Treehugger Tuesday

The following piece was just published in The Christian Science Monitor:

What our ancestors' hankering for big eggs meant for a 500-pound bird

Scientists examined burnt fragments of the massive eggshells to determine the link between humans and the bird's extinction.
By Christina Beck, Staff  - January 29, 2016

Ancient humans ate the eggs of gigantic, flightless birds, a recent study finds.

The study was conducted by a team of Australian and American scientists, who analyzed burn patterns on eggshell fragments.

The giant bird, which scientists have dubbed Genyornis newtoni, weighed roughly 500 pounds and stood about seven feet tall. Its eggs would have been the size of cantaloupes, and likely weighed 3.5 pounds. Genyornis was just one of many massive ancient animals, a group that scientists collectively call megafauna.

Other gargantuan examples of Australia’s frightening animal past include a 1,000 pound kangaroo and a wombat the size of a moderately sized car. Despite their impressive size, these megafauna were no match for humans; about 85 percent of these animals went extinct after people arrived on the scene.

The study, published Friday in the science journal Nature Communications, is the first to shine some light on the connection between humans and the extinction of Australia’s gigantic megafauna.

"We consider this the first and only secure evidence that humans were directly preying on now-extinct Australian megafauna," Gifford Miller, a geology professor at University of Colorado, Boulder.

The cause of Australia’s megafauna extinction has been much debated in scientific circles for over a hundred years.

One popular theory is that climate change catalyzed a mass extinction among the megafauna. However, the continental drying that occurred about 40,000-60,000 years ago (main suspect) was less severe than an earlier climate shift during the Pleistocene epoch.

Since the megafauna were able to survive through the Pleistocene’s climatic shift, it seems unlikely that later, less severe climate change would do them in.

"The lack of clear evidence regarding human predation on the Australia megafauna had, until now, been used to suggest no human-megafauna interactions occurred,” says Professor Miller, “despite evidence that most of the giant animals still roamed Australia when humans colonized the continent."

Scientists are not sure precisely when humans arrived in Australia. They do know that the continent’s earliest inhabitants landed on Australia’s northern coast after a several hundred mile raft journey from Indonesia, and that by about 47,000 years ago they had scattered across the continent.

To determine the link between humans and Genyornis, scientists first examined eggshells from the bird’s nesting sites in sand dunes. Using optically stimulated luminescence dating, an age determining technique that examines quartz grains in the eggshells to determine when they were last exposed to sunlight, scientists dated the shells to between 44,000 and 54,000 years old.

In about 200 of the 2,000 egg sites that scientists sampled, the eggshells were blackened and burned.

In order to rule out wildfire as the reason for the burned shells, scientists studied the amino acid decomposition of the eggshells. Instead of being uniformly burned all over, as eggs caught in wildfire would be, the amino acids in the shells exhibited a gradient of decomposition. They were more burnt on one end than the other, indicating cooking fires rather than wild fires.

The burnt eggshell fragments were also found in tight clusters, and exhibited signs of being cooked in fires up to 1,000 Fahrenheit, far hotter than a natural bush fire.

Try as they might, Miller and his team were unable to come up with a scenario in which the eggshell blackening occurred due to natural causes. Miller says, "We instead argue that the conditions are consistent with early humans harvesting Genyornis eggs, cooking them over fires, and then randomly discarding the eggshell fragments in and around their cooking fires."

Ancient emu eggshells in Australia have been found to exhibit the same characteristics of the burnt Genyornis eggshells, adding strength to the team’s argument.