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Problems with this study:

Posted by David_Peters on 22 Aug 2009 at 20:15 GMT

The authors showed "that skimming is considerably more energetically costly than previously thought for Rynchops and that pterosaurs weighing more than one kilogram would not have been able to skim at all." The experiments were precisely done and measured. The authors were correct with regard to azhdarchid skimming, which seems unlikely.

Unfortunately two factors were not considered.

1. The wrong jaw fragments were tested. The jaw fragment attributed to Thalassodromeus sethi (DGM 1476-M) probably belongs to a dsungaripterid, a different sort of pterosaur with a probable stork-like lifestyle. The jaw curves dorsally and the rami broaden more a than in the more complete Thalassodromeus skull, which has a dorsal cross section of a much narrower triangle. Other pterosaurs such as Nyctosaurus, have a much more needle-like, Rynchops-type of beak, including a much longer dentary than rostrum. Nyctosaurus should have been the subject of the study.

2. The ability of pterosaurs to fly into the wind was not considered. Doing this can greatly reduce the "ground speed," or in this case their speed relative to the water they are skimming over. By reducing their "ground" speed, pterosaurs could have greatly reduced hyrodynamic drag while skimming or dipping, no matter what shape their beak was.

No competing interests declared.

RE: Problems with this study:

SHUM replied to David_Peters on 27 Jun 2013 at 07:46 GMT

In response to David Peter's two points:

1. The jaw fragment used for "T. sethi" has been incorrectly attributed as the type specimen DM 1476-M. It was in fact the fragment SAO 25 1093 described in Veldmeijer et al (2005, our reference [28]). Table 2 should have the "Thalassodromeus" holotype attributed as DM 1476-M and the fragment as SAO 25 1093. "Nyctosaurus" was not chosen as our study specimen as we were interested in the idea that "T. sethi" was a skimmer as postulated by Kellner & Campos (2002). "Nyctosaurus" does have an elongated lower mandible with some lateral compression (see David's blog post here: http://pterosaurheresies....), but it is still considerably thicker than that of "Rynchops" and would have suffered increased drag relative to the extant bird. As we note the likely lower body mass of pterosaurs compared to birds may have compensated slightly for this.

2. Headwind effects can be both positive and negative and, while having the potential to reduce ground speed, can also incur energetic costs (Sachs (2013) summarises the literature well). "Rynchops" seem to prefer low-wind conditions as surface waves also increase drag effects and presumably means they cannot immerse their beak as deeply as in still water. Dipping is a very likely feeding method for pterosaurs previously thought to skim-feed.

Sachs, G. (2013) J. Theor. Biol. 316:35-41

No competing interests declared.