Leptostomia: the pterosaur with a remarkably narrow beak

Leptostomia begaaensis was named from two small, separate jaw fragments in Cretaceous rocks of Morocco. Both are exceptionally narrow, flattened and toothless. Their form prompted a proposal that the pterosaur probed soft sediment for small animals, but neither jaw tip, a wing skeleton nor direct food remains are known. The two fossils are assigned to the same species by anatomical comparison; they need not come from the same individual.

Quick facts

Two separate fossils from the Kem Kem Group

The type material came from Aferdou N'Chaft near Hassi El Begaa in Morocco's Errachidia Province. The species name refers to Hassi El Begaa. Holotype FSAC-KK 5075 is a 48 mm upper rostrum piece with its tip missing. Paratype FSAC-KK 5076 is 67 mm of lower jaw symphysis, recovered separately.

Both are attributed to the upper Ifezouane Formation of the Kem Kem Group, probably spanning the Albian to early Cenomanian interval. Neither is a complete skull. Their similar proportions support assignment to one species, but do not demonstrate one individual. Alanqa is another Moroccan pterosaur known from jaw material, with different diagnostic anatomy.

A thin beak with strong walls

The toothless jaw fragments are dorsoventrally flattened and taper at a very low angle, around three degrees or less. Their bony walls are relatively thick around a small central cavity. A ridge on the upper element corresponds to a groove on the lower one. The original team used computed tomography to inspect these internal features.

Small foramina occur in rows on the bone surfaces. They may have transmitted vessels or nerves, but cannot prove a sensory tip when the tips and soft tissues are missing. Measurements of preserved pieces should not be presented as a securely measured full beak length.

The probing idea and its limits

Roy Smith and colleagues compared the narrow jaws with beaks of living birds that probe soft ground for invertebrates. It is a functional hypothesis, not a trace of feeding. No stomach content, prey residue or feeding mark is associated with Leptostomia. Apatorhamphus illustrates the diversity of Moroccan jaw fossils; a shared region does not establish a shared diet.

No wing bone assigned to Leptostomia fixes its wingspan or mass. A possible azhdarchoid affinity was discussed in the original work, but a precise family remains difficult to support from two jaw fragments. A later review of Kem Kem pterosaurs stressed that the fragments cannot be assumed to come from one individual.

What the images can responsibly portray

An animal searching in mud illustrates the authors' feeding proposal. The full body, wing shape, colour, exact beak tip and behaviour shown in such art extend beyond the recovered fossils.