A newly described species of Spinosaurus, unearthed from ancient river sediments in the Sahara, is reshaping what paleontologists thought they knew about where the giant predator lived and hunted. Named Spinosaurus mirabilis, it is the first new species added to the Spinosaurus genus in more than a century, and its river-system setting sets it apart from earlier finds tied to ancient coastlines.
The first new Spinosaurus species since the genus was named
Spinosaurus was first named in 1915, based on fossils that were later destroyed during World War II bombing raids, leaving paleontologists to work for decades from incomplete and often disputed material. Spinosaurus mirabilis marks the first time researchers have formally described an entirely new species within the genus since that original naming, a gap of more than a hundred years shaped as much by the scarcity of well-preserved spinosaurid fossils as by the difficulty of interpreting the ones that did survive.
That rarity is what makes a reasonably complete new specimen significant on its own, independent of any single anatomical detail it reveals. Spinosaurid fossils are unusually fragmentary compared with many other large predatory dinosaurs, in part because their skeletons include lightly built, semi-aquatic adaptations that do not always preserve well.
Because so much of the original Spinosaurus material was lost before modern preservation techniques and casting methods existed, much of what scientists have inferred about the genus since 1915 has relied on later finds, photographs, and detailed drawings made before the original specimens were destroyed. That reconstruction-by-proxy approach has left considerable uncertainty around basic questions of anatomy and behavior that a more complete specimen, like the one described for Spinosaurus mirabilis, can help resolve.
A river system far from the coast
The fossils were recovered from the Farak Formation in central Niger, at a remote site known as Jenguebi, in rock layers dated to roughly 95 million years ago during the Cenomanian age. Unlike many earlier spinosaur discoveries, which came from deposits associated with ancient coastlines or near-shore marine environments, the sediments around Spinosaurus mirabilis formed in an inland river system located hundreds of kilometers from where the nearest coastline would have been at the time.
That distinction matters because it extends the known range of spinosaurid habitats well beyond the coastal and estuarine settings most previous specimens came from, suggesting the group was not confined to environments close to the sea.
Paleontologists studying the Farak Formation have also noted that inland river deposits tend to preserve a different mix of plant and animal fossils than coastal sediments do, offering researchers a broader picture of the ecosystem a large predator like Spinosaurus mirabilis would have shared with other animals. That context can help clarify what other species it may have competed with or preyed upon, questions that are harder to answer from coastal deposits alone.
A crest unlike any other non-avian dinosaur’s
Spinosaurus mirabilis is distinguished in part by a tall, scimitar-shaped crest running along its skull, measured at roughly 20 inches, which researchers have described as larger than the head ornamentation found on any other known non-avian dinosaur. The function of such a prominent crest remains a subject of debate among paleontologists, with display to other members of the same species considered a more likely explanation than any direct role in hunting.
Crests and sails have shown up repeatedly across the spinosaurid family, most famously in Spinosaurus aegyptiacus’s tall dorsal sail, and researchers studying mirabilis have suggested the head crest may have served a similar signaling function within the species rather than any obvious defensive or predatory purpose.
Display structures of this kind are relatively common across the broader dinosaur family tree, showing up in forms ranging from bony head crests to skin frills, and are typically interpreted as tools for signaling age, sex, or individual identity to other members of the same species rather than as weapons or predatory tools. Because soft tissue rarely survives fossilization, researchers studying crested dinosaurs generally have to infer a structure’s likely size and shape in life from the bone alone, which leaves its exact appearance when the animal was alive open to some interpretation.
Built for hunting in the water
Like other spinosaurids, Spinosaurus mirabilis carried a long, narrow snout lined with conical teeth suited to gripping slippery prey rather than shearing through it, an arrangement researchers describe as a “fish-snaring” jaw. Combined with the river-system setting of its discovery, that anatomy supports the broader picture of spinosaurids as animals that spent significant time hunting fish from rivers and riverbanks rather than pursuing prey purely on land.
Researchers have also pointed to skeletal features consistent with a partly aquatic lifestyle among spinosaurids more broadly, including dense limb bone structure that would have aided buoyancy control in water, though the specific evidence available for Spinosaurus mirabilis remains more limited than for better-preserved relatives.
That fish-snaring jaw shape recurs across several spinosaurid species found in both Africa and South America, reinforcing the idea that the family as a whole adapted early to a semi-aquatic hunting style distinct from most other large predatory dinosaurs of the era. Researchers have generally treated the conical, interlocking tooth pattern seen in spinosaurids as a strong anatomical signal of a diet weighted toward fish and other aquatic prey, in contrast to the blade-like, serrated teeth typical of land-hunting predators from the same broader time period.
What the discovery adds to the spinosaurid family tree
Because Spinosaurus mirabilis is only the second well-documented species placed directly in the Spinosaurus genus, its anatomy gives researchers a rare point of comparison for testing ideas about how the genus varied across time and geography. Its inland river setting, in particular, gives paleontologists a reason to reconsider how widely spinosaurids ranged beyond the coastal habitats that have dominated the fossil record for the group until now.
It also reinforces a broader trend in dinosaur paleontology over the past two decades, in which spinosaurids have gone from a poorly understood, sparsely represented group to one of the more actively studied branches of the predatory dinosaur family tree, driven largely by a steady trickle of new specimens from North Africa.
Comparisons like these depend heavily on having more than one well-preserved specimen to work from, which is precisely what has been in short supply for Spinosaurus specifically, even as other spinosaurid genera have accumulated a somewhat larger fossil record in recent decades. Researchers studying the broader group have said that filling out the family tree species by species, rather than relying on a small number of well-known specimens to represent an entire genus, is likely to keep reshaping ideas about how varied spinosaurid anatomy and habitat use really were.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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