this article lead me to Wikipedia articles for Etruscan and Rongorongo which then led me to the article for language isolate
https://en.wikipedia.org/wiki/Language_isolate
fascinating
"In some situations, a language with no ancestor can arise. This frequently happens with sign languages—most famously in the case of Nicaraguan Sign Language, where deaf children with no language were placed together and developed a new language.[7]"
also learned this from the Wikipedia article on Language isolate
@packetcat the linguists were brought in to teach some stubborn kids an existing sign language and were delighted when they realized the kids were just coming up with one of their own instead