Tyrannosaurs had small arms

img_3614I’m on the road in Japan having just made it to Katsuyama, home of the famous Fukui Prefectural Dinosaur Museum. That I’ll get to see tomorrow and in due course posts will follow, but in the mean time you will have to be satisfied by this very quick post. The title is hardly spectacular – I’m not sure anyone with even a passing knowledge and interest in dinosaurs is not aware of the fact that the giant tyrannosaurs like Tyrannosaurus had proportionally small arms. However, this photo is a really good illustration of just how small some of them were.

The humerus (upper arm bone) in question is a genuine one of a Tarbosaurus (basically the asian Tyrannosaurus and very simiular in size and shape) that I found in the collections in Okayama a few days ago. As you can see, it is essentially the same size as my own upper arm, yet I am notably not an 8 metre and 6 ton theropod dinosaur (it’s from a sub-adult animal, and admittedly an adult would have been quite a bit bigger, but you get the general idea). In short, tyrannosaurs really do have small arms.

5 Responses to “Tyrannosaurs had small arms”


  1. 1 Jaime A. Headden 26/01/2009 at 5:39 am

    Note also that for it’s size, the arm is roughly the same size as a human arm; or rather, the same length. It is a good deal more robust, and likely more muscular. And that’s Tarbosaurus. Tyrannosaurus has a far more robust arm than Tarbosaurus does.

  2. 2 David Hone 26/01/2009 at 4:49 pm

    I have spent the day looking over a pair of casts of similarly sized adult Tyrannosaurus and Tarbosaurus mounted together and I couldn`t see any major differences in the size / shape / robustness of the humerus at all )and both were casted off originals and not duplicates or models). Have you got a reference for that difference Jamie?

  3. 3 Jaime A. Headden 27/01/2009 at 6:21 pm

    I beleive my reference stems from Maleev’s work on Tarbosaurus bataar, type and/or paratype from his monographic work, and compared to the FMNH Tyrannosaurus rex humerus, “Sue”. This MIGHT be a case of size-matters, but I think the PIN 551 specimen is among the largest for Asian tyrannosaurs. My understanding may also stem from an impression, false or not, that the tarbosaur humerus is more curved and is smaller relative to, say, femoral length than the tyrannosaur one. This is based on a good deal of anecdotal information, as well, however, although while I have seen some of these bones personally, I was not inclined at the time to measure them and scale them to one another and their respective “metrics” of the femora/skull/scapula etc.

  4. 4 David Hone 27/01/2009 at 8:32 pm

    I did have another closer look today and while I could not measure them directly (they were mounted) they looked pretty similar. I would say the Tyrannosaurs one was proportionally a bit longer and a bit more robust, but then it was also the larger specimen of the two. Overall though they were very simialr (as indeed one wuld expect). I’ll have to dig ut the Maleev paper when I am back in Beijing.


  1. 1 Blog Carnival, Edition #4: Texas Troubles, Big Dinosaurs, and a Danny McBride Interview | Dinosaur Tracking Trackback on 30/01/2009 at 12:42 am

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