Rhamphorhynchus n28: unidentified food mass? or overlooked egg in the abdomen?

Figure 1. Rhamphorhynchus intermedius (n28) reconstructed.

Figure 1. Rhamphorhynchus intermedius (n28) reconstructed.

Rhamphorhynchus intermedius (Koh 1937, n28 in the Wellnhofer 1975 catalog) is a well preserved basal specimen (derived from the C3 specimen of Campylognathoides) with a mass inside of its torso, only part of which has been identified as a Solhnhofen fish (Figs. 2,3).

Figure 2. Wellnhofer 1991 illustrates the abdominal mass as part of a fish and other unidentified elements.

Figure 2. Wellnhofer 1991 illustrates the abdominal mass as part of a fish and other unidentified elements.

The rest of the abdominal mass
is unidentified (Fig. 2). Wellnhofer 1991 considered it food. Considering its shape, size and placement, I wonder if the posterior mass is actually a nearly full term egg (Fig. 3). I don’t think it makes much sense to consider such an abdominal mass as “unidentified food” when no other known specimen has a similar mass of undigested food. That would mean the stomach could expand to fill the abdomen. Usually the only thing that crowds out other organs and air sacs is an egg or a number of eggs in other reptile taxa. Check out this kiwi X-ray for an extreme example.

Figure 3. Skeletal elements of Rhamphorhynchus intermedius (n28) along with an ingested fish and what appears to be a possible egg.

Figure 3. Skeletal elements of Rhamphorhynchus intermedius (n28) along with an ingested fish and what appears to be a possible egg. Note the overlapping sets of gastralia. It looks like the jaws of the fish are displaced here. Wellnhofer did not see the large eyeball identified here. Note the left scapula and coracoid are inverted. There sternal complex has a similar unexpectedly bumpy texture as the purported egg.

Rhamphorhynchus intermedius
is a medium-sized Rhamphorhynchus nesting at the very base of the clade between the larger Campylognathoides and the smaller Bellubrunnu. Thus it is a transitional taxon, step one in an extreme example of phylogenetic miniaturization. No one understood this nesting prior to the phylogenetic analysis documented at ReptileEvolution.com because no one included a long list of Rhamphorhynchus specimens in analysis prior to or since. I’d like to encourage other pterosaur workers to do so and test this hypothesis of relationships.

Texture
The “egg” has an odd texture, but then so does the sternal complex. Not sure why.

Previous examples?
Two smaller examples of “something else” in the abdomen of – or just aborted from the abdomen – other specimens of Rhamphorhynhcus can be seen here and here.

References
Koh TP 1937. Unterscuchungen über die Gattung Ramphorhynchus. – Neues Jahrbuch Mineralogie, Geologie und Palaeontologie, Beilage-Band 77: 455-506.
Wellnhofer P 1975a-c. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.

wiki/Rhamphorhynchus

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