Dinosaur which had the longest neck was Mamenchisaurus. Its neck had even 13 – 15 m (43 – 49 ft) in length.
Source: https://dinoanimals.com
Mamenchisaurus means ‘Mamenchi lizard’ and it lived from the Oxfordian to Tithonian ages of the late Jurassic Period in China. The largest species, M. sinocanadorum, may have reached 35 m (115 ft) in length.
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