Tethydraco: a debated pterosaur from Late Cretaceous Morocco

Tethydraco regalis is a large pterosaur named from the late Maastrichtian phosphate beds of Morocco. Its holotype, FSAC-OB 1, is a crushed left humerus, and other isolated bones were referred to the species in the original description. The naming authors regarded it as a pteranodontid, but a later study assigned an articulated wing from the same deposits to Tethydraco and argued that its proportions fit an azhdarchid better. That wing does not overlap the type in a way that settles the identification, so both the genus’s anatomy and its family placement remain debated. The pterosaur catalogue keeps the competing interpretations visible rather than presenting a complete skeleton as known.

Quick facts

Named from Morocco’s phosphate deposits

Nicholas Longrich, David Martill and Brian Andres named Tethydraco regalis in 2018 during a review of pterosaurs from the uppermost Cretaceous phosphates of Morocco. The holotype, FSAC-OB 1, came from Couche III at Sidi Daoui in the Ouled Abdoun Basin. The specimen is a crushed left humerus with parts missing. The generic name refers to the ancient Tethys Sea and the Greek-derived word for dragon; regalis means royal.

The phosphate beds preserve a diverse marine vertebrate assemblage close to the end of the Cretaceous. They are especially important because pterosaur remains are usually scarce and often isolated. A marine deposit can collect bones from animals that lived in different nearby habitats, so the setting describes burial and preservation more directly than it describes the animal’s precise daily range.

What the type humerus can show

The upper arm bone has a broad deltopectoral crest, a muscle attachment surface important in pterosaur wing anatomy. Its shape and proportions were compared with humeri of other pterosaurs. From the preserved length, the original authors proposed a wingspan of about five metres. This is a model based on scaling, not a direct measurement of a complete extended wing. Because the bone is crushed and incomplete, its shape and dimensions must also be interpreted with care.

The 2018 authors referred additional isolated bones to Tethydraco, including ulnae and hind-limb elements. Such referrals were plausible within the assemblage but difficult to prove because the isolated pieces do not overlap the holotype in enough diagnostic anatomy. They do not form one skeleton simply because they came from the same phosphate beds.

A second wing and a different family hypothesis

In 2021, Claudio Labita and David Martill described FSAC-CP 251, a partial articulated wing from Maastrichtian phosphates in Morocco. The specimen preserves the upper arm, radius and ulna, parts of the wrist and metacarpus, and the first wing phalanx. They assigned it to Tethydraco regalis and argued that the shape of the humerus, the deltopectoral crest and the ratios among wing bones better matched an azhdarchid than a pteranodontian.

This proposal would substantially change what is inferred about Tethydraco, but it depends on assigning the wing to a genus whose type is a separate humerus. The 2021 wing includes its own humerus, allowing comparison, yet the question is whether the similarities are diagnostic enough to establish conspecificity. Later work has noted differences between the crest of the articulated wing and the holotype. Without overlapping diagnostic material or a skeleton physically connecting the specimens, the referral cannot be treated as settled.

The result is not that one study erased the other. The holotype remains the name-bearing specimen, and its classification must be anchored to its own anatomy. FSAC-CP 251 may reveal a Moroccan azhdarchid, may belong to Tethydraco, or may represent another pterosaur. Each option makes different predictions that future material could test.

What can be said about its appearance and ecology?

The humerus demonstrates a large pterosaur, and the original wingspan estimate is often repeated as roughly five metres. A full wingspan is still inferred. The type has no skull, so it cannot directly establish whether the animal had teeth, a head crest or the proportions of the snout. The later wing supplies more limb anatomy only if its referral is accepted. Reconstructions that add a particular head shape or complete body therefore rely on comparisons with a chosen family.

Likewise, no stomach contents or prey are known. A pteranodontid or azhdarchid comparison may suggest different feeding models, but the fossils described here do not demonstrate a specific diet. The phosphates formed in a marine setting and include marine animals; this does not prove that the pterosaur fed in open water. Its flight style, soft tissues, colours and behaviour remain unknown.

Tethydraco is thus a case where one named species carries a larger taxonomic question: how much can isolated bones from a rich deposit be combined? The humerus is real and diagnostic enough to anchor the name, while the wider skeleton and family identity remain open to testing.