Pterosaur Cervicals: 8 or 9?

Bennett (2004) reported, “The cervical series of the specimen (the third known Scaphognathus, SMNS 59395) consists of 9 vertebrae if the first vertebrae that bears a large rib that articulates with the sternum is interpreted as the first dorsal vertebra.”  This was a break with tradition, in which pterosaurs were considered to have 8 cervicals.

Scaphognathus SMNHS 59395

Figure 1. Scaphognathus SMNHS 59395 with cervicals colored green and orange, dorsal colored purple and blue, sternum in red. Click for more info.

Vertebra number 9 always lies completely within the torso, despite not articulating with the sternum. Hence the traditional number of 8 makes more morphological sense. Vertebra number 9 also shares more traits in common with number 10 than number 8.

Bennett (2004) reported that Pterodactylus had 7 cervicals and large [unspecified] pterodactyloids had 9 cervicals, the latter resulting from the cervicalization of the anterior two dorsal vertebrae.” Unfortunately, I can find no examples of either. Large or small, all pterosaur specimens in reptileevolution.com have 8 cervicals.

The skull of the SMNS 59395 specimen of Scaphognathus

Figure 2. The skull of the SMNS 59395 specimen of Scaphognathus with bones color coded. Note there were 4 premaxillary teeth, as in most other pterosaurs and all sister taxa, not 2 as Bennett (2004) reported.

On a side note, Bennett (2004) reported there were only two teeth in the premaxilla of SMNS 59395. I found four (Fig. 2) as in most other pterosaurs and all known sisters. I saw the specimen before it was prepared. But I was able to “see” four teeth in photos. Here Bennett (2004) might have made a different determination if he had realized that two teeth would have been autapomorphic, but no phylogenetic analysis was performed.

Prepared and unprepared images of the SMNS 59395 specimen of Scaphognathus.

Figure 4. Prepared and unprepared images of the SMNS 59395 specimen of Scaphognathus. Click to enlarge.

There’s a nice articulated wing ungual present in this undisturbed completely articulated specimen.

Finally, Bennett (2004) considered SMNS 59395 a “juvenile with unfused girdles, carpals, and tarsals.” No phylogenetic analysis was offered. Here, after phylogenetic analysis, the smaller SMNS specimen was found to be distinct in several traits from the larger No. 109 specimen, and derived taxa were smaller still. So SMNS 59395 was likely a precocious small adult, not a juvenile. A juvenile should have been virtually identical to the adult, only smaller, because that’s the pattern we see in embryos, the only pterosaurs for which we have an exact ontogenetic age – zero.

This data was gleaned from photos. Bennett (2004) had the specimen in hand. Some of these conclusions, like whether vert #9 was a cervical or a dorsal goes back to the choices we make as paleontologists. Phylogenetic analysis helps.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bennett SC 2004. New information on the pterosaur Scaphognathus crassirostris and the pterosaurian cervical series. Journal of Vertebrate Paleontology, 24(Suppl. to #3):38A.

1 thought on “Pterosaur Cervicals: 8 or 9?

  1. Pingback: DinoAstur - » Nuevos datos de Scaphognathus, un pterosaurio del Jurásico de Alemania

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