Sunday, 26 July 2009

Was Rhamphorhynchus a skim feeder?

Whilst translating a passage from Peter Wellhofers' work on the Rhamphorhynchoidea, I came across this specimen from the collection of Karl Strobl.

Specimen No. 28: Fig. 24; Plate. 8, Fig. 1-3. Wintershof. Sammlung KARL STROBL, Eichstätt.
Part and counterpart of an entire skeleton with excellent preservation.

The individual is seen from the side; the arms are pushed forwards, the flight fingers in parallel with backbone extend backwards. Impressions of the flight skin and the narrow, lance shaped tail sail are present. The lower jaw extremity is relatively high, blunted in front. The upper edge line of the skull is concave. The front edge of the Infra-temporal opening is formed by the Quadrato-jugale. The cranial length measures 55.5mm.
The gastral skeleton consists of 6 curved bones still in situ; the middle pieces are displaced forwards. The Pubis is widened ventral, so that to the Ischium appears as a bay than rather a round opening. The Prepubis is strengthened centrally and hook-shaped (fig. 10 e).
Within the body cavity is a compressed fish tail and numerous single fish bone fragments indicating the stomach contents. Beside this lies 6-7mm long bananas-shaped small sausages like gastric stones of 1.5mm diameter and with zigzag-shaped textured surface (ref. fig. 44 b).

This specimen clearly shows that this individual had eaten a fish which was swallowed whole, head first. The use of gastric stones to aid mechanical digestion is an indication of a more specialised digestive system. This rhamphorhynchus may have had a gizzard, similar to that seen in birds, or a muscular and thick stomach wall to enable the churning of contents to allow the enzymes and gastric stones to break down the food both chemically and mechanically.

Very few pterosaurs give information about stomach contents, and in this case it leads to a question about fishing methods. Did rhamphorhynchus use a surface skimming technique to fish, or was it a shallow diver. It is impossible to say for certain, but the evidence is compelling. The jaws would certainly be able to scoop up a fish from near the surface of the water. and such a technique would have needed a very precise flying skill and good control of the jaws and neck.

The jaw on this specimen shows an impression of an upturned bony sheath at the end of the lower jaw. Such a structure, being free of teeth, would lend itself to surface skimming. This is a strong clue to the feeding habits of this type of Rhamphorhynchus and the group as a whole.

Wellnhofer, P. 1975 Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Teil II. Systematische beschreibung. Paläontographica A 148, 132–186.


  1. I think someone should do a trough isnpection of Rhamphorhynchus material and see if there's any observable pathologies on skull and mandible. If I remember correctly individuals of Skimmers (Rhynchops) often have injuries on their jaws due to accidental impact with debree on the water surface and sometime under the surface. If Rhamphorhynchus indeed skimmed I would expect to have some pathologies as seen in skimmers.

  2. This could be worth investigating. There are over 100 specimens of Rhamphorhynchus, though less than half have skull remain, many having partial skulls or showing damage due to decomposition. There is sound evidence that this species had a horn sheath to the end of the jaw, the sheath (or beak!) being larger on the lower jaw. Most skulls do not preserve this feature, but some do. There must be someone who could investigate this - it must be worthy of a PhD.

  3. Skimmers bang into their prey using the dorsal rim of their mandibles. It appears that is not the case with pterosaurs, like Rhamphorhynchus and Nyctosaurus. They likely speared their prey, probably at lower flight speeds in windier conditions.