Dinosaurs were scaly, sluggish reptiles
The old claim turned out to be wrong and was rejected by evidence.
TaughtDinosaurs were cold-blooded, slow-moving, scaly reptiles: essentially oversized lizards.
NowMany dinosaurs had feathers, and the group was active and warm-blooded or something close to it. The first clearly feathered dinosaur, Sinosauropteryx, was described from China in 1996.
What actually happened
The rethink started earlier than the evidence that clinched it. John Ostrom's work on Deinonychus in 1969 and Robert Bakker's arguments through the 1970s made the case that dinosaurs were active animals with bird-like posture, and the idea filtered into popular culture by the time Jurassic Park came out in 1993.
What settled it was a run of extraordinary fossils from the Yixian Formation in Liaoning, China, starting with Sinosauropteryx in 1996. These preserved filaments, then unmistakable feathers, on animals that were clearly not birds. Feathers are now known across a broad swath of the dinosaur family tree, and some fossils preserve melanosomes that let researchers reconstruct actual colors. If your textbook's illustration was a green-brown lizard dragging its tail, every element of that picture is wrong.
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Sources
- American Museum of Natural History: Dinosaurs among usamnh.org
- Smithsonian: The origin of feathersnaturalhistory.si.edu
Who was taught this
Still standard through 1999, so anyone who finished school between 1950 and 1996 learned the earlier version.