Before 2014, paleontologists had only a handful of fossils from the tail of Spinosaurus. They theorized that its tail, like that of other theropods, was primarily used to balance the forward-leaning center of gravity and was most likely rigid. They thought the tail was also a secondary means of aquatic propulsion, adding thrust to the movement of the limbs as it crawled and waded in the shallows. (Read about how the bizarre Spinosaurus makes history as first known swimming dinosaur.)
Excavations in 2018 in Morocco found 131 additional bone fragments, including 36 vertebrae, fundamentally changing our understanding of the Spinosaurus tail.
The latest find paints a much clearer picture of the tail. It is far more elongated vertically and less rigid