Lucy had neighbors: A review of African fossils

If "Lucy" wasn't alone, who else was in her neighborhood? Key fossil discoveries over the last few decades in Africa indicate that multiple early human ancestor species lived at the same time more than 3 million years ago. A new review of fossil evidence from the last few decades examines four identified hominin species that co-existed between 3.8 and 3.3 million years ago during the middle Pliocene. A team of scientists compiled an overview that outlines a diverse evolutionary past and raises new questions about how ancient species shared the landscape.

The perspective paper, "The Pliocene hominin diversity conundrum: Do more fossils mean less clarity?" will be published June 6, 2016 as part of a Human Origins Special Feature in the Early Edition of the Proceedings of the National Academy of Sciences.

Authors Dr. Yohannes Haile-Selassie and Dr. Denise Su of The Cleveland Museum of Natural History and Dr. Stephanie Melillo of the Max Planck Institute for Evolutionary Anthropology in Germany provide an up-to-date review of middle Pliocene hominin fossils found in Ethiopia, Kenya and Chad. The researchers trace the fossil record, which illustrates a timeline placing multiple species overlapping in time and geographic space. Their insights spur further questions about how these early human ancestors were related and shared resources.

"It is now obvious that more than one species of early hominin co-existed during Lucy's time," said lead author Dr. Yohannes Haile-Selassie, curator of physical anthropology at The Cleveland Museum of Natural History. "The question now is not whether Australopithecus afarensis, the species to which the famous Lucy belongs, was the only potential human ancestor species that roamed in what is now the Afar region of Ethiopia during the middle Pliocene, but how these species are related to each other and exploited available resources."

The 1974 discovery of Australopithecus afarensis, which lived from 3.8 to 2.9 million years ago, was a major milestone in paleoanthropology that pushed the record of hominins earlier than 3 million years ago and demonstrated the antiquity of human-like walking. Scientists have long argued that there was only one pre-human species at any given time before 3 million years ago that gave rise to another new species through time in a linear manner. This was what the fossil record appeared to indicate until the end of the 20th century. The discovery ofAustralopithecus bahrelghazali from Chad in 1995 and Kenyanthropus platyops from Kenya in 2001 challenged this idea. However, these two species were not widely accepted, rather considered as geographic variants of Lucy's species, Australopithecus afarensis. The discovery of the 3.4 million-year-old Burtele partial foot from the Woranso-Mille announced by Haile-Selassie in 2012 was the first conclusive evidence that another early human ancestor species lived alongside Australopithecus afarensis. In 2015, fossils recovered from Haile-Selassie's ongoing research site at the Woranso-Mille area of the Afar region of Ethiopia were assigned to the new species Australopithecus deyiremeda. However, the Burtele partial foot was not included in this species.

"The Woranso-Mille paleontological study area in Ethiopia's Afar region reveals that there were at least two, if not three, early human species living at the same time and in close geographic proximity," said Haile-Selassie. "This key research site has yielded new and unexpected evidence indicating that there were multiple species with different locomotor and dietary adaptations. For nearly four decades, Australopithecus afarensis was the only known species -- but recent discoveries are opening a new window into our evolutionary past."

Co-author Dr. Denise Su, curator of paleobotany and paleoecology at The Cleveland Museum of Natural History, reconstructs ancient ecosystems. "These new fossil discoveries from Woranso-Mille are bringing forth avenues of research that we have not considered before," said Su. "How did multiple closely related species manage to co-exist in a relatively small area? How did they partition the available resources? These new discoveries keep expanding our knowledge and, at the same time, raise more questions about human origins."

Paleoanthropologists face the challenges and debates that arise from small sample sizes, poorly preserved prehistoric specimens and lack of evidence for ecological diversity. Questions remain about the relationships of middle Pliocene hominins and what adaptive strategies might have allowed for the coexistence of multiple, closely related species. "We continue to search for more fossils," said Dr. Stephanie Melillo of the Max Planck Institute for Evolutionary Anthropology in Germany. "We know a lot about the skeleton of A. afarensis, but for the other middle Pliocene species, most of the anatomy remains unknown. Ultimately, larger sample sizes will be the key to sorting out which species are present and how they are related. This makes every fossil discovery all the more exciting."
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Reference:

EurekAlert. 2016. “Lucy had neighbors: A review of African fossils”. EurekAlert. Posted: June 6, 2016. Available online: http://www.eurekalert.org/pub_releases/2016-06/cmon-lhn060616.php

CSI Stone Age: was 430,000-year-old hominin murdered?

It's the coldest of cold cases: a forensic analysis suggests that an ancient human who lived 430,000 years ago died as the result of a deliberate attack by a right-handed assailant armed with a spear or hand axe. The crime is the earliest evidence of human-on-human violence in the fossil record – and the way the body was found strongly suggests that hominins were engaging in funerary rituals hundreds of thousands of years before our species evolved.

No fewer than 28 hominin skeletons have been recovered from the Sima de los Huesos site in the Atapuerca mountains of northern Spain. An analysis of DNA pulled from one skeleton suggests the tribe may be ancestral to both the Neanderthals and their east Eurasian contemporaries, the mysterious Denisovans

Holes in the head

One of the skulls is interesting for another reason: it has two large holes on the left side of the forehead. Nohemi Sala from Complutense University of Madrid, Spain and her colleagues used forensic techniques to work out how the holes formed. The skull is in 52 pieces, but while most of those fragments have edges that are perpendicular to the surface of the skull – typical of the way dry bone fractures long after death – the edges of the holes in the forehead were oblique in a way that's more consistent with a fresh bone fracture. What's more, both holes were roughly the same size and shape – and both had a distinctive "notch" at a similar location in their outlines. That suggests the holes were injuries sustained close to the hominin's time of death and involving repeated blows from the same object.

"We are pretty sure that these are not circumstantial injuries," says Sala. "Since either of these wounds would likely have been lethal, penetrating the brain, the presence of multiple wounds implies a deliberate act."

The attacker was probably right-handed, judging by the fact that the injuries were to the left side of the face. The weapon may have been a wooden spear, a stone spear tip or a stone hand axe, says Sala.

Ancient funeral

It's "completely compelling", says Debra Martin at the University of Nevada in Las Vegas. "I suspect the farther we push back and find straight up forensic evidence such as these authors have, we will find that violence is culturally mediated and has been with us as long as culture itself has been with us." The find may also help settle a long-standing debate over exactly how so many hominin skeletons came to be preserved together. One idea is that, over time, a number of unlucky individuals fell down the vertical shaft by mistake. An alternative viewpoint is that the dead were deliberately thrown into the pit as part of an early funeral ritual.

The new analysis strongly favours the second view. It's clear that this individual was dead before he or she ended up in the pit, so they can hardly have stumbled into the hole by mistake. "The only possible manner by which a deceased individual could have arrived at the site is if its cadaver were dropped down the shaft by other hominins," says Sala. "Middle Pleistocene hominins were already engaging in funerary behaviour."
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Reference:

Barras, Colin. 2015. “CSI Stone Age: was 430,000-year-old hominin murdered?”. New Scientist. Posted: May 27, 2015. Available online: http://www.newscientist.com/article/dn27611-csi-stone-age-was-430000yearold-hominin-murdered.html

Rising Star cave produces over 200 hominin fossils

When recreational cavers Steve Tucker and Rick Hunter stumbled on the unmistakable traces of  hominin fossil remains it sparked a three-week expedition to the Rising Star Cave in South Africa’s Cradle of Humankind World Heritage Site, just 25 miles  north of Johannesburg.  These fossils were exactly the type of material that Lee Berger had asked their caving club to be on the lookout for.

With the bones hidden 30 metres underground, beyond obstacles including a tight squeeze of only 18 cm wide, it was necessary to assemble a select team of researchers who had excavation experience, caving skills and were of a particular body size required to reach the inner chamber.

Directed by National Geographic Explorer-in-Residence Lee Berger of the University of the Witwatersrand, and supported by cavers from the Speleological Exploration Club of South Africa, these researchers are now  bringing up hominid fossils for experts on the surface to start the analysis.

On the very first day of entering the fossil chamber  the team recovered a hominid fossil in remarkably good condition.

The Rising Star Expedition soon discovered that the cave contains more than one individual and the potential of this site has yet to be fully realised.

Berger has now said that more than 200 hominin fossils have so far been found within the cave and after coming up to the surface, the bones are compared with replicas of previously found hominin remains.

However, the team is holding back on saying where the Rising Star fossils fit on the evolutionary tree. Berger said he expected a scientific paper on the find would be prepared for publication in late 2014.

Meanwhile, National Geographic and the “Nova” science documentary team are working on a TV show about the expedition.

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References:

Past Horizons. 2014. “Rising Star cave produces over 200 hominin fossils”. Past Horizons. Posted: November 18, 2013. Available online: http://www.pasthorizonspr.com/index.php/archives/11/2013/rising-star-cave-produces-over-200-hominin-fossils