New Dinosaur Species: Spinosaurus mirabilis

In the heart of the Sahara, within a dry and seemingly barren landscape, an unexpected discovery has revealed a new giant predator from the Late Cretaceous. At a fossil locality known as Jenguebi, researchers uncovered remains of a previously unknown species of Spinosaurus, named Spinosaurus mirabilis. This dinosaur possessed a distinctive cranial crest, a long and low snout, and widely spaced large teeth toward the rear of the jaws. The fossils come from fluvial sediments deposited roughly 95 million years ago, during the Late Cenomanian stage of the Farak Formation. The inland riverbank setting, far from any marine shoreline, demonstrates that members of the genus Spinosaurus were not confined to coastal habitats. Instead, they were capable of inhabiting river systems deep within continental interiors alongside inland sauropod dinosaurs.

Spinosaurus mirabilis（Image source：Marianorocker22， CC BY-SA 4.0 ）

Three individuals of Spinosaurus mirabilis have been recovered. The holotype specimen (MNBH JEN1) includes the right premaxilla, maxillae, the alveolar margin of the right dentary, and a cranial crest formed jointly by the nasal and prefrontal bones. Two additional specimens preserve fragments of the skull along with vertebrae, femora, tibiae, and pedal phalanges. Compared with Spinosaurus aegyptiacus, the posterior portion of the snout in S. mirabilis is noticeably flatter, with the dorsal and ventral margins running almost parallel. The spacing between the rear teeth is also significantly greater. Both species share specialized interlocking dentitions in which the upper and lower teeth fit between one another during occlusion. These teeth are supported by a festooned external margin of the tooth sockets, a structure that shows convergent similarity with long-snouted crocodilians and some fish-eating pterosaurs.

Holotype snout bones（Image source：Sereno PC et al. (2026)， CC BY 4.0 ）

The most striking anatomical feature is the scimitar-shaped cranial crest. This structure is formed by fused nasal bones with contributions from the prefrontal bones on each side. The crest consists of dense bone supplied by centrally clustered vascular canals, and its surface bears fine longitudinal and cross-hatched grooves. These surface textures suggest that the crest was covered in life by a keratinous sheath, meaning that the living crest may have appeared taller and more dramatic than the preserved bone alone indicates. Comparable structures occur in modern birds such as the helmeted guineafowl, Numida meleagris. In living birds, crests often function in visual display, social communication, or courtship signaling, and the crest of S. mirabilis likely served a similar role.

Numida meleagris（Image source：Diego Delso， CC BY-SA 4.0 ）

All three known crests of S. mirabilis display slight left-right asymmetry that does not appear to result from geological compression. Instead, this asymmetry likely reflects natural variation during life. Comparable irregularity is frequently seen in the casque structures of modern cassowaries (Casuarius). With the currently limited number of fossils, however, it remains impossible to determine whether the crest exhibited sexual dimorphism.

Beyond the skull, several features of the trunk and limb skeleton resemble those of S. aegyptiacus. The first dorsal vertebra displays structural traits resembling cervical vertebrae, the dorsal neural spines are greatly thickened and bear pronounced longitudinal striations, and the anterior caudal vertebrae possess a cruciform cross-section. These features are characteristic of spinosaurids adapted to ambush predation along the water's edge. The tall neural spines along the trunk, neck, and tail formed a sail-like structure that likely functioned primarily as a visual display rather than as a device for propulsion in water.

The fossils of S. mirabilis were discovered in a riparian environment located at least 500 to 1000 kilometers from the nearest marine coastline. Associated fossils include remains of Carcharodontosaurus, rebbachisaurid sauropods, an unidentified titanosaurian dinosaur, and the skull of a large polypterid fish (Polypterus). The close proximity of these fossils indicates that these animals inhabited the same river valley ecosystem. Within this environment, S. mirabilis most likely occupied the ecological role of a wading ambush predator rather than that of a fully aquatic swimmer pursuing prey underwater.

The study also compared seven measurements of body proportions in S. mirabilis with those of 43 living and extinct predatory archosaurs. Principal component analysis placed spinosaurids between semiaquatic wading birds such as herons (family Ardeidae) and shallow-diving birds such as cormorants (family Phalacrocoracidae). They are clearly separated from terrestrial predators and crocodilians. These results indicate that the proportions of the neck and hind limbs in spinosaurids were particularly suited to standing in water deeper than 1.5 meters while capturing fish.

In evolutionary terms, the new fossil evidence supports a three-stage history for spinosaurids. The first stage began in the Jurassic, when early spinosaurids evolved elongated snouts, enlarged clusters of premaxillary teeth, and posteriorly displaced nostrils. These features likely formed the foundation for a fish-catching lifestyle. The second stage occurred during the Early Cretaceous, when spinosaurids expanded widely along the shores of the Tethys Ocean. In the Northern Hemisphere the baryonychine lineage dominated, while the Southern Hemisphere hosted diverse spinosaurines such as Irritator from Brazil. The third stage began around 100 million years ago, following the opening of the Equatorial Atlantic Gateway. During this period, advanced spinosaurines including Spinosaurus aegyptiacus and the newly discovered Spinosaurus mirabilis became giant ambush predators specializing in fish within African ecosystems.

Tethys Ocean（Image source：Lennart Kudling， CC BY 3.0 ）

These animals reached their maximum body size during the early to middle Cenomanian. Afterward, however, the fossil record becomes silent during the Turonian. This disappearance may be linked to the Cenomanian–Turonian boundary event, a period marked by dramatic sea-level rise, climate change, and large-scale reorganization of marine ecosystems. Extensive flooding of continental lowlands may have altered riverine habitats across North Africa, contributing to the eventual extinction of spinosaurids. Even inland species such as S. mirabilis likely did not escape these environmental changes.

The discovery of Spinosaurus mirabilis therefore fills an important geographic and ecological gap in the late history of spinosaurids. It also invites a reassessment of how these dinosaurs lived. Rather than being fully aquatic hunters, they were likely riverbank predators that stalked prey in shallow water. Along the edges of ancient rivers and lakes, these animals probably signaled to one another using their towering sails and crests while employing their elongated snouts and interlocking teeth to ambush fish.

Author: Shui-Ye You

Reference:

Sereno PC et al. (2026). Scimitar-crested Spinosaurus species from the Sahara caps stepwise spinosaurid radiation. Science.

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