Paleontology

Why did the world’s biggest ape go extinct?

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The 300-kilogram primate couldn’t adapt when a changing environment forced a dietary shift.

An artist impression of the giant ape from southern China shown face on
Gigantopithecus blacki was the largest ape that ever lived, and might have gone extinct because it could not adapt when its environment changed.Credit: Garcia/Joannes-Boyau (Southern Cross University)

The world’s biggest primate might have gone extinct because it couldn’t reach the most nutritious fruits, according to a study published today in Nature1. The paper also offers clues on why the giant ape’s contemporary, an ancient orangutan, continued to thrive almost 300,000 years ago as the environment changed.

With an estimated height of 3 metres and weighing a hefty 200–300 kilograms, Gigantopithecus blacki was the largest primate to ever roam Earth. Anthropologist Ralph von Koenigswald discovered one of the ape’s massive teeth in a Hong Kong apothecary nearly 90 years ago. Since then, researchers have unearthed four jawbones and roughly 2,000 more teeth in caves scattered across China — but no other parts of a skeleton have been found. The scant fossil evidence has made it notoriously difficult to build an accurate picture of G. blacki, let alone the circumstances that led to its disappearance, says study co-author Kira Westaway, a geochronologist at Macquarie University in Sydney, Australia. “We just don’t know much about it,” she says.

To solve the mystery of its extinction, Westaway and her colleagues analysed fossils and sediments from 22 caves in Chongzuo and Bubing Basin in southern China. They used six dating methods to find the exact timeframe of G. blacki’s demise, and reconstructed the giant ape’s environment in the period before it went extinct using a range of techniques — such as pollen analysis and investigating sediment layers under a microscope. The researchers also analysed chemical traces in the enamel of G. blacki’s teeth to investigate how its diet changed over time, and compared these signatures with those seen in the teeth of its close relative Pongo weidenreichi, an extinct orangutan that lived alongside the giant ape.

Their work revealed that G. blacki disappeared between 295,000 and 215,000 years ago, slightly later than previously estimated (420,000–330,000 years ago)2. During G. blacki’s heyday some 2.3 million years ago, the landscape was blanketed by dense forests with the odd patch of grassland. When the researchers analysed G. blacki’s teeth from this period, they found several distinct bands of various trace elements. The clearer and more distinct these bands are, the more trace elements the teeth contain, which means that the giant ape was eating a wide variety of foods and drinking plenty of water.

A changing landscape

But from around 700,000 years ago, pollen analysis showed that the landscape began to change, with forests becoming more open as the seasons changed more drastically. By this time, G. blacki’s teeth showed more-blurred bands, a sign that it was forced to consume a less nutritious, more fibrous diet as its favourite forest foods and water sources became scarcer. The researchers also found fewer G. blacki fossils during this period, indicating that populations were dwindling.

A model Gigantopithecus jaw containing a fossil fragment is seen from the side next to a much smaller gorilla jaw
A gorilla’s lower jaw bone (left) and a reconstruction from a fragment of a Gigantopithecus blacki jaw bone (right).Credit: Natural History Museum, London/Science Photo Library

On the other hand, the teeth of the tree-climbing P. weidenreichi continued to show relatively clear banding, suggesting that it adapted to the changing environment with greater ease than its ground-dwelling relative.

Westaway suspects that the orangutan might have climbed trees to grab foods that were out of reach for G. blacki. The fossils also showed that G. blacki grew in size during this time, whereas P. weidenreichi became smaller, making it more nimble than the massive ape, she adds.

Between 295,000 and 215,000 years ago, G. blacki was nowhere to be seen in the fossil record whereas P. weidenreichi was still found to be relatively abundant. The thick forests that once supported the giant ape had become sparse during this time , with open grasslands and ferns dominating the ancient landscape.

The study provides the most precise picture of the circumstances around G. blacki’s extinction to date, says Hervé Bocherens, a palaeobiologist at the University of Tübingen in Germany. But he adds that more fossils need to be found to improve body-mass estimates, which would allow researchers to better understand the giant ape’s dietary needs and what made it more vulnerable to change than other herbivores in the forest.

Westaway and her team are on the hunt for more G. blacki fossils, particularly its thigh bones, which would give researchers a better idea of its size and biology. “There’s still a lot more evidence out there,” says Westaway. “It’s just trying to find the right cave.”

Paleobiology

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Childhood field trips to natural history museums were, for many of us, our first brush with the field of paleobiology. Paleobiologists still use many of the tools and methods we associate with the study of ancient animals: exploration, digging, fossil collecting, and microscope work. In recent years, however, the field has become less of a collecting and describing science and moved increasingly into the analytical, data-driven realm.

Spectroscopy, DNA sequencing, X-ray computed tomography scans, and computer models of movement are bringing new insight into ancient organisms, including animal behavior, diet, and evolution (1). Scanning electron microscopes, for example, indicate some feathered dinosaurs were brilliantly colored. Computerized locomotion models indicate how ancient animals may have walked. Isotopic analysis of ancient human hair indicates whether the owner had a more uniform or varied diet.

Beyond incorporating new analytical methods, paleobiology has moved into the applied sciences, gaining a voice in conservation biology. Because the climate has oscillated in the past, for example, preserved records of species distributions, assemblages, individual size, and other measurements can hint at what the future holds and how we can manage ecosystems for preservation and biodiversity (2).

Recent work studying tropical fossils suggests conditions became so hot during the Early Triassic that few plants or animals survived. Those animals left were primarily stunted (3). Paleobiology also lends weight to the importance of habitat preservation, especially along migration corridors. The seasonal migration routes traveled by herds of pronghorn antelope in western Wyoming have been used for 5,000 to 6,000 years. Those routes must be saved if the species is to be (2). Beyond informing policy, some researchers advocate paleobiology training for wildlife managers themselves, helping them answer forensic questions, such as: Are these the remains of a poached animal? (2).

A few biologists, however, question the field’s usefulness for conservation. The ancient record is spotty. Sampling is a product of luck as much as anything. Not all organisms are equally preserved and soft-bodied animals are hardly preserved at all. The links between past environmental and biological changes can be complex, nonlinear, or seemingly absent.

“Even a decade ago, the prevailing wisdom about fossil accumulations was that they were hopelessly biased,” writes Julien Louys, “to the extent that it would be difficult to ever meaningfully compare fossil communities to modern ones. That has luckily proved not to be the case” (4).

Instead, Louys argues, important measurements, such as species composition, trophic structure, abundance, and even genetic diversity, to an extent, can be traced through time, informing and guiding conservationists as they seek to protect modern ecosystems.

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(2012) Lethally hot temperatures during the Early Triassic greenhouse. Science338(6105):366–370.

 

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Source : http://www.pnas.org

 

Great whites ‘not evolved from megashark.

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A new fossil discovery has helped quell 150 years of debate over the origin of great white sharks.

Carcharodon hubbelli, which has been described by US scientists, shows intermediate features between the present-day predators and smaller, prehistoric mako sharks.

The find supports the theory that great white sharks did not evolve from huge megatooth sharks.

The research is published this week in the journal Palaeontology.

Palaeontologists have previously disagreed over the ancestry of the modern white sharks, with some claiming that they are descended from the giant megatooth sharks, such as Megalodon (Carcharocles megalodon).

“When the early palaeontologists put together dentitions of Megalodon and the other megatooth species, they used the modern white shark to put them together, so of course it’s going to look like a white shark because that’s what was used as a model,” explained Professor Dana Ehret of Monmouth University in New Jersey who lead the new research.

Modern day white sharks show similarities in the structure of their teeth with the extinct megatooth sharks.

As they both sport serrations on the cutting edges, early scientists working on the animals used this as evidence for the sharks being closely related.

“But we actually see the evolution of serrations occurring many times in different lineages of sharks and if you look at the shape and size of the serrations in the two groups you see that they are actually very different from each other,” Professor Ehret told BBC News.

“White sharks have very large, coarse serrations whereas megalodon had very fine serrations.”

Now, additional evidence from the newly described species shows both white shark-like teeth shape as well other features characteristic of broad-toothed mako sharks that feed on smaller fish rather than primarily seals and other large mammals.

“It looks like a gradation or a transition from broad-toothed makos to the modern white shark. It’s a transitional species, and you don’t see that a whole lot in the fossil record,” Professor Ehret said.

The mako-like characteristics of the new species, named Carcharodon hubbelli in honour of Gordon Hubbell – the researcher who discovered it in the field – were only found due to the incredible preservation of the fossil.

“A big issue in shark palaeontology is that we tend to only have isolated teeth, and even when you find associated teeth very, very rarely are they articulated in a life position,” continued Professor Ehret.

“The nice thing about this new species is that we have an articulated set of jaws which almost never happens and we could see that the third anterior tooth is curved out, just like in the tooth row of mako sharks today,” he said.

David Ward, an associate researcher at the Natural History Museum, London, who was not involved in the study told BBC News: “Everyone working in the field will be absolutely delighted to see this relationship formalised.”

The mosaic of both white shark-like and mako-like characters had been spotted by the researchers in an initial description of the fossil, but the age of the fossil meant their conclusion that the species was intermediate between a mako ancestor and modern white sharks wasn’t fully accepted.

“Some folks said ‘well, it makes a great story, but it’s not old enough because by this time, the early Pliocene, we see full blown white sharks in the ocean.'”

This led Ehret and his team to revisit the original site the fossil was taken from the Pisco Formation in Peru to re-examine the geology of the area, guided by the original field notes of Gordon Hubbell.

“Gordon gave us two photographs from when he actually collected the specimen and then a hand drawn map with a little ‘X’ on it. We tried to use the map and we didn’t have much luck.

“But using the two pictures of the excavation, my colleague Tom Devries was able to use the mountains in the background.”

“We literally walked through the desert holding the pictures up, trying to compare them. That’s how we found the site.”

Not only did they find the site, but the team were able to discover the precise hole from which the fossil had been excavated in 1988, before making a lucky escape from the desert.

“We made it back to Lima with about three hours to spare before an earthquake hit and shut down the transcontinental highway for two weeks. It was quite a trip.”

By analysing the species of molluscs found fossilised at the site, the team found that the shark was actually two million years older than had been thought, making it roughly 6.5 million years old.

“That two million year push-back is pretty significant because in the evolutionary history of white sharks, that puts the species in a more appropriate time category to be ancestral or… an intermediate form of white shark.”

“We’ve bolstered the case that white sharks are just highly modified makos… It fits the story now,” Professor Ehret told BBC News.

Source:BBC