The antorbital fenestra of Anurognathus

As we discussed several times earlier, the reconstruction of the skull of Anurognathus has been disfigured by Bennett (2007). He mistook a maxilla for a giant sclerotic ring preserved on edge. So his reconstruction (Fig. 1, left) with its giant eyeball and tiny antorbital fenestra, is distinctly different from all other anurognathid pterosaurs. Just yesterday we looked at the longer neck in the Anurognathus holotype, partially hidden by matrix.

At left the traditional Bennett (2007) interpretation. On the right, interpretation based on finding and tracing paired bones.

Figure 1. At left the traditional Bennett (2007) interpretation based on misidentifying a maxilla as the sclerotic ring. On the right, DGS interpretation based on finding and tracing paired bones.

Bennett considered his new specimen to be conspecific with the holotype. So, in his mind the two specimens were virtually identical.

Let’s test that idea.
Here (Fig. 2) I thought it would be helpful to take a closer look at the holotype of Anurognathus to see if that big opening also contained an orbit and was bordered by the correct bones, or not. Here’s how Bennett (2007) interpreted it (note the bone labels):

Anurognathus ammoni according to Bennett who considered the jugal a squamosal and who considered a nasal a frontal.

Figure 2. Anurognathus ammoni according to Bennett who considered the jugal a squamosal and  a nasal and prefrontal were both considered frontals. Bennett also flipped the “squamosal” so the narrow portion would contact the postorbital, which was not done here. Left half of the premaxilla is removed in the reconstruction at right. Bennett’s depressions (dep) are more teeth. See figure 4. Even so, due to the posterior position of the ascending process of the maxilla (amp) The naris is much larger than in the SMNS specimen. Adding a lacrimal below the frontal and above the jugal produces an area in which the orbit can reside, much smaller than the SMNS specimen. All restored bones are brown.

Where is the giant sclerotic ring?
In the Bennett (2007) interpretation of Anurognathus (Fig. 1 left), he identified a giant sclerotic ring in the anterior half of the skull. The holotype of Anurognathus (Fig. 2) preserves that portion, but there’s no ring here. Where is it? (It’s not there.)

Here’s an attempt to rectify those mistakes going back to the holotype:

Anurognathus skull in situ.

Figure 1. Anurognathus skull in situ.

Figure 2. Anurognathus skull bones identified. Pink = lacrimals. Bright blue = jugal. Dark blue = fronts. Orange = nasals. Tan = scleral ring segments. Lacrimals are always anterior to the orbit. Jugals are always ventral to the orbit. So the large opening is an antorbital fenestra.

Figure 2. Anurognathus skull bones identified. Pink = lacrimals. Bright blue = jugal. Dark blue = fronts. Orange = nasals. Tan = scleral ring segments. Lacrimals are always anterior to the orbit. Jugals are always ventral to the orbit. So the large opening is an antorbital fenestra. As you can see, some of the bones are readily identified as bones. Others can be identified by impressions. See reconstruction in figure 3. There’s not much to the postorbital skull, which is narrow and composed of small bones.

The new study of the skull of Anurognathus identifies most of the bones of the skull and not too far from their in vivo positions and in line with the morphologies of other anurognathid skulls (Fig. 4). The Bennett (2007) skull is clearly the odd man out, the little monster. The sclerotic ring is behind the lacrimal (Figs. 3,4), above the jugal and below the postfrontal, as it should be.

Anurognathus ammoni (holotype) skull reconstructed from DGS tracing in figure 2.

Figure 3. Anurognathus ammoni (holotype) skull reconstructed from DGS tracing in figure 2. As in Dimorphodon, Peteinosaurus, the IVPP embryo and Jeholopterus the maxilla continues anterior to the ascending process. The lack of same in the other anurognathids requires more study.

Figure 1. Anurognathid skulls in phylogenetic order.

Figure 4. Anurognathid skulls in phylogenetic order. The Bennett skull (2013) is autapomorphic (odd and unique) in virtually all regards.

This reconstruction of the Anurognathus holotype skull supersedes all other of my prior attempts, which are now in my waste bin. This is a difficult subject and mistakes in interpretation can be made by anyone, including yours truly. I invite comments and constructive criticisms if you see where an improvement can be made. Let’s get this right together!

Reconstructions of the entire Anurognathus can be seen here.

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 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81(4):376-398.
Bennett SC 2008. Morphological evolution of the wing of pterosaurs: myology and function. Zitteliana B28: 127-141.
Döderlain L 1923Anurognathus ammoni, ein neuer Flugsaurier. Sitzungsberichte der Königlich Bayerischen Akademie der Wissenschaten, zu München, Mathematischen-physikalischen Klasse: 117-164.
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeontologica Polonica doi: 10.4202/app.2009.0145 online pdf
Peters D 2001. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15:277–301.

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