Bennett’s anurognathid: the search for giant eyeballs continues…

Wednesday, July 14, 2021 14:42

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Today we’re going tackle, again, the myth
of the SMNS 81928 anurognathid pterosaur, the one reconstructed with giant owl-like eyes (Figs. 1 in blue, 6, 7). This odd reconstruction has become popular with paleo-artists. It began with Bennett 2007 and his unique reconstruction of the SMNS 81928 specimen (Figs. 6, 7), which he incorrectly referred to Anurognathus (Fig. 5).

Before we get started, let’s remember, back in the day
there were no other flat-head anurognathids known. Bennett was working with a bauplan of Anurognathus (Fig. 5), in which the narrow skull was crushed laterally, like Dimorphodon. A wide, flat skull crushed in dorsal view, like the SMNS 81928 specimen, was a relatively new experience, preceded only vaguely by Jeholopterus and Dendrorhychoides.

A more accurate reconstruction of the SMNS 81928 specimen
is shown below (Fig. 1 in black). It matches several other flat-head anurognathids published since 2007, including the CAGS Z070 specimen, Vesperopterylus and ‘Discodactylus‘ ( = NJU-57003, Fig. 4). That passes the test of reproducibility. By contrast, Bennett’s owl-eye reconstruction has never been found in other taxa. It remains unique.

Figure 1. The SMNS 81928 anurognathid specimen. Above: based on DGS tracings. Below: based on Bennett’s mistaking a maxilla for half of a sclerotic ring and other mistakes. Freehand drawings always bear the mark of the artist, which can be inappropriate when trying to figure out something that requires more strict precision and less flair.

Redoing the tracing and reconstruction
of SMNS 81928 seemed necessary today because the first attempt was not as clearly presented as it is now (Figs. 2, 3), in color, bone by bone.

Because human eyes alone, or with microscopic aid,
cannot disentangle and reassemble the fragile, flattened elements of the SMNS 81928 skull, that makes it a great specimen to demonstrate the value of DGS (Digital Graphic Segregation, Fig. 2, 3). This Photoshop method uses the computer monitor as a microscope. Bones are colored on separate layers (Fig. 2). Then these colored shapes are moved onto a blank field to be slid around digitally (Fig. 3). This minimizes any errors, biases and inspirations that come with freehand drawing.

Despite its benefits and widespread use,
the DGS method has been criticized. Results have been ignored and ridiculed since it was first shared in 2003 (Jeholopterus image in the masthead above right).

Users of µCT scans
have been coloring digital bones to segregate one from another for the past several years. So this technique is becoming commonplace. Workers know this aids bone identification. DGS can even be animated.

Figure 2. Skull of the SMNS 810928 anurognathid with elements identified by DGS colors. Bennett did not realize that one maxilla had flipped during settling and the other had drifted below the rest of the skull. Nor did he see the row of teeth on the bone he identified as belonging to the eyeball.

Results
Again, I could not confirm Bennett’s observations. This time, like last time, no giant eyeball (sclerotic ring) could be identified in the SMNS 81928 specimen (Fig. 2). What Bennett 2007 identified as a giant half of a sclerotic ring is once again identified as a curved maxilla with teeth (Fig. 3). A pair of ordinary, small sclerotic rings were identified, both located in the back half of the skull, as in all other pterosaurs. The present reconstruction (Fig. 3) remains strongly similar to the bauplan of other pterosaurs and especially other flathead anurognathids (e.g. Fig. 4). That’s why they are preserved in and most easily reconstructed in dorsal view. The occipital elements provide a good estimate for skull height/depth at the occiput. These increasingly common flat-head anurognathids were all about that mouth getting bigger and wider while saving weight in the rest of the skull, largely distinct from other anurognathids.

Figure 3. Elements transferred from figure 2 to create a reconstruction of the SMNS 81928 anurognathid skull in dorsl view. This is a flathead pterosaur, much wider than tall. Those straight yellow-green bones are epipterygoids, common in lepidosaurs.

Conclusions:
This is one of those times when the consensus is wrong. Bennett 2007 was wrong. Flat-head anurognathids did not have large eyeballs in the front half of the skull.

Figure 4. Another view of the paper reconstruction of the skull and mandibles of Discodactylus.

I was wrong, too.
Earlier I thought the long, straight, yellow-green bones (Figs. 2, 3) might be stapes (ear bones), but now I understand them to be epipterygoids, common in lepidosaurs, largely overlooked in pterosaurs.

As you can see
(Fig. 2), without digital segregation of some sort, the SMNS 81928 specimen is virtually impossible to understand (Figs. 6, 7). A reconstruction (Fig. 3) is necessary, even after the layered bones have been identified.

Figure 5. The flat-head pterosaur, a private specimen (on the left) attributed by Bennett (2007) to Anurognathus ammoni (on the right).

Skeletal reconstructions are common in dinosaurs,
relatively rare in pterosaurs (Fig. 5). Bennett’s attempt (Fig. 7) was so different from other pterosaur reconstructions that it should have sent him back to the fossil to try to understand it better. Few fossils are more difficult than this one is. This is especially so considering: 1) the relative lack of comparable reconstructions before 2007; and 2) the extreme crushing and layering of the elements in this previously unheard of type of pterosaur. Bennett was understandably perplexed (Fig. 6), but gave it his best shot.

Figure 7. At left the traditional Bennett (2007) interpretation widely copied for all anurognathids by paleo-artists. On the right, interpretation based on tracing bones that fit the pattern of related pterosaurs, despite the flattened overall morphology, now found in other related anurognathids.

If anyone can duplicate Bennett’s 2007 conclusions and reconstructions
in any anurognathid, please step forward. In the last twenty+ years, no one has done so.

This pterosaur myth follows in the well-trod footsteps of those
who continue to believe that pterosaurs are close to dinosaurs, that pterosaur membranes extended to the shins and ankles, and that pterosaur hatchlings had short rostra and large eyes.

Figure 8 Model of Jeholopterus, the famous vampire pterosaur with the original skull in place.

PS
It gets worse… A few years ago, Triebold Paleontology bought my crude, small, but full scale sculpture of another anurognathid, Jeholopterus (Fig. 8), for commercial reproduction. Before putting it in their catalog, Triebold took off the correct skull and replaced it with Bennett’s mythical reconstruction. That’s how widely and deeply Bennett’s 2007 mistake has spread.

References
Bennett SC 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81(4):376-398.

https://pterosaurheresies.wordpress.com/2014/02/13/anurognathid-eyes-the-evidence-for-a-small-sclerotic-ring/

https://pterosaurheresies.wordpress.com/2011/12/01/the-evolution-of-anurognathid-skulls/

Source: https://pterosaurheresies.wordpress.com/2021/07/15/bennetts-anurognathid-the-search-for-giant-eyeballs-continues/