Spinosaurus mirabilis: The Crested Giant That Rewrites Spinosaurid Geography

The most famous fish-eating dinosaurs in the fossil record - the spinosaurids, relatives of the enormous Spinosaurus aegyptiacus - were thought to have lived close to the edge of the sea. Their elongated crocodile-like skulls, their dense bones, and their waterlogged burial sites all pointed toward coastal or aquatic lifestyles. Then a team led by Paul Sereno traveled deep into Niger's Sahara and found something that does not fit that picture at all.

Spinosaurus mirabilis, described in Science by Sereno and 29 co-authors, lived between 100 and 95 million years ago in a forested riparian habitat 500 to 1,000 kilometers from the nearest marine shoreline. It is the first undisputed new species of Spinosaurus in more than a century, and it comes with an anatomical feature so distinctive that the team initially did not recognize what they had found when they lifted the first fragments off the desert surface in November 2019.

A Crest That Took Years to Understand

The scimitar-shaped bony crest of S. mirabilis is large, blade-like, and curving. When the team first encountered pieces of it during the initial expedition, the shape was so unexpected that they needed to return with a larger team in 2022 and recover two more crest fragments before the anatomy became clear.

CT scanning and digital reconstruction at Sereno's South Side Fossil Lab in Chicago revealed the crest's internal structure: surface texture and vascular canals consistent with a keratin sheath in life. The researchers interpret it as a display structure - possibly brightly colored, rising toward the sky as a visual beacon used for species recognition or competition. It is not, in their assessment, a structure that would have aided swimming or locomotion.

A second anatomical signature marks the skull: interdigitating tooth rows in which lower teeth protrude outward between upper teeth, forming an interlocking trap effective for catching slippery fish. This tooth arrangement, seen also in aquatic ichthyosaurs, semi-aquatic crocodilians, and flying pterosaurs, is a defining feature of spinosaurids and confirms the animal's fish-eating identity despite its inland location.

How the Discovery Happened

The expedition's starting point was a single line in a French geological monograph from the 1950s mentioning a sabre-shaped fossilized tooth in the central Sahara - a site no one had revisited in more than 70 years. Sereno's team went searching for it. Unable to locate the original site at first, they were eventually led deep into the sand seas by a local Tuareg man on his motorbike, who guided them to a fossil field where he had seen enormous bones. With limited time before needing to return to camp, the team recovered teeth and jaw bones - including the first fragments of what would become S. mirabilis.

"No one had been back to that tooth site in over 70 years. It was an adventure and a half wandering into the sand seas to search for this locale and then find an even more remote fossil area with the new species," Sereno said.

Three Phases of Spinosaurid Evolution

The placement of S. mirabilis within spinosaurid phylogeny supports a model of three evolutionary phases. The first phase began in the Jurassic Period, when the lineage developed its elongated skull adapted for fish-catching. The second phase, in the Early Cretaceous, saw spinosaurids spread along the coastal margins of the ancient Tethys Sea. The third phase - represented by S. mirabilis and its South American relatives - produced specialists for shallow-water predation in the inland river systems of northern Africa and South America, as the Tethys coastline receded.

S. mirabilis was buried alongside long-necked sauropod dinosaurs in river sediments, consistent with a habitat of forested floodplains dissected by rivers. The bones were not transported far from where the animal died. Sereno envisions the animal as a wader - comfortable in two meters of water but primarily stalking shallow river traps for the large fish of the Cretaceous period.

Visualization and Public Access

Back in Chicago, paleoartist Dani Navarro in Madrid used digital skull renderings produced by the research team to reconstruct the animal in flesh, creating a scene of S. mirabilis contending over a coelacanth carcass. Animators in Chicago and Italy brought the reconstruction to life. A replica skull and a touchable model of the scimitar crest will join Sereno's existing dinosaur exhibit at the Chicago Children's Museum starting March 1, 2026.

The discovery adds to Niger's paleontological legacy. Sereno has been working in the country for three decades and is leading the construction of the Museum of the River in Niamey, a zero-energy institution designed to display Niger's fossil and archaeological heritage for local and international audiences.