Linda Dyani, Albany Museum
The unprecedented discovery of an ancient lamprey growth series from Makhanda was revealed in the prestigious scientific journal, Nature on the 10th of March 2021. Supported by information from rare juveniles of other (slightly less ancient) lampreys 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).
For the second time lamprey fossils found by Dr Rob Gess of the Albany Museum from the 360 million year old Waterloo Farm black shales near Makhanda/Grahamstown are central to a paper in Nature. The original description in 2006 of Priscomyzon, an exquisitely preserved lamprey fossil from Waterloo Farm was met with excitement around the world, because this was the oldest record of a lamprey (predating four of the world’s five major extinction events) – yet it was essentially almost identical to modern adult lampreys. 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. Adult lampreys are therefore, clearly extremely successful, having arisen before the first four-legged-animals moved onto land and survived, with little change, ever since.
This suggested that modern lampreys were swimming time capsules that could give unique insights into the biology and genome (DNA) of a truly ancient lineage. In many ways this is true. But only, it is now revealed, with regard to adults.
Since the 19th century, biologists have treated the larvae/juveniles of lampreys as a relic of deep evolutionary ancestry. These blind, filter-feeding, worm-like larvae (ammocoetes) burrow in stream beds and filter water for minute food particles, before slowly transforming into free-swimming, eyed, actively feeding adults. Crucially, 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 ourselves. Hence, 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.
However, the new fossils discoveries from Makhanda 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. Less complete (previously unpublished) partial growth series of three types of slightly younger lampreys from North America support the finding. Distant human ancestry seemingly did not include a lamprey-larva-like stage. Lampreys now appear to be a highly evolved side branch which shared a common ancestor with us – probably a jawless fish enclosed in bony armour.
So it’s time to rewrite the textbooks !
The research article is: Non-ammocoete larvae of Palaeozoic lampreys by Tetsuto Miyashita, Robert Gess, Kristen Tietjen & Michael Coates
The research was conducted in collaboration with the University of Chicago by the ‘Devonian Ecosystems Project’ based at the Albany Museum, 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).
Comment from Mr Manzi Vabaza, Manager of the Albany Museum
“The Albany Museum is really proud of Dr Rob Gess’ latest spectacular discovery, which is one of a number published in the world’s most prestigious journals. Rob’s lifetime efforts in conserving the Waterloo Farm site, collecting, curating and researching the fossils that have been excavated over many years, is an accomplishment for which our community can be really proud. One of our treasures is the Waterloo Farm fossil collection, curated at the historic Old Priest House in Beaufort Street. This collection is of great international significance and attracts researchers from all over the world. The fact that Rob Gess’ research is on a local fossil site in Makhanda is a massive bonus for our little town, and for our Museum. The Waterloo Farm collection only exists because of Rob’s tireless efforts, at times undertaken at his own expense. His foresight, vision and effort have brought immense credit to South African palaeontology and highlighted our country’s rich fossil record.”