Dragons of my childhood – about a dinosaur that supposedly dived

Smoki mojego dzieciństwa – o dinozaurze, który podobno nurkował

As more information became available about the unusual predator that was Spinosaurus, speculation arose as to whether it was better adapted to life on land or in water. His diet, which consisted mainly of fish, though not exclusively, has long been pointed out. In 2004. A sensation was caused by the spine of a pterosaur, probably Irritator challengeri, from the Lower Cretaceous, with a tooth stuck in one of the vertebrae. In the holotype of Baryonyx, the remains of an herbivorous iguanodon were found.

However, the strongly elongated jaw of Spinosaurus with a peculiar rosette that acted like a pinion, and conical teeth resemble crocodilomorphs more than other theropods. The convergent evolution of the jaws of a spinosaur and a conger, one of the marine eels, has been described. This unique mandibular morphology is a special adaptation for catching small and agile prey (a study was conducted on the mandible of Dryomimus – MNN individual GFD500-503). Attention was drawn to the reduced and receding nostrils, which limited water intake, and the supposedly elevated position of the eye sockets in the skull for better visibility just above the surface of the water.

Through biomechanical comparative analysis of Baryonyxa walkeri with other theropods and modern gavials and alligators, it was shown that its skull was similarly optimized to that of the gavial, as the tubular mouths of both species are highly resistant to the torsional stresses that occur when overpowering large fish. The forelimbs are unusually large for a theropod, and the huge claws may have been used as tools to catch prey. Bones of the hind limb (femur, tibia, fibula and metatarsals) u Spinosaura aegyptiacus do not have marrow cavities (osteosclerosis), which most dinosaurs, especially theropods, have, as confirmed by an Alb-dated fossil of a juvenile tibia (LPP-PV-0042) found in the Araripe Trough, in northeastern Brazil, and therefore millions of years older than the Moroccan spinosaurus.

The bone density of the hind limbs of spinosaurids is 30-40 percent. larger than in other theropods. The legs could therefore act as ballast, making it easier to control buoyancy. A short, massive thigh with a very permanent flexor muscle attachment, a reduced pelvis and flat foot claws correspond to the aquatic propulsion obtained through the legs. The neck and torso lengthened, and the center of mass was shifted forward, in front of the knee joint, unlike in terrestrial theropods. Some have even fantasized about the role of the dorsal sail in diving, comparing the silhouette of a fully submerged spinosaur to a sailfish. They even concluded that it may have played an important role in the active pursuit of underwater prey. However, this was contradicted by subsequent biomechanical studies.

The crowning evidence of spinosaur relationships with water, however, was provided by a study of oxygen isotopes from their dental enamel by Romaine Amiot’s team. The results were compared with an analysis of enamel found in terrestrial theropod species and semi-aquatic crocodiles and turtles during the same period in the same area. Studies have shown that spinosaurids spent a large part of their lives in water, similar to today’s crocodiles and hippos, but different from other theropods. Fish was most likely the main component of their diet.

And what about this dive?

2014 was probably the last year that Nizar Ibrahim, Paul C. Sereno, Cristiano Dal Sasso, Nathan Myhrvold and Matteo Fabbri subscribed to a single article on Spinosaurus, decrying its semi-aquatic lifestyle.They recalled, for example, the pressure receptors distributed along its snout. They theorized that it hunted sharks, latimeriids, sawfish, pinnipeds and ray-finned fish. However, it showed that he would walk poorly on two legs, so he would have to support himself when moving on land.

In 2019. Thomas Arden and his team put forward the theory that Spinosaurus was a highly specialized arboreal predator. Of a different opinion were Hone and Holtz, who pointed out that such sensors, as mentioned by Ibrahim’s team, are also found in other large and non-aquatic theropods. All theories were verified by a find from Morocco, the description of which was published in 2020.

FSAC-KK Riddle 11888

FSAC-KK 11888 is a fossil of Spinosaurus aegyptiacus, discovered in the Cretaceous-derived Kem Kem deck in southern Morocco. This is the most complete skeleton of a Cretaceous theropod from the continent of Africa – it was found there, among other things. As much as 80 percent. his backbone. After careful analysis of the tail with its abundance of nerve endings, it was deduced that the spinosaur’s dermal sail covered more than just the back. This made its tail similar to that of a newt or eel with mechanics analogous to that of a crocodile. The two-dimensional tail model of Spinosaurus was compared with tail models of two theropods: Coelophysis bauri and Allosaurus fragilis, and two semi-aquatic theropods: Crocodylus niloticus and Triturus dobrogicus.

Mechanical modeling made it possible to assume eight times the acceleration and more than twice the efficiency of movement in water of the spinosaurus compared to other theropods, but it was far from the Nile crocodile or the Danube newt. Nizar Ibrahim, Cristiano Dal Sasso and Matteo Fabbri and their team presented the hypothesis that Spinosaurus had a fully aquatic lifestyle. Powered by a tail, it was supposed to be an effective underwater predator! They believe that both Spinosaurus aegiptiacus and Baryonyx walkeri dived, unlike Suchomimus tenerensis.

Come to the water, whale

The return of vertebrates to an aquatic environment has happened more than 30 times on the paths of evolution. Why shouldn’t it also apply to dinosaurs! The scientific sensation of dinosaurs (not ichthyosaurs or mozasaurs) hunting underwater circulated the world in 2020, sparking screaming headlines in the media, starting with National Geographic. Spinosaurus has once again become the most famous of all theropods, and a video showing it diving can be found on the Chicago-based Field Museum‘s website. It would follow, however, that when he went ashore, he moved on four paws, which must have made him clumsy in that environment. Moreover, the bones of aquatic lifestyle dinosaurs are not expected to be found far beyond the former marine environment.

Resistance due to buoyancy

Making spinosaurids aquatic dinosaurs, however, requires a bit more than just proving that their tail was a high-energy source of propulsion and their bones were much denser. Still in 2018. Donald Henderson created the first digital models of Spinosaurus and Dryomimus to study their buoyancy and locomotion. He substantiated his work by comparing it with models of an alligator and an emperor penguin.

The calculations led him to conclude that Spinosaurus, yes, could float, but there is nothing unique about it, because the same capabilities were available to other theropods, such as Tyrannosaurus rex, Allosaurus fragilis, Coelophysis bauri and Struthiomimus altus. Moreover, Spinosaurus would have been unstable, with a tendency to topple over due to the sail. He also did not have the strength to take the plunge. According to him, Spinosaurus or Dryomimus only hunted aquatic organisms on the surface, just as grizzlies do.

Robot battles

In 2022. Paul C. Sereno and Nathan Myhrvold and their team built a biomechanical model of a spinosaur with specific features of its anatomy. It was 14 meters long and weighed 7390 kg, while its density was about 17 percent lower. than the density of water and slightly more than the density of a crocodile. It was noted that the lack of marrow in the bones of the lower limbs is more than compensated for by the marrow cavities of the forelimbs and the hollow spaces of the vertebrae of the front tail and neck. It was concluded that Spinosaurus could not have been an aquatic dinosaur: it had too much buoyancy to dive, and became unstable in deep water.

Due to the position of the center of gravity and the center of buoyancy, the sail destabilized the animal on the surface of the water. Extravagances in the form of a leathery sail in reptiles living today, like the basilisks famous for running on the surface of the water, are meant to inflict chic rather than serve a practical purpose, besides being collapsible. In Spinosaurus, the sail increased underwater resistance by 33.4 percent. That’s not the way the secondarily adapted ichthyosaurs or cetaceans went!

In addition, the animal had a very stiff spine, and the tail didn’t give it much drive compared to its muscle mass. On the surface of the water it moved at a speed of 0.8 m/s, underwater at a maximum of 1.4 m/s. That’s not much compared to mackerel sharks, swordtails, orcas and dolphins, which reach speeds of 10 to 33 m/s. To dive, he would have to extract 15-25 times more power from his tail than what he had at his disposal.

I’m no whale

Myhrvold and his team negated in 2024. way of using the statistical methods that Fabbri had used two years earlier to prove the fully aquatic lifestyle of Spinosaurus and Baryonyx. It was concluded that the data and methods do not support the conclusion that Spinosaurus aegyptiacus and Baryonyx walkeri were underwater hunters – the data that was used to compare underwater predation with other lifestyles was constructed in such a way that it cannot be used for accurate classification.

The nail in the coffin of the aquatic theory, however, are the fossils of Spinosaurus that have been discovered in coastal sediments of ancient shallow inland basins in Niger, far from the marine shoreline – all large, secondarily aquatic vertebrates are marine or have marine ancestors. Spinosaurus also made long-distance trips to land, where it moved on two legs – the powerful claws of its front limbs did not evolve for support. Serano’s group insists on the terrestrial-water lifestyle of spinosaurus and baryonyx, as in hippos, and hunting fish from ambush, as in grizzly bears. Is this the latest iteration of the paleontologists’ dispute over this issue? I have a feeling that it won’t.


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