Editing Quetzalcoatlus (section)

==Paleoecology==
[[File:AlamosaurusDB.jpg|thumb|left|Restoration of a herd of ''[[Alamosaurus]]'', a giant sauropod dinosaur characteristic of the fauna ''Quetzalcoatlus'' inhabited]]
Definitive fossils of ''Quetzalcoatlus'' have only been found from the [[Javelina Formation]] of Texas, though similar and potentially congeneric azhdarchids are known from isolated bones across North America. The formation consists of around {{cvt|140|m|ft}} of [[fluvial]] deposits from the middle to late [[Maastrichtian]], and is gradually overlain by [[Black Peaks Formation]] which contains the [[Cretaceous–Paleogene boundary]]. At the time of sedimentation, the coastline of the seaway was around {{cvt|300|to|400|km|mi}} southeast of the formation.<ref name="lehman2021"/> The fauna is dominated by the large [[sauropod]] ''[[Alamosaurus]]'', which has been considered characteristic of the fauna of the [[Lancian]] of southern [[Laramidia]], with ''Quetzalcoatlus'' noted in association despite its relative inabundance.<ref name="lehman2001">{{cite book|last=Lehman|first=T. M.|year=2001|chapter=Late Cretaceous dinosaur provinciality|title=Mesozoic Vertebrate Life|editor-last1=Tanke|editor-first1=D. H.|editor-last2=Carpenter|editor-first2=K.|publisher=Indiana University Press|pages=310–328}}</ref> Specimens of ''Quetzalcoatlus'' are only known from the upper half of the formation where they are the most common vertebrate, with [[magnetostratigraphy]] and [[uranium–lead dating]] demonstrating that these deposits were from the latest Maastrichtian around 67 to 66 [[million years ago]]. Additional pterosaur specimens that may be ''Quetzalcoatlus'' are found in older parts of the formation, though the single oldest pterosaur fossil belongs to the azhdarchid ''[[Wellnhopterus]]''. As ''Q. lawsoni'' is known only from the upper part of the formation, and those of ''Q. northropi'' are from the top of the Javelina or the base of the Black Peaks Formations, it is possible that the three taxa succeeded each other, though uncertainty allows for some overlap of the species of ''Quetzalcoatlus''.<ref name="lehman2021">{{cite journal|last1=Lehman|first1=Thomas M.|date=2021|title=Habitat of the giant pterosaur ''Quetzalcoatlus'' Lawson 1975 (Pterodactyloidea: Azhdarchoidea): A paleoenvironmental reconstruction of the Javelina Formation (Upper Cretaceous), Big Bend National Park, Texas|journal=Journal of Vertebrate Paleontology|volume=41|issue=sup1|pages=21–45|bibcode=2021JVPal..41S..21L|doi=10.1080/02724634.2019.1593184|s2cid=245009158|doi-access=free}}</ref>

Even if ''Q. lawsoni'' and ''Q. northropi'' coexisted, their remains are found in different [[facies]] so they may have lived in different habitats. Specimens of ''Q. northropi'' are found in stream-channel deposits consisting of [[sandstone]] and [[conglomerate (geology)|conglomerate]], where scattered skeletons, limb bones of ''Alamosaurus'', and local log jams are also found. In places, the conglomerates contain accumulations of small bones such as vertebrae, scales, teeth, and osteoderms of [[gar]], [[fish]], [[turtles]], and [[crocodilians]], and shells of [[gastropods]]. The flow in these streams fluctuated dramatically and was possibly [[ephemeral]] with short duration flooding events. While abandoned channel-lake deposits are the least common in the formation, most specimens of ''Q. lawsoni'' have been found in them. As the channels were abandoned or cut off from active flow, the lakes would develop where sediments would accumulate and occasionally be flooded by nearby streams. Burrows can be found throughout these deposits, bones are normally excrusted with [[calcite]], and the [[carbonate]]s present suggest photosynthetic algae and microbes as found in [[alkaline lake]]s. The lakes were several hundred meters wide but only a few meters deep at their maximum extent, though the main fossil layer is from a single prolonged lake development.<ref name="lehman2021"/>

The overbanks surrounding the channels and lakes were covered in a mature forest represented by ''[[Javelinoxylon]]'' and [[araucariaceae]]n conifers showing a warm, dry, and nonseasonal environment of a tropical lowland. Much of the wood is infested with dry-wood [[termites]]. Slender aquatic vines and [[palm frond]]s and stalks can be found throughout the abandoned channel-lake deposits. [[Bioturbation]] in the lakes show it supported an abundant fauna of soft-bodied [[invertebrates]] including [[crustacean]]s, [[insect]]s and [[annelid]]s with intermittent freshwater [[bivalve]]s and gastropods. Common aquatic vertebrates found elsewhere are absent, suggesting an inhospitable environment that was perhaps too [[alkaline]]. ''Q. lawsoni'' may have fed on the invertebrate fauna, and has a body plan similar to modern wading birds found in alkaline environments such as [[crane (bird)|cranes]] and [[storks]]. The area surrounding lakes was vegetated with palmetto palms and trees in an [[evergreen]] or [[semideciduous]] forest with a closed canopy over {{cvt|30|m|ft}} tall. No nearby elevation or branches were present to assist with launching for ''Q. lawsoni'' so it must have been capable of takeoff from limited open spaces and of aerial maneuvering in dense forest. ''Q. northropi'' in contrast is found in channels suggesting a [[riparian]] habitat and more solitary lifestyle, but its absence from other similar riparian habitats of the time suggests something was preferable about the Javelina environment. The floodplain would have has a mean average temperature of {{Convert|16–22|C|F|abbr=on}} and a dry and nonseasonal climate, so it ''Quetzalcoatlus'' did migrate in flocks, it would not have been in response to seasonality. The closest modern equivalent to the environment of ''Quetzalcoatlus'' would be the coastal plains of southern Mexico.<ref name="lehman2021"/>

=== Feeding and ecological niche ===
[[File:Arambourgiania philadelphiae.png|thumb|left|''Arambourgiania philadelphiae'', a close relative of ''Quetzalcoatlus'', squabbling over a small theropod captured on the ground]]
In 1975, Douglas Lawson rejected the notion that ''Quetzalcoatlus'' might have had a [[Piscivore|fish-eating]] (piscivorous) lifestyle like pteranodontids. The Big Bend site where the holotype was discovered is roughly {{Convert|250|mi|km|abbr=on}} removed from the coastline, and since Lawson believed that the river systems of the locality were too small to support an animal the size of ''Q. northropi'', he instead suggested that it was a scavenger, similar to vultures. The holotype was found in close association with the skeletons of ''[[Alamosaurus]]'', a [[Titanosauria|titanosaur]] [[Sauropoda|sauropod]], which Lawson cited as further evidence.<ref name="lawson1975" /> However, [[David Martill]] dismissed this connection, noting that the association was nothing more than circumstantial evidence.<ref name="witton&naish2008" /> Due to the light construction of ''Quetzalcoatlus''<nowiki/>' beak, it would have had to wait for other predators to open up a carcass before it could feed. Another issue is that, while many scavenging birds have extremely flexible necks allowing them to efficiently probe for meat, ''Quetzalcoatlus'' had a stiffer neck, and would not have had the same advantages. Since ''Q. lawsoni''<nowiki/>'s beak was relatively weak and unhooked, being compared by Wann Langston Jr. to chopsticks, it is unlikely that it could have torn flesh from a carcass.<ref name="padian2021" /> In the coming decades, further hypotheses regarding ''Quetzalcoatlus''<nowiki/>' ecology were put forward. Lev Alexandrovich Nesov, in 1984, suggested that ''Q. northropi'' and other azhdarchids were piscivorous after all, and that they were ecological analogs to modern [[Rynchops|skimmers]], which feed by skimming the water's surface.<ref name=":4" /> He did not, however, indicate any morphological indicators for this behavior, and indeed, azhdarchids lack many of the adaptations necessary for such a feeding method (such as robust, aerodynamic beaks with shock-absorbing structures, and the neck flexibility necessary for skimming). Thus, skimming is very unlikely.<ref name="witton&naish2008" /> Another hypothesis, proposed by Langston, is that azhdarchids probed for burrowing invertebrates, using its beak to pluck them from the substrate. Among the evidence provided by Langston was extensive [[bioturbation]] of the strata around ''Quetzalcoatlus'' fossils, indicative of extensive invertebrate activity;<ref name=":3" /> this has since been suggested to be totally circumstantial.<ref name="witton&naish2008" /> Such a lifestyle has subsequently been suggested for ''Q. lawsoni''.<ref name="lehman2021" /> However, wading animals tend to have large, long and broad feet, with a high surface area. This contrasts the morphology seen in ''Q. lawsoni'' and other azhdarchids, which had small, narrow feet.<ref name="witton&naish2008" />
[[File:Pterosaurs_at_Royal_Festival_Hall.jpg|thumb|Reconstruction of ''Q. northropi'' hunting terrestrially, on London's [[South Bank]] for the [[Royal Society]]'s 350th anniversary exhibition]]
The predominant model of azhdarchid feeding behavior is the "terrestrial stalking" hypothesis, which suggests that they fed upon small terrestrial prey. A predecessor to this hypothesis was proposed by [[Gregory S. Paul]] in a 1987 correspondence published in the journal ''[[Nature (journal)|Nature]].''<ref name=":5">{{Cite journal |last=Paul |first=Gregory S. |date=1987 |title=Pterodactyl habits — real and radio-controlled |url=https://www.nature.com/articles/328481a0 |journal=Nature |language=en |volume=328 |issue=6130 |pages=481 |doi=10.1038/328481a0 |bibcode=1987Natur.328..481P |issn=1476-4687}}</ref> Paul suggested that ''Q. northropi'' was analogous to modern storks, specializing in plucking small vertebrates, such as frogs and turtles, from around watercourses.<ref name=":5" /><ref>{{Cite book |last=Paul |first=Gregory S. |url=https://archive.org/details/dinosaurspastpre0000unse_t8m4 |title=Dinosaurs past and present |date=1987 |publisher=[Los Angeles, Calif.] : Natural History Museum of Los Angeles County in association with University of Washington Press, Seattle and London |others=Internet Archive |isbn=9780938644231 |editor-last=Czerkas |editor-first=Sylvia Massey |editor-link=Sylvia Czerkas |edition=2nd |chapter=The Science and Art of Restoring the Life Appearance of Dinosaurs and Their Relatives: A Rigorous How-to Guide |editor-last2=Olson |editor-first2=Everett C. |editor-link2=Everett C. Olson |chapter-url=http://gspauldino.com/Howto.pdf}}</ref> This initial iteration was supported by [[Sankar Chatterjee]] and R. J. Templin, who believed that many pterodactyloids adopted such a lifestyle.<ref name=":6" /> Lifestyles analogous to modern herons were also proposed by Kevin Padian and Donna Braginetz in 1988,<ref>{{Cite journal |last1=Padian |first1=Kevin |author-link1=Kevin Padian |last2=Braginetz |first2=Donna |date=1988 |title=The flight of pterosaurs |journal=Natural History |volume=12 |issue=97 |pages=58}}</ref> and by S. Christopher Bennett in 2001.<ref>{{Cite journal |last=Bennett |first=S. Christopher |date=January 30, 2001 |title=The Osteology and Functional Morphology of the Late Cretaceous Pterosaur Pteranodon Part I. General Description of Osteology |url=http://www.schweizerbart.de/papers/pala/detail/260/100954/The_Osteology_and_Functional_Morphology_of_the_Lat?af=crossref |journal=Palaeontographica Abteilung A |language=en |volume=260 |issue=1–6 |pages=1–112 |bibcode=2001PalAA.260....1B |doi=10.1127/pala/260/2001/1 |issn=0375-0442}}</ref> In a 2008 paper on the paleoecology of azhdarchids, [[Mark P. Witton|Mark Witton]] and [[Darren Naish]] reviewed previous models of their ecology and found the majority to be untenable. The anatomy possessed by azhdarchids was, to them, indicative of terrestrial prey capture. They argued that the family were ecologically closest to storks or [[ground hornbill]]s, and coined the term "terrestrial stalker" to collectively describe them.<ref name="witton&naish2008" /> 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.<ref name=":1" /> The internal anatomy of ''Q. lawsoni''{{'}}s cervical vertebrae suggests that it, and other mid-sized azhdarchids, may have been able to pick up prey animals weighing {{Convert|9–13|kg|lb|abbr=on}} at maximum; prey size would have been further limited by the size of ''Q. lawsoni''{{'}}s skull and [[Esophagus|gullet]] rather than body mass.<ref name=":2" /> ''Q. lawsoni''{{'}}s skull does not exhibit [[cranial kinesis]], meaning that the skull was essentially a rigid unit, and as such it was likely incapable of masticating hard objects.<ref name="padian2021" />

''Q. northropi'' fossils have been 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 favored [[Riparian zone|riparian]] environments. ''Q. lawsoni'', on the other hand, is found in great numbers in [[facies]] that likely represent [[Soda lake|alkaline lakes]]. It may have lived like modern [[Sociality|gregarious]] wading birds, feeding on small invertebrates such as [[annelid]]s, [[crustacean]]s and [[insect]]s that inhabit such environments, and using its beak to probe for burrowing invertebrates. The two species, if contemporaneous, were likely separated by such behavioral and ecological differences.<ref name="lehman2021" /> In a 2021 study, Claudio Labita and David 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.<ref name="pterosaur wing">{{cite journal |last1=Labita |first1=Claudio |last2=Martill |first2=David M. |date=2021 |title=An articulated pterosaur wing from the Upper Cretaceous (Maastrichtian) phosphates of Morocco |journal=Cretaceous Research |volume=119 |page=104679 |bibcode=2021CrRes.11904679L |doi=10.1016/j.cretres.2020.104679 |s2cid=226328607}}</ref>

Pterosaurs were 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 {{convert|2|m|ft|abbr=on}} 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]].<ref name="Longrich20182">{{cite journal |last1=Longrich |first1=Nicholas R. |last2=Martill |first2=David M. |last3=Andres |first3=Brian |last4=Penny |first4=David |date=2018 |title=Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary |journal=PLOS Biology |volume=16 |issue=3 |pages=e2001663 |doi=10.1371/journal.pbio.2001663 |pmc=5849296 |pmid=29534059 |doi-access=free}}</ref>

=== Contemporary fauna ===
Beyond the dominant sauropod ''Alamosaurus'' the Javelina Formation is known from a diverse vertebrate fauna throughout its channel, overbank, and lake deposits. Both the pterosaurs ''Quetzalcoatlus'' and ''Wellnhopterus'' are known, and the dinosaur megafauna is represented by the [[ceratopsids]] ''[[Bravoceratops]]'' and ''[[Torosaurus utahensis]]'', [[hadrosaurids]] assigned to ''[[Gryposaurus]]'', ''[[Kritosaurus]]'' and [[Saurolophinae]], [[ankylosaurs]], and an indeterminate species of ''[[Tyrannosaurus]]''.<ref name="lehman2021"/><ref name="lehman2016">{{cite journal |last1=Lehman |first1=Thomas M. |last2=Wick |first2=Steven L. |last3=Wagner |first3=Jonathan R. |year=2016 |title=Hadrosaurian dinosaurs from the Maastrichtian Javelina Formation, Big Bend National Park, Texas |journal=Journal of Paleontology |volume=90 |issue=2 |pages=1–24 |bibcode=2016JPal...90..333L |doi=10.1017/jpa.2016.48 |s2cid=133329640}}</ref> Smaller [[theropods]] including the [[dromaeosaurid]] ''[[Saurornitholestes]]'' and an indeterminate [[troodontid]] have been found, as well as a variety of fishes, smaller reptiles, and [[mammals]].<ref name="lehman2021"/><ref name="tweet2018">{{cite journal |last1=Tweet |first1=J.S. |last2=Santucci |first2=V.L. |year=2018 |title=An Inventory of Non-Avian Dinosaurs from National Park Service Areas |url=http://npshistory.com/publications/paleontology/nmmnhs-79-703.pdf |journal=New Mexico Museum of Natural History and Science Bulletin |volume=79 |pages=703–730}}</ref> Most fishes, smaller reptiles and mammals were found through the screening of [[microfossil]] localities, which also discovered scraps of dinosaurs. Fish include the [[stingray]] ''[[Dasyatis]]'', the [[bowfin]], the gar ''[[Atractosteus]]'', while amphibians include an indeterminate [[frog]], and reptiles are represented by the lizard ''[[Glyptosaurus]]'', the [[snake]] ''[[Dunnophis]]'', and the crocodile ''[[Brachychampsa]]''. Mammals are very common in microfossil sites of both the Black Peaks and Javelina Formations, represented in the latter by the [[multituberculate]]s ''[[Ptilodus]]'', ''[[Mesodma]]'', ''[[Stygimys]]'', and ''[[Viridomys]]'', indeterminate [[theria]]ns, and the [[metatheria]]ns ''[[Peratherium]]'', ''[[Gelastops]]'', ''[[Bryanictis]]'', ''[[Mixodectes]]'', ''[[Palaechthon]]'', ''[[Eoconodon]]'', ''[[Carsioptychus]]'', ''[[Haploconus]]'', ''[[Ellipsodon]]'', and ''[[Promioclaenus]]''.<ref name="standhardt1986">{{cite journal|last=Standhardt|first=B.R.|year=1986|title=Vertebrate paleontology of the Cretaceous/Tertiary transition of Big Bend National Park, Texas|journal=Unpublished Dissertation, Louisiana State University|pages=1–298}}</ref>