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An ancient ape that was larger than a full-grown male
gorilla has now revealed molecular clues to its evolutionary roots.

Proteins extracted from a roughly 1.9-million-year-old tooth
of the aptly named Gigantopithecus blacki
peg it as a close
relative of modern orangutans
and their direct ancestors, say
bioarchaeologist Frido Welker of the University of Copenhagen and his
colleagues.

Protein comparisons among living and fossil apes suggest
that Gigantopithecus and orangutan
forerunners diverged from a common ancestor between around 10 million and 12
million years ago, Welker’s group reports November 13 in Nature.

Since it was first described in 1935, based on a molar
purchased from a traditional Chinese drugstore in Hong Kong, G. blacki has stimulated debate over
its evolutionary links to other ancient apes. Almost 2,000 isolated teeth and
four partial jaws of G. blacki have
since been found in southern China and nearby parts of Southeast Asia. G. blacki fossils date from around 2
million to almost 300,000 years ago. The sizes of individual teeth and jaws
indicate that G. blacki weighed
between 200 and 300 kilograms.


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Proteins preserve better in teeth and bones than DNA does,
but both molecular forms break down quickly in hot, humid settings. “We were
surprised to find any proteins this old at all, especially in a fossil from a
subtropical environment,” Welker says. Proteins consisting of chains of amino
acids can be used to sort out living and fossil species of various animals, including
hominids
(SN: 5/1/19).

Researchers generally regard G. blacki as an orangutan relative that evolved to live in forests
and eat fruits, leaves, stems and possibly tubers. But that assumption has
rested on thin evidence, says biological anthropologist Terry Harrison of New
York University.

“This new [protein] analysis provides the first compelling
evidence that Gigantopithecus was
more closely related to the orangutan than to any other ape,” Harrison says.

Gigantopithecus
In this illustration, the ancient Asian ape Gigantopithecus looks much like an orangutan. Proteins from a Gigantopithecus tooth point to a close evolutionary link between the extinct ape and orangutan ancestors.Ikumi Kayama/Studio Kayama LLC

Welker’s team retrieved amino acid sequences from six
proteins in a G. blacki molar
previously found in southern China’s Chuifeng Cave. Five of those proteins are
commonly found in living chimps, bonobos, gorillas, orangutans and humans,
enabling comparisons of accumulated differences in the amino acid arrangements between
G. blacki and those five present-day primates.
Orangutans displayed the fewest protein disparities with G. blacki, signaling a particularly close evolutionary link between
living red apes and the ancient Asian ape. Using those protein comparisons, the
age of the G. blacki tooth and
previous estimates of when various living apes diverged from common ancestors,
Welker’s group calculated the timing of a common ancestor for orangutans and G. blacki.

The sixth protein has been linked to a process by which minerals
are produced to harden bones and teeth. That protein may have contributed to
the formation of especially thick tooth enamel in G. blacki, the researchers speculate.

No attempt was made to remove DNA from the ancient ape
tooth. Even in colder regions than southern China, only much
younger fossils have yielded DNA
(SN:
3/14/16
).

Ancient proteins from other Asian fossil apes dating to
between around 12 million and 6 million years ago are needed to further clarify
the evolutionary position of G. blacki,
says paleoanthropologist Russell Ciochon of the University of Iowa in Iowa
City. Ciochon suspects that Indopithecus
giganteus
, a fossil ape that inhabited what’s now northern India and
Pakistan during that period, was a potential ancestor of G. blacki.

Protein analyses of fossil orangutans that lived in
Southeast Asia at the same time as G.
blacki
may also help untangle how and why red apes died out in China after
approximately 126,000 years ago, but still live on two Indonesian islands,
Ciochon says. Such research could provide insights into how best to save endangered
orangutans today
(SN: 2/15/18).

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