But apparently, not all of the sentient dinosaurs perished; it would seem, based on other TV shows, that at least one species survived to evolve down through the ages into what humans would call "dragons". (Over in the Tooniverse, many species of dinosaurs survived, still sentient, but they became the slaves of the emerging dominant species - humans. But again, they also "devolved" into dragons; some of whom were evil killers lusting after gold. A more gentle breed of dragons finally passed through the dimensional veil to establish their own lands where they could live in peace with limited human contact.)
During the Middle Ages, one of the dragons was challenged to combat by St. George. However, the dragon was reluctant to fight, as he was more of a dilettante who wanted nothing more than to be left alone in order to write his poetry. He considered himself a troubadour, not a terrible lizard. Luckily, the reluctant dragon and St. George were able to work out a plan in which their reputations could be upheld and the villagers would be satisfied that they were safe.
Another sentient dragon from that time was placed in a magical form of suspended animation and was revived in the 20th Century. He ended up in New Haven, Connecticut, where he found employment as a weatherman's sidekick on a local TV station, WWEN. (It could be that this dragon was descended from Charlene Sinclair. In relation to that, the reluctant dragon who faced St. George may have been descended from Charlene's older brother, Robbie Sinclair. By the way - the Sinclair children were all adopted in the egg stage.)
There was a race of intergalactic superior beings who were known in legend as "The Preservers", who transported basic human stock to various planets in order for them to flourish in evolution. The same was also done for whales. It could be that it was also done for these dragons, for we saw that the Space Family Robinson encountered a space-faring dragon and the knight who pursued her. (Sir Sagramonte and Gundemar could have been the reincarnations of St. George and the dragon troubadour respectively, doomed to relive their entwined karma down through the ages.)
Other species of dinosaurs evolved to be more humanoid in appearance; but they could have been from a different species of reptilian life, left behind on Earth by those same Preservers from some other planet. That would mean they could be related to the intergalactic humanoid lizards who tried to take over the Earth back in the 1980s. (Among the tribe of Iddiocy to which I belong, there is a name for such alien lizards. It is "Getorpho".)
I don't know if it's happening on the main Toobworld, or in some alternate TV dimesnion, but there are intelligent dinosaurs who still walk among the humanfolk. But they adapted a scientific technique in which they were able to assume human form and thus escape detection.
<'Shirley Temple's Storybook' - "The Reluctant Dragon"
'Star Trek' - "The Paradise Syndrome"
"Star Trek IV - The Voyage Home"
'Lost In Space' - "The Questing Beast"
'Land Of The Lost'
'Arthur Conan Doyle's The Lost World' - "More Than Human"
'V: The Mini-Series'
'V: The Series'