiths.
If we're talking about being lost at some point between 0AD and, say...1900 AD, then it was probably just not economically viable to make it. Damascus steel is very labor-intensive to produce and does not offer significant structural advantages compared to regular mild or tempered steel. Certainly not in applications where most metal was used in the middle ages (hint: it was warfare).
For example, it makes no sense to make a full-plate armor or a musket out of Damascus steel. It would be mostly a status item, rather than a practical tool.
Hence when we say "lost", it likely just means people looked at it and decided it wasn't worth the time outside of niche applications. And since it was niche, there is very few historical artifacts, that make it look "lost", when in reality, there just weren't too many of these items to begin with.
I do not know where you've got your version from (especially that it was lost between 0AD and the 20th century, when it actually had been the 19th and 20th and Damascus steel didn't exist before the 6th century), but I know about this one:
Many people in Europe saw these steels and tried to recreate the effect through processing. However, they could not discover the secret, and could not make it. Though there was a demand for Damascus steel, in the 19th century it stopped being made. This steel had been produced for 11 centuries, and in just about a generation, the means of its manufacture was entirely lost. The reason it disappeared remained a mystery until just a few years ago.
As it turns out, the technique was not lost, it just stopped working. The "secret" that produced such high quality weapons was not in the technique of the swordsmiths, but rather on the composition of the material they were using. The swordsmiths got their steel ingots from India. In the 19th Century, the mining region where those ingots came from changed.
So it was never really lost. As far as we know it simply wasn't produced in 1 particular region (Europe) for a relatively short amount of time (1 century).
And, like I said before, it did not offer any significant structural advantages for its labor inefficiency. So "Damascus steel" is just 1 minor technique of producing a specific steel alloy, with many substitutes that had been used in its place.
It's not like human civilization suddenly lost the technology of steel production and forging.
Lost tech is a meme. I could say the modern humanity lost the tech of making horse armor, but it is just inaccurate semantics. We can still make metal and we can still make armor in the shape of a horse, we just don't, because there's no demand for it.
I don't think I'd count the Antikythera device. My understanding is that the mystery with it is how it was made. The astronomical and mathematical knowledge to design it was well known among the Greeks.
If Antikythera devices were common, with say every ship having one, every town and village temple having one, every school having one, and so on we'd have a big mystery because we don't think the Greeks had the technology for mass production of mechanisms with the necessary accuracy and precision.
But we've only found one, and we don't know how long it took to build.
The Antikythera device could be the work of one builder and his assistants over a lifetime, financed by someone very wealthy and able to supply as many slaves as the builder wanted. It could even have been built over more than one lifetime, if the sponsor was a government.
When you are not in a hurry and you have a lot of laborers you can make very precise mechanisms with little more technology than blocks of metal and hand files.
As Teller of Penn & Teller once observed, "Sometimes magic is just someone spending more time on something than anyone else might reasonably expect". Penn has said "The only secret of magic is that I’m willing to work harder on it than you think it’s worth".
In case anyone here hasn't seen it, I want to share this very cool youtube series of an Australian clock maker creating a replica of the Antikythera device using only tools believed to be available to the ancient Greeks: https://www.youtube.com/watch?v=ML4tw_UzqZE&list=PLZioPDnFPN...
Or is this some Quadrant sourced opinioning?