Meet Spinosaurus: The First Swimming Dinosaur

Spinosaurus aegyptiacus is among the weirdest dinosaurs to have ever roamed the Earth. It is 50 feet long and seven tons in weight, with an enormous "sail" upon its back, an elongated snout resembling a crocodile's, and conical teeth. Past reconstructions of its body included a narrowing tail akin to those of its theropod cousins. But now, a new discovery of an almost complete tail showed what looks like a giant paddle.

The discovery is published in the Nature journal. The description of the tail makes it the most extreme adaptation in the water ever found in such a large dinosaur. It widens our understanding regarding how dinosaurs lived.

Paleontologist and comparative anatomist Nizar Ibrahim, National Geographic's Emerging Explorer 2017-2019 grantee and lead researcher in the study of the fossil, says that the dinosaur is trying to create a fish's tail. The bone's structure, coupled with state-of-the-art tail movement robotic modeling, provide a compelling answer involving a long-standing argument among paleontologists. This argument is the question of how long Spinosaurus spent swimming, with the implied question of how close large predatory dinosaurs got towards aquatic life.

Ibrahim and other colleagues already argued in 2014 for Spinosaurus being the first semi-aquatic dinosaur, but peers questioned it. With the newly analyzed fossil tail bones, this may finally settle the issue: Spinosaurus may not have merely flirted with the water but had full-fledged swimming capacity. The findings suggest that it spent a lot of time swimming in the water. Université Hassan II paleontologist Samir Zouhri, research team member, says that the tail of the animal is unambiguous and that it really swam.

Other scientists now agree that the tail does seem to point to a Spinosaurus that is semi-aquatic. Tom Holtz, a paleontologist at the University of Maryland, says it is certainly a surprise, and that the animal is weirder than previously thought.

The team had found over 30 tail vertebrae of Spinosaurus by 2018. Some of them neatly match Stromer's 1934 illustrations of fragmentary spinosaurid tail bones. This supports the view that a spinosaurid dinosaur lived in the Cretaceous period in North Africa, spanning Egypt to Morocco.

Ibrahim's team also failed to find duplicate bones in the Morocco dig, which points to these fossils belonging to a single individual; this is extremely unusual in the site beds' riverbeds.

A real swimmer

With the help of Harvard Museum of Comparative Zoology vertebrate paleontology curator Stephanie Pierce and her colleague fish biologist George Lauder, robotic computer modeling showed that Spinosaurus' tail had over eight times more forward aquatic thrust and double the efficiency compared to the non-spinosaurid tails of Allosaurus and Coelophysis. This suggests that Spinosaurus spent a lot of time under the water, and could have navigated rivers like a massive crocodile. It is an unprecedented discovery. Ibrahim's team also think Spinosaurus had webbed feet, and they want to examine how widely the animal splayed its appendages.

It is hoped that the dinosaur's bones and the researchers studying them can spark the beginning of the first museum of natural history of Morocco, and possibly inspire others in North Africa to share the dream of those lost worlds they are treading on beneath the ground. Ibrahim dreams of building a home for the Spinosaurus that will become an icon and symbol of African paleontology.