Dissecting Ozbert the ostrich


After last week's look at an emu dissection, it seemed only logical to follow up with dissection pics of another ratite. So when John Hutchinson of the Royal Veterinary College (RVC) mentioned his dissection photos of Ozbert the ostrich, I asked politely, and received. Note that all photos are © John Hutchinson and Jason Moore, and are used with permission. Ozbert's suspended cadaver is shown here [note the gigantic calf muscles and extruded phallus].

Ozbert, donated by a British ostrich farm, was huge, tipping the scales (when plucked) at 129 kg (the world record is supposedly 160 kg) [scales shown below]. Ostrich feathers presumably account for about the same percentage of mass as they do in emus (c. 7.5%), so Ozbert would have been a bit heavier when alive. Ozbert's untimely death came as a result of combat with another male: he was kicked, fatally, at the base of the neck, and you can see the resulting neck injury in one of the photos below. The ability of ostriches to kill lions and hyenas by kicking is pretty well known, and captive specimens have at least tried to kill people in the same way too. Evidently, ostriches can also kill other ostriches. Not surprising given their hindlimb musculature, on which read on...


Before getting to the hindlimb (the focus of interest for the RVC folks), let's note a few other things. Firstly: necks. If you're interested in necks - and I am - those of ostriches are particularly interesting, not least of all because they're one of the longest extant tetrapod necks in existence. There are 17 vertebrae in the ostrich neck, and the way in which they move when the bird bends, raises, or lowers its neck has been of great interest to those with a special interest in this sort of thing (e.g., Dzemski & Christian 2007). There is actually some very neat CT data on ostrich neck movement, and on what happens to the zygapophyses when the neck moves, but it's not published yet. More on this at some stage in the future. Ostriches are well known for being able to swallow large, sometimes strangely shaped, objects. The skin of the ostrich neck is particularly flexible and you may have seen the photos where a guy is sticking his hand down an ostrich's throat: the skin is so pliable that, as he extends his fingers within the throat, it looks like he's wearing a glove.

Here's where - at long, long last - we come back to the weird pectoral girdle. As several readers correctly noted, the ostrich pectoral girdle is weird in that the furcula (or wishbone) is absent and what appear to be two separate, paddle-like elements are fused to the scapulocoracoids. These are accessory ossifications called procoracoid processes, and there has been some controversy as to whether they represent separate elements, or ventral extensions of the scapulae (thanks to Lars Dietz for help here). The forelimb (or wing) bones are long and gracile (note in the image below how long and slender the upper arm is: there is no propatagium in ratites), and the carpometacarpus is tridactyl: rheas also have tridactyl hands, whereas kiwi, cassowaries and emus are all monodactyl (and moa had no hands, or arms, at all). As you can see from the photo here, digits I and II both have claws, but this is only obvious when the feathers have been removed. The fatal injury sustained to the neck base is also visible here...


Finally, we get to the hindlimb. Of incidental interest is the fact that, while many ostrich specimens used in research now originate from the ostrich farming industry, the incidence of hindlimb deformities in captive ostriches is apparently quite high (Hahulski et al. 1999), with one of the commonest deformities being tibiotarsal rotation (where the distal end of the tibiotarsus is rotated such that what should be the anterior surface of the bone faces outwards or nearly so).

Ostrich hindlimb muscles are unbelievable, accounting for about 33% of the animal's total mass (in humans, hindlimb muscle mass accounts for 17-20% of total mass). Ostriches at the RVC lab have served us well; several key papers on ostrich anatomy and biomechanics incorporate data from these animals (Smith et al. 2006, 2007, Jindrich et al. 2007: some of those are available for free here. See also Rubenson et al. 2007). There are about 36 hindlimb muscles: their relations, insertion points and actions were all described by Smith et al. (2006). Here is John, busy dissecting and making observations...


The biggest hindlimb muscle is the gastrocnemius. It has three distinct heads (medial, lateral and caudal), accounts for about 18% of the hindlimb muscle mass, and is of course responsible for ankle extension. Its tendon is one of the biggest and widest in the limb. Owing to the size of the bird and the length of its feet, the flexor tendons that attach to its toes are large (the four main ones are all at least 25 cm long). Their size and hence the ease with which they can be separated and handled means that they are being considered for use in human surgical repairs (Karakurum et al. 2003).


The gastrocnemius is actually pretty unusual among the larger hindlimb muscles in being located in the distal part of the limb: all the other large hindlimb muscles are proximally located, which makes sense given that animals that run quickly want their distal limb segments to be as light as possible [the image above shows the thigh and pelvic musculature. Anterior is to the right. Among others, we can see the iliotibialis lateralis and iliofemoralis externus and, at extreme right, the iliotibialis cranialis]. Muscle size correlates directly with power, so the huge cross-sectional area of the gastrocnemius makes it the most powerful hindlimb muscle (though let's note that other, more proximal muscles also produce a lot of power, like the iliotibialis lateralis and iliofibularis). Ostrich feet are among the most specialised of any bird: they're didactyl (the two toes are III and IV), and digit IV lacks a claw. While I could ramble on at this point and say a lot more, I'm afraid my time is up and I have to move on.

I plan to post more 'annotated' dissection pics in future: if you have photos like those featured here, or those used in the emu article, I'd be very interested in featuring them here on the site. The more exotic the beast, the better. And so, we finish by saying a sincere and hearty thanks to John Hutchinson, Jason Moore, and the other RVC staff involved for the use of these images. And thanks also to Ozbert, for he served us well.

For previous Tet Zoo ratite articles see...

Refs - -

Dzemski, G. & Christian, A. 2007. Flexibility along the neck of the ostrich (Struthio camelus) and consequences for the reconstruction of dinosaurs with extreme neck length. Journal of Morphology 268, 701-714.

Hahulski, G., Marchellin-Little, D. J. & Stoskopf, M. K. 1999. Morphologic evaluation of rotated tibiotarsal bones in immature ostriches (Struthio camelus). Journal of Avian Medicine and Surgery 13, 252-260.

Jindrich, D. L., Smith, N. C., Jespers, K. & Wilson, A. M. 2007. Mechanics of cutting maneuvers by ostriches (Struthio camelus). Journal of Experimental Biology 210, 1378-1390.

Karakurum, G., Güleç, A., Büyükbebeci, O. & KaradaÄ, E. 2003. The ostrich: an excellent tendon source for the biomechanical studies. Gülhane Tip Dergisi (Gulhane Medical Journal) 45, 180-181.

Rubenson, J., Lloyd, D. G., Besier, T. F., Heliams, D. B. & Fournier, P. A. 2007. Running in ostriches (Struthio camelus): three-dimensional joint axes alignment and joint kinematics. Journal of Experimental Biology 210, 2748-2562.

Smith, N. C., Payne, R. C., Jespers, K. J. & Wilson, A. M. 2007. Muscle moment arms of pelvic limb muscles of the ostrich (Struthio camelus). Journal of Anatomy 211, 313-324.

- ., Wilson, A. M., Jespers, K. J. & Payne, R. C. 2006. Muscle architecture and functional anatomy of the pelvic limb of the ostrich (Struthio camelus). Journal of Anatomy 209, 765-779.

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I was wondering if anyone has ever done a study on ornithomimosaurs, examining if they had any skill in kicking. I won't be surprised if ornithomimosaurs got rid of annoying dromaeosaurs or even young tyrannosaurs with well-aimed kicks.

"As several readers correctly noted, the ostrich pectoral girdle is weird in that the furcula (or wishbone) has split into two separate, paddle-like elements that are fused to the scapulocoracoids."

Are you sure this is correct? Figure 10 here:
Vickaryous MK, Hall BK (2006): Homology of the reptilian coracoid and a reappraisal of the evolution and development of the amniote pectoral apparatus. J Anat. 2006 March; 208(3): 263â285.
seems to label the paddle-like thing as a procoracoid process. I've also found some 19th century papers on Google Books that mentioned that the homologies of the ostrich's pectoral girdle were controversial, with Cuvier calling this element a furcula and Owen calling it an acromial process, but this is the most recent I could find. When you posted the picture of the pectoral girdle, I found some old sources that say the ostrich lacks a furcula, and this seems to confirm it.

By Lars Dietz (not verified) on 04 May 2009 #permalink

Lars, thanks for this. I had only read that the 'accessory' structure was a horribly modified furcula and was not aware of the procoracoid identification. The Vickaryous & Hall (2006) paper seems to resolve the issue. I will change the text accordingly...

Thanks for the fun article, Darren.

I should note that tibiotarsal rotation (sometimes colloquially called "rubber bone disease") is a big problem in many captive birds bred for deliciousness. The causes are still poorly understood and perhaps multifarous including obesity, rapid growth (especially of edible mass) outstripping mechanical maturity of the skeleton (i.e. they put on weight too fast and deform their young, still-elastic bones), nutrition, inbreeding etc.

We have a substantial research project running (with one of the world's biggest broiler chicken breeders, Cobb-Vantress Inc) trying to understand this and other problems in chickens (and other neornithines). Amusingly, that project spun off of my T. rex/giant chicken research; the company saw my work and saw a neat connection with their poultry's musculoskeletal problems. Chunky chickens and giant theropods likely faced similar problems of low strength/weight ratios. There are some cool evolutionary questions in this too, despite the bizarreness (and disturbing nature) of broiler chickens in general.

(tangent over; you just touched on something of huge veterinary importance that I'm very interested in lately)

Why actually "Ozbert"?

By David MarjanoviÄ (not verified) on 04 May 2009 #permalink

Reminds me of that year I had to joint the Kelly Bronze turkey before cooking - it was one big mother of a bird, the tendons in the legs were amazing. And a b$$$$$$ to cut through to bone the legs, too.

Made five different extremely delicious dishes for the Christmas period, though. All those tendons = lots of jelly for the turkey and apricot pie. I'm hungry now...

On subject, jointing a table bird does give you a fine lesson in anatomy and the attachment points of various muscles. It's always interesting.

By DunkTheBiscuit (not verified) on 04 May 2009 #permalink

Are those gigantic calf muscles and an extruded phallus, or are you just happy to see me?

By Christ, I Need… (not verified) on 04 May 2009 #permalink

The tridactyl forearm with claws, is this an evolutionary reversal from winged ancestors, or are ostriches and kin direct descendents of animals that have always had clawed forelimbs or is the jury out on that? It's cool in any case. Great article.

I think rheas have two digits in the forelimb, not three (but three in the hindlimb)

I've only tried ostritch once, and it was very tough, is it always like that?

Anyhow, great article, but yeah, my mouth is watering.

By Tim Morris (not verified) on 04 May 2009 #permalink

or are ostriches and kin direct descendents of animals that have always had clawed forelimbs

Most birds have at least a claw on the thumb. That includes chickens and turkeys. See the rhea dissection post.

By David MarjanoviÄ (not verified) on 05 May 2009 #permalink

Ozbert's name was a spur of the moment thing; we needed a name and it stuck. Twinkletoes was already taken from a previous ostrich escapade.

I'm not sure of the evolutionary polarity in terms of keratinous claws. I suspect it's a holdover for most birds to some degree. Odd birds like the hoatzin indicate that the developmental potential to form at least keratinous claws, if the holdover is not present in all birds, is still there. But I haven't bothered to look into it much yet. Hindlimbs keep us plenty busy. :)

By John Hutchinson (not verified) on 05 May 2009 #permalink

I think rheas have two digits in the forelimb, not three (but three in the hindlimb)

Nope, rheas do indeed have three digits in the carpometacarpus (though there may well be freaks where phalanges are absent on digit III).

As for manual claws in neornithines, their phylogenetic distribution strongly indicates that they've been retained all the way through avian evolution, though with numerous losses here and there. As David said, this was covered in the emu dissection article.


I wonder where did you get the specimen? Did you dissect it alone?