Palaeontology

07 October 2017: New evidence suggest we are much older than 300,000 years

In a recent blog I wrote about new dates for skulls found in the cave of Jebel Irhoud in Morocco in the 1960s. Originally assessed as belonging to Homo neanderthalensis (an assessment that was soon challenged), a reappraisal published in Nature this year confirmed they were in fact H. sapiens skulls; the great surprise was that the reappraisal determined them to be at least 300,000 years old.

Jebel Irhoud

Cast of Jebel Irhoud 1 from the Australian National University. Photo: Simon Brown

New work done by scientists in Sweden and South Africa, and reported in Science, have now dated DNA obtained from a 2000-year-old Khoe-San skeleton apparently unmixed with Bantu or Eurasian DNA, as having separated from other H. sapiens sometime between 260,000 and 350,000 years ago.

The San are the First People of South Africa, Botswana and Namibia. Indeed, they may be the First People, the ancestral group all modern humans are descended from, or at the very least very closely related to them.

The San are the most genetically diverse of all humans living today. In an episode of Catalyst on the ABC about her research on San DNA, Professor Vanessa Hayes said, ‘There’s more similarity between myself and a Han Chinese than between two San people.’

Bushman

San hunter/gatherer

As reported in Science, the recent work on San DNA involved several ancient individuals, but the standout dates were given by DNA from the genome of a hunter-gatherer boy known as Ballito Bay A. The scientists concluded that, ‘ … our results show that the deepest split among modern humans (the estimated latest time for the emergence of H. sapiens) occurred at between 350 kya and 260 kya.’

Given that the skulls found in Morocco have been dated to at least 300,000 years ago, it would seem not unreasonable to consider the older dates for the emergence of H. sapiens – 350,000 years ago – being closer to the mark than the lower date of 260,000 years ago.

This new evidence also adds weight to the theory that our species may have partly evolved in South Africa.

In the last eight months, we have seen conservative estimates for the age of our species jump from 190,000 years old to almost double that. It’s been an extraordinary year for palaeoanthropology.

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29 September 2017: What ancient hominid left her footprints in Crete?

There is strong evidence that a hominid walked in Crete in the late Miocene, about 5.7 million years ago.

In an article in the 31 August 2017 issue of the Proceedings of the Geologists’ Association, the authors describe the discovery in western Crete of tracks in rock accurately dated to the Messinian age. To quote the abstract, ‘The tracks indicate that the trackmaker lacked claws, and was bipedal, plantigrade, pentadactyl and strongly entaxonic.’

Trachilos footprints Andrzej Boczarowski

Ancient hominid footprints near Trachilos, Crete. Photo: Andrzej Boczarowski

In plain English, the authors are describing footprints impressed in rock that suggest the creature that made them walked on two feet, not four (bipedal), that it walked on its whole foot rather than just on its toes or claws (plantigrade), that it had five digits on each limb (pentadactyl), and that its big toe was bigger than its other toes (entaxonic).

In short, a footprint that resembles those that are left behind by hominins – the family of humans that includes you and me.

The paper caused a small storm in palaeoanthrapological circles for two reasons. First, there is little direct evidence anywhere of bipedalism before the Pliocene (the epoch immediately following the Miocene, starting around five million years ago), and second, there was no evidence of bipedalism outside of Africa before the Pliocene.

If the tracks discovered in Crete have been accurately dated, and the evidence seems strong on this point, then several intriguing possibilities present themselves.

First, that bipedalism, as palaeoanthrapological orthodoxy has it, evolved in Africa in a species that subsequently migrated to Eurasia (or possibly one of that species’ close descendants made the journey) much earlier than first believed.

Second, that bipedalism in our family may have evolved in Eurasia and not Africa.

Third, that bipedalism evolved more than once in our family. This would make it an extraordinary example of convergent evolution.

At this point, without completely discounting it, the first possibility seems the most unlikely, simply because there is no evidence – fossil or footprint – to support it. However, if this turns out to be the correct answer, a prime candidate would have to be Orrorin tugenensis, the oldest hominid for which we have strong evidence for bipedalism. Orrorin lived in Kenya in the late Miocene, so the dates fit.

The second possibility has been championed by scientists who think it may have been left by Graecopithecus freybergi, a hominin known by one mandible and a few teeth discovered in Greece. Although we do not know if Graecopithecus was bipedal, a recent paper proposed that its dental morphology suggests it is the oldest hominin and that therefore humans first appeared in Eurasia and not Africa.

Graecopithecus_tooth

Teeth from Graecopithecus freybergi

While this claim has been controversial, if Graecopithecus was the first hominin then it was almost certainly bipedal and may well have left impressions of its footprints in Crete. However, generally speaking dentition follows diet. Our teeth can evolve quickly to take advantage of new resources in food, so it is possible that despite its human-like teeth Graecopithecus was a hominid (a member of the family that include great apes as well as humans) but not specifically a member of the tribe Hominini. If this is the case, then Graecopithecus is only our distant cousin rather than an ancestor.

This leads to the third possibility, that bipedalism evolved more than once in the hominid clade. If this is the case, then there is one other strong Eurasian candidate for the owner of those footprints left behind in Miocene Crete, and some scientists think this candidate may have been bipedal.

Oreopithecus bambolii is known from 9-7-million-year-old fossils discovered in Italy from the 1870s. The best and most complete fossil was found in lignite, earning it the name of the Abominable Coalman.

For a long time the position of Oreopithecus in the hominid record has been controversial, most disagreement revolving around whether it is part of the ape or the human family.

Oreopithecus

Oreopithecus bambolii – the ‘Abominable Coalman’

Work done on Oreopithecus in the 1990s controversially proposed it was bipedal, although with a curiously positioned big toe that meant its foot may have acted almost like a tripod. This suggests it could walk on two feet, but probably not at any great pace.

A recent survey of the hominid’s spine, however, has led some scientists to think Oreopithecus was not fully bipedal. Furthermore, the footprints in Crete do indicate a more conventionally shaped foot.

The tracks were discovered in Crete, and dated to the Messinian age when the sea level of the Mediterranean was probably similar to now. Graecopithecus somehow would have had to make it across the equivalent of the Aegean Sea to reach Crete, and Oreopithecus across the Ionian and Aegean seas. Orrorin would have had to make it all the way from Africa. Of course, many animals throughout history have crossed seas and even oceans to reach isolated islands, including members of the hominid clade (Homo erectus to Java and Homo floresiensis to Flores, for example), but to date there is no fossil evidence of either Graecopithecus or Oreopithecus having lived – let alone walked – on Crete.

(This blog entry is based on an idea proposed by Colin Groves, Emeritus Professor of Bioanthropology at the Australian National University.)

15 July 2017: New dates for Homo naledi and (surprise!) new dates for H. sapiens

I originally intended to write about how recent dates discovered for Homo naledi meant that it and H. sapiens, our own species, had only the narrowest window in time to cross paths, but recent finds in Morocco have put paid to that. The announcements of the two sets of dates occurred within days of each other, and demonstrate just how quickly our knowledge of early human evolution is itself evolving.

Homo_naledi_holotype_specimen_(DH1)

Holotype specimen of H. naledi (Photo: Lee Roger Berger research team)

The new information for H. naledi appeared in three papers published in eLife (here, here and here) in May 2017, and provided more detail about when this newly discovered species walked the Earth, as well as announcing the discovery of a second area – the Lesedi Chamber in the Rising Star cave system about 50 km northwest of Johannesburg in South Africa – containing yet more H. naledi remains.

(For more on the first discovery, see in an earlier blog the interview I did with Elen Feuerriegel, one of the ‘underground astronauts’ involved in the recovery of the H. naledi remains in the Dinaledi Chamber).

Morphologically, the new species contained features that positioned it somewhere between the Australopithecines and the early members of our own genus, Homo; this would place it somewhere around two million years old. Confusingly, however, the bones found in the Dinaledi Chamber were still made up of hydroxylapatite, a form of calcium that takes up around 70% of the weight of human bones. Normally, fossilization results in the hydroxylapatite being replaced by minerals like silica. This suggested a more recent existence for H. naledi.

And the bones spoke true. The new papers give dates for the remains that placed it between 335,000 and 236,000 years old. Since the conservative dates for our own species up to May were 190,000 years ago, or 260,000 if you count the Florisbad skull as belonging to our own species instead of another such as H. heidelbergensis, it seemed unlikely, if remotely possible, that our ancestors crossed path with H. naledi.

But then came the second announcement.

A paper published in Nature in June 2017 revealed that H. sapiens remains discovered at a cave called Jebel Irhoud in Morocco, approximately 100km west of Marrakesh, and retrieved largely during the 1960s, have now been dated to extend as far back as 300,000 years, pushing it way beyond Florisbad and well within reach of H. naledi.

Jebel_Irhoud_1._Homo_Sapiens

Irhoud 1(Photo: Ryan Somma)

The skulls among these finds are not shaped like modern human skulls; the remains were originally classified as belonging to a sort of African Neanderthal. But the faces are flat, like our own, without the prominent inflated brow ridge of Neanderthal.

Where exactly they lie in the long line of human evolution is not known for certain, but their location and their age suggest strongly that they are archaic H. sapiens and not some other species.

While this does not change the overall pattern of human evolution as currently understood, it does dramatically extend the time that our species has existed, and strengthens the argument that the cradle of modern humanity was indeed Africa.

08 May 2917: Update on Homo floresiensis

Since my last blog on Homo floresiensis almost a year ago, two new discoveries have pushed back the origin of the species to at least 700,000 years ago and clarified its line of descent.

The original remains were found in Liang Bua cave on the Indonesian island of Flores in 2004. A short hominin that stood about a metre high, almost inevitably the new species was dubbed the ‘Hobbit’.

H. floresiensis

Homo floresiensis almost certainly not descended from …

There was initial controversy in some corners about whether the remains represented a new species or diseased specimens of Homo sapiens. Mounting evidence that it was indeed a new species climaxed with the announcement in June 2016 that fossils found in the So’a Basin of central Flores in 2014 possess characteristics that are morphologically similar to those found in Liang Bua fossils.

At 700,000 years old, these new fossils are the most ancient hominin remains yet found in Flores, and strongly suggest the ancestors of H. floresiensis first reached the island long before anatomically modern humans had evolved in Africa.

The main debate subsequently shifted to whether or not H. floresiensis was descended from Homo erectus – whose fossils were first discovered in Java – or some other early hominin.

H. erectus

Home erectus, but possibly from …

If descended from H. erectus, the Hobbit was an excellent example of ‘island dwarfism’, where populations of larger animals restricted in geographical range – usually islands – decrease in size over time. (Ironically, smaller animals in the same situation, lacking predators, tend to increase in size.)

A new paper published in the Journal of Human Evolution in April this year, however, presents strong evidence that H. floresiensis most likely descended from an earlier hominin. In the words of the authors, the results of their research indicates it is ‘a long-surviving relict of an early (>1.75 Ma) hominin lineage and a hitherto unknown migration out of Africa … ’

H. habilis

Homo habilis.

Using Bayesian phylogenetic methods and ‘parsimony’, the authors conclude that H. floresiensis is sister either to H. habilis alone or to a clade consisting of other hominin species including H. erectus and H. sapiens. However, they point out that a close phylogenetic relationship between H. floresiensis and H. erectus or H. sapiens can be ruled out.

These findings are important for two reasons.

First, they should finally put paid to any theory that the Hobbits are simply pathological specimens of our own species.

Second, it suggests that our hominin ancestors were migrating from their African homeland long before Home ergaster – the probable ancestor of H. erectus and sister species – decided to emigrate to pastures new some two million years ago.

Wanderlust, it seems, is an essential part of our genetic makeup.

16 May 2016: New dates for the ‘Hobbit’

Homo floresiensis

Photo: Ryan Somma

Updating my blog celebrating the 10th anniversary of the discovery of Homo floresiensis, better known as the ‘Hobbit’, a letter in Nature has revised the most recent dates for the remains from 12,000 years back to 60,000 years. The sediment layers in the cave of Liang Bua on the Indonesian island of Flores, where the remains were discovered, had not been laid evenly, leading to an initial miscalculation.

Stone artefacts attributed to H. floresiensis are dated more recently, to 50,000 years ago.

The biggest implication of the new dates is that it is now less likely that the ‘Hobbit’ coexisted at the same time as H. sapiens on Flores. Although it cannot be ruled out, the earliest dates for human occupation at Flores is 50,000 years, leaving a very narrow window of opportunity.

11 February 2016: Digging for relatives

DSC02344

Elen Feuerriegel with thermoplastic copy of H. naledi lower jaw.

“Sometimes I can’t believe it happened,” said Elen Feuerriegel as the 3D printer by her side chugs out a thermoplastic copy of the cranium of an ancient human.

“I’m doing something ordinary, something I do every day, and then remember that two years ago I was working 30 metres underground recovering the remains of Homo naledi, a previously unknown human species.”

Feuerriegel, a PhD student in palaeoanthropology at the Australian National University, was one of six excavators – dubbed underground astronauts by an excited media – who retrieved the bones of up to 15 individuals from a small and almost inaccessible cave.

Part of an expedition organised by Professor Lee Berger from the University of Witwatersrand to investigate the Rising Star Cave in South Africa, it was the task of the Feuerriegel and the other five excavators to reach a small and unmapped annex to the cave system called the Dinaledi Chamber.

“To get to the chamber meant worming our way through a fissure that in one place narrowed to just 18 centimetres,” Feuerriegel said. “The fissure itself was a 12-metre drop that ended in a tiny landing, followed by another four metre drop to the floor of the chamber.”

What Feuerriegel first saw there will stay with her for the rest of her life.

“It was a wonderful, exhilarating experience. It was incredible amount of fossil material in one place. It was almost impossible to move without stepping on a jaw or leg bone.

“As our eyes got used to the dimness and we became more experienced at discerning fossils in the floor sediment, new finds seemed to appear out of nowhere.”

Despite her interest in science starting as a young teenager, her appearance at the Rising Star Cave System was never a given. She reached palaeoanthropology through a route almost as torturous as the entrance to the Dinaledi Chamber.

“My first love was marine biology, particularly sharks. That somehow morphed into a fascination with volcanoes. Then my mum, an information architect, helped me put together a web page for a school project I did on human evolution.”

Feuerriegel speaks about evolution through natural selection with a focused passion.

“For me, evolution is the great leveler. We humans are as subject to evolutionary forces as other species.”

The American crime procedural CSI: Crime Scene Investigation also stirred in her an interest in anatomy.

She did her first degree in sociocultural anthropology at the University of Queensland. “I’d given up on the idea of palaeoanthropology until I did an intensive summer course on human evolution.”

With an honours degree in her pocket, Feuerriegel came to the ANU to do her masters, and in 2013 began her PhD in palaeoanthropology.

Later that year, Lee Berger put the call out for people with a special and unusual skill set.

“He wanted skinny palaeoanthropologists who were also experienced climbers or cavers.”

Feuerriegel, who enjoyed wall-climbing and hiking, and had previously worked in a mine shaft in Sima de las Palomas in Spain looking for the remains of Neanderthals, applied for one of the openings.

Underground astronauts

The Underground Astronauts: Becca Peixotto, Alia Gurtov, Elen Feuerriegel, Marina Elliott, K. Lindsay Hunter, Hannah Morris. Photo: John Hawks

“Despite the specialist skill set, there were 60 applicants. I was one of six chosen.”

Within three weeks of an online interview, Feuerriegel found herself in South Africa retrieving the remains of a new human species, Homo naledi.

“We worked in two shifts, each with three excavators and two support cavers. Each shift lasted anywhere between three and six hours, depending on the task. The expedition tried to get at least two shifts down in the chamber every day, and sometimes three.

“For the first few days it could take up to an hour to get down from the surface to the chamber, but by the end of our stay there we’d reduced that to 20 minutes, giving us much more time for the real work.”

Towards the end of the work, seasonal rains raised the water table.

“There was no danger to us – the site was well above the water table – but conditions gradually got worse and surfaces more and more slippery.”

In the end, the excavators recovered the remains of 15 individuals, male and female, ranging in age from neonatal to an older female with very worn teeth.

Feuerriegel said she’s sure what the team discovered is a new species of ancient human.

“Morphologically, Homo naledi sits somewhere in the bridge between the latter Australopithecines and the early Homo, having features of both as well as some unique features all of its own. Exactly where it fits is something we don’t know yet.

“The other thing we don’t know at this point is how old the remains are. The bones we found had not yet been replaced with minerals like silica, but were still made up of hydroxylapatite, a form of calcium.”

She said if the remains proved to be between two and three million years old, H. naledi is the earliest definite example of Homo with skeletal material representing the whole body.

“If the remains are between one and two million years old, the date’s about right for a hominin of H.  naledi’s morphology.

“And if the date is less than one million years old, it means we have multiple species of hominins existing at the same time in South Africa. In that case, H. naledi’s small braincase and primitive morphology must make us seriously reconsider what it means to be a member of our own genus.”

Early reaction among some palaeoanthropologists hasn’t been all positive.

“Claims that the remains represent an early form of Homo erectus are fanciful,” Feuerriegel said. “A lot of critics have also focused on Lee’s description of the appearance of the bodies in one place as ‘ritual’.

“In this case, we aren’t suggesting anything spiritual, only that it represents repeated and deliberate behaviour.”

One of the career highlight for any palaeoanthropologist is to be one of the official ‘describers’ of a new species; thanks to her time in South Africa, Feuerriegel, at the age of 26 and still at least six months from finishing her PhD, is one of the names on the scientific paper officially naming the new species.

“I’ll also be lead author on a paper describing H. naledi’s upper limb, an area of morphology I’m particularly interested in.”

Feuerriegel said humans hold themselves on a pedestal as a species, above and apart from our ancestors.

“If there’s one thing H. naledi illustrates, it’s that the characteristics and behaviours we believe make us unique are not so unique after all.”

12 May 2015: Dinosaurs and birds

Archaeornithura meemannae

Archaeornithura meemannae (Credit: Zongda Zhang)

Remarkable new finds announced by China’s Institute of Vertebrate Paleontology and Paleoanthropology includes the earliest date yet established for a true bird and a bird-related dinosaur with leathery wings.

In a summary report on their website, Michael Balter said a team of paleontologists led by Min Wang and Zhonghe Zhou found 130 million year old fossils of two ancient wading birds in northeast China. The two remains of Archaeornithura meemannae show many features that belong to modern birds, including fan-shaped tail feathers and “the U-shaped wishbone familiar to anyone who has carved a roast chicken.” The fossils, dating back 130 million years, pushes “back the lineage that led today’s birds by at least 5 million years.” The report suggests this means the origins of true birds is older still. In an article in Nature, scientists from the Institute described a new species of scansoriopterygidae dinosaur they called Yi qi (pron. ‘yee chee’). Not only is this the shortest binomial ever given to a dinosaur, it’s also the first dinosaur found with striking evidence of ‘bat-like’ wings. Although other species of scansoriopterygidae were first described as early as 2002, this is the first fossil found with convincing evidence of membranous wings. Sometimes defined as ‘avian dinosaurs’, the scansoriopterygidae group belongs to a clade that ultimately lead to true birds. While it is not believed the group are direct ancestors of birds, they are examples of yet another evolutionary experiment in flight. Institute palaeontologist Corwin Sullivan said the while the dinosaur probably did not fly like a bird, “our guess would be that Yi qi was gliding or maybe combining gliding with some relatively inefficient flapping.”