A 40-foot dinosaur that might have been a herbivore

Nature · Published 20 October 2026 Swipe more like this →

In short: Imagine a massive theropod that might have spent its days grazing instead of hunting. This extinct dinosaur from Cretaceous North Africa challenges our assumptions about meat-eaters. Depending on which fossils scientists include in its record, this creature could have reached a staggering forty feet in length.

Deltadromeus was first described in 1996 by Paul Sereno based on an incomplete postcranial skeleton found in the Kem Kem Beds of Morocco. Dating to the Cenomanian stage (100-95 million years ago), the holotype specimen (SGM-Din 2) suggests a creature roughly 8 metres (26 ft) long and weighing about 1,050 kilograms (2,310 lb). However, if fossils from Egypt—originally thought to be the genus Bahariasaurus—actually belong to Deltadromeus, the animal could have reached 12.2 metres (40 ft) in length, making it comparable in size to a Tyrannosaurus rex.

The anatomy of Deltadromeus is a puzzle of conflicting traits. It possesses extremely slender hindlimbs, with a lower leg 7.5% longer than the average theropod of its size, indicating it was highly cursorial (built for running). Its tail vertebrae feature broad neural spines and pleurocoels to store air sacs. Yet, while its body plan resembles a predator, its classification is in constant flux. Some analyses place it as a basal coelurosaur, while many more recent studies identify it as a ceratosaur—a group that includes the herbivorous Limusaurus.

This taxonomic instability has profound ecological implications. If Deltadromeus is indeed a ceratosaur closely related to herbivorous species, it may have filled a niche traditionally held by ornithischians. This would suggest a highly complex ecosystem in Cretaceous North Africa, where diverse theropods partitioned resources in a landscape of mangrove forests and wetlands. Because many of the defining fossils were destroyed in the 1945 Bombing of Munich, scientists remain divided on whether Deltadromeus is a unique genus, a synonym of Bahariasaurus, or a distinct lineage of 'change runners'.

The mystery persists due to a lack of overlapping fossils between the Moroccan holotype and the Egyptian remains. While some researchers suggest it could be a noasaurid or even a megaraptoran, the lack of definitive evidence means its true role in the prehistoric food web remains one of paleontology's most intriguing debates.

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