The long and fascinating history of Spinosaurus just got a little more complex. For most of the past century, Spinosaurus was a complete enigma to paleontologists; the original fossils discovered in 1911 were destroyed during WWII and subsequent discoveries were fragmentary. This lack of fossil material prevented paleontologists from understanding the true nature of Spinosaurus, with most depictions looking like a sailed version of Tyrannosaurus (think Jurassic Park 3).
This view changed in 2014 through the work of paleontologist Nizar Ibrahim, who finally uncovered enough of a specimen to definitively give Spinosaurus a “face”. Ibrahim’s Spinosaurus wasn’t your typical theropod by any means; his model demonstrated a sailed quadruped that was more accustomed to living in oceans and rivers than it was on land. At the time, his discovery was controversial because his findings were far outside the accepted norms of theropod appearance and behaviour. Additionally, skeptics of Ibrahim questioned how an eight-ton dinosaur with two-meter long sails was able to swim. These doubts reached their peak in 2018, when a paper written by Don Henderson of the Royal Tyrell Museum concluded that due to its physiology, Spinosaurus would have made for a poor swimmer. As Henderson said, the notion of an aquatic Spinosaurus was figuratively “dead in the water”…. Until now.
On April 29th, Ibrahim came back with a vengeance – a new Spinosaurus specimen that provides indisputable evidence of aquatic behaviour within the species. Whereas previous specimens lacked bones from the tail, Ibrahim’s latest discovery contained over 30 tail vertebrae. While finding new tail vertebrae may not sound like a game changer, these new bones weren’t ordinary. Atop each vertebra lay elongated neural spines, which would have vastly increased the surface area of the tail. While an increased tail surface area would be an inconvenience for any land-dwelling carnivore reliant on mobility, it is advantageous to aquatic animals. The increased surface area would have made the tail powerful and flexible, which would have allowed for Spinosaurus to use its tail as a paddle. In a similar fashion to a modern crocodilian, Spinosaurus would have used its tail to propel through currents with great speed and power. These attributes would have been crucial for Spinosaurus, as its preferred prey of massive coelacanths and sawfish would have made for formidable opponents.
The recent discovery of a tail has finally confirmed what had long been suspected; Spinosaurus is the world’s first semi-aquatic dinosaur. While it may seem outlandish, the adaptation Spinosaurus undertook makes a lot of sense when examined closely. When Spinosaurus was alive some 95 million years ago, its habitat in northern Africa was dominated by vast river systems teeming with large prey. By transitioning to a semi-aquatic lifestyle, Spinosaurus was able to exploit the resources within its ecosystem to the fullest. Further, recent studies have revealed that Spinosaurus shared its habitat with other large predators, including three large predatory dinosaurs as well as massive pterosaurs and crocodiles. By venturing to the water, Spinosaurus was able to avoid competition with more dangerous predators, ensuring its survival over the course of millions of years.
Since it has become a regular for paleontologists to re-vision the appearance of Spinosaurus, I wouldn’t be surprised if I have to rewrite this article in a year or two! When (not if) that happens, I will be excited to talk about what is one of the weirdest animals of all time.
For a more in-depth article on the history of Spinosaurus, check out The 100 Year Old Dinosaur Mystery.
I do not take credit for any images in this article.
Spinosaurus in its habitat illustrated by Mark Winton, found at his blog here
Size comparison of Spinosaurus illustrated by Mario Lanzas, found here
The skeleton of Spinosaurus can be found here
Greshko, Michael. “Fierce ‘Semiaquatic’ Dinosaur May Have Been an Awkward Swimmer.” National Geographic, 17 Aug. 2018, www.nationalgeographic.com/science/2018/08/news-spinosaurus-dinosaurs-buoyancy-swimming-fossils/.
Ibrahim, N., Maganuco, S., Dal Sasso, C. et al. Tail-propelled aquatic locomotion in a theropod dinosaur. Nature 581, 67–70 (2020). https://doi.org/10.1038/s41586-020-2190-
Ibrahim N, Sereno PC, Varricchio DJ, Martill DM, Dutheil DB, Unwin DM, Baidder L, Larsson HCE, Zouhri S, Kaoukaya A (2020) Geology and paleontology of the Upper Cretaceous Kem Group of eastern Morocco. ZooKeys 928: 1-216. https://doi.org/10.3897/zookeys.928.47517
Pickrell, John. Weird Dinosaurs. Columbia University Press, 2017.
Treat, Jason. “Bizarre Spinosaurus Makes History as First Known Swimming Dinosaur.” National Geographic, 29 Apr. 2020, www.nationalgeographic.com/science/2020/04/first-spinosaurus-tail-found-confirms-dinosaur-was-swimming/.