Arambourgiania

Arambourgiania; Temporal range: Maastrichtian PreꞒ Ꞓ O S D C P T J K Pg N
	Holotype fossil cast at Museum Histoire Naturelle, Paris
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Pterosauria
Suborder:	†Pterodactyloidea
Family:	†Azhdarchidae
Subfamily:	†Quetzalcoatlinae
Genus:	†Arambourgiania; Nessov vide Nessov & Yarkov, 1989
Species:	†A. philadelphiae
Binomial name
	†Arambourgiania philadelphiae; (Arambourg, 1959)
Synonyms
	Genus synonymy Titanopteryx ; Arambourg, 1959 (preoccupied) ; Species synonymy Titanopteryx philadelphiae ; Arambourg, 1959 ;

Arambourgiania is a genus of azhdarchid pterosaur that lived during the Maastrichtian age of the Late Cretaceous, in what is now Jordan. Additional fossil remains from United States and Morocco have also been found, but their assignment to Arambourgiania is only tentative. The original specimen was discovered in the 1940s by a railway worker near Russeifa, Jordan. After examination by paleontologist Camille Arambourg, a new species was named in 1959, Titanopteryx philadelphiae. The generic name means "titan wing", as the fossil was initially misidentified as a huge wing metacarpal (it would be later identified as a cervical (neck) vertebra), while the specific name refers to the ancient name of Amman (the capital of Jordan), Philadelphia. The genus "Titanopteryx" would later be problematic, as it had already been taken by a fly. Because of this, paleontologist Lev Nessov in 1989 named a new genus, Arambourgiania, in honor of Arambourg. The new species was now known as Arambourgiania philadelphiae.

Arambourgiania is one of the largest flying animals ever discovered. Initial wingspan estimates ranged from 11 to 13 m (36 to 43 ft), which would have made it the largest known pterosaur. However, due to Arambourgiania only presenting fragmentary specimens, recent research has suggested more moderate wingspan estimates. Some of the latest studies put the wingspan anywhere between 8 to 10 m (26 to 33 ft), which would still be among the largest known flying creatures. Arambourgiania has often been compared to other gigantic pterosaurs such as Quetzalcoatlus and Hatzegopteryx in terms of size.

Arambourgiania is a member of the family Azhdarchidae, which incudes some of the largest known pterosaurs ever. One of the closest relatives of Arambourgiania is Quetzalcoatlus, as multiple studes have found both pterosaurs to be grouped together within Azhdarchidae.

History of discovery

Holotype cervical vertebra of Arambourgiania (F) compared to those of other azhdarchids

In the early 1940s, a railway worker during repairs on the Amman-Damascus railroad, near the city of Russeifa in Jordan, found a fossil bone measuring 60.96 cm (2 ft). This specimen was acquired in 1943 by the director of a nearby phosphate mine, Amin Kawar, who brought it to the attention of British archeologist Fielding after the Second World War. This generated some publicity — the bone was even shown to Abdullah I of Jordan — but more importantly, it made the scientific community aware of the find.^[1]

In 1953, the fossil was sent to the National Museum of Natural History in Paris, France, where it was examined by French paleontologist Camille Arambourg. In 1954, he concluded the bone was the wing metacarpal of a giant pterosaur. Afterwards, in 1959, he named a new genus and species: Titanopteryx philadelphiae. The generic name meaning "titan wing" in Greek, referring to the enormous size of the fossil, while the specific name refers to the ancient name of Amman that was used by the Greeks: Philadelphia. Arambourg let a plaster cast be made and then sent the fossil back to the phosphate mine; this last aspect was later forgotten and the bone was assumed lost.^[1]

While studying and describing the closely related pterosaur Quetzalcoatlus in 1975, American paleontologist Douglas A. Lawson concluded that the bone was not a metacarpal but a cervical (neck) vertebra.^[2]

Arambourgiania was named after paleontologist Camille Arambourg

In the 1980s, Russian paleontologist Lev Nesov was informed by an entomologist that the name Titanopteryx had already been given by Günther Enderlein to a fly from the Simulidae family in 1935. Therefore, in 1989, he renamed the genus into Arambourgiania, honoring Arambourg.^[3] However, the name "Titanopteryx" was informally kept in use in the West, partially because the new name Arambourgiania was assumed by many to be a nomen dubium (dubious name).^[4]

In early 1995, paleontologists David Martill and Eberhard Frey traveled to Jordan in an attempt to clarify matters. In a cupboard of the office of the Jordan Phosphate Mines Company they discovered some other pterosaur bones: a smaller vertebra and the proximal and distal extremities of a wing phalanx — but not the original material of Arambourgiania. However, after their departure to Europe, engineer of the mine Rashdie Sadaqah investigated further and in 1996 he established that the original fossil had been bought from the company in 1969 by geologist Hani N. Khoury, who had then donated it in 1973 to the University of Jordan. It was still present in the collection of this institute and now it could be restudied by Martill and Frey.^[5]^[6]^[4]

Later, Frey and Martill rejected the suggestion that Arambourgiania was a nomen dubium or an identical pterosaur to Quetzalcoatlus, affirming its validity to replace the preoccupied name "Titanopteryx".^[5]^[4]

In 2016, an azhdarchid cervical vertebra (MPPM 2000.23.1) was described from the Coon Creek Formation of McNairy County in Tennessee, United States. It was referred to A. philadelphiae, which may potentially extend the geographic range of Arambourgiania to North America.^[7] However, this specimen was later referred to as cf. Arambourgiania, indicating a species of uncertain affinities.^[8] In 2022, American paleontologist Gregory S. Paul stated that it may not even belong to Arambourgiania itself.^[9]

Ulna bone from the Ouled Abdoun Basin of Morocco that may belong to Arambourgiania

In 2018, topotype specimens were located in Bavarian State Collection for Palaeontology and Geology in Munich, Germany that were placed there in 1966 from Jordan. These probably represent additional elements of the holotype individual. They are identified as cf. Arambourgiania and include the fragments of two cervical vertebrae, a neural arch, a left femur, a possible radius, and a metacarpal IV, as well as other indeterminate fragments.^[10] The incomplete left ulna of the "Sidi Chennane azhdarchid" from Morocco has also been identified as cf. Arambourgiania.^[11]

In 2024, the describers of the genus Inabtanin discovered a large partial right humerus of a large pterosaur in the Ruseifa Phosphate Mines, near the Jordanian capital of Amman, which was where the holotype of Arambourgiania was recovered. They concluded that the specimen belonged to A. philadelphiae and that it is comparable in size and shape to the humerus of the type species of Quetzalcoatlus, Q. northropi.^[12]

Description

Length of the holotype cervical vertebra of Arambourgiania (first above) compared to other azhdarchid cervical vertebrae

The holotype of Arambourgiania, UJA VF1, consists of a very elongated cervical vertebra, probably the fifth. Today the middle section is missing; the original material was about 62 cm (24 in) long, but had been sawed into three parts. Most of the fossil now consists of an internal infilling or mold; the thin bone walls are missing on most of the surface. The holotype does not present the whole vertebra; a piece is absent from its posterior end as well.^[4]

Size of Arambourgiania (far right) compared to a human, Tyrannosaurus, and Balaur, the latter two lived roughly at the same time as Arambourgiania

Size of Arambourgiania (center left) compared to a human, Nyctosaurus (beside the human), and Quetzalcoatlus northropi (right). Note the very similar size of Arambourgiania and Q. northropi

Frey and Martill estimated the total length of the holotype to have been 78 cm (31 in), using for comparison the relative position of the smallest diameter of the shaft of the fifth cervical vertebra of Quetzalcoatlus. The total neck length was extrapolated at about 3 m (9.8 ft) using the same method. From the relatively slender vertebra, the length dimension was then selected to be compared to that of Quetzalcoatlus as well, estimated at 66 cm (26 in) long, which results in a ratio of 1.18. Applying that ratio to the overall size, Frey and Martill in the late 1990s concluded that the wingspan of Arambourgiania was 11 to 13 m (36 to 43 ft), larger than the estimated wingspan of Quetzalcoatlus, which measured 10 to 11 m (33 to 36 ft). This would have made Arambourgiania the largest pterosaur ever known.^[5]^[4] In 1997, paleontologist Lorna Steel and colleagues reconstructed a life-sized skeleton of Arambourgiania based on better-known related pterosaurs. They set its wingspan at 11.5 m (38 ft), within the range of Frey and Martill's estimate.^[6]

Skeletal reconstructions of Arambourgiania (C) and the related Hatzegopteryx (A), and Quetzalcoatlus lawsoni (D), with known parts in gray

Subsequently, the estimates proposed by Frey and Martill in the late 1990s were taken into question, with later estimates of the wingspan of Arambourgiania being more moderate. This was due to the remains being too fragmentary to estimate a gigantic size. In 2003, the researchers who described the related pterosaur Phosphatodraco stated that the wingspan of Arambourgiania was more likely at 7 m (23 ft), though this measurement was not given a rationale.^[13] In 2010, paleontologists Mark Witton and Michael Habib argued that a 7 m (23 ft) wingspan is an underestimate for Arambourgiania, while a 11 to 13 m (36 to 43 ft) wingspan would be too much.^[14]

Estimated size of Arambourgiania (dark turquoise; upper left) compared to contemporary pterosaurs, birds, and a human. Hatzegopteryx and Quetzalcoatlus northropi are also depicted (dark brown; lower left)

In his 2022 pterosaur book, Paul proposed that Arambourgiania had a wingspan of 8 to 9 m (26 to 30 ft), which would be smaller than that of Quetzalcoatlus northropi, the which he kept at 10 to 11 m (33 to 36 ft). Arambourgiania would have also had a smaller wingspan than that of the related Hatzegopteryx, which Paul situated at 10 to 12 m (33 to 39 ft). Just like both Arambourgiania and Quetzalcoatlus, Hatzegopteryx is also another pterosaur that consistently ranks among the largest known flying animals.^[9] In a 2024 study, the wingspan of Arambourgiania was estimated to be around 10 m (33 ft) based on a large humerus comparable in size to that of Q. northropi. This new estimate for the wingspan of Arambourgiania is slightly larger than Paul's 2022 estimate, but does not surpass the wingspan of Quetzalcoatlus.^[12]

Classification

Quetzalcoatlus (skeleton depicted) is among the closest relatives of Arambourgiania, with many studies finding them as sister taxa

Arambourgiania was initially assigned to a newly named subfamily called Azhdarchinae by Nesov in 1984. It was still known as "Titanopteryx" at the time of the assignment. Azhdarchinae also included the pterosaurs Azhdarcho and Quetzalcoatlus. Nesov assigned the subfamily as part of the family Pteranodontidae, based on its members featuring toothless beaks just like the pteranodontids.^[15] Unaware of the creation of Azhdarchinae, American paleontologist Kevin Padian created the family Titanopterygiidae, which included both "Titanopteryx" and Quetzalcoatlus.^[16] Two years later, in 1986, Padian would synonymize the two terms and elevate Azhdarchinae to family level, creating the Azhdarchidae as it is known today.^[17]

Restoration of two Arambourgiania fighting over a small theropod

The placement of Arambourgiania in the family Azhdarchidae has always been agreed upon, which is in a derived position within the subfamily Quetzalcoatlinae, but its placement regarding other genera of the family has been somewhat disputed. One of its closest relatives is Quetzalcoatlus, as both pterosaurs have consistently been found together in multiple phylogenetic analyses, either as sister taxa or close to each other.^[18]^[11]^[19]^[20] However, there have also been several studies opposing this placement and have instead favored a closer relationship between Arambourgiania and the azhdarchids Mistralazhdarcho and Aerotitan.^[21]^[22]^[23]

Below are two cladograms showing different studies regarding the position of Arambourgiania within Azhdarchidae. The first one is based on the phylogenetic analysis by American paleontologist Brian Andres in 2021, which places Arambourgiania within the subfamily Quetzalcoatlinae as the sister taxon to both species of Quetzalcoatlus, Q. northropi and Q. lawsoni.^[19] The second cladogram is based on the 2023 study by paleontologist Rodrigo Pêgas and colleagues, in which they placed Arambourgiania in a trichotomy with Mistralazhdarcho and Aerotitan within Quetzalcoatlinae, contrasting its placement as the sister taxon of Quetzalcoatlus.^[23]

Topology 1: Andres (2021).

Azhdarchidae

Azhdarchinae

Azhdarcho lancicollis

Albadraco tharmisensis

	Aerotitan sudamericanus

	Mistralazhdarcho maggii

Quetzalcoatlinae

	Aralazhdarcho bostobensis

	Phosphatodraco mauritanicus

Eurazhdarcho langendorfensis

Zhejiangopterus linhaiensis

Cryodrakon boreas

Wellnhopterus brevirostris

Hatzegopteryx thambema

Arambourgiania philadelphiae

	Quetzalcoatlus lawsoni

	Quetzalcoatlus northropi

Topology 2: Pêgas and colleagues (2023).