Paleo Profiles: Spinosaurus

From the National Geographic Museum

A recent discovery, as of writing, has once again changed how we view the large, carnivorous dinosaur Spinosaurus. Every new discovery revolutionises how we see this dinosaur, and truly shows how diverse dinosaurs were as a group. While fairly accurate for its time of release, Jurassic Park III boasted that they were showing a carnivore larger than Tyrannosaurus, but since then new discoveries have completely changed how we see Spinosaurus. A new discovery could mean this blog could become quickly outdated. I also want to stress, the recent paper is still somewhat contested so bare that in mind while reading today.

Discovery and Fossils

Saying that Spinosaurus changed with each discovery is an understatement. The first fossils of Spinosaurus were discovered in the Bahariya Formation in Egypt in 1912, and was later formally described by German palaeontologist Ernst Stromer. He could tell from the fragmentary remains that it was a theropod, the bipedal carnivorous dinosaurs, but it had curious neural spines which formed a sail on its back. Due to this, Stromer named it Spinosaurus aegyptiacus, 'Spined Lizard from Egypt', and with the fragmentary remains he based the reconstruction on another, recently discovered, big theropod - Tyrannosaurus. Spinosaurus was reconstructed as being like a T rex with a sail on its back, but scientific knowledge of the 1910s meant that it was portrayed as dragging its tail along the ground. Stromer would discover many other dinosaurs from Egypt, but they are all sadly lost. An Allied bombing raid in 1944 destroyed the museum which kept Stromer's fossils, and the specimens were destroyed. As a result, a new reconstruction wasn't made until the 1990s! With the destruction of Stromer's specimens palaeontologists found it hard to identify which fossils belonged to Spinosaurus, however, new discoveries and other spinosaurids being found, such as the Baryonyx from England, allowed a new reconstruction. This one changed the skull from resembling a tyrannosaur, to the one we have today with an elongated jaw - this is the reconstruction used in Jurassic Park III. In 1996 a new find from Morocco indicated a possible second species, but that it still heavily debated with palaeontologists debating whether it is the same species as the first one discovered. Then, in the mid-2000s, it was discovered to have a small crest on its head, and in the late-2000s a well-preserved snout revealed a series of nerves. Isotope analysis, mixed with this, indicated that Spinosaurus was largely a fish eater - something long theorised which was now confirmed.

From 1915 to 2014 to 2020, from National Geographic

A 2014 paper, led by Nizar Ibrahim revolutionised how Spinosaurus has been reconstructed. This paper made the dinosaur a quadruped, semi-aquatic, and had a newly shaped sail, which was likely covered in some skin. This caused waves in the palaeontological community, albeit for some controversial reasons. Many agreed that Ibrahim's reconstruction, which utilised 3D modelling, offered a new insight into the life of Spinosaurus - palaeontologists had realised that it was top-heavy, but a quadrupedal lifestyle would solve that issue. However, as Ibrahim had combined several specimens together it was criticised, and the reconstruction shortened the hind legs of the Spinosaurus. It was seen as being a combination, and not an actual specimen, and the now shorter hind legs created issues with other spinosaurids. Baryonyx and Suchomimus, for example, had much longer hind legs, although the only specimens of these animals were juveniles. Others have theorised that younger spinosaurids had longer legs which ceased to grow at the same rate as the rest of the body as the animal aged. This brings us to 2020. Ibrahim and his team had discovered more tail bones of a Spinosaurus, something which had not been found before. Neural spines and chevrons were found on the tail, these spines were long, and did not overlap allowing flexibility. This means that the tail was adapted to an aquatic lifestyle - it has a resemblance to a crocodile's tail. Spinosaurus had gone from a sailed bipedal lizard which dragged its tail on the ground, to a fish-eating, aquatic or semi-aquatic dinosaur.

Biology

The spines at the National Geographic Museum

We've largely looked at the biology of the Spinosaurus in the discussion about the fossils discovered, so we'll go over it quickly here. The most iconic aspect of Spinosaurus is its 'sail'. Since the early-2000s it has been debated whether it was a sail or a hump - something which would heavily determine what type of lifestyle the Spinosaurus had. One theory, which is widely accepted regardless of whether it was a hump or sail, is that it could be used for display - bright and intimidating colours, including the sheer size of it, could be used to deter rivals or attract mates. When it was more accepted that dinosaurs were cold-blooded, a theory argued that the sail could be used for thermoregulation with the Spinosaurus basking in the sun to warm itself up. However, it has largely been found that dinosaurs, especially larger dinosaurs, were more warm-blooded than cold, with them likely being somewhere in-between. Consequently, this theory has largely gone out of favour. The hump theory argues that it is a fatty buildup to sustain the dinosaur while it was searching for new food reserves. Since 2014, it has generally been seen as some form of 'sail' with skin covering it. With recent discoveries revealing an increasingly aquatic lifestyle, a likely function was to aid in locomotion. Ibrahim's findings have revealed a much more streamlined animal making it more aerodynamic to cut through the water. The 'sail' would serve as a way to cut through the water more efficiently.

The new tail, from National Geographic

The new paper is still being debated - Mark Witton, for example, has argued that the tail bones may not be entirely suited to an aquatic lifestyle. However, we do see a lifestyle mostly suited for the water, maybe a semi-aquatic one like a crocodile. Ibrahim has reconstructed the dinosaur with webbed feet, for example. Before 2014 it was assumed to be a terrestrial animal which fed on fish - the long snout with crocodile-like teeth was suited to grabbing hold of fish, it had strong forearms to swipe at its prey, and its skull seemed adapted to standing for long-hours at the waterside. The BBC documentary Planet Dinosaur, for example, used this idea. This theory had Spinosaurus hunting like a heron or stork, largely based on the skull. The eyes and nostrils are high up the head while the snout was covered in nerves and receptors. The snout could be in the water to detect movement, while the nostrils and eyes could be out of the water, so it could see what it was hunting and it could still breathe. However, the recent discoveries has changed how this would work. Instead, Spinosaurus would hunt like a crocodilian - using its sensitive snout to find fish and turtles through the murky waters. With the nostrils and eyes high up the head, this would allow the Spinosaurus to poke its head out of the water while remaining submerged. The new shorter hind legs is part of the aquatic lifestyle - short but muscular to give propulsion to power the dinosaur through the water.

Finally, we have the size of the Spinosaurus itself. Until relatively recently many of the established sizes were estimates. Even today, the size of the Spinosaurus is still based on estimates. Back when Spinosaurus was thought to be bipedal estimates placed the dinosaur at over 4 metres in height (discounting its sail), but the recent findings have placed this as being around 3 metres (again discounting the sail). The original height placed it as being one of the most, if not the most, tallest carnivorous dinosaurs - taller than the Tyrannosaurus. Spinosaurus is still very big coming to a minimum length of 15 metres (about 49 foot), and its largest length is estimated to be around 18 metres (59 foot). Its skull was big coming to around 1.75 metres (5.7 foot) from snout to the back of the skull. It was full of teeth evolved to grasp hold of fish, these teeth could be over an inch in length.

When and Where 

Unfortunately for Jurassic Park III fans, Spinosaurus would never have met Tyrannosaurus. Not only is it found in an entirely different continent, but it lived several million years before the Tyrannosaurus came about. Tyrannosaurus evolved at the very end of the Cretaceous period being one of the last dinosaurs, whereas Spinosaurus lived in the early Cretaceous until the late Cretaceous. The oldest fossils date around 112 million years ago, and the most recent fossils have been dated to around 93 million years ago. This was a time when large, carnivorous dinosaurs became very diverse. There were the spinosaurids, abelisaurids, tyrannosaurids, carcharodontasaurids to name a few. Spinosaurus, meanwhile, lived in two areas - the Bahariya Formation in Egypt and the Kem Kem Beds in Morocco. As a result, both species are named in reference to where they have been found: Spinosaurus aegyptiacus and Spinosaurus maroccanus. However, as mentioned earlier, there have been debates about whether the Moroccan species is actually the Egyptian species. 

The World of Spinosaurus

From National Geographic, Art by Davide Bonadonna

Knowing that Spinosaurus was aquatic, or semi-aquatic, you may be wondering why the Spinosaurus lived in the arid regions of North Africa. However, back in the Cretaceous North Africa was a shoreline and a mangrove forest creating the perfect environment for a giant, crocodile-like dinosaur. Both sites where the dinosaur has been found are full of a diverse range of fish and aquatic life - sharks, sawfish, coelacanths, lung fish, ammonites, crabs, oysters, rays, and crocodiles. A mangrove swamp full of life with access to the sea proved to be the perfect habitat for the Spinosaurus. Other dinosaurs lived in the region including the giant sauropods (long-necked dinosaurs) Paralititan and Aegyptosaurus. However, the Bahariya Formation and Kem Kem Beds were full of giant carnivorous dinosaurs - these places have been described as possibly the most dangerous places to go on safari in history. Possibly the largest carnivorous dinosaur Carcharodontosaurus were found here, as well as many other big carnivores like Deltadromeus and Rugops being just the most well known. With so many carnivores around it is evident that they had to specialise to avoid competition, Spinosaurus could happily hunt the waves to avoid contact with a hungry Carcharodontosaurus. This does not mean there were overlaps in prey. The spinosaurid Baryonyx has been found to have preyed upon the herbivorous Iguanodon, so it is not too far-fetched that the Spinosaurus could prey on dinosaurs which went too close to the shoreline. Neural spines have been found with chunks taken out of them by a large carnivore, likely Carcharodontosaurus, indicating that at times clashes could have happened. 

The sources I have used are as follows:

-Michael Greshko, 'Bizarre Spinosaurus makes history as first known swimming dinosaur', National Geographic, (29/04/2020), [Accesed 08/05/2020]

-Jason Treat and Mesa Schumacher, 'Reconstructing a Gigantic Aquatic Predator', National Geographic, (29/04/2020), [Accessed 08/05/2020]

-'Spinosaurus', Prehistoric-Wildlife.com, [Accessed 08/05/2020]

-Ben G Thomas, 'The New Look of Spinosaurus', YouTube, (03/05/2020), [Accessed 08/05/2020]

-Trey the Explainer, '"New" Spinosaurus', YouTube, (30/05/2015), [Accessed 08/05/2020]

-Nizar Ibrahim, Simone Maganuco, Cristiano Dal Sasso, Matteo Fabbri, Marco Auditore, Gabriele Bindellini, David M. Martill, Samir Zouhri, Diego A. Mattarelli, David M. Unwin, Jasmina Wiemann, Davide Bonadonna, Ayoub Amane, Juliana Jakubczak, Ulrich Joger, George V. Lauder & Stephanie E. Pierce, 'Tail-propelled aquatic locomotion in a theropod dinosaur', Nature, 581, (2020), 67-70

-Nizar Ibrahim1, Paul C. Sereno, Cristiano Dal Sasso, Simone Maganuco, Matteo Fabbri, David M. Martill, Samir Zouhri, Nathan Myhrvold, and Dawid A. Iurino, 'Semiaquatic adaptations in a giant predatory dinosaur', Science, 345:6204, (2014), 1613-1616

-Thomas Holtz, 'Spinosaurs as crocodile mimics', Science, 282:5392, (1998), 1276-1277

-Simone Maganuco and Cristiano Dal Sasso, 'The smallest biggest theropod dinosaur: a tiny pedal ungual of a juvenile Spinosaurus from the Cretaceous of Morocco', PeerJ, (2018), 6

-Jan Gimsa, Robert Sleigh, and Ulrike Gimsa, 'The riddle of Spinosaurus aegyptiacus’ dorsal sail', Geological Magazine, 153:3, (2016), 544-547

-Planet Dinosaur, (2011), BBC, 14 September

Thank you for reading. For other Paleo Profiles we have a list here, and for other blog posts we have a Facebook or catch me on Twitter @LewisTwiby.