Spinosaurus likely stood on its hind legs, with dense bones suited for walking upright. Credit: James Gurney
Phys.org has an article about the on-going controversy on whether Spinosaurus aegyptiacus was fully aquatic. S. aegyptiacus was discovered in 1915 in Egypt by Ernst von Stromer. It lived during the Cretaceous Period about 99 to 93.5 million years ago. The original skeleton was destroyed during WW II. A new specimen was found in 2014, which was the basis of a 2014 paper published by a team led by Paul Sereno at the University of Chicago that redescribed the animal. In 2020, a team in the UK published a paper that postulated that S. aegyptiacus lived an aquatic lifestyle based on the density of its bones, its center of gravity, and a fin down its tail. Now, the original team have published a new paper, which refutes the aquatic lifestyle theory due to new evidence.
The team also calculated that Spinosaurus would have been too buoyant to fully submerge itself regularly, needing 15 to 25 times the estimated power of its tail. The bone and muscle structure of the tail wouldn't have been flexible enough to propel it smoothly through water, unlike the fleshy tail flukes on whales or light, springy fish fins. The heavy, bony sail on its back also would have made it an awkward swimmer that struggled to right itself, unlike alligators and crocodiles that can easily spin and roll to pursue their prey.
Finally, Sereno's team turned to the geographic fossil record to argue that Spinosaurus could not be a highly specialized, fully aquatic predator. More of its fossils have been found in two inland basins in Niger, far from any prehistoric marine coastline. They were buried in riverbank deposits alongside other large herbivores and suggests that they lived along both marine and freshwater habitats.
In the new paper, the authors conclude that this evidence is a strong confirmation that Spinosaurus aegyptiacus is "a semiaquatic bipedal ambush predator that frequented the margins of both coastal and inland waterways."
