The South African National Roads Agency SOC Ltd (SANRAL)’s assistance in rescuing fossiliferous shales from roadworks in the Eastern Cape continues to bear internationally important results.
SANRAL’S involvement with Late Devonian research goes back to 1999 when they assisted renowned South African palaeontologist Dr Robert Gess to rescue 30 tons of fossiliferous shale ahead of roadworks at Waterloo Farm, 2 km south of Makhanda (Grahamstown) in the Eastern Cape.
All but one of the Priscomyzon specimens in the new study have been recovered by Dr Gess whilst slowly excavating his way through these rocks, which have also provided a huge range of other important fossils including Africa’s earliest tetrapod remains (published in Science in 2016), about 20 other types of fish including Africa’s earliest coelacanths from the world’s oldest coelacanth nursery, scorpion remains representing Gondwanas earliest land living animals and a whole range of plants including remains of Africa’s earliest trees.
The Priscomyzon hatchling specimen was found in 2008 when SANRAL facilitated Dr Gess’ rescue operations at Waterloo Farm during further roadworks.
“SANRAL’s support for the Devonian Ecosystems Project is ongoing. In 2015 when we initiated roadworks along the N2 east of Makhanda (Grahamstown) SANRAL again enlisted Dr Gess’ assistance in mitigating heritage loss, resulting in the discovery of further Late Devonian fossil sites 20 km to the east of Waterloo Farm.
” This led to a plan to develop a roadside information centre about the local Late Devonian heritage discoveries beside the N2 between Makhanda and Ngqushwa (Peddie),” said Mbulelo Peterson, SANRAL’s Southern Region Manager.
“We are working with Dr Gess to erect information boards at a landscaped rest area. The information boards on the project and discovery of fossils will be situated about 25km from Makhanda,” said Steven Robertson, SANRAL’s Southern Region Project Manager.
The rest areas will have information on all the sites along this stretch of the N2, including Waterloo Farm – illustrated via reconstructions by esteemed scientific illustrator, Maggie Newman.
The latest discoveries do not come from SANRAL’S most recent construction projects along this section of the N2, during which important fossils were also discovered, but rather from a horde of fossiliferous shale carefully mined out with their assistance ahead of roadworks at Waterloo Farm, to the south of Makhanda (Grahamstown) in 1999.
The 30 tons of rock was carefully stored in sheds to protect it from the weather and Dr Gess has been meticulously working through it, on and off, since then – when not busy working on other sites.
“Had the rocks not been rescued a massive part of South Africa’s palaeontological heritage would have been lost – as research on the shales rescued from Waterloo Farm is time consuming and could not have been conducted during the roadworks themselves,” said Dr Gess.
The 360-million-year-old shale is the most important fossil containing deposit of its age in the southern hemisphere and has yielded a unique record of life in an ancient coastal lagoon, from stem tetrapods and diverse fish to delicate waterweeds.
Deposited under oxygen poor conditions the fine-grained mud sometimes preserved even the most delicate soft tissue, including impressions of skin, cartilage and even eyeballs.
On Wednesday, in the prestigious journal, Nature, Dr Gess, who is based at the Albany Museum and Rhodes University in Makhanda (Grahamstown), together with colleagues from the University of Chicago, reveals a growth series of fossil lampreys that he has been assembling from the shale, over the last 15 years.
Gess explained that lampreys are intriguing fish, still found today, that (together with Hagfish) are the only surviving fish from before fish had jaws.
The fossils from Makhanda belong to the oldest species of fossil lamprey in the world (Priscomyzon riniensis), originally described in Nature in 2006 on the basis of a single adult specimen recovered from the Waterloo Farm shale horde.
Seven additional lamprey fossils from the site form the central story in a new paper, also published in Nature. (The article: Non-ammocoete larvae of Palaeozoic lampreys, by Tetsuto Miyashita, Robert Gess, Kristen Tietjen & Michael Coates).
Unlike the original specimen the new specimens are all juveniles that form a life history series from a newly hatched individual only 1.5 cm long up to a specimen only a little smaller than the original 4.2 cm long adult.
Supported by the discovery of rare juveniles of other (slightly less ancient) lampreys from North America the series overturns long held ideas as to what modern lampreys may tell us about the origin of vertebrates (animals with backbones such as goldfish, lizards, crows and people).
Modern lampreys are of particular interest to scientists as these bizarre fish are (together with their cousins the hagfish) the only living group of vertebrates branching from the family tree of animals before they had developed jaws.
They are eel-like in shape and feed by latching onto other fish with a round sucker that surrounds their mouth, securing their grip with circles of teeth on the sucker and then drinking their victim’s blood after rasping a hole with special teeth on their tongue.
Yet their larvae are extremely different from their parents. Known as ammocoetes they are blind, filter-feeding, worm-like creatures that burrow in streambeds and filter water for minute food particles, before slowly transforming into free-swimming, sighted, actively feeding adults.
According to Dr Gess, this strange life history was thought to echo transformations some 500 million years ago which gave rise to all fish lineages, including the one that ultimately led to people.
“The last invertebrate ancestor of vertebrates is often portrayed as ammocoete-like, and the earliest vertebrate as being lamprey-like. But for this to be a reasonable model, both ammocoetes and lampreys would need to hark back to the dawn of our (vertebrate) history,” said Gess.
However, the new fossil discoveries contradict the conventional wisdom that our long chain of ancestors ever included a lamprey-like fish. Painstaking excavation of shale samples from Waterloo Farm have revealed a growth series of Priscomyzon illustrating its development from hatchling to adult.
Remarkably, the smallest preserved individuals, barely 15mm in length, still carried a yolk sac, signalling that these had only just hatched before entering the fossil record.
Of crucial importance: even the hatchlings were already sighted with large eyes and armed with a toothed sucker, much like the blood-sucking adult phase of modern lampreys and completely unlike their modern larval counterparts.
This drastically different structure of ancient lamprey infants provides evidence that modern lamprey larvae are not evolutionary relics. Rather, the modern filter-feeding phase is a more recent innovation that allowed lampreys to populate and thrive in rivers and lakes.
“We now know that it is only lamprey adults that have remained similar in appearance since very ancient times, not ammocoetes – which discounts the long-held view that they could preserve the image of one of our early ancestors. Biologists will have to rethink where we come from,” he added.
Research was conducted in collaboration with the University of Chicago by the ‘Devonian Ecosystems Project’ based at the Albany Museum in Makanda (Eastern Cape, South Africa), a partner of the DSI-NRF Centre of Excellence in Palaeosciences; funded by the Millennium Trust, the DSI-NRF Centre of Excellence in Palaeosciences, the NRF and the NSCF (natural Science Collections Facility).
SANRAL advertised a tender last week for phase three of the N2 Makhanda to Fish River Pass road upgrade.
It is anticipated that construction will start in the second half of this year and will include the next phase of development of the Devonian heritage node.
Image: Specimens and interpretive drawings of the growth series of Priscomyzon specimens surrounding an artist’s impression of their life form. Image credit Nature