Dating the Broken Hill Skull – H. heidelbergensis Younger than Previously Thought

Palaeoanthropologists have long recognised that the evolution of the hominins and our own species (Homo sapiens), was complicated and not simply a linear transgression from one species to another.  Human fossil remains are exceptionally rare and sometimes, a new study can upend previously assumed concepts and ideas.  For example, a team of scientists including researchers from the Natural History Museum (London), Australian National University (Canberra), University College Dublin, Muséum national d’Histoire naturelle (Paris), University of the Free State (South Africa), University of Wollongong (Queensland), University of Southampton and Griffith University (Queensland), have published new dating information for a hominin skull discovered in 1921.

The skull representing Homo heidelbergensis turns out to be much younger than previously thought.

The Famous Broken Hill Skull (Kabwe 1) Homo heidelbergensis

Picture credit: The Trustees of the Natural History Museum

Studying Homo heidelbergensis

Writing in the academic journal “Nature”, the researchers conclude that this skull, previously thought to be around half a million years old, was much younger with an estimated date of between 274,000 and 324,000 years of age.  This result suggests that in the later stages of the Middle Pleistocene of Africa (Chibanian stage), there were many different types of hominin living at the same time.  Homo sapiens, H. heidelbergensis/H. rhodesiensis and Homo naledi were all contemporaneous.

The Broken Hill Skull

The skull studied, referred to as the Broken Hill specimen, currently resides in the collection of the Natural History Museum (London) and is on display in the Human Evolution gallery, but there are ongoing discussions about the return of this fossil to Africa.

The skull was discovered in 1921 by an African miner and his Swiss co-worker Tom Zwigelaar at the lead and zinc mine located at Broken Hill, which at the time was in northern Rhodesia but is now Kabwe in Zambia, hence the reference to the fossil skull as Kabwe 1.  Other fragmentary human remains were also found at the mine (partial upper jaw, tibia, sacrum and two elements from a femur from another individual).  The fossils were donated by the mining company to the then British Museum (Natural History Museum), at the time of their discovery anthropologists regarded these fossils as the most significant hominin fossils found on the African continent.

Early Photographs of Kabwe 1 (Broken Hill Skull)

Picture credit: Griffith University (Queensland)

Problems Dating the Skull and Fossil Bones

Nearly a hundred years ago, data recording surrounding such an important fossil discovery was nowhere near as thorough at it is today.  Mining work continued in the area where the skull and other bones had been found so any evidence to help accurately date the fossils was subsequently lost.  Assigned to Homo heidelbergensis, the skull was originally dated to around 500,000 years ago.  However, these researchers, led by Professor Rainer Grün (Environmental Futures Research Institute at Griffith University), subjected the skull and the other hominin fragments from the site to radiometric dating and determined that these people lived between 274,000 and 324,000 years ago.

Commenting on the importance of this research, Professor Grün stated:

“The new best age estimate of the fossil impacts our understanding of the tempo and mode of modern human origins”.

One of the co-authors of the scientific paper, Professor Chris Stringer (Natural History Museum), added:

“Previously, the Broken Hill skull was viewed as part of a gradual and widespread evolutionary sequence in Africa from archaic humans to modern humans.  But now it looks like the primitive species Homo naledi survived in southern Africa, H. heidelbergensis was in Central Africa, and early forms of our species existed in regions like Morocco and Ethiopia.”

Homo rhodesiensis and Piltdown Man

It was Sir Arthur Smith Woodward, the curator of the Geology Department at the British Museum who proposed the new species Homo rhodesiensis to describe the Kabwe 1 skull as “Rhodesian Man”.  However, most scientists now consider H. rhodesiensis to be junior synonym of H. heidelbergensis or possibly an African sub-species of it.  Despite a prestigious academic career, Sir Arthur is best remembered for his association with the Piltdown Man hoax of 1912.  Even on his deathbed, he still believed that the fossil remains found in a Sussex gravel bed at Barkham Manor, near to Piltdown Common, represented a species of archaic human, unlike any other species of early hominin known to science.

Unfortunately, for Sir Arthur, five years after he died, new dating techniques proved the human skull bones from the site to be less than 500 years old.

The new, younger date for the Kabwe 1 skull also casts a cloud over the provenance of stone tools associated with hominin fossils from the late Middle Pleistocene.  As scientists have evidence to indicate Homo heidelbergensis present in Africa as recently as 300,000 years ago, stone tools from this date may not have been crafted by our species.

Not All the African Stone Tools Around 300,000 Years of Age Can be Ascribed to our own Species

Picture credit: Dr Nicholas Conrad/University of Tubingen

The new age estimate for Kabwe 1 raises questions about our own evolution.  It casts doubts on the presumption that H. heidelbergensis/H. rhodesiensis was a direct ancestor of our species Homo sapiens.  This research suggests that there were multiple contemporaneous hominin lineages in Africa during the later stages of the Middle Pleistocene, reflecting a similar model found in Eurasia.

• African hominins (late Middle Pleistocene) – H. sapiens, H. naledi, H. heidelbergensis/H. rhodesiensis
• European/Asia hominins (late Middle Pleistocene) – H. neanderthalensis, H. luzonensis, H. floresiensis, the Denisovans and perhaps also H. heidelbergensis and H. erectus

Everything Dinosaur acknowledges the assistance of a media release from Griffith University in the compilation of this article.

The scientific paper: “Dating the skull from Broken Hill, Zambia, and its position in human evolution” by Rainer Grün, Alistair Pike, Frank McDermott, Stephen Eggins, Graham Mortimer, Maxime Aubert, Lesley Kinsley, Renaud Joannes-Boyau, Michael Rumsey, Christiane Denys, James Brink, Tara Clark and Chris Stringer published in Nature.

To read an article about the presence of H. heidelbergensis in Kent: Giant Prehistoric Straight-tusked Elephant Butchered by H. heidelbergensis.

The Everything Dinosaur website: Everything Dinosaur.

Meet Your Oldest Ancestor – Ikaria wariootia 

A team of international scientists have identified the first ancestor of animals that show bilateral symmetry, in ancient marine sediment around 555 million years old.  Palaeontologists had predicted that such an organism would be identified in Ediacaran sediments, essentially a creature with a body plan that has been adopted by the majority of the Kingdom Animalia, now thanks to the use of sophisticated three-dimensional laser scans funded by NASA, the “smoking gun” evidence has been found.

A Life Reconstruction of the Earliest Bilaterian Known to Date (I. wariootia)

Picture credit: Sohail Wasif/University California Riverside

Ikaria wariootia – The Size of a Rice Grain but a Big Discovery!

Writing in the journal “Proceedings of the National Academy of Sciences of the United States of America”, the researchers, which included scientists from University California Riverside and the South Australian Museum, examined tiny trace fossils, essentially burrows and borings into an ancient Ediacaran seabed (Ediacara Member, South Australia).

Proximal to some of these traces were very small oval impressions.  Thanks to funding from a NASA exobiology grant, the team were able to employ a sophisticated three-dimensional laser scanner to map these depressions in the ancient rock.  Computer-generated images revealed a worm-like organism with a cylindrical body and faintly grooved musculature.  A distinct head and tail were also identified.  This little animal represents the earliest bilaterian, a hugely significant step in the evolution of life on Earth.

The transition from simple, microscopic forms of life to the abundance and variety of complex creatures in the Cambrian remains quite poorly understood.  However, the beautifully preserved remains of soft-bodied organisms, many of which look like nothing alive today, associated with the ancient strata of the Ediacara Hills of South Australia have permitted palaeontologists the opportunity to learn about life on our planet prior to the evolution of hard body parts such as shells and exoskeletons.

Bizarre Body Forms

Many of the creatures identified from their fossils had bizarre body forms such as the circular Dickinsonia (below), but scientists had predicted that animals with bilateral symmetry would be present in this ecosystem, it was just a question of finding them.

A Circular Impression of an Organism from the Ediacara Hills (South Australia) – Dickinsonia costata Fossil

Picture credit: Dr Alex Liu (Cambridge University)

The Development of Bilateral Symmetry

The development of bilateral symmetry was a critical step in the evolution of animal life, giving organisms the ability to move purposefully and a common, yet successful way to organise their bodies.  In the scientific paper, the research team describe Ikaria wariootia as ranging in size between 2 and 7 millimetres in length and being around 1 to 2.5 millimetres wide.   The largest specimens were about the size of a grain of rice, just the right size to have made the burrows and borings (trace fossils).

The discovery of Ikaria wariootia is consistent with predictions based on modern animal phylogenetics, that the last ancestor of all bilaterians was simple and small and represents a rare link between the Ediacaran and the subsequent record of animal life.  Put simply, I. wariootia is on the same part of the animal family tree as the majority of animals alive today and that includes us (Homo sapiens).

Ikaria wariootia Impressions Preserved in Ancient Marine Sediment

Picture credit: Droser Laboratory/University of California Riverside

Commenting on the significance of the discovery, one of the authors of the scientific paper, Scott Evans (University of California Riverside), stated:

“We thought these animals should have existed during this interval [Ediacaran], but always understood they would be difficult to recognise.  Once we had the 3-D scans, we knew that we had made an important discovery.”

Examining Ediacaran Trace Fossils

Analysis of modern animals and Ediacaran trace fossils predicted that the oldest bilaterians would be very small with simple body plans.  The research team found that the size and shape of Ikaria matched the predictions that had been made with regards to the maker of the trace fossil Helminthoidichnites, indicating sediment displacement and purposeful animal movement.

Importantly, in the Ediacara Member, Helminthoidichnites occurs stratigraphically below classic Ediacara body fossils such as Dickinsonia.  Together, these suggest that Ikaria represents one of the oldest total group bilaterians identified to date, with very little deviation from the characters and traits predicted for their last common ancestor.

In addition, these trace fossils persist into the Phanerozoic Eon (from the Cambrian Period onwards),  providing a critical link between the Ediacaran and Cambrian biota.

A Three-Dimensional Laser Image of a Scan of a Rock Depression Revealing the Body Plan of Ikaria wariootia

Picture credit: Droser Laboratory/University of California Riverside

What’s in a Name?

The genus name comes from Ikara, which means “meeting place” in the local Adnyamathanha dialect.  It is the Adnyamathanha term for a grouping of mountains known as Wilpena Pound.  The trivial name comes from Warioota Creek, which runs from the Flinders Ranges to Nilpena Station in the Ediacara Hills.  It may look a fairly simple animal to us, but back in the Ediacaran Ikaria was one of the most complex organisms around.  It burrowed in thin layers of well-oxygenated sand on the ocean floor in search of organic matter, indicating rudimentary sensory abilities.

The depth and curvature of Ikaria represent clearly distinct front and rear ends, supporting the directed movement found in the burrows.  The walls of the burrows preserve evidence of “v-shaped” ridges, which indicate that Ikaria moved by contracting muscles across its body like an earthworm.  This is known as peristaltic locomotion.

Everything Dinosaur acknowledges the assistance of a media release from the University of California Riverside in the compilation of this article.

The scientific paper: “Discovery of the oldest bilaterian from the Ediacaran of South Australia” by Scott D. Evans, Ian V. Hughes, James G. Gehling and Mary L. Droser published in the Proceedings of the National Academy of Sciences of the United States of America.

The Everything Dinosaur website: Everything Dinosaur.