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Quetzalcoatlus

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Quetzalcoatlus
Temporal range: Late Cretaceous (Maastrichtian), 68–66 Ma
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Skeletal reconstruction of Q. lawsoni
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Order: †Pterosauria
Suborder: †Pterodactyloidea
Family: †Azhdarchidae
Subfamily: †Quetzalcoatlinae
Genus: †Quetzalcoatlus
Lawson, 1975
Type species
†Quetzalcoatlus northropi
Lawson, 1975
Other species
  • †Q. lawsoni
    Andres and Langston Jr., 2021
Synonyms

Quetzalcoatlus (/kɛtsəlkoʊˈætləs/) is a genus of azhdarchid pterosaur that lived during the Maastrichtian age of the Late Cretaceous in North America. The first specimen, recovered in 1971 from the Javelina Formation of Texas, United States, consists of several wing fragments and was described as Quetzalcoatlus northropi in 1975 by Douglas Lawson. The first part of the name refers to the Aztec serpent god of the sky, Quetzalcōātl, while the second part honors Jack Northrop, designer of a tailless fixed-wing aircraft. The remains of a second species were found between 1972 and 1974, also by Lawson, around 40 km (25 mi) from the Q. northropi locality. In 2021, these remains were assigned the name Quetzalcoatlus lawsoni by Brian Andres and (posthumously) Wann Langston Jr.

Quetzalcoatlus northropi has gained fame as a candidate for the largest flying animal ever discovered, though estimating its size has been difficult due to the fragmentary nature of the only known specimen. Wingspan estimates over the years have ranged from 5.2–25.8 m (17–85 ft), though this has more recently been narrowed down to around 10–11 m (33–36 ft) based on extrapolations from more complete members of the Azhdarchidae, the family to which Quetzalcoatlus belongs. The smaller and more complete Q. lawsoni had a wingspan of around 4.5 m (15 ft). The proportions of Quetzalcoatlus were typical of azhdarchids, with a very long neck and beak, shortened non-wing digits that were well adapted for walking, and a very short tail.

Historical interpretations of the diet of Quetzalcoatlus have ranged from scavenging to skim-feeding like the modern skimmer bird. However, more recent research has found that it most likely hunted small prey on the ground, in a similar way to storks and ground hornbills. This has been dubbed the terrestrial stalking model and is thought to be a common feeding behavior among large azhdarchids. On the other hand, the second species, Q. lawsoni, appears to have been associated with alkaline lakes, and a diet of small aquatic invertebrates has been suggested. Similarly, while Q. northropi is speculated have been fairly solitary, Q. lawsoni appears to have been highly gregarious (social).

For years it was uncertain how Quetzalcoatlus took off. Early models using a bipedal (two-legged) posture, such as that of Sankar Chatterjee and R.J. Templin in 2004, were heavily reliant on a relatively low body weight (about 70 kg (150 lb) in Chatterjee and Templin's case) and struggled to explain how takeoff was achieved. Based on the work of Mark P. Witton and Michael Habib in 2010, it now seems likely that pterosaurs, especially larger taxa such as Quetzalcoatlus, launched quadrupedally (from a four-legged posture), using the powerful muscles of their forelimbs to propel themselves off the ground and into the air.

Research history and taxonomy

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Discovery and naming

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The first Quetzalcoatlus fossils were discovered in Texas from the Maastrichtian Javelina Formation at Big Bend National Park (dated to around 68 million years ago[1]) in 1971 by Douglas A. Lawson, who was then a geology graduate student from the Jackson School of Geosciences at the University of Texas, Austin.[2] The material initially recovered consisted of a left radius and ulna, several fused carpals, and the end of the fourth metacarpal (the bone of the hand to which the wing digit attached). Altogether, the material comprised a partial left wing from an individual (TMM 41450-3) later estimated at over 10 m (33 ft) in wingspan.[3] Further material from the same specimen was later uncovered in the form of a humerus and the first two phalanges (finger bones) of the wing, though were initially catalogued instead as TMM 41450-1.[4] In a thesis discussing the paleoecology of the Big Bend, Lawson gave the remains the provisional name "Pteranodon gigas", suggesting that they belonged to an animal "nearly twice as large as any previously described species of Pteranodon".[5]

Cast of the holotype humerus

In 1973, Mr. William Amaral discovered a second Big Bend site, around 40 km (25 mi) from the first.[6] Field crews from the University of Texas, led by Wann Langston Jr. of the Texas Memorial Museum, investigated the so-called Amaral site between 1973 and 1974, and unearthed three fragmentary skeletons of much smaller individuals. In 1975, Lawson announced the original find in an article in Science, and stated that a detailed description of both TMM 41450-3 and the Amaral specimens was in preparation.[7] This initial effort led nowhere, and such a description was only published in 2021.[5] Instead, Lawson published a letter to the same journal a few months after his original announcement, in which he designated the humerus of TMM 41450-3 as the holotype of a new genus and species, Quetzalcoatlus northropi. The genus name refers to the Aztec feathered serpent god, Quetzalcōātl.[8] The specific name honors John Knudsen Northrop, the founder of Northrop Corporation, who drove the development of large tailless flying wing aircraft designs resembling Quetzalcoatlus.[5] From 1975–1983, additional Quetzalcoatlus specimens were collected from the Big Bend, including skull remains, ribs, cervical vertebrae and limb elements. In 1979, Wann Langston Jr. uncovered wing elements associated with a humerus (TMM 42138-1.2), an element previously only known from TMM 41450-3. Expeditions between 1987–1996 yielded only fragmentary material.[4]

Taxonomic history

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The holotype specimen of Q. northropi was not properly described and diagnosed until 2021,[5] and until then, the status of the genus Quetzalcoatlus was noted as problematic. Mark Witton et al. noted that the holotype of Q. northropi represents elements which are typically considered undiagnostic to generic or specific level and that this complicates interpretations of azhdarchid taxonomy. For instance, Witton et al. suggested that the Q. northropi type material is of generalized enough morphology to be near identical to that of other giant azhdarchids, such as the overlapping elements of the contemporary Romanian giant azhdarchid Hatzegopteryx. Assuming that Q. northropi could be distinguished from other pterosaurs (i.e., if it was not a nomen dubium), the possibility of it representing the same taxon as Hatzegopteryx was noted. However, Witton et al. also noted that the skull material of Hatzegopteryx and then-unnamed Q. lawsoni differ enough that they cannot be regarded as the same taxon.[9] These issues could only be resolved by Q. northropi being demonstrated as a valid taxon and its relationships with Q. lawsoni being investigated. An additional complication to these discussions is the likelihood that huge pterosaurs, such as Q. northropi, could have made transcontinental flights, suggesting that locations as disparate as North America and Europe could have shared giant azhdarchid species.[9]

A 2008 Mark Witton depiction of Q. northropi made to illustrate the then-novel terrestrial stalker hypothesis. Though this theory remains accepted, the anatomy is now considered inaccurate.[10]

Initially, it was assumed that the smaller specimens of Quetzalcoatlus were juvenile or subadult forms of the larger Q. northropi. Later, when more remains were found, the possibility emerged that they belonged to a separate species. This possible second species from Texas was provisionally referred to as a Quetzalcoatlus sp. by Alexander Kellner and Wann Langston Jr. in 1996, indicating that its status was too uncertain to give it a full new species name.[6] The smaller specimens are more complete than the Q. northropi holotype, and include four partial skulls, though they are much less massive, with an estimated wingspan of 4.5–5.5 m (15–18 ft).[5][11] This species was named Q. lawsoni in 2021, in honor of the genus' original describer.[5]

Reclassified or indeterminate fossils

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In 1982, fragmentary azhdarchid remains, in the form of a wing phalanx, a partial femur, a vertebra and a tibia, were uncovered in strata from the Dinosaur Park Formation of Canada.[12] While initially assigned to Quetzalcoatlus,[13] the discovery of additional remains allowed its referral to a new genus and species, Cryodrakon boreas, in 2019.[14] In 1986, jaws and cervical (neck) vertebrae from a pterosaur were uncovered in the Javelina Formation, from which the original specimens of Quetzalcoatlus originated. In his 1991 book on pterosaurs, Peter Wellnhofer assigned the remains to Quetzalcoatlus sp.,[15] leading to a reconstruction by illustrator John Sibbick of a Quetzalcoatlus with a short beak. In 2021, Brian Andres and Wann Langston Jr. dubbed the short-beaked Javelina pterosaur Wellnhopterus brevirostris, after Wellnhofer and the shortness of its beak.[5] The same remains were named "Javelinadactylus sagebieli" in a now-retracted paper by Hebert Campos.[16] An azhdarchid cervical (neck) vertebra (BMR P2002.2), discovered in 2002 in strata from the Maastrichtian age Hell Creek Formation (alongside a Tyrannosaurus rex specimen), was originally assigned to Quetzalcoatlus.[17] In 2021, Andres and Langston Jr. determined that BMR P2002.2 was a putative azhdarchiform.[5] A cervical vertebra (FSAC-OB 14) similar to that of Quetzalcoatlus is known from Mongolia.[18]

Description

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Size

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See also: Pterosaur size
Size comparison of a human to Q. northropi (green) and Q. lawsoni (blue)

Quetzalcoatlus is regarded as one of the largest pterosaurs,[19] though its exact size has been dificult to determine. In 1975, Douglas Lawson compared the wing bones of Quetzalcoatlus northropi to equivalent elements in Dsungaripterus and Pteranodon and suggested that it represented an individual with a wingspan of around 15.5 m (51 ft), or, alternatively, 11 m (36 ft) or 21 m (69 ft).[7] Estimates put forward in subsequent years varied dramatically, ranging from 5.2–25.8 m (17–85 ft), owing to differences in methodology.[5] From the 1980s onwards, estimates were narrowed down to 11–12 m (36–39 ft).[5] More recent estimates based on greater knowledge of azhdarchid proportions place its wingspan at 10–11 m (33–36 ft).[9][20] Q. lawsoni was estimated to have a wingspan of around 4.5 m (15 ft).[5] In 2022, Gregory S. Paul estimated that Q. lawsoni had a wingspan of 5 m (16 ft) and a body length of 3.5 m (11 ft).[21]

Comparison of Q. northropi with a Cessna 172 light aircraft.

Body mass estimates for giant azhdarchids are problematic because no existing species shares a similar size or body plan, and in consequence, published results vary widely.[3] Crawford Greenewalt gave mass estimates of between 30–440 kg (66–970 lb) for Q. northropi, with the former figure assuming a small wingspan of 5.2 m (17 ft).[8] A majority of estimates published since the 2000s have hovered around 200–250 kg (440–550 lb).[22][19] In 2021, Kevin Padian and his colleagues estimated that Q. lawsoni would have weighed 20 kg (44 lb).[20] In 2022, Gregory S. Paul estimated that Q. lawsoni had a body mass of 65 kg (143 lb).[21]

Skull

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A complete skull of Quetzalcoatlus is not known, so reconstructions necessarily draw from the eight specimens of Q. lawsoni that preserve skull elements. The skull of Q. lawsoni, based on the length of the mandible, was about 94–96 cm (37–38 in) long.[5][6] Like other azhdarchoids, it had a long, toothless beak that consisted largely of the premaxilla and maxilla. The nasoantorbital fenestra, an opening combining the external naris (nostril) and antorbital fenestra, was very large, with more than 40% of its height being above the orbit. The orbit is small and obovate (an inverted egg shape).[5] At the base of the beak, formed from the premaxilla, was a crest, referred to by some authors as a sagittal crest.[5][6] Though its exact form has yet to be determined, it is possible, based on what is preserved, that two distinct morphotypes exist: one with a squared sagittal crest and a tall nasoantorbital fenestra, and one with a more semicircular sagittal crest and a shorter nasoantorbital fenestra. The beak was long and slender. Its tip is not preserved in any specimen, so it is not clear how it was shaped.[5] The beak likely had a gape of around 52 degrees.[6] The mandibular symphyses would have widened slightly as the jaw opened, widening it to a certain degree, which has led to suggestions of some sort of gular pouch.[5][6]

Postcrania

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Skull reconstruction of Q. lawsoni

Quetzalcoatlus had nine elongated cervical (neck) vertebrae that were compressed dorsoventrally (top to bottom), and accordingly better suited for dorsoventral motion than lateral (side-to-side) motion. However, the lateral range of motion was still extensive, and the neck and head could swing left and right about 180 degrees.[20][23] The neural spine of the seventh cervical vertebra was short, unlike in other azhdarchids.[5] The vertebrae at the base of the neck and the pectoral girdle (shoulder girdle) are poorly preserved. The first four dorsal (back) vertebrae are fused into a notarium, as in some other pterosaurs and birds: the vertebral count of the notarium is unlike Zhejiangopterus, which may be a close relative, but like Azhdarcho. Most other dorsal vertebrae are absent, except for those integrated into the sacrum. Seven true sacral vertebrae are preserved. No caudal (tail) vertebrae are preserved. The pelvis of one Q. lawsoni specimen (TMM 41954-57) is large compared to that of other specimens, with deep posterior (rear) emargination and no preserved symphisis. This suggests sexual dimorphism similar to that suggested for other monofenestratans (i.e. Darwinopterus, Anhanguera and Nyctosaurus).[20]

Based on the limb morphology of Q. lawsoni, related azhdarchids such as Zhejiangopterus and other pterosaurs, Quetzalcoatlus was likely quadrupedal.[3][19][20] Quetzalcoatlus and other azhdarchids have fore and hind limb proportions more similar to modern running ungulate mammals than to members of other pterosaur clades, implying that they were uniquely suited to a terrestrial lifestyle.[3] The humerus was short and robust, with considerable mobility, whereas the femur was more gracile. The wing finger may have been held between the body and proximal limb elements whilst on land.[20] The first digit is the smallest, and the third is the biggest, with the exception of the wing finger.[5] Like in all pterosaurs, forelimb musclature was extensive, and flapping power came from several muscle groups on the torso, forearm and manus (hand).[19] Terrestrial locomotion in Quetzalcoatlus likely involved a pacing gait, wherein the limbs on one side of the body would move at 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 was completed, the same process would repeat on the opposite side of the body.[20]

Classification

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A comparison of Quetzalcoatlus cervical vertebrae on the left with the Phosphatodraco holotype on the right

When describing Quetzalcoatlus in 1975, Douglas Lawson and Crawford Greenewalt opted not to assign it to a clade more specific than Pterodactyloidea,[8] though comparisons with Arambourgiania (then Titanopteryx) from Jordan had been drawn earlier that year.[7] In 1984, Lev Alexandrovich Nessov erected the subfamily Azhdarchinae within Pteranodontidae to contain Azhdarcho, Quetzalcoatlus, and Titanopteryx.[24] Unaware of that subfamily, in the same year, Kevin Padian erected the family Titanopterygiidae to accommodate Quetzalcoatlus and Titanopteryx, defining it based on the length and general morphology of the cervical vertebrae.[25] Two years later, in 1986, noting commonalities not only in contained genera but in diagnostic features, he rendered Titanopterygiidae a junior synonym of Azhdarchinae, elevating the latter to family level and forming the family Azhdarchidae.[26] In 2003, the clade Azhdarchoidea was defined by David Unwin. Azhdarchids were determined to form a clade, Neoazhdarchia, with Tapejaridae. Montanazhdarcho from North America and Zhejiangopterus from China were incorporated into Azhdarchidae.[27] In the supplementary material for their 2014 paper describing Kryptodrakon progenitor, Andres, James Clark and Xing Xu named a new subfamily, Quetzalcoatlinae, of which Quetzalcoatlus is the type genus.[28]

The relationship between Quetzalcoatlus and other giant azhdarchids, like Arambourgiania and Hatzegopteryx, is not certain. In 2021, Brian Andres recovered them as sister taxa, with Arambourgiania being the sister taxon of Quetzalcoatlus and Hatzegopteryx being slightly more basal.[29] However, Rodrigo V. Pêgas et al., in 2022, instead recovered Quetzalcoatlus as part of one of two quetzalcoatline branches, alongside Cryodrakon; the other giant azhdarchid genera were recovered on the other branch.[30] A similar dichotomy was recovered by Leonardo Ortiz David et al. that same year, with the inclusion of Thanatosdrakon as Quetzalcoatlus' sister genus.[31]

The first of the below phylogenetic analyses shows the results of Andres (2021).[29] The second shows the results of Ortiz David et al. (2022).[31]

Paleobiology

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Feeding and ecological niche

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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.[3]

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).[3][32]

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.[33] In a 2021 study, Labita and Martill noted that azhdarchids might have been less terrestrial than suggested by Witton and Naish, since azhdarchid fossils were known from marine strata, such as Phosphatodraco from Morocco and Arambourgiania from the phosphates of Jordan. They noted that no azhdarchids had been found in truly terrestrial strata, and proposed they could instead have been associated with aquatic environments, such as rivers, lakes, marine and off-shore settings.[34]

Q. northropi is found in plains deposits, and due to the paucity and location of its remains, was speculated by Thomas Lehman to have been a solitary hunter that favoured riparian environments. Q. lawsoni, however, is found in great numbers in facies that likely represent alkaline lakes. It may have lived like modern gregarious wading birds, feeding on small invertebrates such as annelids, crustaceans and insects that inhabit such environments. The two species, if contemporaneous, were likely separated by such behavioural and ecological differences.[35]

Pterosaurs are generally thought to have gone gradually extinct by decreasing in diversity towards the end of the Cretaceous, but Longrich and colleagues suggested this impression could be a result of the poor fossil records for pterosaurs (the Signor-Lipps Effect). Pterosaurs during this time had increased niche-partitioning compared to earlier faunas from the Santonian and Campanian ages, and they were able to outcompete birds in large size based niches, and birds therefore remained small, not exceeding 2 m (6.6 ft) wingspans during the Late Cretaceous (most pterosaurs during this time had larger wingspans, and thereby avoided the small-size niche). To these researchers, this indicated that the extinction of pterosaurs was abrupt instead of gradual, caused by the catastrophic Chicxulub impact. Their extinction freed up more niches that were then filled by birds, which led to their evolutionary radiation in the Early Cenozoic.[32]

Locomotion

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

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.[33]

Azhdarchids are also the only group of pterosaurs to which trackways have been assigned, such as Haenamichnus from Korea, which matches this group in shape, age, and size. 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. According to Witton, their proportions indicate they were not good swimmers, and though they could probably launch from water, they were not as good at this as some other pterosaur groups.[33]

Flight

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Restoration of a Quetzalcoatlus in flight

The nature of flight in Quetzalcoatlus and other giant azhdarchids was poorly understood until serious biomechanical studies were conducted in the 21st century. A 1984 experiment by Paul MacCready used practical aerodynamics to test the flight of Quetzalcoatlus. MacCready constructed a model flying machine or, ornithopter, with a simple computer functioning as an autopilot. The model successfully flew with a combination of soaring and wing flapping.[36] The model was based on a then-current weight estimate of around 80 kg (180 lb), far lower than more modern estimates of over 200 kg (440 lb).[37] The method of flight in these pterosaurs depends largely on their weight, which has been controversial, and widely differing masses have been favored by different scientists. Some researchers have suggested that these animals employed slow, soaring flight, while others have concluded that their flight was fast and dynamic.[3] In 2010, Donald Henderson argued that the mass of Q. northropi had been underestimated, even the highest estimates, and that it was too massive to have achieved powered flight. He estimated it in his 2010 paper as 540 kg (1,190 lb), and argued that it may have been flightless.[37]

Quetzalcoatlus skeleton mounted in a flying pose at the Royal Ontario Museum.

Other flight capability estimates have disagreed with Henderson's research, suggesting instead an animal superbly adapted to long-range, extended flight. In 2010, Mike Habib, a professor of biomechanics at Chatham University, and Mark Witton, a British paleontologist, undertook further investigation into the claims of flightlessness in large pterosaurs. After factoring wingspan, body weight, and aerodynamics, computer modeling led the two researchers to conclude that Q. northropi was capable of flight up to 130 km/h (80 mph) for 7 to 10 days at altitudes of 4,600 m (15,000 ft). Habib further suggested a maximum flight range of 13,000–19,000 km (8,000–12,000 mi) for Q. northropi.[38] Henderson's work was also further criticized by Witton and Habib in another study, which pointed out that, although Henderson used excellent mass estimations, they were based on outdated pterosaur models, which caused Henderson's mass estimations to be more than double what Habib used in his estimations and that anatomical study of Q. northropi and other big pterosaur forelimbs showed a higher degree of robustness than would be expected if they were purely quadrupedal.[19] This study proposed that large pterosaurs most likely utilized a short burst of powered flight to then transition to thermal soaring.[23] However, a study from 2022 suggests that they would only have flown occasionally and for short distances, like the Kori bustard (the world's heaviest bird that actively flies) and that they were not able to soar at all.[39] Studies of Q. northropi and Q. lawsoni published in 2021 by Kevin Padian et al. instead suggested that Quetzalcoatlus was a very powerful flier.[20]

Launching

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Early interpretations of Quetzalcoatlus launching relied on bipedal models. In 2004, Sankar Chatterjee and R.J. Templin used a 70 kg (150 lb) model and utilised a running launch cycle powered by the hind limbs, in which Q. northropi was only barely able to take off.[40] In 2008, Michael Habib suggested that the only feasible takeoff method for a 200–250 kg (440–550 lb) Quetzalcoatlus was one that was mainly powered by the forelimbs.[41] In 2010, Mark Witton and Habib noted that the femur of Quetzalcoatlus was only a third as strong as what would be expected from a bird of equal size, whereas the humerus is considerably stronger, and affirmed that an azhdarchid the size of Quetzalcoatlus would have great difficulty taking off bipedally. Thus, they considered a quadrupedal launching method, with the forelimbs applying most of the necessary force, a likelier method of takeoff.[19] In 2021, Kevin Padian et al. attempted to resurrect the bipedal launch model, using a comparatively light weight estimate of 150 kg (330 lb). They suggested that Quetzalcoatlus' hind limbs were more powerful than previously suggested, and that they were strong enough to launch its body as high as 8 ft (2.4 m) off the ground without the aid of the forelimbs. A large breastbone would support the necessary muscles to create a flight stroke, allowing Quetzalcoatlus to gain enough clearance to begin the downstrokes needed for takeoff. Padian et al. also suggested that the legs and feet were likely tucked under the body during flight, as in modern birds.[20]

Paleoenvironment

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Quetzalcoatlus is known from the Lancian portion of the Javelina Formation, in a fauna dominated by Alamosaurus.[42] It co-existed with another azhdarchid known as Wellnhopterus, as well as an additional pterosaur taxon, suggesting a relatively high diversity of Late Cretaceous pterosaur genera.[18][5] The depositional environment represents a floodplain which was probably semi-arid, analogous in terms of climate and flora to the coastal plains of southern Mexico, consisting of an evergreen or semideciduous tropical forest.[42][35] These forests consisted largely of angiosperm trees such as Javelinoxylon, conifers related to the modern Araucaria, and woody vines, with a closed canopy in excess of 30 m (98 ft) in height. The remains of both Quetzalcoatlus species are found in association with freshwater environments. Q. lawsoni, in particular, is strongly associated with abandoned channel and lake facies, which are rare in the Javelina Formation. These facies preserve a diverse fauna of gastropods and bivalves, though the vertebrate fauna known from other aquatic environments belonging the Javelina, such as crocodiles, fishes and turtles, are absent. This suggests that the environment was inhospitable compared to normal stream channels, and high carbonate precipitation suggests that the water may have been highly alkaline. Eggshell fragments that may be attributable to Quetzalcoatlus suggest that they may have nested around alkaline lakes.[35]

Cultural significance

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Models on London's South Bank for the Royal Society's 350th anniversary exhibition

In 1975, artist Giovanni Caselli depicted Quetzalcoatlus as a small-headed scavenger with an extremely long neck in the book The evolution and ecology of the Dinosaurs[43] by British paleontologist Beverly Halstead. Over the next twenty-five years prior to future discoveries, it would launch similar depictions colloquially known as "paleomemes" in various books, as noted by Darren Naish.[44]

In 1985, the US Defense Advanced Research Projects Agency (DARPA) and AeroVironment used Q. northropi as the basis for an experimental ornithopter unmanned aerial vehicle (UAV). They produced a half-scale model weighing 18 kg (40 lb), with a wingspan of 5.5 m (18 ft). Coincidentally, Douglas A. Lawson, who discovered Q. northropi in Texas in 1971, named it after John "Jack" Northrop, a developer of tailless flying wing aircraft in the 1940s.[45] The replica of Q. northropi incorporates a "flight control system/autopilot which processes pilot commands and sensor inputs, implements several feedback loops, and delivers command signals to its various servo-actuators". It is on exhibit at the National Air and Space Museum.[46]

In 2010, several life-sized models of Q. northropi were put on display on London's South Bank as the centerpiece exhibit for the Royal Society's 350th-anniversary exhibition. The models, which included both flying and standing individuals with wingspans of over 10 m (33 ft), were intended to help build public interest in science. The models were created by scientists from the University of Portsmouth.[47]

See also

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References

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  1. ^ Lehman, Thomas M.; Mcdowell, Fred W.; Connelly, James N. (2006). "First isotopic (U-Pb) age for the Late Cretaceous Alamosaurus vertebrate fauna of West Texas, and its significance as a link between two faunal provinces". Journal of Vertebrate Paleontology. 26 (4): 922–928. doi:10.1671/0272-4634(2006)26[922:FIUAFT]2.0.CO;2. S2CID 130280606.
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Bibliography

[edit]
  • Wellnhofer, P. (1991). The Illustrated Encyclopedia of Pterosaurs. Crescent Books. ISBN 978-0-517-03701-0.
  • Witton, M. P. (2013). Pterosaurs: Natural History, Evolution, Anatomy (1st ed.). Princeton University Press. ISBN 978-0-691-15061-1.
[edit]
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