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Arambourgiania

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Arambourgiania
Temporal range: Maastrichtian
Holotype fossil cast at Museum Histoire Naturelle, Paris
Scientific classification Edit this 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
Species synonymy
  • Titanopteryx philadelphiae
    Arambourg, 1959

Arambourgiania (meaning "Camille Arambourg's") is a genus of pterosaur, an extinct group of flying reptiles, that inhabited Jordan during the Maastrichtian age of the Cretaceous period, around 72 to 66 million years ago. Additional fossil remains from the United States and Morocco have also been found, but their assignment to Arambourgiania is only tentative. The holotype (name-bearing) specimen was discovered in 1943 by a railway worker near Russeifa, Jordan. After examination of the specimen by paleontologist Camille Arambourg, he described it as belonging to a new genus and species in 1959, Titanopteryx philadelphiae. The generic name means "titan wing", as the fossil was initially misidentified as a 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 name "Titanopteryx" would later be problematic, as it had already been taken by a fly. Because of this, paleontologist Lev Nessov in 1989 renamed the genus to Arambourgiania, in honor of Arambourg. Since 1943, additional isolated remains including vertebrae, wing bones, and hindlimb bones have been assigned to the genus.

Due to the fragmentary nature of the Arambourgiania fossils, there is little direct information about its anatomy. Its cervical vertebrae are extremely elongated, with the holotype vertebra measuring 77–78 cm (2 ft 6.31 in – 2 ft 6.71 in) in length. Based on the complete neck of its relative Quetzalcoatlus, Arambourgiania had a total neck length of 3 m (9 ft 10 in), longer than those of giraffes. Its vertebrae were also more lightly built and weakly muscled than those of its robust, short-necked relative Hatzegopteryx. 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, given the fragmentary remains, more recent research has suggested wingspans anywhere between 8 to 10 m (26 to 33 ft), which would still place the genus among the largest known flying animals.

Arambourgiania is a member of the family Azhdarchidae, which includes some of the largest known pterosaurs. Azhdarchids are thought to have had a terrestrial stalker lifestyle, similar to that of extant storks, though some studies have pointed out that azhdarchids are frequently found in marine deposits. This includes Arambourgiania, whose fossils are exclusively known from oceanic or coastal localities, indicating that azhdarchids may have consumed aquatic prey as well. The bones of Arambourgiania are extremely hollow and lightly built with adaptations for soaring. One of the closest relatives of Arambourgiania is Quetzalcoatlus, as multiple studies have found both pterosaurs to be grouped together within Quetzalcoatlinae. In Jordan, Arambourgiania fossils are known from the Ruseifa Formation which had deep marine environment that was deposited during the Maastrichtian. At this time, Jordan was submerged under the Tethys Sea and had a diverse composition of marine life, including mosasaurids, elasmosaurids, bony fish, and selachians. Arambourgiania is one of two pterosaurs known from Jordan, the other being Inabtanin.

History of research

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Arambourgiania was named after paleontologist Camille Arambourg, who first studied the specimen

In 1943, during phosphate mining operations near the town of Ruseifa, Jordan, a railway worker found a several fossil fragments associated with an incomplete fossilized cervical (neck) vertebra measuring 60.96 cm (2 ft) in length. Later in the same year, these fossils were acquired by Amin Kawar, the director of a nearby phosphate mine. Kawar brought the fossils to the attention of Dr. T. Harding, the Director of Antiquities at the British Residence in Amman (at the time Jordan was a British protectorate) who then examined the remains. The vertebra generated some publicity — it was even shown to Abdullah I of Jordan. Subsequently, the fossils were transferred to the Hebrew University of Jerusalem where reports of their origin, anatomy, and location were filed, with copies then sent to the Jordan Phosphates Mines Company. Unfortunately, these reports have since been destroyed, though there may be existing records at the Hebrew University. The phosphates in which the fossil was found belong to the Ruseifa Formation, which dates to the Maastrichtian age (72–66 million years ago) of the Late Cretaceous period.[1][2]

In 1953, the vertebra was sent to the National Museum of Natural History in Paris, France, where it was examined by French paleontologist Camille Arambourg. In 1954, Arambourg interpreted the vertebra as the wing metacarpal of a giant pterosaur, and in 1959 named the new genus and species Titanopteryx philadelphiae. The generic name Titanopteryx comes from the ancient Greek roots titan, in reference to the giant Greek Titans, and pteryx meaning "wing", while the specific name refers to the ancient name of Amman that was used by the Greeks: Philadelphia. The new species was based on the misidentified wing metacarpal, making this fossil the holotype specimen; several more elements had been found at the time but were undescribed and unidentified.[2][3] Arambourg had a plaster cast made and then sent the fossil back to the offices of the Jordan Phosphates Mines Company; this latter aspect was later forgotten, and the bone was assumed lost.[4][2]

Despite being the largest pterosaur known to science, the pteranodontid Pteranodon was still widely recognized as the largest pterosaur known to science until the description of Quetzalcoatlus.[5] In 1975 while studying Quetzalcoatlus, American paleontologist Douglas A. Lawson correctly concluded that the holotype was not a metacarpal but a cervical vertebra.[6] In the 1980s, an entomologist informed Russian paleontologist Lev Nesov that the name Titanopteryx had already been given to a fly from the Simuliidae family in 1935. Therefore, in 1989, he created the new genus name Arambourgiania, honoring Arambourg, with -iania being a suffix indicating possession.[7] However, the name "Titanopteryx" was informally kept in use in the West despite being a preoccupied name.[8][9]

In 1995, paleontologists David Martill and Eberhard Frey traveled to Jordan in an attempt to find the vertebra and to clarify the identity of Arambourgiania. In a cupboard of the office of the Jordan Phosphate Mines Company, Martill and Frey 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.[3] However in 1996, after the departure of Martill and Frey to Europe, Rashdie Sadaqah, the engineer of the mine, found out that the holotype had been purchased by the geologist Hani N. Khoury in 1969, who then donated it to the University of Jordan in 1973. The fossil was still present in the collection of this institute, and therefore could be restudied by Martill and Frey.[2][10][1] In their redescription, the two authors affirmed that Arambourgiania was a distinct taxon.[2][1]

Additional specimens

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Afro-Arabia

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Map of sites preserving Arambourgiania.
Navesink Formation
Coon Creek Formation
Jordan Phosphates
Khouribga Phosphates (type locality)
Merchantville Formation
Mishash Formation
Fossil localities of Arambourgiania. Legend:
A. philadelphiae; A. sp.; Formerly referred specimens

In 2018, a set of fragmentary azhdarchid specimens housed in the Bavarian State Collection for Palaeontology and Geology of Munich, Germany were described by paleontologists David Martill and Markus Moser. These fossils were obtained by Jean Otto Haas in 1955 and came from the same location where the holotype of Arambourgiania was found; though it is uncertain whether Haas found the specimens by himself or purchased them, they were later catalogued in his personal collection before ending up in the Bavarian State Collection in 1966. The azhdarchid fossils in the collection include six fragmentary specimens referred to as cf. A. philadelphiae, consisting of an incomplete metacarpal IV (SNSB-BSPG 1966 XXV 501), a potential cervical vertebra fragment (SNSB-BSPG 1966 XXV 503), a left femur (thighbone) fragment (SNSB-BSPG 1966 XXV 506), a possible radius (forearm bone) fragment (SNSB-BSPG 1966 XXV 507), another cervical vertebra fragment (SNSB-BSPG 1966 XXV 508), and a potential neural arch (SNSB-BSPG 1966 XXV 512). It is possible that these specimens come from the same individual as the holotype due to their same origin, lack of overlap, and comparable size. However, due to the lack of detailed data on their origin, it is impossible to verify this. Additionally, the holotype was unearthed in 1943 whereas the six specimens were obtained 12 years later.[3]

In 1992, Lewy and colleagues described a pair of endocasts (a natural cast of the brain cavity) which had been unearthed from upper Campanian or early Maastrichtian-aged phosphates belonging to the Mishash Formation located near Mitzpe Ramon, Israel. Lewy referred these endocasts to Titanopteryx (=Arambourgiania) sp. on the basis of their similarity to the endocasts of pterosaurs.[8] However, these endocasts have no overlap with any described fossils of Arambourgiania and, according to a 2014 study, most likely belong to birds instead on the basis of their length of around 3 centimetres (1.2 in) and bird-like structure.[11]

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

In 2018, paleontologists Nicholas Longrich, David Martill, and Brian Andres described an incomplete left ulna of the "Sidi Chennane azhdarchid" from the Ouled Abdoun Basin of Morocco which they tentatively identified as ?Arambourgiania. This ulna came from the Sidi Chennane mine located in the basin, a group of phosphatic sandstones dating to the Maastrichtian, which contains a host of other pterosaur genera from several different families.[12]

In 2024, the describers of the genus Inabtanin reported a 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.[13]

North America

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On 15 August 1982, Ralph Johnson unearthed an azhdarchid cervical vertebra (YPM VPPU 023497) from rock layers of the Maastrichtian-aged Navesink Formation located in Monmouth County, New Jersey in the United States.[14] In 1983, this vertebra was referred to Titanopteryx (=Arambourgiania) sp. on the basis of its elongation and lateral compression, though it is extremely poorly preserved.[15] The assignment of this specimen came into question in the 2025 description of Infernodrakon, where the authors considered the specimen as aff. Arambourgiania sp. due to its broader cross section than the known specimens of Arambourgiania and the lack of further study of the fossil.[16] Between 1971-73, two amateur fossil collectors John Brzostoski and Harold Mendryk discovered a cervical vertebra (YPM-PU 21820), a humerus (YPM-PU 22359), and an associated femur and tibia (YPM-PU 21821) in the Early Campanian-aged Merchantville Formation of New Castle County, Delaware in the United States.[17] Initially described as pterosaur specimens that are similar to Pteranodon,[17] Gallagher tentatively identified them as cf. ?Titanopteryx in 1993,[9] while Averianov identified them as indeterminate azhdarchids in 2014.[11] In 2021, Averianov and colleagues suggested that the cervical vertebra (YPM-PU 21820) belongs to a pteranodontid or even Pteranodon itself based on its pneumaticity,[18] a referral also suggested previously by Bennett (1994) and Barrett et al. (2008).[19][20]

In 1999, a fragmentary azhdarchid cervical vertebra (MPPM 2000.23.1) was discovered by Memphis local Wendy Melton-Beeson and collected by paleontologist T. Lynn Harrell Jr. that same year. The cervical vertebra had been taken from rocks in Selmer, Tennessee belonging to the lower Coon Creek Formation, dating to late Campanian in age,[21] older than the Maastrichtian-aged remains found in Jordan.[1] In 2016, Harrell, Gibson and Langston referred the cervical to A. philadelphiae on the basis of its size, morphology, and differences from the cervical vertebrae of Quetzalcoatlus. This specimen may potentially extend the geographic range of Arambourgiania to North America,[21] although its identity has since been contested. In 2021, Andres and Langston referred to it as cf. A. philadelphiae,[22] whereas in 2022, American paleontologist Gregory S. Paul stated that it may not belong to Arambourgiania.[23] In 2025, the describers of Infernodrakon considered this specimen as Arambourgiania sp. but not A. philadelphiae due to the morphological differences and temporal separation from the holotype. This same study also noted morphological similarities between MPPM 2000.23.1 and YPM VPPU 023497 from the Navesink Formation.[16]

Description

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Speculative life reconstruction

Arambourgiania was among the largest azhdarchids and rivalled in size by Quetzalcoatlus and Hatzegopteryx[12][23][24] (and possibly Cryodrakon).[23] Azhdarchids were split into two primary categories: short-necked taxa with short, robust beaks (i.e. Hatzegopteryx[25] and Wellnhopterus), and long-necked taxa with longer, slenderer beaks (i.e. Zhejiangopterus). Of these, Arambourgiania is of uncertain affiliation.[26] Based on the limb morphology related azhdarchids such as Zhejiangopterus and Quetzalcoatlus and pterosaurs at large, in addition to azhdarchid tracks from South Korea, Arambourgiania was likely quadrupedal.[27][28][24] As a pterosaur, Arambourgiania would have been covered in hair-like pycnofibres, and had extensive wing-membranes, which would have been distended by a long wing-finger.[26] There have been various models of the morphology of pterodactyloid wings,[24] though multiple well-preserved specimens suggest that azhdarchids had broad wings, with a brachiopatagium extending down to the ankle. The aspect ratio of azhdarchid wings was 8.1, similar to that of storks and birds of prey that engage in static soaring (relying on air currents to gain altitude and remain aloft).[27]

Anatomy

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Neck vertebra of Arambourgiania (F) alongside those of other azhdarchids

Arambourgiania is known from fragmentary remains, including an incomplete holotype cervical vertebrae, other partial cervical vertebrae, a partial radius and humerus, two phalanges (bones that make up the toes), and a partial femur.[13] The holotype of Arambourgiania, UJA VF1, consists of a very elongated cervical vertebra, probably the fifth one in the cervical series. Today the middle section is missing; the original material combined with its plaster was about 62 cm (2 ft 0.41 in) long, but had been sawed into three parts. Martill et al. (1998) estimated its complete length at 77–78 cm (2 ft 6.31 in – 2 ft 6.71 in) based on the related Quetzalcoatlus. 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 a complete vertebra, and a piece is absent from its posterior end as well.[1]

The posterior (back) portion of the vertebra is 44 mm (1.73 in) horizontally at its smallest point and 55 mm (2.17 in) vertically at its smallest point with a near circle-shaped cross section. As for the anterior (front) portion, the carina sagitalis ventralis is blunt and merges into the spinous process, making it have a low and slim profile. Arambourgiania preserves a circular, internal tube inside of the cervical vertebrae, a feature observed in other azhdarchids and the Dsungaripteridae.[2] The pneumatophores of the holotype cervical vertebra are significantly larger than its neural canal, a trait corresponding with maturity indicating adulthood, though to an extent unseen in other azhdarchids. Arambourgiania lacks a dorsally (top) positioned pneumatic foramen above its neural canal, a trait typically present in relatives like Cryodrakon, distinguishing it from other azhdarchids.[29] Fragments of other cervical vertebrae have been unearthed from Jordan as well as in the United States, though none as complete as the holotype. A fragment of a neural arch from either an anterior dorsal vertebra or a cervical 7, but it is too incomplete and worn to surmise much information.[3]

Of the topotype specimens, several come from the limbs. The proximal portion of a left metacarpal IV is known, with a preserved length of 128 mm (5.04 in). The internal structure has a D-shaped cross section and a thin covering of cortical bone. The distal (part away from body) portion of an abraded left femur was also unearthed, with a total preserved length of 142 mm (5.59 in). Its shaft has an ovular to compressed ovular cross section from shaft to distal end. The bone is gently curved, as is typical of femora. A probable distal radius fragment is 108 mm (4.25 in), though is extremely worn. Its posterior end is more expanded at its proximal end than the anterior end, a trait typical of pterosaur wings.[3] An incomplete ulna unearthed in Morocco was referred to Arambourgiania and has a preserved length of 362 mm (1 ft 2.25 in) leading to an estimated complete length of 600–700 mm (1 ft 11.62 in – 2 ft 3.56 in). As for its anatomy, it is laterally compressed with a broad tubercule on its distal end and low flange, similar to the condition seen in Azhdarcho.[12] The incomplete right humerus shaft referred to Arambourgiania measures 185 mm (7.28 in) in preserved length and 80 mm (3.15 in) in minimum dorsoventral (top down) width, making it smaller than that of Quetzalcoatlus. It bears both an ovular and D-shaped cross section at different points of the humerus' width as well as thin, 2 mm (0.08 in) cortical bone. This indicates a humerus composed of 90% air by volume, making it extremely well adapted for flight.[13]

Size

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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 77–78 cm (2 ft 6.31 in – 2 ft 6.71 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 ft 10 in) 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 (2 ft 2 in) long, which results in a ratio of 1.18. This neck length is among the largest known for a non-sauropod tetrapod, exceeding those of animals like the extant giraffe, the extinct mammals Paraceratherium, the extinct reptile Tanystropheus, and dinosaurs like Gigantoraptor and Therizinosaurus.[5][30] Applying that 1.18 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.[2][1] 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.[10]

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.[31] 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.[32]

In his 2022 pterosaur book, Paul proposed that Arambourgiania had a wingspan of 8 to 9 m (26 to 30 ft), making it smaller than that of Quetzalcoatlus northropi, 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 from Romania, which Paul situated at 10 to 12 m (33 to 39 ft). Just like both Arambourgiania and Quetzalcoatlus, Hatzegopteryx is also among the largest known flying animals to ever exist.[33] 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.[13] In 2018, "Sidi Chennane Azhdarchid" ulna that was referred to Arambourgiania was estimated to be smaller than other Arambourgiania individuals, with a wingspan of around 9 m (30 ft).[12]

Classification

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

Arambourgiania was initially assigned to a newly named subfamily called Azhdarchinae by Nesov in 1984, though 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.[34] Unaware of the creation of Azhdarchinae, American paleontologist Kevin Padian created the family Titanopterygiidae, which included both "Titanopteryx" and Quetzalcoatlus, which was created on the basis of cervical form and proportions, and it was differentiated from Pteranodontidae, which also received a definition by Padian the same year.[35][36] Two years later, in 1986, Padian would become aware of the existence of Azhdarchinae and would make Titanopterygiidae a junior synonym of it, as he believed that the diagnoses of the cervical vertebrae for both groups were identical. He removed Azhdarchinae from Pteranodontidae based on his previous diagnoses, and he would further elevate it to family level, creating Azhdarchidae as it is known today.[37][36] Since the 1980s, many genera have been named or reassigned to the genus, with fossils of azhdarchids known from every continent besides Antarctica.[11][16]

The placement of Arambourgiania within the family Azhdarchidae has been consistent in various studies, which is in a derived (advanced) position in the subfamily Quetzalcoatlinae. However, its specific location within the group has been somewhat disputed. One of the closest relatives of Arambourgiania is Quetzalcoatlus, as both pterosaurs have consistently been found together in multiple phylogenetic analyses, either as sister taxa or close to each other.[38][36][39] 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.[40][41][42]

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 Quetzalcoatlinae as the sister taxon to both species of Quetzalcoatlus, Q. northropi and Q. lawsoni.[36] 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.[42]

In some studies, the azhdarchids Mistralazhdarcho (above) and Aerotitan (below) have been recovered as the closest relatives of Arambourgiania

Paleobiology

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Feeding and ecological niche

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Life reconstruction of two Arambourgiania fighting over a small theropod

In 2008, Mark Witton and Darren Naish pointed out that although azhdarchids have historically been considered to have been scavengers, probers of sediment, swimmers, waders, aerial predators, or stork-like generalists, most researchers until that point had considered them to have been skim-feeders living in coastal settings, which fed by trawling their lower jaws through water while flying and catching prey from the surface (like skimmers and some terns). In general, pterosaurs have historically been considered marine piscivores (fish-eaters), and despite their unusual anatomy, azhdarchids have been assumed to have occupied the same ecological niche. Witton and Naish noted that evidence for this mode of feeding lacked support from azhdarchid anatomy and functional morphology; they lacked cranial features such as sideways compressed lower jaws and the shock-absorbing adaptations required, and their jaws instead appear to have been almost triangular in cross-section, unlike those of skim-feeders and probers.[27]

Witton and Naish instead stated that azhdarchids probably inhabited inland environments, based on the taphonomic contexts their fossils have been found in (more than half the fossils surveyed were from for example fluvial or alluvial deposits, and most of the marine occurrences also had fossils of terrestrial lifeforms), and their morphology made them ill-suited for lifestyles other than wading and foraging terrestrially, though their feet were relatively small, slender, and had pads, not suited for wading either. These researchers instead argued that azhdarchids were similar to storks or ground hornbills, generalists they termed "terrestrial stalkers" that foraged in different kinds of environments for small animals and carrion, supported by their apparent proficiency on the ground and relatively inflexible necks. Witton and Naish suggested that their more generalist lifestyle could explain the group's resilience compared to other pterosaur lineages, which were not thought to have survived until the late Maastrichtian like the azhdarchids did (pterosaurs went extinct along with the non-bird dinosaurs during the Cretaceous-Paleogene extinction event 66 million years ago).[27][12]

Witton elaborated in a 2013 book that the proportions of azhdarchids would have been consistent with them striding through vegetated areas with their long limbs, and their downturned skull and jaws reaching the ground. Their long, stiffened necks would be an advantage as it would help lowering and raising the head and give it a vantage point when searching for prey, and enable them to grab small animals and fruit.[27] The prevalence of Arambourgiania fossils in oceanic deposits suggests that it died at sea or was washed out.[2][43] This includes the oceanic deposits at the Coon Creek Formation,[21] the Ruseifa Formation,[4][1] and the Khouribga Phosphates.[12] However, in a 2021 study , Labita and Martill noted that azhdarchids might have been less terrestrial than suggested by Witton and Naish, since the Moroccan azhdarchid fossils were from marine strata, as was Arambourgiania. They noted that no azhdarchids had been found in truly terrestrial strata,[11] and proposed they could instead have been associated with aquatic environments, such as rivers, lakes, marine and off-shore settings.[44]

Locomotion

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

Witton summarized ideas about azhdarchid flight abilities in 2013, and noted they had generally been considered adapted for soaring, although some have found it possible their musculature allowed flapping flight like in swans and geese. Their short and potentially broad wings may have been suited for flying in terrestrial environments, as this is similar to some large, terrestrially soaring birds. Albatross-like soaring has also been suggested, but Witton thought this unlikely due to the supposed terrestrial bias of their fossils and adaptations for foraging on the ground. Studies of azhdarchid flight abilities indicate they would have been able to fly for long and probably fast (especially if they had an adequate amount of fat and muscle as nourishment), so that geographical barriers would not present obstacles.[26]

Possible azhdarchid trackway Haenamichnus from Korea (left) and feeding posture inferred from the tracks

Azhdarchids are the only group of pterosaurs to which trackways have been confidently assigned, such as Haenamichnus from Korea, which matches this group in shape, age, and size.[45] One long trackway of this kind shows that azhdarchids walked with their limbs held directly underneath their body, and along with the morphology of their feet indicates they were more proficient on the ground than other pterosaurs.[26] Terrestrial locomotion in azhdarchids like Quetzalcoatlus likely involved a pacing gait, wherein the limbs on one side of the body would move at roughly the same time, followed by those of the opposite side. For example, the forelimb on one side of the body would lift off the ground and move forward first, to avoid colliding with the hind foot, and the hind limb would follow suit. The forefoot would be planted in the ground just before the hind foot. Once the stride completed, the same process would repeat on the opposite side of the body.[26][24]

A 2024 study by paleontologist Kierstin Rosenbach and colleagues included the description of the humerus of Arambourgiania. They compared it to that of soaring birds and suggested that Arambourgiania itself was also a soarer. The humeral shaft displays several adaptations to soaring flight, such as its arrangement of diaphyseal ridges which are similar to those in vultures. The humerus also lacks struts, a trait associated with torsional loadings from soaring. Soaring is defined as sustained powered flight that needs launch and maintenance flapping, whereas gliding is sustained by gravity. This is in contrast to the contemporary pterosaur Inabtanin, which had a style of flight closer to those of continuously flapping birds. The ability for large azhdarchids like Arambourgiania to soar corresponds with geologic data, with Arambourgiania living in a marine environment suggesting that it and other giant azhdarchids were volant and could implement thermal soaring in their flight.[13]

Neck biomechanics

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Skeletal diagrams showing Zhejiangopterus (left, as preserved without skull, right, as reconstructed), one of the two other azhdarchids known preserved with a relatively complete neck (the other is Quetzalcoatlus)

The lithe, thin-walled vertebrae of Arambourgiania indicate the neck was much weaker than that of Hatzegopteryx. This can be quantified using relative failure force, which is the bone failure force of a vertebra divided by the body weight of the pterosaur that it belongs to, estimated at 180 to 250 kg (400 to 550 lb) for Arambourgiania and Hatzegopteryx. While Arambourgiania's neck vertebrae fail at about half of its body weight, the posterior neck vertebrae of Hatzegopteryx can withstand anywhere between five and ten body weights, depending on the loading of the bone. Even the hypothetically longer anterior neck vertebrae of Hatzegopteryx would be able to withstand four to seven body weights.[25] Although the centrum of Arambourgiania is much more lighltly built than that of Hatzegopteryx, their ratios of bone radius to bone thickness (R/t)[28] are roughly the same (9.45 for Hatzegopteryx and 9.9 for Arambourgiania). This may represent a compromise between increasing bending strength and buckling strength. Higher R/t ratios lead to improved bending strength, but weaker buckling strength. To compensate for this, Hatzegopteryx shows a number of other adaptations to improve buckling strength, namely the distinctive internal structures of the bones and the large articular joints of the vertebrae, the latter of which helps to distribute stress.[25] In order to support the robust head, the neck of Hatzegopteryx was likely strongly muscled, in contrast to that of Arambourgiania with its fewer muscle attachments.[25]

Paleoecology

[edit]
Map of Europe and the Middle East during the Maastrichtian, showing the extent of the Tethys Sea.

Fossils of Arambourgiania are confidently known only from Ruseifa, Jordan, though specimens potentially belonging to the genus have been described from Morocco and the Southern United States as well. In Jordan and Morocco, Arambourgiania fossils come from sites that during the Maastricthian were covered by the Tethys Sea.[46] This was a large sea extending across Europe, the Middle East, and North Africa during the Late Cretaceous and Paleogene. Other Maastrichtian-aged azhdarchid pterosaurs are known from the Tethys Sea as well, including Inabtanin from Jordan, Phosphatodraco, a Quetzalocatlus-like azhdarchid, and possibly Arambourgiania itself from Morocco,[31][12] Hatzegopteryx and several other azhdarchids from Romania,[47][48][49] and indeterminate azhdarchids from Spain[50] and France.[51][11]

Jordan

[edit]

In Jordan, Arambourgiania fossils have been unearthed from a series of phosphate mines in Ruseifa dating to the Maastrichtian age of the Late Cretaceous period (72-66 Ma). During this time period, Jordan was underwater and located at the southern margin of the Mediterranean Tethys Sea.[52] These phosphate mines have been labeled as the Ruseifa Formation,[52] Amman Formation,[53] or the Al-Hasa Phosphorite Formation, with little consensus on a formal name.[54] However, the Ruseifa Formation is the most recently adopted and commonly used title. The Ruseifa Formation, the underlying Wadi Sir Formation, and the overlying Muwaqqar Formation make up the Balqa Group. The Ruseifa Formation is composed of four units, the first of which is the origin of many Arambourgiania fossils.[2] The phosphates where Arambourgiania is known from have been interpreted as a deep marine environment whereas the higher layers belong to shoreline environments.[13] However, other researchers have stated that these phosphates are derived from a shallow marine deposit.[55][56]

Fossils here are preserved through the infilling of bone by limestone matrix, resulting in well preserved, 3D fossils being available for study.[13] Contemporary fauna to Arambourgiania from the phosphates includes a diversity of marine reptiles including the mosasaurids Globidens, Platecarpus, Prognathodon, and Halisaurus, many of which are known from teeth, indeterminate elasmosaurids, indeterminate chelonoids, and an isolated crocodyliform tooth.[54] Fish are also prevalent in this formation, with bony fishes known from the enchodontid Enchodus, aulopiform Stratodus, pycnodontid Stephanodus, anguillioform Pseudoegertonia, and indeterminate pycnodontids. As for the cartilaginous fishes, the sharks Cretolamna, Scapanorhynchus, Squalicorax, Plicatoscyllium, and the ray Rhombodus have been found in the Ruseifa phosphates.[57] This faunal composition is very similar to that of the Maastrichtian of Syria and the rest of the Mediterranean Tethys Sea.[43][54]

See also

[edit]

References

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