Paleontologists have described a previously unknown species of mosasaur — a group of extinct marine reptiles that patrolled Cretaceous seas alongside dinosaurs on land — based on fossils unearthed in Egypt’s Dakhla Oasis.
Halisaurus arambourgi, a species of mosasaur from Late Cretaceous of Marocco. Image credit: DiBgd / CC BY-SA 4.0.
Halisaurus auriculatus lived roughly 70 million years ago during the early Maastrichtian age, the final age of the Cretaceous period.
The species belonged to Halisaurinae, a subfamily of generally small- to medium-sized mosasaurs.
“The Halisaurinae are a subfamily of Mosasauridae characterized by relatively small size, and primitive jaw and tooth morphology,” said Ain Shams University paleontologist Ahmed Ali Shaker and his colleagues.
“Halisaurines have historically been one of the rarest and least known groups of mosasaurs.”
“Currently, the group comprises eleven species, assigned to the genera Eonatator, Halisaurus, Phosphorosaurus, and Pluridens, and range stratigraphically from the Santonian to the uppermost Maastrichtian.”
“Fossils of Halisaurinae are now known around the world in North and South America, Africa, Asia, and Europe, particularly in the low latitude seas surrounding Africa.”
“Discoveries of this group became important in understanding the diversity and evolution of mosasaurs, showcasing adaptations that helped these reptiles flourish in the oceans of the Cretaceous period.”
Halisaurus auriculatus’ remains were found in 2024 in the Dakhla Shale, near the village of Teneida in the Dakhla Oasis in Egypt’s Western Desert.
The fossil included a partial skull, jaw bones, and assorted vertebrae and limb bones, all preserved in three dimensions.
The specimen was associated with scattered elements of bony fishes, turtle shell fragments, and plesiosaur vertebrae.
According to the study, Halisaurus auriculatus is distinguished by unusually long, slender jaws lined with more than 20 teeth on each side, along with a highly modified ear structure unlike any seen before in this family of reptiles.
These features point to a fast-biting but relatively weak jaw, paired with specialized hearing that may have helped the animal hunt small prey such as fish and squid in dim light, whether at night or in deeper water.
Notably, Halisaurus auriculatus was found in the same rock layer and general area as another mosasaur, Halisaurus hebae, described by some of the same researchers in 2023.
The two species differ substantially in skull and jaw anatomy, leading the study authors to suggest that the two animals divided up the available food resources rather than competing directly — a phenomenon called niche partitioning.
“Halisaurus auriculatus is distinguished from the coeval Halisaurus hebae by long, slender jaws, a high tooth count and unique specialization of the quadrate,” they said.
“These suggest adaptation for a fast bite but low bite force, and perhaps specializations of the auditory apparatus for underwater hearing.”
“These features suggest specialization on small prey and niche partitioning between halisaurines in the fauna.”
“Halisaurines were a diverse component of the Tethys and Atlantic in the Maastrichtian, highlighting their ecological significance within Late Cretaceous marine ecosystems.”
The findings appear online in the journal Acta Palaeontologica Polonica.
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A.A. Shaker et al. 2026. A new species of halisaurine mosasaurid from the Upper Cretaceous of Egypt. Acta Palaeontologica Polonica 71 (3): 589-604; doi: 10.4202/app.01310.2025
