Updated April 21, 2022
with the addition of Prehistoric Planet information.
Figure 1. Hatzegopteryx elements to scale with the more completely known Quetzalcoatlus sp. and Quetzalcoatlus northropi (largely hypothetical). Scaling up Q. sp. to the size of Quetzalcoatlus puts the humerus to the size of Q. northropi and Hatzegopteryx (based on the partial humerus). However the hypothetical skull of Hatzegopteryx, based on the pterygoid/quadrate is both much wider and much longer than the scaled up Q. northropi skull. A bigger skull means a more robust neck for Hatzegopteryx, etc. etc. — which gives it less of a chance of flying due to its greater mass and no greater humerus. Zhejiangopterus and Azhdarcho also shown to scale. Zhejiangopterus also has a relatively larger skull and smaller humerus, but has no other flightless traits, like a large torso or robust skeletal elements.
Fun with scale bars
Based on the humerus, Hatzegopteryx (Buffetaut et al. 2003, Fig. 1) was larger than Quetzalcoatlus northropi (Lawson 1975), one of the largest pterosaurs of all time. Based on the pterygoid / quadrate and jugal (Fig. 1), Hatzegopteryx was much larger (if the skull and rostrum had similar proportions to Q. northropi), based on the scale bars.
We have a good narrow mandible for Q. sp. (Kellner and Langston 1996). We also have its palatal elements. The pterygoid and humerus are the only bones both taxa share in common. These few elements, along with the scale bars, form the basis for these largely hypothetical reconstructions and restorations (Fig. 1).
Figure 2. Quetzalcoatlus sunning itself, distorted somewhat, according to the skeleton standing beside it. Original image from the YouTube preview of Prehistoric Planet.
Added 4.21.2022: Some journalists are saying this is supposed to be a CGI Hatzegopteryx on the beach. Since relatively little is known of Hatzegopteryx (e.g. cervicals, partial humerus, partial dentary), that provides wide latitude for restoring the rest of the animal with imagination. If this is Hatzegopteryx, let’s look at what little is known. Here (Fig 2.1) is the Hatzegopteryx humerus to scale with Q northropi and Q lawsoni. Missing parts for Hatzegopteryx are restored based on Q northropi from Andres and Langston 2021. The diameter of the shaft at the break indicates the Hatzegopteryx humerus was overall larger than Q northropi, likely creating a larger pterosaur. Now, look at the deltopectoral crest. It is reduced. The pectoral flapping muscles were smaller in the larger pterosaur. That means Hatzegopteryx was less volant to non-volant considering the potential size of the larger Hatzegopteryx.
It’s hard to figure out what the rest of the pterosaur looked like based on just a few palatal bones. But it appears that the much larger skull of Hatzegopteryx might tip the scales toward flightlessness. If so, Hatzegopteryx would not be the first flightless pterosaur known. That honor goes to JME Sos 2428 (Peters 2013), a Late Jurassic protoazhdarchid.
That robust jugal counts too.
The jugal of Hatzegopteryx was not a fragile, slender bone, but a robust one, according to Buffetaut et al. (2002). So Hatzegopteryx was not trying to save weight by having paper thin bones.
Wikipedia reports, “In Hatzegopteryx, the skull bones are stout and robust, with large-ridged muscle insertion areas. In their 2002 description, Buffetaut and colleagues suggested that in order to fly, the skull weight of this pterosaur must have been reduced in some unconventional way (while they allowed that it could have been flightless, they found this unlikely due to the similarity of its wing bones to flying pterosaurs). The authors theorized that the necessary weight reduction was accomplished by the internal structure of the skull bones, which were full of small pits and hollows (alveoli) up to 10 mm long, separated by a matrix of incredibly thin bony struts (trabeculae), a feature also found in some parts of Hatzegopteryx wing bones. The authors pointed out that this unusual construction, which differed significantly from the irregular internal structure of other pterosaur skulls, resembles the structure of expanded polystyrene, the substance used to make Styrofoam. They noted that this would allow a sturdy, stress-resistant construction while remaining lightweight, and would have allowed the huge-headed animal to fly.”
More on Hatzegopteryx
Hatzegopteryx was found in the upper part of the Middle Densus-Ciula Formation (Upper Cretaceous, Late Maastrichtian). Holotype (FGGUB R 1083): fragments of a skull and associated partial humerus. Referred material: Femur (FGGUB R 1625).
Figure 2.1 Added April 21, 2022 with photo images of Quetzalcoatlus in comparison to Hatzegopteryx.
The humerus was odd
There is no preserved indication of a posterior tuberosity of the humerus, as shown in Quetzalcoatlus and Pteranodon. The cross-section of the shaft near the deltopectoral crest was round, not hollowed out as in Quetzalcoatlus and Pteranodon. There is no indication of a typical shoulder joint, as in flying pterosaurs. Those parts may be worn away.
Figure 3. Click to enlarge. Hatzegopteryx palate elements added to Quetzalcoatlus species elements and vice versa. The basisphenoids have not been documented in azhdarchids or sister taxa, but appear to be paired rather than single, as Buffetaut et al. proposed. Paired elements are primitive and are found in Dorygnathus, the closest known sister with these elements visible.
The basisphenoids in basal pterosaurs are paired and connect the braincase to the quadrate/pterygoid suture. In certain derived forms the basisphenoids merge. Buffetaut et al. imagined that they merged, as they do in Pteranodon, but no azhdarchid shows that and the base of the occiput appears to have paired basisphenoid breaks, not a single one. Pteranodon had a much narrower occiput, more appropriate for a single basisphenoid.
Buffetaut E, Grigorescu D and Csiki Z. 2002. A new giant pterosaur with a robust skull from the latest Cretaceous of Romania. Naturwissenschaften, 89(4): 180-184.
Buffetaut E, Grigorescu D and Csiki Z 2003. Giant azhdarchid pterosaurs from the terminal Cretaceous of Transylvania (Western Romania). In: Buffetaut E, Mazin J-M, eds. Evolution and Palaeobiology of Pterosaurs, Geological Society of London, Special Publication, 217, (2003) pp 91–104.
Kellner AWA and Langston W 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from late Cretaceous sediments of Big Bend National Park, Texas. – Journal of Vertebrate Paleontology 16: 222–231.
Lawson DA 1975. Pterosaur from the latest Cretaceous of West Texas: discovery of the largest flying creature. Science 187: 947-948.
Peters D. 2013. A flightless pterosaur. Journal of Vertebrate Paleontology supplement program and abstracts: 191.