Tech UPTechnologyWhen the fish swam in the Sahara

When the fish swam in the Sahara

It must be a strange experience to walk through the Sahara and come across remains of fish, crocodiles, sharks, snakes and other marine life. It is clear that these clues can only point to one fact: in the current largest hot desert in the world there was enough water to house this fauna.

The Tuaregs , nomads who live in the Sahara, have always been certain that the dunes they cross today were not always there, but that water flowed through those lands in ancient times. These rumors were studied by researchers in search of scientific evidence. What conclusions have the studies reached? Well, it has been shown that not only were there fish, but that some of the largest marine creatures of prehistory lived in the Sahara.

flooded continents

In contrast to the vast expanse of sand that is today the Sahara Desert, between 50 and 100 million years ago it was periodically traversed by warm, shallow waters. Known as the Trans-Saharan Seaway , its formation is due to the global rise in sea level experienced by the Earth after the breakup of the Gondwana supercontinent at the end of the Mesozoic . It was a waterway that connected the current Gulf of Guinea with the Mediterranean Sea. Its size and channel varied over time (as do all water currents), but it is estimated that it could cover 3,000 km² of the African continent and reach a depth of 50 meters . This immense sea left extensive sedimentary strata, very conducive to fossilization. Numerous extinct species of vertebrates, invertebrates, plants and microbes were petrified for posterity, a valuable material that paleontologists use to study and reconstruct important events in the history of the Earth such as the Cretaceous-Paleogene mass extinction and the Thermal Maximum from the Paleocene-Eocene.

Great tides flooded most of the continents. These are phenomena that have received decent scientific attention, but the Trans-Saharan Seaway has often been overlooked. Partly due to political decisions, but also because of the difficulty of searching for fossil remains in the changing dunes under unbearable heat. “I was amazed at the quality and diversity of the marine fossils we found in the Sahara desert,” said Leif Tapanila, a professor of geosciences at Idaho State University. “Few paleontologists had worked in the region, given its remoteness and scorching 50-degree temperatures.”

science arrives

Luckily, a group of researchers carried out a study with years of effort and research that has helped them to tell us what it was like and what was in the Sahara at that time. In 2019 they published a synthesis in the Bulletin of the American Museum of Natural History in which they collect twenty years of work.

“The ancient seaway left intriguing and previously unclassified phosphate deposits that quite possibly represent the most extensive vertebrate macrofossil bone beds known anywhere on Earth ,” states the study led by Maureen O’Leary, Professor of Anatomical Sciences at Stony Brook University (United States).

Forests and sharks in the Sahara

The study takes us on a fascinating journey through time to learn how different the ecosystem was compared to the current one in Mali. Paleoecological reconstructions in the scientific publication speak of evergreen broadleaf forests and some of the oldest mangroves ever studied. The Trans-Saharan Seaway had some of the largest predators of its clades. Among them, prehistoric species of crocodiles, snakes and giant fish.

Among the fauna mentioned in the study, we can highlight the Palaeophis colossaeus , a sea serpent that could measure 30 or 40 meters in length. Rhabdognathus aslerensis and Cretalamna maroccana were huge species of crocodile and shark, respectively.

The spectacular size of the fossil remains found was one of the great unknowns to be resolved by the researchers. The theory they support is based on endemism . In other words, the trans-Saharan maritime route changed its course and generated intermittent isolation. This could have created aquatic islands in which the gigantism of the species was stimulated , since they could have more resources that were not shared and the absence of predators. It is a type of evolution that has been previously observed in species that inhabit terrestrial islands.


Bamford, M. K. et al. 2002. An extensive deposit of fossil conifer wood from the Mesozoic of Mali, southern Sahara. Palaeogeography, Palaeoclimatology, Palaeoecology, 186, 1-2, 115-126. DOI: 10.1016/S0031-0182(02)00447-9.

O’Leary, M. A. et al. 2019. Stratigraphy and paleobiology of the Upper Cretaceous-Lower Paleogene sediments from the Trans-Saharan Seaway in Mali. Bulletin of the American Museum of Natural History, 436. URI:

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