Extinct Moa Birds Of New Zealand Were Not As Robust As Previously Thought

By Josh Lieberman on December 18, 2013 5:49 PM EST

moa
Moa birds were not as robust as we once thought, a new study suggests. (Photo: Wikimedia Commons)

The bones of New Zealand's extinct Giant moa bird, whose latin name Dinornis robustus means "robust strange bird," were not actually that robust, according to a University of Manchester study published today in PLoS ONE. With some species (possibly) reaching 13 feet, the moa was one of the largest-ever birds, but the study suggests that their leg bones were fairly similar to distant relatives like ostriches and emus. 

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In the study, led by biomechanics researcher Charlotte Brassey and palaeobiologist Richard Holdaway at New Zealand's University of Canterbury, researchers first needed to figure out how heavy moa were. They scrapped the traditional approach of taking one bone of an animal and scaling it up in relation to the size of the bones of other similar living species. The researchers explained that that approach may work in some cases, but it not when a leg bones like the moa's large leg bones have unusual proportions.   

"If we'd wanted to estimate the weight of a saber-toothed cat, no one would have suggested measuring canine tooth length and then scaling up the tooth size of your standard tabby," explained Brassey. "That's because we know that the saber-toothed cat had unusually oversized canines compared to house cats. It wouldn't be a fair comparison, and you'd end up with a ludicrously high estimate of the body weight of the saber-toothed cat."

As with the saber-tooth cat, the "disproportionately wide leg bones" of moa made the scaling-up approach impractical. Brassey believes that previous research using the scale-up approach may have given overestimates of how large moa were.

Instead of figuring out moa mass using just the leg bones, the researchers scanned entire moa skeletons to get an estimate, digitally filling in bones that were lacking from specimens. As they had imagined, they found that moa weighed less than previous research has suggested, but that they moa were still pretty big: the largest moa weighed a whopping 440 pounds. 

"If you don't get the body mass right, the rest of your analysis will just spit out the wrong numbers," said William Sellers, who co-authored the study. "By using the whole skeleton rather than just a single bone we get much better mass estimates, and we can even calculate how good this estimate actually is."         

Using their body mass estimate, the researchers then performed a Finite Element Analysis. This technique is used in civil engineering to test the strength of bridges and other structures; the researchers describe it as a way of "virtually crash-testing" an object. This part of the study found that different moa supported their bodies in a variety of ways, which suggested that different moa species had "separate evolutionary histories" from one another.  

Moa were completely unknown to Western science until 1840, when a moa bone made its way to the English naturalist Richard Owen, who would go on to name 13 moa species within a decade. By 1907, there were at least 38 species of moa identified, but by 2006, better science had narrowed the number of moa species down to just ten. The last moa species is believed to have gone extinct less than 600 years ago. 

But wait, there's more moa news. Another study published recently in Proceedings of the 8th International Meeting of the Society of Avian Palaeontology and Evolution claims that the moa is not the ancestor of the kiwi--a national symbol of New Zealand. The kiwi and moa were long believed to be related, but the study says that the kiwi is actually related to the Australian emu.

We will keep you abreast of any further moa news as it breaks.        

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