Just another family day at the beach - 90,000 years ago
Palaeontologists find unique evidence of an ancient family at play
Barefoot, the family crested a dune on the Garden Route and gazed out at the Indian Ocean 2km away. The salty tang in the air and the distant crash of waves on the rocky shoreline told them their destination was near.
Eager to reach the sea, they began to run down the 20-degree slope in front of them, some of them even leaping in excitement as they went.
What happened next is not known, but the historical importance of this everyday sequence of events is difficult to overstate.
That’s because it provides some of the first evidence of human activity in the late Ice Age, 90,000 years ago.
The family’s joyful descent of the dune was captured in their footprints, which have been discovered in the last two years in a cave between Buffalo Bay and Brenton-on-Sea, just west of Knysna.Those prints — dozens of them — fill a 71,000-year gap in the ancient history of Homo sapiens. They are the first evidence of modern human activity between 117,000-year-old tracks in Langebaan on the Cape west coast and 46,000-year-old evidence from a cave in Greece.
“It’s the holy grail,” said Charles Helm, the semi-retired family doctor who with his wife Linda and friend Guy Thesen found the fossilised footprints. The discovery crowned a 10-year endeavour in which he and his family spent their holidays — they live in Canada — prowling 275km of coastline between Witsand in the west and Robberg in the east in search of fossil tracks.
Helm, who is affiliated with the African Centre for Coastal Palaeoscience at Nelson Mandela University in Port Elizabeth, and a team of international researchers have just announced the find in an article in the open-access journal Scientific Reports.Who is Charles Helm?
Charles Helm grew up in Cape Town and graduated from the medical school at the University of Cape Town in 1981.
In 1992, he moved to Tumbler Ridge, a remote community in northern British Columbia, to work as a family doctor.
In 2000, his eight-year-old son Daniel and a friend discovered a long dinosaur trackway, sparking Helm's interest in ichnology – the branch of palaeontology concerned with the study of fossilised tracks.
Helm told Times Select: “I was taught by the best (Dr Richard McCrea and Dr Lisa Buckley) and acquired the necessary dinosaur-tracking skills. Returning to the family home in Great Brak River each year, I realised that there was a host of fossil tracks in the region, and that the same principles I had learned in Canada applied on the Cape south coast.
“We have identified over 100 tracksites since. Four scientific papers have been published on this since December 2017, the hominin paper being the most recent. One documenting giraffe tracks east of Still Bay was published recently in South African Journal of Science .
“Ichnology has become a family passion – incredibly rewarding and fulfilling.”
In 2015, Helm’s daughter discovered footprints from a family of predators related to Tyrannosaurus rex.
“I’m pretty much full-time into palaeontology having retired as a family doctor after 25 years here in Tumbler Ridge,” said Helm. “And I just love it. It’s a wonderful challenge.”The 10m-long cave in which he found up to 40 tracks is at the foot of a coastal cliff near an outcrop called Castle Rock — the exact location is being kept secret — and, Helm told Times Select, the footprints had been uncovered by wave erosion.
“This [discovery] adds to the relatively sparse global record of early hominin tracks and represents the largest and best preserved archive of Late Pleistocene [Ice Age] hominin tracks found to date. The tracks were probably made by Homo sapiens,” he wrote in Scientific Reports.
The footprints are the third set of human tracks found in South Africa but by far the most numerous. At Nahoon, in East London, three tracks were found in 1964 but the site collapsed shortly afterwards. Three more tracks were found near Langebaan in 1997, and they are now at the Iziko South African Museum in Cape Town.The new find is extraordinary for the amount of detail Helm and his team have been able to extract from the well-preserved footprints.
“A number of individuals made the tracks while moving down the dune surface,” Helm wrote. “Many tracks exhibit deep heel impressions. One trackway contains footprints that are clearly larger than the others [maximum length 27cm with heel drag or 23cm without heel drag; maximum width 10.5cm; maximum depth 5.5cm], while the rest are smaller [often about 17cm long].”
In one of the trackways, “a short-long [variable or alternating] gait pattern is evident. Such a gait may be employed when moving fast down a dune slope while heel-planting, thereby aiding stability.”
Applying a formula (footprint length multiplied by 6.67) used for the Nahoon and Langebaan tracks, Helm estimated the heights of the nascent humans responsible for the tracks at 153.4cm for the tallest and around 116cm for the shortest.“The pace lengths ... of 75cm, 85cm and possibly greater than 105cm on a dune slope ... imply a more rapid trackmaker velocity, and may be consistent with a running gait,” Helm wrote. But he said more information was needed for an accurate estimate of the speed at which individuals were moving.
The discovery adds to the southern Cape’s reputation as a focal area for research into the emergence of modern humans. Said Helm: “The Cape south coast figures prominently in this research. [Its] sites provide early evidence for art and jewellery, stone tool heat treatment ... and the first systematic use of seafood in the human diet.”
It wasn’t only early humans who roamed South Africa’s southern coastal plain in the late Ice Age. The cave and its immediate surroundings also contain “tracks of elephant, various sizes of even-toed ungulate, large carnivore, the extinct giant Cape horse, probable juvenile ostrich and small, unidentifiable tracks”. Elsewhere along the beach and in the cliffs above there are rhinoceros and buffalo tracks.Helm said there was almost certainly more to be found in the cave about early humans. “The occurrence of tracks in both lateral walls of the cave, and at the junctions of the ceiling with both lateral walls and with the inner wall, suggests that more tracks could easily be exposed.
“These tracks may be preserved with superior detail compared with those currently visible, many of which are partially eroded.”
Photogrammetry of the track surfaces has produced digital data which can be used to create full-size replicas of the entire track-bearing surface using 3D printing and Helm hopes they will find a home in South African museums.
There are plans to apply for a permit to try to expose further tracks. This may uncover data on the size of the group – Helm believes it was a family – that made them.Footprints that had palaeontologists dancing on the ceiling
In photographs of the 10-metre long cave where the footprints were found, Charles Helm is prostrate because the distance between floor and ceiling is just 47cm.
Most of the footprints he found are on the ceiling of the cave, and they protrude from the surface. How does this happen? Helm explained to Times Select:
“This is a common question, and an interesting one. It also explains, I think, why the footprints were not discovered earlier, as I think they have been exposed and visible for some time. (Perhaps, also, because not everyone goes crawling into the back of a tiny cave.)“Those of us who are ichnologists and search for fossil tracks know to look under every overhang and ceiling, as that it where the best tracks are often found. Without one’s mind being open to this possibility, others might walk straight past an obvious track hanging down from a ceiling and ignore it, because their brains are not primed to appreciate it for what it is.
“Some tracks do indeed get preserved as impressions (moulds) in the surface in which they were made, usually sand or mud now turned to rock. These are the ‘obvious ones’.
“What we have reported on is a natural cast surface. Imagine first something like a gentle drizzle or heavy dew — something to moisten the dune surface without altering the tracks. Then imagine a bit of wind that gently fills in the tracks with sand and covers them all. They are then buried (in this case for 90,000 years) and then something happens to re-expose them, in this case wave action.“The initial moisture allows for a cleavage plane that can separate the layer in which the tracks were made from the infill layer. In this case the layer in which the tracks were made was more easily eroded by the waves, and was removed. What we are left with is the infill layer, still very well preserved. The tracks therefore appear to hang down from the ceiling and are known as natural casts.
“The likelihood is that wave action created this sea cave and removed the layer in which the tracks had been made. The current ceiling is the well-preserved infill layer, which is more resistant to erosion, and the natural cast tracks therefore protrude down from the ceiling.
“This is not a rare phenomenon. Here where I work in Canada with dinosaur tracks, for example, over half of what we discover is in the form of natural casts.
“Another way of approaching this is to understand that there has been minimal or no tectonic activity here, so what you see is what you get. The layers we see are at their original angles of deposition (in this case about 20 degrees, which was the angle of the dune). So it is straightforward. Elsewhere it gets more complex where rock layers have been folded and tilted.”