Dinosaurs: How long did they live? (2009)
theguardian.com
theguardian.com
It is likely that a dinosaur of the size of T-Rex would overheat if covered with feathers.
It is still possible that T-Rex had feathers when very young and then lost them when growing large enough.
Previously it was believed that the pterosaurs were covered by some kind of hair (i.e. unbranched), not by feathers.
(Most depictions of pterosaurs in movies are probably wrong, because they do not show even the hair, whose existence has been known for many years, much less that the hair was in fact some kind of bird-like down, which is a very recent discovery.)
The pterosaurs are not dinosaurs, but they are related to dinosaurs, probably closer to them than to crocodiles.
If it is true that the pterosaurs also had feathers, it is unlikely that feathers have evolved twice, as they are much more complex than hair.
In that case, the ancestor of all dinosaurs already had feathers. We know that there are many kinds of large dinosaurs, especially most of the large herbivores, which did not have feathers. If the common ancestor had feathers, then all the large featherless dinosaurs have lost their feathers, like the elephants and the rhinoceroses, which have lost their hair, presumably for improved cooling.
useful and interesting to see that everyone here is saying "yes" to the birds question
hm? pointers please.. if they lay eggs then that is "reptile" no? I don't claim to know, I am asking..
Birds lay eggs and are definitely warm blooded. Not to mention the odd mammal that lays eggs like the platypus.
https://v.redd.it/vn0qwpongl391
One of the coolest discoveries IMO is the tucking position, which is usually attributed more or less exclusively to birds.