Ancient Asian Primates Decimated by Climate Change

The lineage of primates that led to the monkeys, the apes and eventually the hominins (that’s us), originated in Asia.  Palaeoanthropologists and palaeontologists tend to agree on this as the known fossil record suggests a Far Eastern evolutionary heritage for our distant ancestors.  However, there is a conundrum, if the anthropoids (those flat-faced monkeys that led to the apes and ourselves), evolved in Asia, then why didn’t this evolutionary line continue and lead to higher apes and hominins from Asia?

For models and figures of prehistoric animals: Prehistoric Animal Figures and Replicas.

Fossil Primates

The fossil record indicates that the earliest anthropoid fossils date from 45 million years ago (Asian fossil discoveries).  In African strata some seven or eight million years younger, the first fossils of African anthropoids are found.  We can conclude from this fossil evidence that the anthropoids first evolved in Asia, only making their way to Africa around 38 million years ago, with the hominins evolving something like 33 million years later, but only in Africa, so what caused the Asian anthropoids to stall?

Thanks to some remarkable fossil finds from China, scientists have solved this primate puzzle, it seems that dramatic climate change some 34 million years ago, nearly wiped out Asian primates, decimated populations and rendered much of that continent as “no go” areas for our distant cousins.

Ancient Teeth and Bones Provide an Important Breakthrough in Our Understanding of Primate Evolution

Different types of ancient primate from southern China identified from their fossilised jaws and teeth.

Picture credit: Chinese Academy of Sciences

Studying Fossil Primate Teeth

The picture above shows the different types of fossil teeth and jawbone used by the scientists to identify new species of Asian Oligocene primates.

In a study published in the journal “Science”, researchers from the University of Kansas in collaboration with colleagues from the Chinese Academy of Sciences, report on the identification of six new species of primates from a site in southern China.  Described as a “mother lode”, these extremely rare and precious fossils shed light on how some Asian primates survived the global cooling event that marked the end of the Eocene Epoch.

Eocene to Oligocene Transition (EOT)

The end of the Eocene Epoch is marked by a significant extinction event.  It may not have been as devastating as the end Cretaceous extinction that led to the demise of something like 70% of all large terrestrial animals, but nonetheless, there was a considerable amount of faunal turnover with many long-established genera (such as the early whales), becoming extinct.  Some 34 million years ago, the Earth cooled dramatically.  Global temperatures fell from an average of around 21 degrees Celsius to around 16 degrees Celsius.

Scientists remain uncertain as to the cause of the cooling, although there was considerable tectonic plate activity, volcanism and a number of extraterrestrial impacts during the Late Eocene.  Some studies have indicated a fall in atmospheric carbon dioxide at this time.  This “greenhouse gas”, so feared today, because of its affect on global warming, may have been reduced in the atmosphere to such an extent that the Earth entered a phase of dramatic cooling.  It is at this time that Antarctica began to change into the frozen wasteland we know today.

The Impact of Global Cooling

As the Earth grew colder so the tropical forests shrank and the available habitat for Asian primates was greatly reduced, the six newly described species were part of an ecosystem that clung on in southern China, an area where a tropical climate still persisted.

Commenting on the significance of this decade long study, co-author of the scientific paper, K. Christopher Beard, (senior curator at the University of Kansas Biodiversity Institute) stated:

“Primates like it warm and wet, so they faced hard times around the world — to the extent that they went extinct in North America and Europe.  Of course, primates somehow survived in Africa and southern Asia, because we’re still around to talk about it.”

The Key to Understanding the Evolution of Primates

As anthropoid primates first appeared in Asia, these new fossil discoveries help scientists to understand the fate of primates on that continent, which is fundamental to understanding early primate and ultimately ape evolution.

Senior curator Beard added:

“This has always been an enigma.  We had a lot of evidence previously that the earliest anthropoids originated in Asia.  At some point, later in the Eocene, these Asian anthropoids got to Africa and started to diversify there.  At some point, the geographic focal point of anthropoid evolution — monkeys, apes and humans — shifted from Asia to Africa.  But we never understood when and why.  Now, we know.  The Eocene-Oligocene climate crisis virtually wiped out Asian anthropoids, so the only place they could evolve to become later monkeys, apes and humans was Africa.”

Working with colleagues from the Chinese Academy of Sciences (Institute of Vertebrate Palaeontology and Palaeoanthropology), specifically Xijun Ni, Qiang Li and Lüzhou Li, the researchers were able to shift through the 34-million-year-old sediments to find teeth and jaw fragments that enabled them to erect six new species.  The fossils were recovered from the upper part of the Caijiachong Formation, Yuezhou Basin, Yunnan Province, through a combination of careful site mapping and scree washing.  It seems that whilst much of Asia became inhospitable for primates, this part of China retained tropical forest so a number of species ended up being crowded into a limited space.

A List of the Six New Species of Primate Named

1. Yunnanadapis folivorus (pronounced You-nan-ah-dap-is) a member of the Strepsirrhini (lemurs).  In the fossil teeth photograph above Y. folivorus is A.
2. Yunnanadapis imperator (pronounced You-nan-ah-dap-is) a member of the Strepsirrhini (lemurs).  In the fossil teeth photograph above Y.  imperator is B.
3. Laomaki yunnanensis (pronounced Lay-oh-ma-key) a lemur-like primate (Strepsirrhini).  In the photograph of the fossil teeth above L. yunnanensis is C.
4. Gatanthropus micros (pronounced Gat-anthro-pos) another lemur-like primate.  In the fossil teeth picture above G. micros is D.
5. Oligotarsius rarus (pronounced Olee-go-tar-see-us) the only member of the Tarsiidae (Tarsiers) described from this location.  O. rarus is represented by E in the fossil teeth picture above.
6. Bahinia banyueae (pronounced Ba-hin-nee-ah), the only anthropoid identified, superficially similar to today’s marmosets, represented by F in the fossil teeth photograph above.

Differences in Oligocene Primate Faunas

The team’s research suggests that the Eocene-Oligocene transition (EOT) led to completely different primate faunas in Asia compared to Africa and the Near East.  In Africa, the anthropoid primates radiated, diversified and became dominant.  However, in Asia, it was the lemur-like primates the Strepsirrhini that seem to have dominated.  The EOT acted as an evolutionary filter dramatically altering the evolution of primates around the world.

The EOT Acted as an Evolutionary Filter Changing Primate Evolution

Changing Primate Faunas due to Eocene to Oligocene transition.

Picture credit: Chinese Academy of Sciences

The EOT changed the evolutionary history of the primates, acting as a filter.  When the composition of early Oligocene primate faunas of Asia and Afro-Arabia are compared, we see that in Asia it was the lemur-like primates (Strepsirrhini) that rose to dominance, whereas in Afro-Arabia, the lemurs became much rarer and it was the anthropoid apes that diversified and became prominent.

The Rare Oligotarsius

Tarsier fossils are incredibly rare in the fossil record, and very little is known about the evolution of the Tarsiidae, the trivial name of O. rarus recognises this.  The teeth of Oligotarsius are very similar to modern tarsiers found today in Indonesia and the Philippines.  This suggests that extant tarsiers are little changed from their ancient ancestors.

Dr Beard explained:

“If you look back at the fossil record, we know that tarsiers once lived on mainland Asia, as far north as central China.  The fossil teeth described in this paper are nearly identical to those of modern tarsiers.  Research shows that modern tarsiers are pretty much living fossils, those things have been doing what they do ever since time immemorial, as far as we can tell.”

A Vulnerability of All Primates?

This new study underscores a vulnerability of perhaps, all primates, that is how they cope when there is dramatic climate change.  The global cooling of the EOT altered primate evolution and transformed the primate faunal mixes of both Asia and Africa.  The EOT is an opposite climate effect to what we are experiencing today.  Thirty-four million years ago the world cooled, today people are very concerned about global warming, the key point is this, whether the climate warms or grows cold, primates seem to be more sensitive to a changing world than other mammals.  This could mean very bad news for our own species.

Food for Thought

It is a sobering thought, but what if the Eocene-Oligocene cooling had not taken place?  Asian anthropoids would have continued to evolve and diversify, potentially with far-reaching consequences for all primates, including hominins and our own species.  Homo sapiens (that’s us), evolved in Africa some 220,000 years ago, however, had this ancient cooling not occurred, the outcome in terms of anthropoid and ultimately human evolution could have been very different.

For an article on potentially the oldest primate: The Oldest Primate To Date?

To read about Miocene Tarsiers from Thailand: Miocene Tarsier Fossils from Thailand.

Ediacaran Faunal Out Competed by Newly Evolved Animals

A remote fossil site in Namibia has helped strengthen the theory that the fauna of the Ediacaran was unable to survive the radical “re-engineering of marine ecosystems” that resulted with the evolution of more advanced biological organisms.  Newly evolved metazoans (animals that have three types of tissue layer in the embryo and are multi-cellular), altered the marine environment so much that most of the older, largely immobile, species that had dominated the Ediacaran geological period died out.

Ediacaran Fauna

A Late Precambrian (Ediacaran) Marine Environment

Life in the Ediacaran.

Picture credit: John Sibbick

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The Ediacaran Geological Period

The Ediacaran geological period is defined as the last geological period of the Proterozoic (early life), it lasted from around 635 million years ago to 542 million years ago and this geological period saw the emergence of a diverse variety of soft-bodied multi-cellular creatures, most of which have no living descendants today.  The ecosystems that existed were very simple with short food chains, multi-cellular life was bizarre with many organisms shaped like discs, tubes or fronds.

Towards the end the Ediacaran more advanced and crucially mobile organisms began to evolve.  Food chains became more complicated with the evolution of active predation amongst organisms.  These new species were “ecological engineers” who changed the environment in ways that made it more and more difficult for Ediacaran organisms to survive.  That is the conclusion of the research team which studied the Namibian fossil remains.

Assistant Professor Simon Darroch Searching the Namibian Site for Fossils

Searching for fossils dating from the Ediacaran (southern Namibia).

Picture credit: Sarah Tweedt, Smithsonian Institution

Important Fossil Site

Writing in the journal “Palaeogeography, Palaeoclimatology, Palaeoecology”, the scientists, which include Simon Darroch (Assistant Professor of Earth and Environmental Sciences at Vanderbilt University located at Nashville Tennessee), report that they have found one of the best-preserved examples of a mixed community of Ediacaran and metazoan organisms preserved in strata from the Zaris sub-basin of southern Namibia.

The Biota Replacement Model

Palaeontologists had predicted that evidence would be found in the fossil record to indicate ecosystems dominated by Ediacaran organisms being replaced by ecosystems dominated by organisms whose fossil record persist into the Cambrian and beyond.  The Namibian fossils provide the best evidence yet of a close ecological association between these distinct types of life-form.

Assistant Professor Darroch explained:

“Until this, the evidence for an overlapping ecological association between metazoans and soft-bodied Ediacaran organisms was limited.  Here, we describe new fossil localities from southern Namibia that preserve soft-bodied Ediacara biota, enigmatic tubular organisms thought to represent metazoans and vertically oriented metazoan trace fossils.  Although the precise identity of the trace makers remains elusive, the structures bear several striking similarities with a cone-shaped organism called Conichnus that has been found in the Cambrian period.”

Conichnus Trace Fossils from Namibia – Evidence of Biota Replacement

Conichnus burrows are trace fossils. The surface bumps represent vertical tubes that were originally occupied by anemone-like animals that may have fed on Ediacaran larvae.

Picture credit: Vanderbilt University/Darroch

Conichnus is an ichnogenus (known only from trace fossils), that may have been some form of anemone that fed on Ediacaran larvae.  The scientists also report that they have found strands of Ediacaran frond-like organisms with animal fossils preserved in place coiled around their holdfasts.  The Namibian fossil material provides a snapshot of a transitional ecosystem prior to the Cambrian explosion which led to the evolution of much more modern looking food chains.

Assistant Professor Darroch stated:

“Both animal burrows – ‘trace fossils’ – and the remains of animals themselves sharing the same communities, lets us speculate about how these two very different groups of organisms interacted.”

Lessons for Today

Although the research team are studying the remains of organisms preserved in rocks that were laid down more than 540 million years ago, the biota replacement model that these fossils seem to confirm has relevance for our planet today.  Some of the fossil strata shows the preserved body fossils of a bizarre metazoan called Shaanxilithes, these fossils are coiled found the anchoring, trace fossil (a holdfast) of a frond-like organism),

Shaanxilithes Fossils (Ediacaran Strata – Namibia)

Shaanxilithes are odd, annulated and ribbon-like fossils that start showing up near the end of the Ediacaran period. In this fossil they are wrapped around Aspidella holdfasts.

Picture credit: Vanderbilt University/Darroch

Simon explained:

“There is a powerful analogy between the Earth’s first mass extinction and what is happening today.  The end-Ediacaran extinction shows that the evolution of new behaviours can fundamentally change the entire planet, and today we humans are the most powerful ‘ecosystems engineers’ ever known.”

This research entitled: “A mixed Ediacaran-metazoan assemblage from the Zaris sub-basin, Namibia”, builds on an earlier scientific paper published last year that examined a large number of animal burrows preserved in the Namibia rocks that were interpreted as representing the fossil record of a community under stress.

The Disc-Like Structures Represent the Holdfasts of Ediacaran Organisms

The disc-like fossils are the preserved remains of holdfast structures used by the Ediacaran species Aspidella that went extinct about a million years after these individuals died and were preserved.

Picture credit: Vanderbilt University/Darroch

The picture above shows the preserved remains of several disc-like fossils in the Namibian strata.  These have been interpreted as the holdfast, anchoring structures of the fern-like Aspidella.  Once thought to be an ancestral jellyfish, at the time it was first studied, it was the first Precambrian body fossil to have been formally scientifically described.  These disc shapes are now interpreted as trace fossils, examples of the benthic, immobile fauna of the Ediacaran, that was being replaced by more complex and mobile metazoans.

Stirring Up Sediments

Hunting and eating the Ediacaran fauna might not have been the only destructive behaviour of the more complex mobile organisms that represented emerging fauna that would dominate the Cambrian.  The researchers also point out that mobile Cambrian animals would have stirred up nutrients leaving them in suspension above the sea floor, far away from the reach of the benthic Ediacaran life-forms.  In essence, the microbial mats and more complex but ultimately, confined to the sea floor Ediacaran fauna, would have found that nutrients that once always fell to the seabed were now suspended in a new marine ecosystem, effectively placing these nutrients out of reach.

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