Why the giant azhdarchid Arambourgiania philadelphiae needs a fanclub

Two giant azhdarchids, Arambourgiania philadelphiae, attempt to portion a troodontid. The troodontid objects.

When people talk about giant azhdarchid pterosaurs (odds are most readers of this blog don't need an introduction to azhdarchids, but if you do, click here) they typically mention two taxa. The first is Quetzalcoatlus northropi, a giant Texan pterosaur discovered in the 1970s and now one of the most famous pterosaurs of all (Lawson 1975, Langston 1981). The second is Hatzegopteryx thambema, a relatively robust giant discovered in the 1990s and initially - because of its size and reinforced bone construction - thought to be a giant predatory dinosaur (see Buffetaut et al. 2003). From internet forums to TV show producers, if you want to chat about giant pterosaurs, these species are your most likely subjects.

Many readers will be aware that these aren't the only giant azhdarchids, however. The record of these animals cannot be described as extensive, but it is sufficient to indicate that they were present across most of the world and probably not particularly rare in Late Cretaceous ecosystems. But most fossils of giant azhdarchids are unnameable on account of being too fragmentary, being represented by parts of undiagnostic anatomy, or being too poorly preserved. This makes it all the more surprising that the third named giant azhdarchid doesn't get much attention: the Maastrichtian species Arambourgiania philadelphiae, known from several bones from phosphate mines in Jordan.

I'm not sure why we generally overlook this giant. Perhaps it's because Arambourgiania - 'Arambourg's giant' - is one of those old-fashioned names which works better in translation than the original Greek. It certainly doesn't sound as evocative or exotic as Quetzalcoatlus or Hatzegopteryx. Moreover, it's the least known of the three named giants, being primarily represented by a long - 620 mm - cylindrical neck vertebra, and not much else. The other named giants are not well represented either, but we have more than a handful of bones for them, and they're represented by intuitively intriguing anatomies: giant wing skeletons, bits of skull and jaw and so on. But whatever the cause, there are reasons to consider our relative neglect of Arambourgiania as unwarranted. It may not be as well-known as Quetzalcoatlus, or as immediately intriguing as Hatzegopteryx, but if you're interested in giant azhdarchids (and, hey, who isn't?) you this animal deserves your attention just as much as the other species. Here are just three reasons why.

History has been unkind to Arambourgiania

We typically start the story of giant azhdarchid studies in the early 1970s and the discovery of Quetzalcoatlus, but Arambourgiania was found and described long before then. Indeed, it's among the first accounts of an azhdarchid in scientific literature. When exactly the first Arambourgiania material was unearthed remains mysterious - it was likely the late 1930s or early 1940s - but the holotype cervical vertebra emerged in a scientific paper in 1954 thanks to French palaeontologist Camille Arambourg. Five years later, he would name this bone Titanopteryx philadelphiae (Arambourg 1959), a title which would be modified to Arambourgiania in the 1980s once the preoccupation of Titanopteryx by a black fly became apparent.

Aramboug misidentified this vertebra as being wing metacarpal of a large pterosaur (below). This might seem surprising - how do you confuse a vertebra for a wing bone? - but this tubular bone must have been a bizarre object to him. Consider that no-one in the 1950s had a clue what an azhdarchid was; that no-one imagined pterosaurs could have the incredibly long necks now known for azhdarchids; and that there weren't any pterosaur specialists at this time (pterosaur researchers collectively took a breather in the early-mid part of the 20th century, only really returning to work from the 1970s onwards). The vertebra itself is near-devoid of features we would expect from an axial element, with only the lightest development of typical vertebral processes, and it has a near circular cross section, a condition at odds with a typical pterosaur vertebra but pretty typical of limb bones. In the context of the time, wing metacarpal was not a silly suggestion.

Despite his misidentification, Arambourg made one thing very clear in his reports: his animal was big. In both his 1954 and 1959 works he wrote that this bone, fragmentary as it was, clearly indicated an animal vastly superior in size to the 7 m wingspan Pteranodon, then considered the largest flying animal of all time. This is important: as early as the 1950s Arambourgiania was being interpreted as evidence that pterosaurs with wingspans rivalling small planes once existed.

Arambourg's (1954) illustration of the Arambourgiania vertebra as a wing metacarpal.

What Arambourg didn't do was elaborate on this point further: he made no fanfare about 'largest flying animal of all time' or whatever, though he might have been justified in doing so. I quite admire Arambourg's restraint in not running too far with the size of his giant: sometimes it's good to admit we don't have enough data to provide a full answer to certain questions, and given how bizarre this bone must have seemed he probably made the right call in being conservative. But his lack of excitement about his gigantic animal might explain why little fuss was made over Arambourgiania after the 1950s. The discovery of Quetzalcoatlus in the 1970s made the vertebral identification of the Arambourgiania holotype clear (Lawson 1975; Wellnhofer 1978), but no mention was made of its significant size compared to the then newly discovered Quetzalcoatlus vertebrae, nor its implication that giant azhdarchids were not only gigantic in wingspan, but must be enormous in neck proportions too.

Other authors missed the significance of Arambourgiania too. For instance, when writing about giant pterosaur flight in 1974, Cherrie Bramwell and G.R. Whitfield stated that Pteranodon was the largest flier ever. Ross Stein's (1975) work on a similar topic provided the same fact, and Wellnhofer's (1978) review of Pterosauria made no mention of the size of Arambourgiania. It wasn't until the 1980s and 1990s that Arambourg's interpretations finally penetrated the pterosaur research zeitgeist, but by this time a flurry of media and scientific attention had made Quetzalcoatlus 'the' giant pterosaur. Arambourgiania would eventually get more dedicated scientific treatment - including wingspan estimates - in the mid 1990s (Frey and Martill 1996; Steel 1997; Martill et al. 1998), but this did little to elevate the status of Arambourg's work and his giant in the story of giant azhdarchid research.

I have to admit that I'm as guilty as anyone in not been kind to Arambourgiania. In Witton (2010), a paper on the history of giant pterosaur discoveries, I didn't even feature it in this figure of 'world record' claims of pterosaur wingspans and equivalent standing heights. A, a 3 m span Andean condor (Vultur gryphus); B, 3 m span wandering albatross (Diomedea exulans); C, Marsh’s 1876 7.6 m span Pteranodon longiceps; D, Stoyanow’s 1936 (apocryphal, and never published in a peer reviewed journal) 10 m span Jurassic pterosaur; E, Harksen’s 1966 9.1 m span Pteranodon sternbergi (now considered too big - 6-7 m max is likely for Pteranodon); F, Lawson’s 1975 11 m span Quetzalcoatlus northropi; G, Buffetaut et al. (2002) 12 m span Hatzegopteryx thambema (probably a smidgen too large); H, another apocryphal giant, a 20 m wingspan form announced at the BA Festival of Science. I want to stress that this animal really, really doesn't exist. Humans used for scale are 1.75 m tall.

Of course, it's easy to see why the 1970s discovery ofQuetzalcoatlus had the impact it did: the fossil material was better, it was announced in Science, and the Texan team did a lot of work to promote their discovery (indeed, there might be more information about Quetzalcoatlus in popular articles than in scientific papers...). By contrast, Arambourg presented Arambourgiania in a couple of very dry articles, published all his work on this animal in French*, and without fanfare. Needless to say, history is more likely to record the bigger splashes than the ripples on the pond, and Quetzalcoatlus made a big splash. But with hindsight, I think we can say that the sidelining of Arambourg's work in historic accounts and our frequent omission of Arambourgiania in discussions of these animals is something we should address. Arambourg was saying decades before anyone else that Arambourgiania was significantly bigger than Pteranodon, and we have to recognise the concept of 'truly' giant pterosaurs as his creation. We might have put numbers to his animals with our 10 m wingspan estimates and 200-250 kg mass predictions, but he put the concept on paper first. The fact he did this from such scant material, and at a time when our knowledge of pterosaur palaeontology was rusty, is impressive, and it really doesn't matter that he got a few things wrong. So yeah, from now on I'm saying that Arambourgiania - not Quetzalcoatlus - was, and always has been, the original giant azhdarchid, and that Arambourg knew this decades before anyone else.

Predicted size and neckage of Arambourgiania next to a Masai giraffe and a human wife. Arambourg predicted this 20 years before anyone else, yet we rarely give him any credit for his insight.

Arambourgiania is more than just a neck bone

It's rarely mentioned that Arambourgiania is known from material other than just a gigantic neck bone: a smattering of other bones from the same Phosphate mines might - probably- pertain to the same species. These were re-discovered and outlined by Frey and Martill (1996), and comprise the proximal and distal end of first wing phalanx (below), and a heavily eroded bone interpreted as a second cervical vertebra. Given the uncertainty about their association with the holotype - remember that the circumstance of its collection are lost to history - Frey and Martill classified these as cf. Arambourgiania.

Line drawing and reconstruction of the lesser seen cf. Arambourgiania first wing phalanx fragment (a, c-d). That's the wing phalanx of Quetzalcoatlus sp. in panel b. Scale bars equal 20 mm, which shows the cf. Arambourgiania bone as pretty darned big. From Frey and Martill (1996).

There isn't that much which can be said about the additional cervical - it has some identifiable features, but it's a few flecks of broken bone and bumps of internal mould away from being a featureless tube. It's a little smaller in diameter than the big holotype vertebra, and much shorter. I'm not sure it should be considered as belonging to an animal of the same size as the holotype individual.

The wing phalanx elements however, are more interesting. For one, they're enormous, and look proportionate to the holotype vertebra when juxtaposed in a skeletal reconstruction (below). If they're not from the same individual, they must be from a very similarly sized one. Frustratingly, the wing phalanx ends are broken in a way that hints at the bone shaft bone surviving to the modern day as well, but being lost in recent times.

Arambourgiania (known elements in white, restored, hypothetical neck length of 2.6 m indicated by grey vertebrae) compared to Quetzalcoatlus sp. Note the chunky wing finger bones.

It might be difficult to understand why these scraps of a wing bone are exciting, but they inform us of some fundamental aspects of giant azhdarchid anatomy and wing structure. There aren't many giant pterosaurs where we have recognisable wing and neck material from the same species so, however scrappy it might be, this is already useful material for building a picture of their proportions and appearance. From a functional perspective, they are interesting in showing that wing finger of Arambourgiania articulated with the metacarpal in exactly the same way as it did in smaller pterosaurs. This is good to know, as it confirms the notion that understanding the smaller azhdarchid species is our best route to fathoming the bigger ones. And of further mechanical note is that these elements show the wing finger as proportionally robust, with a big articular surface for the metacarpal/phalanx joint and a wide space for insertion of ligaments pulling the wing open in flight. Increased robustness is a sign of greater resistance to stresses and strains, and a good indication that Arambourgiania had scaled its wing bones to be flightworthy. This is an important counterpoint to proposals from some researchers that the extreme size of giant azhdarchids rendered them flightless. Of course, these scraps of wing bone don't tell us much about flight performance or style, but they are a good indication that flight of some kind was happening in these forms.

The neck of Arambourgiania was a high point of tetrapod evolution, and we need to learn more about it

Of course, we can't talk about Arambourgiania without mentioning its long, tubular neck skeleton. To appreciate it fully, we should outline some generalities of azhdarchid neck anatomy. Proportionally speaking, azhdarchids have some of the longest necks of any tetrapod, a feat all the more remarkable given several aspects of their head and neck skeleton. While the idea of their necks being made of nothing more than simple, near-featureless tubes is overstated, we can't escape the fact that the majority of the azhdarchid neck skeleton had highly reduced features: no big processes, no elongate cervical ribs, no complicated corporeal geometry. This means they had atypically reduced opportunities for muscle attachment and soft-tissue neck support, and they must have been doing something clever to keep their necks aloft - exactly what that was remains a mystery. Like all pterosaurs, azhdarchids also only had seven 'true' cervicals (cervicals eight and nine are 'dorsalised') so that their neck length largely had to stem from just a few bones. This can be seen as peculiar as other long necked reptiles tend to increase their cervical counts to aid elongating their necks, but azhdarchids made do with their ancestral condition. The job of the azhdarchid neck was a significant one: most long necked animals have proportionally small heads, but azhdarchid heads were enormous (see Quetzalcoatlus skeletal restoration, above) and, even allowing for pneumaticity, they probably represented a good chunk of their body mass. Indeed, azhdarchid skulls are big for any tetrapod, their jaws being about about three times longer than their bodies, and those of the giants are predicted as being among the longest of any terrestrial animals, ever. The fact these huge heads were atop these long, skinny neck skeletons is pretty remarkable. In my view we should consider the azhdarchid neck as a real marvel of evolution: these animals did some pretty amazing things with an outwardly simple approach, and achieved some pretty extreme anatomy using a seemingly maladapted approach to enlarging neck tissues.

The 620 mm long holotype of Arambourgiania philadelphiae as illustrated by Martill et al. 1998. Top is ventral view, bottom is left lateral. Anterior is to the left of the image, scale bar is 100 mm. This bone is predicted to reach 770 mm when complete.

Taking all these points and multiplying them across the Arambourgiania holotype cervical suggests this tubular bone is a pretty fantastic piece of anatomy. We can reconstruct the length of the holotype cervical (presumed to be a fifth, the longest bone in the neck) as 770 mm, and this translates to a neck length estimates of 3 m using scaling based on Quetzalcoatlus (Frey and Martill 1996), or 2.6 m using a range of azhdarchid necks (specifically lengths of cervicals III-VII - this from an unpublished dataset). However you want to cut it, it's clear this was a very long-necked animal, perhaps up there with the longest necked of all non-sauropodan terrestrial animals (below). On top of this we have to put a big azhdarchid skull, which is going to be about 2-3 m long for a giant. If these estimates are correct, Arambourgiania would be loaded with 5 m of neck and head, and was supporting the whole lot with a small number of bones resembling packing tubes. It has to be regarded as one of the most 'extreme' tetrapod bodyplans known.

Mike Taylor and Matt Wedel's (2013) take on the non-sauropod contest for longest tetrapod neck. It's a close call in my mind as to who wins out of Arambourgiania and a large Tanystropheus, but the important point is that Arambourgiania has an extremely long neck.

So how did the neck of Arambourgiania work? How did a series of bony tubes support a 2-3 m long head? Where did the muscles attach to on the simple structure of cervical V? Full answers to these questions remain part of a broader mystery about the functionality of azhdarchid necks, and this is something that researchers are only just starting to address. But what we know of Arambourgiania is sufficient to give some provisional, partial insight here. The basic construction of the Arambourgiania cervical is basically similar to what we see in smaller azhdarchids, where large, stiffened joints between the neck bones helped support and reinforce the neck (artists: please stop drawing azhdarchids with S-shaped necks in flight!). But subtle modifications to its vertebrae likely enabled each element to grow to much greater lengths without failing. Most azhdarchid cervicals are dorsoventrally flattened, which makes them weakest against vertical loads. Most of the time, vertical loading is created by the weight of the neck and head, but it will also include any food being picked up. The Arambourgiania cervicals are expanded dorsoventrally to the extent that they are slightly taller than wide (Frey and Martill 1996), reinforcing them against vertical bending, and thus potentially able to support greater weights than their smaller cousins. Furthermore, in expanding the bone dimensions to a near circular cross section, and all the while retaining a characteristically thin pterosaurian bone wall, Arambourgiania likely had vertebrae more resistant to torsion and bending than those of the smaller forms.

So counter-intuitive as it seems, making a neck out of tubes is a good way to produce a strong, long, lightweight skeleton, especially if it has to support heavy loads like a huge head. Pterosaurs used the same tactic to enhance their wings, and it seems azhdarchids - especially Arambourgiania - transferred some of these mechanical properties to their vertebral column. While assessments like this are very basic and clearly only the tip of the iceberg as goes azhdarchid neck mechanics, they demonstrate that Arambourgiania is, and will continue to be, a critical species for understanding the neck proportions, mechanics and scaling of giant azhdarchids.

So, what I'm saying is...

These are just three reasons why we shouldn't be overlooking Arambourgiania when considering the largest pterosaurs. It might not have the sexiest name, and it might not be known from as many elements as the other named giants, but it has historic and anatomical significance that cannot, or should not, be eclipsed by other species. It's clearly an animal that needs to be brought back into the fold of popular science so, the next time giant azhdarchid pterosaurs come up in conversation, remember that there are three named giant species, not just those other two, and that forgotten, old-timer Arambourgiania still has plenty of things to tell us about giant azhdarchid palaeobiology.

Coming really, really soon: you guys like pterosaurs, right?

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References

• Arambourg, C. (1954). Sur la presence dun pterosaurien gigantesque dans les phosphates de Joradanie. Comptes Rendus Hebdomadaires des Seances de l'Academie des Sciences, 238(1), 133-134.
• Arambourg, C. (1959). Titanopteryx philadelphiae nov. gen., nov. sp., ptérosaurien géant. Notes et Mémoires sur le Moyen-Orient, 7, 229-234.
• Bramwell, C. D., & Whitfield, G. R. (1974). Biomechanics of Pteranodon. Philosophical Transactions of the Royal Society B: Biological Sciences, 267(890), 503-581.
• Buffetaut, E., Grigorescu, D., & 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., & Csiki, Z. (2003). Giant azhdarchid pterosaurs from the terminal Cretaceous of Transylvania (western Romania). Geological Society, London, Special Publications, 217(1), 91-104.
• Frey, E., & Martill, D. M. (1996). A reappraisal of Arambourgiania (Pterosauria, Pterodactyloidea): One of the world's largest flying animals. Neues Jahrbuch fur Geologie und Palaontologie-Abhandlungen, 199(2), 221-248.
• Langston, W. (1981). Pterosaurs. Scientific American, 244, 122-136.
• Lawson, D. A. (1975). Pterosaur from the Latest Cretaceous of West Texas. Discovery of the Largest Flying Creature. Science, 187: 947-948.
• Martill, D. M., Frey, E., Sadaqah, R. M., & Khoury, H. N. (1998). Discovery of the holotype of the giant pterosaur Titanopteryx philadelphiae ARAUBOURG 1959, and the status of Arambourgiania and Quetzalcoatlus. Neues Jahrbuch fur Geologie und Palaontologie-Abhandlungen, 207(1), 57-76.
• Steel, L., Martill, D.M., Kirk, J., Anders, A., Loveridge, R.F., Frey, E. J.G. Martin (1997). Arambourgiania philadelphiae: giant wings in small halls. The Geological Curator, 6(8): 305-313
• Stein, R. S. (1975). Dynamic analysis of Pteranodon ingens: a reptilian adaptation to flight. Journal of Paleontology, 534-548.
• Taylor, M. P., & Wedel, M. J. (2013). Why sauropods had long necks; and why giraffes have short necks. PeerJ, 1, e36.
• Wellnhofer, P. 1978. Handbuch der Paläoherpetologie. Teil 19: Pterosauria. Gustav Fischer Verlag, Stuttgart. 82 pp.
• Witton, M. P. (2010). Pteranodon and beyond: the history of giant pterosaurs from 1870 onwards. Geological Society, London, Special Publications, 343(1), 313-323.