The true giants, however, are the azhdarchids, the most common (if not only) pterosaurs in the latest Cretaceous. Although some azhdarchids were of smaller size (2.5-3 m in Montanazhdarcho and Eurazhdarcho), they also reach absurd sizes of 10-12m wingspans. In contrast, the largest living flying birds (the wandering albatross) had wingspans of approximately 3m (but as much as 3.5m), while the largest extinct flying bird, Pelagornis , had a wingspan of 6-7 m. These giant pterosaurs in comparison would have rivalled airplanes with their wingspans, and reached as high as a giraffe when standing.
|Giant azhdarchid Arambourgiania with a giraffe and human for scale. Image copyright Mark Witton.|
So how many giant pterosaurs were there? So far, there are 3 described species of giant pterosaur: Hatzegopteryx thambena  from Romania, Arambourgiania philadelphia  from Jordan, and arguably the most famous of the three Quetzalcoatlus northropi  from the USA. Unfortunately, these are all currently known from pretty fragmentary remains, but there's just enough to get an idea of what kind of things these animals were up to, and how big they really were.
|The proximal humerus fragment of Hatzegopteryx .|
Scale bar is 10 cm.
|Undescribed giant azhdarchid cervical (neck)|
vertebra from Romania .
Arambourgiania philadelphiae is probably the least well known and recognisable of the giant pterosaurs, although it was described first. First described by French palaeontologist Camille Arambourg as "Titanopteryx" philadelphiae in 1959 , it was later redescribed as Arambourgiania philadelphiae by Nesov in 1987, as Titanopteryx was already taken as the name of a beetle. Arambourgiania was originally described from a single partial cervical vertebra, which at the time was described as a metacarpal, but later recognised as a cervical vertebra [8,9]. All of the material comes from the Maastrichtian of Jordan, and additional material including a wing phalanx fragment and a cervical vertebra. Additional specimens exist from other museums that have been undescribed or referred to including the Natural History Museum of London. The best estimate for a wingspan of Arambourgiania philadelphiae is similar to Hatzegopteryx with 10.5m being the estimated greatest wingspan possible .
|Giant Q. northropi humerus (b, c), and|
smaller Quetzalcoatlus sp. humerus (d)
and cervical vertebra (a) 
Quetzalcoatlus northropi, on the other hand, is probably the best known or at least most popular in the media of the giant pterosaurs. From the Maastrichtian of Texas, only a few bones of Q. northropi have been described in the literature. The genus Quetzalcoatlus is known from 2 size morphs: a smaller one generally referred to as Quetzalcoatlus sp., and the giant Q. northropi. First described in 1975 by graduate student Douglas Lawson, Q. northropi is known from a fragmentary wing (humerus, carpals, phalanges), with just the humerus figured in the original description . Approximately 40 km away, a number of much smaller specimens were found and described as the same genus, but a different unnamed species, hence Quetzalcoatlus sp. In total, and at the time of original description in 1975, the material existing for Quetzalcoatlus consisted of four wings, a neck, hind limbs, and the lower jaw. Frustratingly, no more of this material has been described. It represents the best known giant azhdarchid, but it has never been properly described in the literature, although there is hope that this may happen soon.
The lack of description for Quetzalcoatlus is particularly frustrating as it means that additional material from North America cannot be properly described. For example, there is large azhdarchid material from Alberta that is thought to represent at least Quetzalcoatlus sp., and possibly even Quetzalcoatlus northropi. However, until these specimens are properly described, it's unknown if this is the case. Subsequently, a lot of this material is not properly described and people are just waiting for the other material to be described. Hopefully that will come though!
While only 3 species of giant pterosaur are currently known, they seem to not have been restricted to one area as they are known from Europe, the Middle East, and North America. Hopefully more material will be found and described with ongoing studies in Romania and North America especially, and new species may pop up!
|Terrestrially stalking Hatzegopteryx preying on small sauropods in Romania |
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2. Burretaut, E., et al. 2002. A new giant pterosaur with a robust skull from the latest Cretaceous of Romania. Naturwissenschaften 89: 180-184.
3. Arambourg, C. 1959. Titanopteryx philadelphiae nov. gen., nov. sp., ptérosaurien géant . Notes et Mémoires sur le Moyen-Orient 7: 229-234.
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