No dinosaur was built for swimming
The core idea stands, but key numbers or details have changed.
TaughtDinosaurs were land animals. Some may have waded at the water's edge, but none was a true swimmer; nothing in the fossil record showed a non-bird dinosaur adapted to move and hunt underwater the way a fish or a crocodile does.
NowIn April 2020, a nearly complete Spinosaurus tail from Morocco, described in Nature, changed that. The tail was a tall, flexible fin shaped for propulsion, not balance. Robotic models of it produced real thrust in water, making Spinosaurus the first non-bird dinosaur known to have been adapted for active swimming.
What actually happened
Spinosaurus had long been the odd one out (bigger than T. rex, with a sail on its back and a crocodile-like snout) but its lifestyle was guesswork until the tail turned up. More than 30 tail vertebrae carried long bony struts that gave the whole thing the profile of an oar.
The honest hedge: paleontologists still argue about exactly how aquatic it was: a pursuit predator chasing fish underwater, or a giant heron snatching prey from the shallows. Later studies of its unusually dense bones lean toward genuinely submerged hunting, but the debate is live.
What did change is the flat claim: that no dinosaur was ever built to swim. The tail says at least one was.
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Who was taught this
Still standard through 2020, so anyone who finished school between 1950 and 2020 learned the earlier version.