Giant Moa Not So Giant
December 19, 2013

Giant Moa Not Quite As Gigantic As We Thought

Brett Smith for - Your Universe Online

A new study of the extinct giant moa has found the massive flightless birds were actually less robust than previously believed. In the study, which was published in the journal PLOS ONE, researchers conducted computer tomography (CT) scans of full giant moa skeletons to create comprehensive digital images which were used to determine the birds' mass and general constitution. The team also scanned a smaller moa species called Pachyornis australis for comparison.

The study team found the larger moa species had leg bones that resemble those of modern flightless birds that are capable of running fast. The smaller species was found to have an extremely robust skeleton.

“Our research suggests that this group of birds came up with several different solutions to deal with the problem of supporting the large body necessary to process a diet of coarse vegetation,” said Charlotte Brassey, a biomechanics researcher at the University of Canterbury in New Zealand.

“We know that these species of moa were living together in the same locations, at the same time. So we don’t think the differences we’re seeing in leg robustness are adaptations to a particular habitat type,” Brassey said. “Instead it seems they were perhaps engaging in different behaviors, although both could deal with extremely rough terrain.”

Previous similar efforts to gauge the size of an extinct animal have involved basing estimates on leg bones and scaling up according to the size of similar living organisms. However, problems can arise when the bones have abnormal dimensions – as they do in the case of the giant moa.

“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,” Brassey said. “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.

“The same was true for moa,” she added. “We already knew that moa had disproportionately wide leg bones, yet previous estimates of their body mass had been based on those same bones which probably resulted in overestimates.”

After scanning the whole skeletons, the team used a technique common to civil engineering that estimates the strength of bridges or models the behavior of Formula One cars. The analysis showed different groups of moa supported their body weight in different ways and each species had a long history of independent evolution.

The study authors’ estimates were much lower than previous estimates. The team found the bigger moa weighed in at around 440 pounds, equivalent to about 30 family-sized Thanksgiving turkeys.

“If you don’t get the body mass right, the rest of your analysis will just spit out the wrong numbers,” said study author William Sellers, a biologist from the University of Manchester. “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.”