Spinosaurus is First Known Semi-Aquatic Dinosaur

By Jon Tennant | September 11, 2014 1:00 pm
Spinosaurus aegyptiacus trawls for mesozoic fish. Illustration by Brian Engh

Spinosaurus aegyptiacus trawls for mesozoic fish. Illustration by Brian Engh

The meat-eating dinosaur Spinosaurus rose to terrifying fame in Jurassic Park III, when it took down the comparatively small Tyrannosaurus rex. Now, thanks to a newly discovered partial skeleton, Spinosaurus has an even greater claim to fame: this fearsome sail-backed beast spent much of its time in the water, a definitive first for dinosaurs.

Aquatic Hunter

A global team of paleontologists digitally reconstructed the skeleton of Spinosaurus aegyptiacus based on a new specimen from the Kem Kem beds of eastern Morocco. The fossils confirm that Spinosaurus was more than 49 feet (15 meters) long – at least 8 feet longer than T. rex, in line with previous estimates based on more fragmentary specimens. But the new skeleton was shown to be still growing, so a full adult would have been even bigger.

More unusually, there were signs that the dinosaur was a fantastic swimmer. Researchers determined that Spinosaurus had a suite of adaptations that allowed it to spend much of its time in the water and that, contrary to Jurassic Park’s representation, would have required the animal to walk on all four limbs when it was on land. That makes Spinosaurus the first dinosaur known to be adapted to a semi-aquatic lifestyle.

Similar to some extinct marine reptiles such as pliosaurs and also to modern crocodiles, Spinosaurus possessed an array of small openings in the end of its snout that came together to form an internal network. In crocodiles this structure houses pressure sensors used to detect movement in water; Spinosaurus may have used them to find prey such as sharks, sawfish and lungfish. Its conical teeth would have been ideal for catching fish, and its neck and back vertebrae were designed for maximum movement of the head while underwater. Further similarities to crocodiles include the position of the nostrils, which are placed much further back on the skull than any other dinosaur. This would have enabled Spinosaurus to breathe while almost completely submerged.

Taking to the Seas

Spinosaurus’ tail vertebrae were formed in a way that allowed maximum propulsion, suggesting that the dinosaur was a powerful swimmer. Its short legs and flat feet are superficially similar to early ancestors of whales and even some modern mammals that use their hind legs for paddling.

Adaptations to Spinosaurus’ skeleton to facilitate swimming would have hindered it on land, however. Its center of gravity was much further forward than other theropod dinosaurs, meaning it was probably unable to walk on two feet. Some bones in its skeleton were also denser than other theropods, a clear sign that this animal was adapted to spending more time in water.

Finally, the unusual “sail” on the back of Spinosaurus, previously thought to regulate body temperature, now seems likely to have been used for display, remaining exposed above the water while the animal was swimming.

Many animals in the past have evolved from land-dwelling ancestors into swimming marine forms, including early crocodiles, turtles, scaled reptiles, and mammals. Spinosaurus may have been part of a dinosaur lineage that was experimenting with adapting to a fully aquatic life. As it lived alongside numerous other giant predators, including dinosaurs and crocodiles, this would have enabled it to exploit a new feeding niche, reducing competition. It shows us that even the largest predatory dinosaurs were not evolutionary “dead-ends,” but actually successfully evolving into a range of bizarre and diverse forms.

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  • Matt

    “Many animals in the past have from land-dwelling ancestors into evolved into swimming marine forms…” This sentence needs to be corrected. Otherwise, good read.

    • Guest

      Could Spinosaurus collapse it’s sail like modern Sailfish?

      • Jon Tennant

        There isn’t any evidence to suggest that it could. The neural spines were also pretty solid pieces of bone, so it was probably held permanently stiff and erect.

    • Jon Tennant

      Oops, looks like I forgot how to evolution – thanks!

    • Emkay

      the sentence says ‘Many animals in the past have evolved from land-dwelling ancestors into swimming marine forms, including early crocodiles, turtles, scaled reptiles, and mammals.’…. then it says ‘you’re a moron.

      • Matt

        When the article was first published eleven days ago, it read exactly as I COPIED AND PASTED into my comment. The author Jon Tennant replied to my comment, saying thanks for pointing out the typo and he has since corrected it. If you’d like to have conversations with the adults, try to keep up. I hate to be snarky, but I don’t appreciate being called a moron by someone who get here eleven days late.

        • Emkay

          since you did not ‘keep up by removing your post, you’re a snarky ‘fuking moron…

          • Matt

            “you’re a snarky ‘fuking moron…” Insults and cursing, the calling card of the childish. If you cannot have a conversation like an adult, perhaps you should just be quiet. Had the author asked me to delete my comment, I would have gladly done so. I am not in the habit of looking up previous comments and deleting them. However, after looking at your comment history, that may be a good idea for you.

          • Emkay

            the fact that you cannot grasp the concept of deleting a ‘misleading comment’ which would have caused this conversation to ‘not happen’ simply proves you’re a snarky ‘fuking moron!
            and if you reply again..it will prove it!!

          • Matt

            The comment wasn’t misleading and this conversation occurred because of your ignorance. Now I think I’ll follow George Carlin’s advice:
            “Never argue with an idiot. They will only bring you down to their level and beat you with experience.”

          • Emkay

            you obviously can’t read..you proved it! again!

  • Jeff

    Why is Spinosaurus often shown or suggested to have eaten sawfish? Is it just assumed as the two were found within the same area or is there actual evidence of this?

    • Kyle Brown

      they found the barb of a giant saw fish called onchoprisits embedded in a spinosaurus jaw bone they found a few years ago

  • Ruben Pesoa

    Was this the biggest reptile ?

    • born_in_the_sixties

      Not a reptile, a dinosaur. Dinosaurs are not reptiles.

      • Ruben Pesoa

        Didn´t know the differences until this comment. Thanks!

        • Claudia

          Ruben…you are right, a dinosaur IS a reptile…

          • Staden

            Reptiles are defined as the group descending from the last common ancestor of crocodilians, squamates, turtles, and the tuatara. Due partially to the inclusion of turtles, the last common ancestor’s descendants do include birds and dinosaurs. Therefore birds and dinosaurs are reptiles, but mammals (synapsids) are not

          • Claudia

            Exactly…thank you :).

      • Claudia

        Excuse me but…a dinosaur IS a reptile… Born in the sixties you need to go back to school for a refresher course 😉

        • Emkay

          vacationing in the ‘Outer Banks NC this week, my daughter in law found a black hard case with barbs/tentacles on each end? I asked what it was and she told me it was a ‘shark egg case’… I did not believe it until ‘googles later I was convinced… some sharks lay eggs!

          • Metalhead Nick

            Not surprised that you were unaware of this, as you don’t know that a polar bear is a predator…I’d be surprised too though if I saw an egg with tentacles. Most eggs do not have flexible, mobile, elongated organs on them. Or perhaps this also belies your tenuous grasp of biology. I am surprised you have a daughter in law as this implies you have progeny of your own, and that she talks to one as unpleasant as you.

      • Brian Allan

        Regardless of Claudia’s erroneous “findings”, I would agree with dinosaurs NOT being reptiles. Descended from reptiles,yes, but not reptiles.

        • Andrew Befus

          I also always felt that dinosaurs and birds were reptiles. The argument that they “derived from reptiles” seems weak because lizards, turtles, etc are also probably derived from an ancestral reptile lineage. As did mammals… now I’ve confused myself. Suffice to say all classifications of natural things are fuzzy.

          • Emkay

            age of dino’s from 75 million to 200 million years ago, things were quite fuzzy… guessing? mostly…

  • Ravindran Govindaraju

    # My readings vouches me to say , majority of life evolved from sea to land..
    Correct me please !

    • Stephen Block

      Whales.

    • DodgeMiniVan

      I feel the same as you do.

    • Emkay

      ALL life came from the sea..

  • John Stojanowski

    When did it go extinct and what is the best explanation for it?

  • Donna

    Just wanted to applaud the wonderful illustration. Any others from this artist, Brian Engh?

  • i wonder

    could the spinosaurus skull be bigger or small size that the crocodilian?

  • Claudia

    You need to be educated….not only on reptiles 😉 You are ignorant and arrogant, obviously.

    • Emkay

      thats a jerk for ‘ya….

    • Wade Carmen

      Probably a creationist zealot.

  • Brian Allan

    Enjoyable read! Thanks.

  • Wade Carmen

    How are the creationists reacting to this?

    • Emkay

      simple,,god created them…

      • Wade Carmen

        Don’t forget leprechauns and Smurfs.

  • https://www.youtube.com/user/shadowdroid776 BlackRose278

    Do you think that the spine on its back could have been used to help with swimming? In my mind, I can see it as a legitimate sail, allowing it to use the currents and/or wind more effectively while in water.

  • Tarponicus

    It’s possible the sail was for display and thermoregulation. I’m not sure they’d be exclusive although which was the main driver in its evolution is moot.
    The dino/bird angle might shed a few clues.
    There seems to be a leaning toward crocodilian models for spinosaurus, understandably given its lifestyle, but in ‘bird’ terms it’s not as if you see aquatic birds losing their feathers…could Spino have had down or would it not need it through size?

    Blather aside, at least we now have another contender for the loch Ness monster…hump and all!

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