20-metre dinosaur fossil unearthed at construction site in Brazil

A major infrastructure project in northeastern Brazil has uncovered something considerably older than the roads and railways it was built to serve: a giant dinosaur that roamed the region about 120 million years ago.

Scientists have identified the animal as Dasosaurus tocantinensis, a roughly 20-metre-long sauropod that is now the largest known dinosaur discovered in Maranhão. says Science Daily.

The fossils were found about 8 metres underground in Davinópolis during environmental monitoring linked to the construction of a road-rail terminal. Instead of machinery uncovering just another layer of rock, the excavation exposed the remains of an animal that had been buried for more than 100 million years.

A dinosaur with a European connection

The discovery gets even more unusual when scientists look beyond Brazil.

The closest known relative of Dasosaurus tocantinensis lived in what is now Spain. Researchers believe the lineage may trace back to ancient migrations between Europe and South America.

Between roughly 140 million and 120 million years ago, the continents looked dramatically different from today. Land connections across what is now Europe, North Africa and South America may have provided routes for dinosaur ancestors to move across the ancient supercontinent Gondwana.

In other words, the Brazilian giant may have had a family tree stretching across an ancient world in which today's oceans and continents had not yet taken their modern shape.

A remarkably complete giant

For palaeontologists, the discovery is valuable not simply because the dinosaur was enormous, but because so much of it survived.

The specimen includes a femur measuring about 1.5 metres, along with tail vertebrae, ribs, foot bones and other limb elements. Such a relatively complete collection of remains gives scientists a much better opportunity to reconstruct how the animal lived and grew.

Microscopic examination of the bones has offered another clue. The tissues show a growth pattern combining characteristics associated with older groups of sauropods and later titanosaurs, providing insight into how these enormous animals achieved their extraordinary size.

The bones, in effect, preserve a record of a growth strategy that helped turn an animal into a 20-metre-long walking giant.

Its name comes from the landscape

Even the dinosaur's scientific name carries a piece of Maranhão with it.

"Daso" refers to forest, a nod to the region's dense woodland, while "tocantinensis" refers to the nearby Tocantins River.

It is a name that ties an animal from the deep past to the landscape that still exists above its fossilised remains.

When construction becomes a time machine

There is an ironic twist to the discovery.

Large construction projects can pose a threat to archaeological and palaeontological sites, potentially disturbing or destroying deposits that have remained undisturbed for millions of years. But the same projects can also do something palaeontologists rarely get to do themselves: dig deep.

In this case, excavation associated with infrastructure development opened access to rock layers about 8 metres below the surface, revealing fossils that might otherwise have remained hidden.

The result is an unusual meeting of two very different timelines. Modern railways and roads helped expose the remains of a creature that lived long before humans, cities or even the continents looked anything like they do today.

For a few metres of earth beneath a construction site in Maranhão, the future of Brazilian infrastructure briefly collided with the Jurassic-era past — and the past had a 1.5-metre thigh bone to show for it.