The reduction and duplication of the naris in certain pterosaurs

Most pterosaur paleontologists don’t bother with such details.

The reduction (not assumed confluence) and duplication of the naris in derived pterosaurs (Fig. 1) is not due to neotony (contra Unwin and Lü 2013), but due to phylogeny. Along with phylogenetic size reduction the naris became reduced (Fig. 1) in several pterosaur lineages. Evidently, as in certain birds, like gannets, the naris became less important for certain pterosaur lines.

This is at odds with the origin of pterosaurs when the naris became greatly enlarged compared to outgroups like Cosesaurus. Pterosaurs must have spent more time mouth-breathing, or — in the switch from insect-eating to fish-eating — evolved a way to avoid getting water up the nose.

Figure 1. Click to enlarge. The reduction of the naris (red arrow), the appearance of the secondary naris, and the appearance of the secondary ascending process of the maxilla in a line of scaphognathids, all to the same scale.

Figure 1. Click to enlarge. The reduction of the naris (red arrow), the appearance of the secondary naris, and the appearance of the secondary ascending process of the maxilla in a line of scaphognathids, all to the same scale. N0. 12 is basal to germanodactylids and then beyond to pteranodontids, dsungaripterids and tapejarids, most of which lose the naris. The GMu specimen is basal to ornithocheirids and cycnorhamphids. Scale bar = 1 cm.

And along with the reduction and duplication of the naris, these pterosaurs develop a secondary ascending process in the maxilla (blue arrow), always small. There’s even an ascending process of the jugal (light blue bone) laminated against the ascending process of the maxilla. Yes, the naris does eventually disappear in certain taxa, but the bones around it give away its former position.

 

In all cases but one, the reduction of the naris involved the overall reduction of the pterosaur, regardless of rostrum length. That one case is the lineage of Jianchangnathus,  Pterorhynchus and darwinopterids, which we last discussed here.

 

The secondary naris that frequently develops is nothing more than a tiny hole that did not contribute to respiration. So don’t freak out about the concept.

When you have a good phylogenetic tree, you can see how details like this evolve over time and taxa. Removes the mystery, which some folks still don’t appreciate.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s