>>116112922The problem is that holotype specimen of Troodon is a single tooth; when it was first described in the 1850s, we didn't have anything like it, so it was clearly distinct. The fact that it was just a tooth also meant it bounced around taxonomically for a while - it was a lizard until about 1900, then a megalosaur, then a pachycephalosaur, then after Stenonychosaurus was found (with better remains than a tooth) it was figured to be related to it. In the 1980s Stenonychosaurus (among others) was lumped into Troodon, which became a wastebasket for basically all American troodontids. By the 2010s specimens once referred to Troodon were being split off as their own genera, so at one point someone went ahead and pulled the trigger on calling the whole genus dubious since, after all, the type specimen is a single tooth, which at this point is no longer considered unique enough to be diagnostic for the genus, since we have a bunch of more complete relatives now. Stenonychosaurus was re-validated, Troodon was restricted to the tooth. However, if they can ever find a specimen in the same strata the holotype came from that has enough material to diagnose it, Troodon will become a fully valid taxon again; whether or not Stenonychosaurus gets sunk back in would entirely rely on said specimen being similar enough.
That said, the reason the family name is still used is that although the tooth isn't diagnostic enough for a genus, it is still identifiable to the family level. Same reason why Titanosauridae and Ceratopsidae are valid even though their type genera aren't very good. Funny thing is though, our pachycephalosaur material outside their skull domes is very sparse, and a few years ago they found a skull that preserved some of the more anterior teeth, and wouldn't you know they look like theropod teeth, maybe even a bit troodontid-like iirc. So hypothetically the Troodon holotype tooth could end up not being diagnosable to the family level either, time will tell.
