National Geographic

Spinosaurs Were Lousy Croc Mimics

I love dinosaur names. Many of them are so beautifully evocative of the animals they represent. There may be no more perfect title in the history of nomenclature than Tyrannosaurus rex, to pick just one classic. Yet dinosaur names can also be reminders of incorrect interpretations or assumptions about those animals. Stegosaurus – the “roofed lizard” – was so named because paleontologist O.C. Marsh thought the dinosaur’s characteristic plates laid flat on the herbivore’s back as bony tiling, rather than sticking straight up out of the skin as fossil finds later made clear.

Suchomimus may also be a less than apt name. This sail-backed spinosaur was given the “crocodile mimic” moniker by Paul Sereno and colleagues for the dinosaur’s long, shallow snout. The Cretaceous carnivore seemed to have more of a crocodile profile than other deep-skulled predatory dinosaurs. And if spinosaurs had croc-like snouts, perhaps they spent a great deal of time hunting fish (an idea supported by fish in the gut contents of the spinosaur Baryonyx.) Furthermore, a paper by Emily Rayfield and coauthors found that Baryonyx had a skull suited to resisting the kind of forces expected to be created by struggling fish. But now, along with coauthor Andrew Cuff, Rayfield has gone back to the spinosaurs and found that the connection between long, slender jaws and a diet of freshly-caught fish isn’t as clear as previously thought.

The fossil and CT models of the Baryonyx snout, from Cuff and Rayfield, 2013.

The fossil and CT models of the Baryonyx snout. From Cuff and Rayfield, 2013.

Of the spinosaurs known so far, Cuff and Rayfield investigated the snouts of Baryonyx – a roughly 125 million year old genus found in the strata of England – and the famous Spinosaurus from the 97 million year old rock of Egypt and Morocco. Using CT scans to restore the spinosaur snouts, the researchers simulated how the jaws of these dinosaurs would react to the stresses caused by biting, and compared these results to the virtual bites of an African slender-snouted crocodile, an Indian gharial, and an American alligator.

After running the virtual snouts through their biting paces, Cuff and Rayfield found that the upper jaws of the spinosaurs “absolutely outperform all crocodilian taxa” and showed similar resistance to bending and twisting to each other. As far as the front part of the upper jaw is concerned, at least, the spinosaurs were not just like big gharials. The spinosaur jaws were better at dealing with up-and-down stresses than side-to-side stress, as well, which is consistent with their relatively narrow jaws. And the apparent superiority of the spinosaurs seems to have been a result of their size. Rather than being a case of convergent evolution with slender-snouted crocs because of a fish-based diet, spinosaurs might have been able to get away with having relatively narrow jaws thanks to mechanical advantages conferred by size. They weren’t bonecrushers like Tyrannosaurus – not even close – but the spinosaurs had jaws that were capable of doing more than holding onto slippery fish.

The fossil and CT reconstructions of a Spinosaurus snout. From Cuff and Rayfield, 2013.

The fossil and CT reconstructions of a Spinosaurus snout. From Cuff and Rayfield, 2013.

So maybe spinosaurs weren’t dedicated fish-snatchers. The fact that dinosaur remains have been found in the gut contents of Baryonyx and a spinosaur tooth was discovered embedded in a pterosaur bone indicate that these carnivores were capable of consuming a wider variety of flesh, if not actually catching such terrestrial or airborne meals.

Spinosaurs through time were capable of tossing a variety of savory bites down their throats, but the real question is how they did so and whether there was a particular sort of prey they preferred. On that score, we know relatively little, but lucky finds of gut contents, geochemical clues locked in their skeletons, and future attempts to make these dinosaurs bite again might start to show us how these utterly bizarre predators made a living on Cretaceous floodplains.

[Top image from Flickr user theMatthewBlack.]

Reference:

Cuff, A., Rayfield, E. 2013. Feeding Mechanics in Spinosaurid Theropods and Extant Crocodilians. PLoS ONE. 8, 5: e65295. doi:10.1371/journal.pone.0065295

There are 12 Comments. Add Yours.

  1. Thomas R. Holtz, Jr.
    May 31, 2013

    One issue I have with people trying to shoot down spinosaurids as piscivores is that, to my knowledge, no one has proposed spinosaurids as *obligate* piscivores! That is to say, a mimic of Crocodylus might be expected to have a diet like Crocodylus: that is, a mix of fish and tetrapods.

    And this is indeed consistent with the gut content and isotopic evidence.

  2. Jim Kirkland
    May 31, 2013

    They are closer to heron mimics, in that we think they stood and fished with there hands and snout, seasonally, when the Lepidotes (big ganoid scaled fish) were coming in to spawn. Spinosaurs have way more adaptions to fishing than do bears! see: http://www.academia.edu/2469934/THE_CASE_FOR_FISHING_DINOSAURS_AT_THE_ST.GEORGE_DINOSAUR_DISCOVERY_SITE_AT_JOHNSON_FARM_by_Andrew_R._C._Milner_and_James_I._Kirkland

  3. Thomas R. Holtz, Jr.
    May 31, 2013

    I’ve said it before in other venues: spinosaurids seem functionally to combine elements of crocodilians, herons, and grizzlies (on a basic theropod frame).

  4. Thomas R. Diehl
    May 31, 2013

    Yeah, I (still) think the large claw had nothing to do with hunting at all and was used in aquatic locomotion as a hook by which the animal pulled itself through the water with as little movement as possible not to disturb its prey. Only moving your arms with the rest of the body pulled floating in the water acting like a piece of wood might be a very efficient way of sneaking up on prey.

  5. 220mya
    June 3, 2013

    Even the gharial has a pretty high proportion of non-fish prey in its diet. No living crocodylian is an obligate piscivore. So I think the problem goes all the way back to people over-generalizing about the diets of extant longirostrine crocodylians.

  6. Jura
    June 4, 2013

    I don’t see how referring to spinosaurids as croc mimics is as misleading as Stegosaurus. The data from Cuff and Rayfield only serve to counter the claims that spinosaurs were obligate piscivores. Since most crocodylians are very good at tackling terrestrial prey, this still leaves spinosaurs as pretty good croc mimics.

  7. Reed
    June 4, 2013

    You began this post by mentioning dinosaur names. One of the most frustrating things about books on dinosaurs is when the name is from another country (say for example Amargasaurus) it always says “Named for the Amarga Province in Argentina.” But Amarga means something in English too (bitter river). So why don’t the books say the name means “Bitter River Lizard?” So much more descriptive.

  8. Mark Robinson
    June 9, 2013

    @Reed – Books don’t get to decide what a scientific name means – that is something that is (usually) specified by the naming author(s). When a dinosaur (or other life) is named after a place, the author most often intends simply to reference that place (and may not even be aware of what it means in some other language), so that is irrelevant. Occasionally, the intent may be to acknowledge another meaning or even make a pun, and this would be spelt out in the paper that names/describes the new species; eg Scipionyx.

    It’s no different from when something is named after a person – Othnielia is named after Othniel Marsh, it doesn’t mean “lion of God”.

    • Reed
      June 9, 2013

      @Mark Robinson. Thanks for the reply, Mark. I mean, I know books don’t name dinosaurs. But I see your point that the author may not know the original meaning of the name when he names a dinosaur for a place. The Othnielia reference is a great example (thank you). Guess I’ll quit harping on this.

  9. Duane Nash
    June 21, 2013

    Why do I see this notion of spinosaurids “merely being fish eaters” thrown around again and again as some type of insult. Some of these “mere fish” were pretty damn massive and intimidating. Mako Shark sized Lepidotes, huge 20 foot sawfish that would cut a grizzly in half, not to mention diverse and large turtles, crocs and probably marine reptiles too were probably caught too. Just because you are a “mere fish-eater” does not make spinosaurids any less arch predators in their respective environments.

  10. Zshelyz
    July 26, 2013

    “– but the spinosaurs had jaws that were capable of doing more than holding onto slippery fish.” Aside from possibly eating pterosaurs and land animals, perhaps spinosaurs had much bigger fish to eat then?

  11. Marcos K. Pinheiro
    January 12, 2014

    I think that’s great! And I love the spinosaurs! I thought that Baryonyx had a less strong bite than Spinosaurus, but now, new discoveries are revealing more and more new facts and possible lifestyles of those dinosaurs. Still, I hope that some day, nearly complete skeletons of adult Baryonyx and Spinosaurus are found! And I after watching BBC Planet Dinosaur – Lost World, I believe that the spinosaurids were both hunters of fish and mid-sized terrestrial prey and scavengers. However, both Spinosaurus and Baryonyx had lived in enviroments where were other dangerous carnosaurs (Carcharodontosaurus and Neovenator respectively). So they had a tough life too.

Add Your Comments

All fields required.

Related Posts