Why don't giraffes have necks as long as a brachiosaurus?

We think of giraffes as long-necked creatures, but compared to ancient sauropod dinosaurs (a family that includes the brachiosaurus and apatosaurus) even the longest-necked giraffe may as well be nicknamed "Stumpy". In a paper published online at arXiv site, two paleontologists analyzed the biology of sauropods in an attempt to figure out which features allowed the dinosaurs to grow necks six times longer than giraffes.

Turns out, there are some distinct differences — especially in the anatomical architecture of the vertebra closest to both animals' skulls — that really stand out. As this helpful slide shows, a sauropod with the vertebra of a giraffe would be in very bad shape, indeed.

This paper, by the authors' own account, began life "as a late-night discussion over a couple of beers", which means it's basically the paleontology equivalent of "Who would win in a fight: Darth Vader or Superman?" Which is awesome. Better yet, the paper is quite easy to read and the information is organized in a way that will probably make more sense to you than the typical scientific research paper. So dig in! It's worth it! Here's one short excerpt taken from a part discussing some of those differences in the cervical vertebra (the aforementioned vertebra closest to the skull):

Many groups of animals seem to be constrained as to the number of cervical vertebrae they can evolve. With the exceptions of sloths and sirenians, mammals are all limited to exactly seven cervicals; azdarchids are variously reported as having seven to nine cervical vertebrae, but never more; non-avian theropods do not seem to have exceeded the 13 or perhaps 14 cervicals of Neimongosaurus, with eleven or fewer being more typical.

By contrast, sauropods repeatedly increased the number of their cervical vertebrae, attaining as many as 19 in Mamenchisaurus hochuanensis. Modern swans have up to 25 cervical vertebrae, and as noted above the marine reptile Albertonectes had 76 cervical vertebrae. Multiplication of cervical vertebrae obviously contributes to neck elongation.

Read the full study at arXiv

Read a blog post about the study by one of the authors

Via Bora Zivkovic


  1. The cervical vertebrae of the brachiosaurus are absolutely phenomenal.  The world’s largest articulated skeleton is a brachiosaurus in the Museum Für Naturkunde in Berlin.  Check out that brachiosaurus!  http://prometheus.med.utah.edu/~bwjones/2012/07/museum-fur-naturkunde-berlin/

  2. There was a Nature or Science article some time ago that looked at the energetics of sauropods having such long necks.  It turns out that pumping blood to the brain actually takes a lot of energy, but it was compensated by the fact that the sauropod could graze over a larger area with the long neck without moving, making it energetically favorable for the animal.

  3. Giraffes are tall enough for most of the available food sources in their native regions.  Browsing from trees gives them access to an ecological niche that didn’t have much competition, and being tall makes it easier to see predators.  Extra height wouldn’t get them significantly more food, but would make it tougher for their hearts to get blood to their heads, so it’s not a win.

    1. It feels easy to explain evolution, seeing why an adaption works; and, it’s definitely easy to invent adaptions that seem like wins, but don’t actually happen in practice. If they did have longer necks, maybe they’d be able to reach more trees without moving, or some such.
      What’s cool about the paper is they bothered to analyze actual physiological reasons, and that it turn may even yield new insights, and new ideas. ( plus, hey: Giraffes! )

  4. You also have to consider that sauropods had more time to evolve light-but-strong vertebrae compared to azdarchids: 

    Azdarchids had only 65 million years to evolve from something roughly the size of a opossum at the time of the Cretaceous–Paleogene mass-extinction event, compared to 100 million years for the super-heavy sauropodomorphs of late-Jurassic and 185 million years for the super-heavy Titanosaurs of the late-Cretaceous to evolve from a small (chicken- or turkey- sized) bipedal carnivorous archosaur after the Permian–Triassic mass-extinction event (the “Great Dying”).

    It’s an apples-to-oranges comparison: A giraffe’s dinosaur contemporary isn’t Brachiosaurus, but probably something similar to the prosaropod Plateosaurus

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