‘Ancient humans left Africa once’


Human migration out of Africa, picture by P.D. deMenocal and C. Stringer/Nature 2016

From Science News:

Going global

Previous studies have used fossil, archaeological and genetic data to time humans’ colonization of the world (times shown above). New genetic studies may change that map; they suggest small numbers of people left Africa 120,000 years ago, but left little trace in the DNA of present-day people. Most non-Africans inherited their DNA from people who left Africa between about 70,000 and 50,000 years ago, new studies suggest. But a climate study indicates that was the worst possible time for an out-of-Africa migration and suggests people may have left earlier, between 80,000 and 100,000 years ago.

This video says about itself:

Predicted spread of humans around the world | Science News

21 September 2016

Earth wobbles on its axis, causing major climate shifts. Some of those shifts turned the Arabian Peninsula into lush grassland that ancient humans could have traversed as they migrated out of Africa. Researchers at the University of Hawaii at Manoa simulated climate conditions over the last 125,000 years and predicted how those changes would have allowed humans to spread around the globe (increasing intensity of red shows greater predicted migration).

Credit: Tobias Friedrich

The Science News article continues:

Single exodus from Africa gave rise to today’s non-Africans

Genetic data point to a date less than 72,000 years ago but climate scientists disagree

By Tina Hesman Saey

3:28pm, September 21, 2016

One wave of ancient human migrants out of Africa gave rise to all non-Africans alive today, three separate genetic studies conclude.

Those human explorers left Africa about 50,000 to 72,000 years ago, mixed with Neandertals and spread across the world, researchers report online September 21 in Nature. The studies present data from genetically diverse and previously unrepresented populations. Together they offer a detailed picture of deep human history and may settle some long-standing debates, but there is still room to quibble. All non-Africans stem from one major founding population, the studies agree, but earlier human migrations are also recorded in present-day people’s DNA, one study finds. And a fourth study in the same issue of Nature, this one focusing on ancient climate, also makes the case for an earlier exodus.

Scientists have long debated when anatomically modern humans first trekked out of Africa and how many waves of migration there were. Archaeological evidence indicates there were modern humans in Asia by at least 80,000 years ago. Human DNA in a Neandertal woman from Siberia indicates humans interbred with Neandertals outside Africa as long as 110,000 years ago (SN: 3/19/16, p. 6). But those people died out and didn’t contribute DNA to later generations, says Swapan Mallick, an evolutionary geneticist at Harvard Medical School and coauthor of a paper that traced the genetic history of 300 people from 142 populations around the world. The ancestors of today’s non-Africans probably left Africa about 50,000 years ago, Mallick and colleagues calculate.

Data in another study reveal remnants of a much earlier exodus from Africa that persist in the genomes of present-day Papuans, biological anthropologist Luca Pagani of the Estonian Biocentre in Tartu and colleagues report. About 2 percent of the genome of Papuans can be traced back to small bands of humans who left Africa 120,000 years ago. “This expansion was successful in leaving descendants today,” Pagani says. But a massive wave of migrants who left Africa after about 75,000 years ago probably overwhelmed that small trickle, swamping out their genetic signature.

A third study focusing on the genetic history of aboriginal Australians and Papuans from the New Guinea highlands didn’t find traces of a 120,000-year-old migration, but didn’t rule it out either, says study coauthor Eske Willerslev, an evolutionary geneticist at the University of Copenhagen.

Some previous studies have suggested that ancestors of Australians and Papuans came from an earlier wave of migration than other non-Africans did. “Australians and Papuans are descendants of some of the earliest modern human explorers,” Willerslev says. His group’s evidence suggests a single wave of migrants left Africa about 72,000 years ago and settled initially in the Middle East. Ancestors of Europeans and Asians stayed put for thousands of years before splitting into different groups. But Australian and Papuan ancestors kept going. “These guys were heading off on this marvelous journey across Asia,” ending up in Australia and Papua New Guinea about 50,000 years ago, Willerslev says.

Mallick and colleagues also found evidence of a main wave of migration into the Middle East that split into two groups after breeding with Neandertals. Those groups took different routes. One ended up in Europe, the other populated Asia. Instead of Australians and Papuans sprinting ahead of everyone else as an independent group, the researchers say they moved with the ancestors of East Asians and continued to the islands only later.

Pagani and colleagues used a method for analyzing their data that helped them pick out older chunks of DNA, says Mattias Jakobsson, an evolutionary geneticist at Uppsala University in Sweden. That method enabled them to see evidence of the older migration where the other studies couldn’t. But genetic dating methods are far from perfect; they can differ because of inaccurate mutation rates, skewed sampling, biased analyses or other reasons. Future genetic studies of present-day people added to new work on ancient DNA and archaeological evidence may help resolve some of the remaining discrepancies.

Even though results from Pagani’s study seem to disagree with the other two, “it’s a superficial disagreement,” says evolutionary geneticist Joshua Akey of the University of Washington in Seattle who was not involved in any of the studies. “One group is saying 98 percent” of DNA came from the main wave of migration, “while the other groups say it’s 100 percent. … The main conclusion is that the vast majority of ancestry in non-Africans can be traced to a single out-of-Africa dispersal.”

A study of ancient climates may create another discrepancy. It suggests the departure window geneticists propose was the absolute worst time to leave Africa. “Every 20,000 years or so, Earth’s axis wobbles caused massive shifts in climate and vegetation,” says Axel Timmermann, a climate scientist at the University of Hawaii at Manoa. Those fluctuations opened green corridors across northern Africa and the Arabian Peninsula, then turned those same areas to parched deserts.

Timmermann and University of Hawaii colleague Tobias Friedrich did computer simulations of climate and sea level changes over the last 125,000 years to predict when and where humans might have easily moved. By the scientists’ calculations, the timing of a mass human migration out of Africa 60,000 to 70,000 years ago “is the most unlikely scenario from a climate point of view, because … northeastern Africa was completely dry. It was one of the worst drought periods in the entire history, so the corridor was closed,” Timmermann says.

The researchers predict conditions were favorable for migration between 107,000 and 95,000 years ago and again 90,000 to 75,000 years ago. Another window didn’t open until 59,000 years ago, after humans were probably well on their way to Australia. “People could have chased antelope across and they wouldn’t even know they were on a different continent,” Timmermann says. That seamless landscape transition would have been mirrored in people’s mating habits, with populations moving in and out of Africa and mixing freely, he speculates.

Most genetic analyses don’t take that back-to-Africa movement into account, Timmermann says. Back-and-forth mating would make the Africans and non-Africans genetically indistinguishable from each other and obscure the real date at which people left Africa.  Allowing for cross-continent mingling puts people’s exodus from Africa at about 80,000 to 100,000 years ago. Climate shifts that turned Arabia to desert 70,000 years ago would have cut off the connection, making people already outside Africa genetically distinct from Africans. That would show up in the genetic studies as the point at which people left Africa instead of the point-of-no-return.

Some previous genetic research has found evidence of back-to-Africa migrations starting about 45,000 years ago (SN: 6/25/16, p.14).

The climate study reinforces the idea that people had spread out of Africa much sooner than the new genetic evidence indicates, says archaeologist Michael Petraglia of the Max Planck Institute for the Science of Human History in Jena, Germany. He is a coauthor of the Pagani study, but says genetics alone won’t solve all the mysteries of early human history.

Debate over when people left Africa, where they came from inside Africa and who they interbred with as they spread around the globe are far from over, says Petraglia. “I expect some fireworks in the next few years.”

Strange mammoth discovered in California, USA


This video from the USA says about itself:

Strange Mammoth Skull Discovered In California Baffles Scientists

18 September 2016

A unique fossil discovery has baffled scientists as they dig through a California Island looking for clues about human migration and mammoth extinction.

Deep within centuries of dirt, the team uncovered a well-preserved complete mammoth skull on Santa Rosa Island that they say exhibits features unlike any of its kind.

The skull is not large enough to be identified as a Columbian mammoth, yet not small enough to qualify as a pygmy – experts hope the creature’s fossilized teeth will reveal its true identity.

‘This mammoth find is extremely rare and of high scientific importance,’ Just Wilkins, a paleontologist at The Mammoth Site in South Dakota, said in a statement.

‘It appears to have been on the Channel Islands at the nearly same time as humans.’

‘I have seen a lot of mammoth skulls and this is one of the best preserved I have ever seen.’

Mammoths roamed North America some two million years ago, with Columbian mammoths appearing a million years later.

It is believed that the Columbian mammoths migrated to the Channel Islands during the past two ice ages when sea levels were lower and the island land mass was closer to the mainland coast.

Over time, descendants of the migrants downsized from approximately 14 feet to a six feet tall pygmy form, becoming an endemic species known as Mammuthus exilis.

The scientific team is particularly curious about the newly-discovered mammoth’s tusks.

The right tusk protrudes 1.4 meters in a coil characteristic of an older mammal, while the shorter, sloped left tusk is more typical of a juvenile.

From Science Alert:

Palaeontologists can’t explain the strange mammoth skull found in a California park

Its tusks don’t make sense.

BEC CREW

19 SEP 2016

An exceptionally well preserved fossil of a complete mammoth skull has been unearthed on a tiny island off the coast of California, and it’s got palaeontologists rethinking how these massive animals might have lived alongside humans.

Dated to 13,000 years ago, the skull was uncovered near a stream on Santa Rosa Island – part of California’s Channel Islands National Park. That date is important, because it happens to coincide with the age of the Arlington Springs Man – the oldest human skeletal remains found in North America.

“This mammoth find is extremely rare and of high scientific importance,” said one of the team, Justin Wilkins, a palaeontologist from the Mammoth Site museum in South Dakota.

“It appears to have been on the Channel Islands at the nearly same time as humans,” he adds. “I have seen a lot of mammoth skulls and this is one of the best preserved I have ever seen.”

Based on an analysis of the skull, the team suggests that new type of mammoth could have been roaming the Channel Islands with some of its earliest human inhabitants.

The remains of the Arlington Springs Man were also discovered on Santa Rosa Island – about 42 km (26 miles) off the coast of Santa Barbara, California.

Archaeologists have placed his life at the end of the Pleistocene, when the four northern Channel Islands formed one mega-island called Santarosae.

We know from previous evidence that mammoths roamed the continent of North America approximately 2 million years ago, and a species called the Columbian mammoth (Mammuthus columbi) managed to swim to Santarosae between 20,000 and 40,000 years ago.

But this skull doesn’t look like a Columbian mammoth’s.

Over several thousand years, these Columbian mammoths rapidly evolved to suit their new island lifestyle, and shrunk from 4.2 metres tall to 1.8 metres, and their features became so different, a new species arose – the more diminutive pygmy mammoth (Mammuthus exilis), the smallest mammoth in the world.

But this skull doesn’t look like a pygmy mammoth’s either.

The team explains that the skull is not large enough to be a Columbian mammoth’s, but it’s not small enough to be a pygmy mammoth’s. So the two most likely explanations is that this is a juvenile Columbian mammoth, or it could represent a transitional species that was partway through evolving from Columbian to pygmy.

Of course, the juvenile scenario would be a whole lot easier to explain, except for the fact that its tusks are all weird.

“The right tusk protrudes 1.4 metres (4.5 feet) in a coil characteristic of an older mammal, while the shorter, sloped left tusk is more typical of a juvenile,” they explain.

Instead, this could be the first evidence that there were two sets of Columbian mammoth migrations to Santarosae.

“The discovery of this mammoth skull increases the probability that there were at least two migrations of Columbian mammoths to the island – during the most recent ice age 10 to 30,000 years ago, as well as the previous glacial period that occurred about 150,000 years ago,” says one of the team, Dan Muhs, from the US Geological Survey.

It’s important to note that this is pure speculation right now – the team has only done preliminary measurements and analyses on the skull, and will need to prepare their findings for peer-review in the coming months.

But this strange skull could be our first glimpse into how these incredible extinct creatures used their trunks as snorkels not once, but twice, to get a taste of that sweet, sweet island life.

Tyrannosaurus rex in Dutch museum, video


This 9 September 2016 Dutch video shows Tyrannosaurus rex fossil Trix, which arrived recently in Naturalis museum in Leiden in the Netherlands.

Rattlesnakes less venomous than their ancestors


This video from North America says about itself:

GoPro falls into pit of rattlesnakes

9 October 2015

Rattlesnake strikes GoPro and knocks it into pit of snakes.

From Science News in the USA:

Rattlesnakes have reduced their repertoire of venoms

Reptiles’ common ancestor possessed greater variety of toxic proteins

By Laurel Hamers

12:00pm, September 15, 2016

Modern rattlesnakes have pared down their weaponry stockpile from their ancestor’s massive arsenal. Today’s rattlers have irreversibly lost entire toxin-producing genes over the course of evolution, narrowing the range of toxins in their venom, scientists report September 15 in Current Biology.

“After going through all the work of evolving powerful toxins, over time, some snakes have dispensed with them,” says study coauthor Sean B. Carroll, an investigator with the Howard Hughes Medical Institute who is at the University of Wisconsin–Madison. These modern rattlesnakes produce smaller sets of toxins that might be more specialized to their prey.

Carroll, an evolutionary biologist, and his colleagues focused on a family of enzymes called phospholipase A2, or PLA2. Genes in the PLA2 family are one of the main sources of toxic proteins in the deadly cocktail of rattlesnake venom. This set of genes can be shuffled around, added to and deleted from to yield different collections of toxins.

Data from the genome — the complete catalog of an organism’s genetic material — can reveal how those genetic gymnastics have played out over time. Carroll’s team looked at the relevant genome regions in three modern rattlesnake species (western diamondback, eastern diamondback and Mojave) and also measured molecules that help turn genetic instructions into proteins. That showed not just how the genes were arranged, but which genes the snakes were actually using. Then, the scientists blended that data with genetic information about other closely related rattlesnakes to construct a potential evolutionary story for the loss of PLA2 genes in one group of snakes.

The most recent common ancestor of this group probably had a large suite of PLA2 genes 22 million years ago, the scientists found. That collection of genes, which probably came about through many gene duplications, coded for toxins affecting the brain, blood and muscles of the snake’s prey. But 4 million to 7 million years ago, some rattlesnake species independently dropped different combinations of those genes to get smaller and more specialized sets of venom toxins. For instance, three closely related rattlesnake species in the group lost the genes that made their venom neurotoxic.

“The surprise is [the genes’] wholesale loss at two levels: complete disappearance from the venom and complete disappearance from the genome,” Carroll says. In other words, some of the genes are still lurking in the genome but aren’t turned on. The proteins those genes produce don’t show up in the venom in modern snakes. But other genes have left the genome entirely — a more dramatic strategy than simple changes in gene regulation.

Environmental shifts might have encouraged this offloading of evolutionary baggage, Carroll says. If a certain snake species’ main food source stopped responding to a neurotoxin, the snake would waste energy producing a protein that didn’t do anything helpful.

Plus, a rattlesnake doesn’t just invest in producing venom. It also needs to produce antibodies and other proteins to protect itself from its own poison, says Todd Castoe, an evolutionary biologist at the University of Texas at Arlington who wasn’t involved in the study. As a snake’s weapon becomes more complex, its shield does too — and that protection can use up resources.

Researchers also found that venom genes might not be consistent even within a single species of rattlesnake, perhaps because snakes in different areas specialize in different prey. One western diamondback rattlesnake that Carroll’s team sampled had unexpected extra genes that the other western diamondbacks didn’t have. His lab is currently looking into these within-species differences in venom composition to see how dynamic the PLA2 genome region still is today.

As for the ancestral rattlesnake, it’s impossible to say exactly how powerful the now-extinct reptile’s venom was, Carroll says. But the wider variety of enzymes this rattlesnake could hypothetically produce would have given it more flexibility to adapt its poison to environmental curveballs — an ability that Castoe describes as “the pinnacle of nastiness.”

Editor’s note: Sean B. Carroll is on the board of trustees of Society for Science & the Public, which publishes Science News.

Tyrannosaurus rex Trix in Dutch Naturalis museum


This 9 September 2016 video shows Tyrannosaurus rexTrix‘ after her arrival in Naturalis museum in Leiden in the Netherlands.

Ancient Indian primates discovered


This video is called 54 Million Year Old Fossils Point To India As Key In Primate Evolution.

From Science News:

Fossils hint at India’s crucial role in primate evolution

Limb bones may reveal what common ancestor looked like

By Bruce Bower

9:00am, September 8, 2016

Remarkably preserved bones of rat-sized creatures excavated in an Indian coal mine may come from close relatives of the first primatelike animals, researchers say.

A set of 25 arm, leg, ankle and foot fossils, dating to roughly 54.5 million years ago, raises India’s profile as a possible hotbed of early primate evolution, say evolutionary biologist Rachel Dunn of Des Moines University in Iowa and her colleagues. Bones from Vastan coal mine in Gujarat, India’s westernmost state, indicate that these tiny tree-dwellers resembled the first primates from as early as 65 million years ago, the scientists report in the October Journal of Human Evolution.

These discoveries add to previously reported jaws, teeth and limb bones of four ancient primate species found in the same mine. “The Vastan primates probably approximate a common primate ancestor better than any fossils found previously,” says paleontologist and study coauthor Kenneth Rose of Johns Hopkins University School of Medicine.

The Vastan animals were about the size of living gray mouse lemurs and dwarf lemurs, weighing roughly 150 to 300 grams (roughly half a pound), the investigators estimate. Dunn’s group has posted 3-D scans of the fossils to Morphosource.org (SN: 3/19/16, p. 28) so other researchers can download and study the material.

Most Vastan individuals possessed a basic climbing ability unlike the more specialized builds of members of the two ancient primate groups that gave rise to present-day primates, the researchers say. One of those groups, omomyids, consisted of relatives of tarsiers, monkeys and apes. The other group, adapoids, included relatives of lemurs, lorises and bushbabies. The Indian primates were tree-dwellers but could not leap from branch to branch like lemurs or ascend trees with the slow-but-sure grips of lorises, the new report concludes.

Vastan primates probably descended from a common ancestor of omomyids and adapoids, the researchers propose. India was a drifting landmass headed north toward a collision with mainland Asia when the Vastan primates were alive. Isolated on a huge chunk of land, the Indian primates evolved relatively slowly, retaining a great number of ancestral skeletal traits, Rose suspects.

“It’s possible that India played an important role in primate evolution,” says evolutionary anthropologist Doug Boyer of Duke University. A team led by Boyer reported in 2010 that a roughly 65-million-year-old fossil found in southern India might be a close relative of the common ancestor of primates, tree shrews and flying lemurs (which glide rather than fly and are not true lemurs).

One possibility is that primates and their close relatives evolved in isolation on the island continent of India between around 65 million and 55 million years ago, Boyer suggests. Primates then spread around the world once India joined Asia by about 50 million years ago.

That’s a controversial idea. An increasing number of scientists suspect primates originated in Asia. Chinese primate fossils dating to 56 million to 55 million years ago are slightly older than the Vastan primates (SN: 6/29/13, p. 14; SN: 1/3/04, p. 4). The Chinese finds show signs of having been omomyids.

And in at least one respect, Boyer says, some of the new Vastan fossils may be more specialized than their discoverers claim. Vastan ankle bones, for instance, look enough like those of modern lemurs to raise doubts that the Indian primates were direct descendants of primate precursors, he holds.

Dunn, however, regards the overall anatomy of the Vastan fossils as “the most direct evidence we have” that ancestors of early primates lacked lemurs’ leaping abilities, contrary to what some researchers have argued.

Small Cretaceous pterosaurs discovered


This video says about itself:

25 July 2014

Pterosaurs (/ˈtɛrɵsɔr/, from the Greek πτερόσαυρος, pterosauros, meaning “winged lizard”) were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period (228 to 66 million years ago).

Pterosaurs are the earliest vertebrates known to have evolved powered flight. Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the ankles to a dramatically lengthened fourth finger. Early species had long, fully toothed jaws and long tails, while later forms had a highly reduced tail, and some lacked teeth. Many sported furry coats made up of hair-like filaments known as pycnofibers, which covered their bodies and parts of their wings. Pterosaurs spanned a wide range of adult sizes, from the very small Nemicolopterus to the largest known flying creatures of all time, including Quetzalcoatlus and Hatzegopteryx.

From Science News:

Pterosaurs weren’t all super-sized in the Late Cretaceous

Some of the flying reptiles were smaller than a bald eagle

By Meghan Rosen

7:00am, September 12, 2016

Pterosaurs didn’t have to be gargantuan to survive in the Late Cretaceous.

Fragmentary fossils of a roughly 77-million-year-old pterosaur found in British Columbia suggest it had a wingspan of just 1.5 meters, about a quarter that of a bald eagle.

Bald eagles have wingspans of about two meters. So, the newly discovered pterosaus were smaller than bald eagles; but not four times smaller.

The ancient flier is the smallest pterosaur discovered during this time period — by a lot, report paleontologist Elizabeth Martin-Silverstone of the University of Southampton in England and colleagues August 30 in Royal Society Open Science.

Dozens of larger pterosaurs, some with wings spanning more than 10 meters (nearly the length of a school bus), have been unearthed. But until now, scientists had found only two small-scale versions, with wingspans 2.5 to 3 meters long, from the period stretching from 66 million to 100 million years ago.

Some scientists blamed competition with birds for the scarcity of little flying reptiles. Researchers have proposed that, “the only way pterosaurs could survive was by evolving completely crazy massive sizes,” Martin-Silverstone says.

The new find, she says, may mean that, “pterosaurs were doing better than we thought.”