Pterosaurs were the first vertebrates to evolve powered flight and the largest animals to ever take wing. The pterosaurs persisted for over 150 million years before disappearing at the end of the Cretaceous, but the patterns of and processes driving their extinction remain unclear. Only a single family, Azhdarchidae, is definitively known from the late Maastrichtian, suggesting a gradual decline in diversity in the Late Cretaceous, with the Cretaceous–Paleogene (K-Pg) extinction eliminating a few late-surviving species. However, this apparent pattern may simply reflect poor sampling of fossils. Here, we describe a diverse pterosaur assemblage from the late Maastrichtian of Morocco that includes not only Azhdarchidae but the youngest known Pteranodontidae and Nyctosauridae. With 3 families and at least 7 species present, the assemblage represents the most diverse known Late Cretaceous pterosaur assemblage and dramatically increases the diversity of Maastrichtian pterosaurs. At least 3 families—Pteranodontidae, Nyctosauridae, and Azhdarchidae—persisted into the late Maastrichtian. Late Maastrichtian pterosaurs show increased niche occupation relative to earlier, Santonian-Campanian faunas and successfully outcompeted birds at large sizes. These patterns suggest an abrupt mass extinction of pterosaurs at the K-Pg boundary.

Pterosaurs were winged cousins of the dinosaurs and lived from around 200 million years ago to 66 million years ago, when the last pterosaurs disappeared during the Cretaceous-Paleogene extinction that wiped out the dinosaurs. The pterosaurs are thought to have declined in diversity before their final extinction, suggesting that gradual processes played a major role in their demise. However, pterosaur fossils are very rare, and thus, it is unclear whether pterosaurs were really low in diversity at this time or whether these patterns merely result from a paucity of fossils. We describe new pterosaur fossils from the end of the Cretaceous in Morocco, including as many as 7 species. They represent 3 different families and show a large range of variation in size and skeletal proportions, suggesting that they occupied a wide range of ecological niches.

Funding: Research was supported by a Leverhulme Trust Research Leadership award to NRL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Data Availability: All relevant data are included in the paper and its Supporting Information files. The fossil material described here is permanently accessioned at the Faculté des Sciences Aïn Chock, Université Hassan II, Casablanca, Morocco, and is available to qualified researchers.

Copyright: © 2018 Longrich et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

A) Map showing the location of the phosphate mines in Morocco, (B) map showing Sidi Daoui and Sidi Chennane mines, and (C) stratigraphic column for the phosphates of the Sidi Daoui area (after [ 40 ]).

These processes—the Signor-Lipps Effect and changes in the quality of the fossil record—may drive the apparent decline in pterosaurs. If so, improved sampling should reveal additional diversity and disparity in the latest Cretaceous. To test this hypothesis, we studied a remarkable new collection of pterosaurs from the late Maastrichtian [ 38 , 39 ] phosphates of the Khouribga Plateau in Morocco ( Fig 1A ), North Africa [ 40 ]. Here we provide a preliminary description of this fauna and explore its implications for pterosaur extinction.

However, the pterosaur record is highly incomplete, raising the possibility that sampling artifacts drive these patterns. Sampling effects can cause abrupt extinctions to appear gradual [ 27 ], an artifact known as the Signor-Lipps Effect: the last fossil of a lineage appears some point before its extinction. When this artifact affects many species at once, it can cause catastrophic extinctions to appear drawn out [ 27 ]. The Signor-Lipps Effect should be strongest for groups with a highly incomplete record. Pterosaurs represent an extreme case, because their thin-walled, hollow bones have low preservation potential [ 2 ]. The gradual disappearance of pterosaur families, therefore, could be a sampling artifact. Similarly, observed declines in diversity [ 8 ] and disparity [ 9 ] could be driven by changes in the quality of the fossil record [ 8 , 9 ], given that the number of formations preserving pterosaurs declines from the Campanian to the Maastrichtian [ 8 ]. The completeness of pterosaur fossils also decreases [ 28 ] such that the available fossils may provide less information on species richness and disparity. Furthermore, the pterosaur record is dominated by Lagerstätten [ 8 , 11 , 28 , 29 ]—localities with exceptional preservation. Pterosaur diversity is concentrated in these Lagerstätten, notably the Solnhofen [ 2 ], Yixian, Jiufotang [ 11 ], Romualdo [ 2 , 30 , 31 ], Crato [ 10 ], Cambridge Greensand [ 32 , 33 ], and Niobrara [ 34 , 35 ] formations [ 2 , 5 , 10 ], such that a dozen such formations account for around half of known diversity [ 28 ]. However, no Lagerstätten are known from the final 15 million years of the Cretaceous. Finally, end Cretaceous pterosaurs are primarily known from terrestrial horizons, with few occurrences in marine settings [ 22 , 36 , 37 ], which may provide an incomplete record of marine lineages.

Along with a decline in number of families towards the Cretaceous–Paleogene (K-Pg) boundary, pterosaurs’ species richness [ 8 ] and morphological disparity [ 9 ] are thought to decrease prior to their ultimate extinction. These patterns have been interpreted as showing a gradual decline in pterosaur diversity in the late Cretaceous [ 26 ]. If so, the K-Pg extinction may have been the final blow to a group whose extinction had long been underway and was perhaps inevitable [ 6 ].

How and why this long-lived, diverse clade became extinct remains unclear. Pterosaur diversity declined in the mid-Cretaceous [ 5 , 7 , 8 ], but at least 4 clades—Azhdarchidae [ 2 ], Nyctosauridae [ 2 ], Pteranodontidae [ 2 ], and Tapejaridae [ 16 ]—and perhaps a fifth lineage, represented by the enigmatic Piksi barbarulna [ 20 ], persist into the final 25 million years of the Cretaceous, before seeming to gradually disappear towards the end of the Cretaceous. Only a single family, Azhdarchidae, is definitively known from the Maastrichtian [ 2 , 5 , 21 ]. The youngest pteranodontids are early Campanian in age [ 2 , 18 ]. Nyctosaurids persisted until the Campanian at least, but the youngest nyctosaurid, “Nyctosaurus” lamegoi, lacks formation-level provenance data [ 22 ] and may be Campanian or Maastrichtian [ 22 ], making the timing of extinction uncertain [ 22 ]. When Tapejaridae became extinct is also unclear. The Santonian Bakonydraco galaczi [ 23 ] has been interpreted as a tapejarid [ 24 ], extending tapejarids into the middle Late Cretaceous [ 23 ]; the tapejarid Caiuajara dobruskii [ 16 ] could be as young as Campanian or as old as Turonian [ 16 ]. The enigmatic Piksi is late Campanian [ 25 ] in age.

Pterosaurs first appear in the fossil record in the Late Triassic [ 1 – 3 ], tens of millions of years before birds took wing [ 4 ]. Like birds, pterosaurs were archosaurs capable of powered flight; unlike birds, they flew on membraneous wings, supported by an elongate fourth digit, and walked or climbed on all fours [ 2 , 5 , 6 ]. After appearing in the Triassic, pterosaurs radiated in the Jurassic [ 2 , 7 – 9 ], followed by a second radiation of advanced, short-tailed pterodactyloid pterosaurs in the Early Cretaceous [ 2 , 7 – 12 ]. By the mid-Cretaceous, pterosaurs had evolved aerial insectivores, carnivores, piscivores, durophages, and filter feeders [ 2 , 5 , 6 ] and exploited habitats from forests [ 13 ], lakes [ 12 ], coastal plains [ 14 ], and deserts [ 15 , 16 ] to shallow seas [ 2 ] and the open ocean [ 17 ]. The smallest pterosaurs had a wingspan of 50 cm or less [ 13 , 18 ]; the largest had wingspans of 10–11 m and weighed 200–250 kg [ 19 ], making them the largest flying animals ever to evolve.

Results

Geological setting The fossils described here come from the upper Maastrichtian phosphates of the Ouled Abdoun Basin, in northern Morocco. Commercial exploitation of the phosphates has uncovered large numbers of marine vertebrates [41] from the Maastrichtian and early Paleogene [41]. The Cretaceous fauna includes an extraordinary diversity of marine reptiles, including mosasaurs, plesiosaurs, and turtles [41,42], abundant and diverse bony fish [42], sharks [38], and pterosaurs [43], as well as rare dinosaurs [44,45]. Preliminary studies indicate that the fauna is the most diverse and abundant known Maastrichtian marine vertebrate assemblage. These beds have not been formally assigned to a formation; instead, a series of beds or “Couches” are informally designated for the purposes of the mining industry (Fig 1C). Couche III is Late Cretaceous in age, and Couche I and Couche II are early Paleogene. Vertebrate biostratigraphy places Couche III in the upper Maastrichtian [38], and carbon and oxygen isotope chemostratigraphy constrain Couche III to the latest Maastrichtian, within approximately 1 Ma of the K-Pg boundary [39]. The fauna therefore provides a picture of a marine ecosystem just before the K-Pg extinction. Until now, the pterosaur record from the assemblage comprised a single specimen, the holotype of the azhdarchid Phosphatodraco mauritanicus [43]. Over the past 3 years, we have worked with the local fossil industry to assemble a collection of pterosaurs that includes over 200 specimens, ranging from isolated bones to partial skeletons. This collection is currently the largest and most diverse collection of Maastrichtian pterosaurs in the world. Fossils primarily occur as disarticulated bones, but associated bones and, rarely, partial skeletons have also been recovered. Most come from dense, laterally extensive bonebeds in the middle of Couche III at Sidi Daoui, and a minority come from Couche III at Sidi Chennane (Fig 1B). Several specimens originate in a lower layer, about 2 m below Couche III, which is characterized by a fine, pale grey matrix and white bone. The age of these fossils is unknown, and thus, they are not described here.

Systematic paleontology The fauna comprises a minimum of 7 species, including 1 species of Pteranodontidae, 3 species of Nyctosauridae, and 3 species of Azhdarchidae. Archosauria Cope, 1869 Pterosauria Kaup, 1834 Pterodactyloidea Plieninger, 1901 Ornithocheiroidea sensu Kellner, 2003 [46] Pteranodontoidea sensu Kellner, 2003 [46] Pteranodontia sensu Unwin, 2003 [47] Pteranodontidae Marsh, 1876

Simurghia robusta gen. et sp. nov. urn:lsid:zoobank.org:act:CBA04F2E-D7BA-47BC-A76B-1096B1FE4354 Etymology. The genus name refers to the Simurgh, a flying beast from Persian mythology. The species name is from the Latin robusta, “robust.” Holotype. FSAC-OB 7 (Fig 10). PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 10. FSAC-OB 7, holotype right humerus, S. robusta. In (A), dorsal view, (B) ventral view, and (C) posterior view. Abbreviations: dpc, deltopectoral crest; msc, muscle scar; scpr, supracondylar process of the ectepicondyle; vp, ventral pillar; vt, ventral tubercle of the deltopectoral crest. https://doi.org/10.1371/journal.pbio.2001663.g010 Locality and horizon. Middle Couche III, Sidi Daoui, Khouribga Province, Morocco. Diagnosis. Large nyctosaurid, with a humerus that is approximately 165 mm long. The deltopectoral crest is proportionately short and broad, but the apex is strongly expanded with a strongly convex apical margin giving it a fan shape. The ventral pillar is shifted to the proximal margin of the deltopectoral crest. The humeral shaft is proportionately robust and distally expanded. The supracondylar process is hypertrophied and triangular. Description. Simurghia is a large nyctosaurid most closely resembling “N.” lamegoi in terms of size and morphology. The humeral head and ulnar crest are broken away. The humeral shaft is robust, with its distal half expanded and subtriangular as in other Pteranodontia. The deltopectoral crest resembles “N.” lamegoi in being proportionately short and broad, but with a prominent terminal expansion and a strong proximal prong of the apex, such that the proximal margin of the deltopectoral crest is strongly convex. As in other nyctosaurids, there is a strong ridge on the ventral surface of the deltopectoral crest, the ventral pillar, terminating in a tubercle at the apex. However, the ventral pillar lies along the proximal edge of the deltopectoral crest, as in “N.” lamegoi [2,22], whereas the pillar is more distally located in Nyctosaurus, Alcione, and Barbaridactylus. A muscle scar extends proximodistally across the neck of the deltopectoral crest, again as in Alcione. The distal condyles are not preserved, but there is an unusually large, subtriangular supracondylar process, an autapomorphy of Simurghia. Discussion. Simurghia is referred to Nyctosauridae on the basis of the deltopectoral crest, which is hatchet shaped, with a ventral pillar, and weakly curved but not warped. It differs from other nyctosaurids in the broad fan-shaped deltopectoral crest (S6 Fig), the position of the ventral pillar along the proximal margin of the crest, and the hypertrophied supracondylar process. Although Simurghia resembles Alcione, it is unlikely to represent an adult Alcione. Specimens referred to Alcione are all subadults or mature: bones have the dense, avascular surface texture that characterizes adult pterosaurs [51], the condyles are well ossified, the holotype scapulocoracoid is fused, and the synsacrum is fused in a referred specimen. Alcione humeri average 93 mm (n = 12) long and reach a maximum of 102 mm, versus an estimated 165 mm for Simurghia. Assuming isometric scaling, Simurghia would weigh 560% the mass of the average Alcione. Such an extreme size discrepancy exceeds what is expected for intraspecific variation or sexual dimorphism. Furthermore, there are no humeri that are intermediate in length, implying that the sample comes from 2 distinct populations of adults. Finally, Simurghia exhibits features—large size, the very broad, fan-like deltopectoral crest, and the position of the ventral pillar along the medial edge of the deltopectoral crest—that suggest affinities with “N.” lamegoi, not Alcione.

Barbaridactylus grandis gen. et sp. nov. urn:lsid:zoobank.org:act:626E3A52-74AB-401B-BCD9-8849FD4D43F0 Etymology. The genus name refers to North Africa’s Barbary Coast region and the Greek dactylo, “finger.” The species name is from the Latin grandis, “great.” Locality and horizon. Middle Couche III, Sidi Daoui, Khouribga Province, Morocco. Holotype. FSAC-OB 232 (Fig 11), associated skeleton including left humerus, radius and ulna, right femur, left scapulocoracoid, partial right mandible. PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 11. FSAC-OB 232, holotype skeleton of B. grandis. (A) Left humerus in anterior view, (B) right femur in anterior view, (C) right radius and ulna in posterior view, (D) cervical vertebra in ventral view, (E) left scapulocoracoid in medial view, and (F) posterior ramus of the right mandible in medial view. Abbreviations: co, coracoid; cot, cotyle of mandible; cvr, cervical ribs; dm, dorsal margin of mandible; dpc, deltopectoral crest; gl, glenoid; fh, femoral head; gt, greater trochanter; hh, humeral head; hyp, hypapophysis; olp, olecranon process; pex, postexapophysis; pn, pneumatopore; rad, radius; sca, scapula; scp, supracondylar process of the ectepicondyle; uc, ulnar crest; uln, ulna; vm, ventral margin of mandible. https://doi.org/10.1371/journal.pbio.2001663.g011 Referred specimens. FSAC-OB 8, 9, 10 (Fig 12), and 11, humeri. PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 12. FSAC-OB 8, right humerus of B. grandis. In (A), ventral view, (B) dorsal view, and (C) anterior view. Abbreviations: dpc, deltopectoral crest; hh, humeral head; uc, ulnar crest; pf, pneumatic foramen; vp, ventral pillar; vt, ventral tubercle. https://doi.org/10.1371/journal.pbio.2001663.g012 Diagnosis. Large nyctosaurid, with a humerus that is up to 225 mm long. The humerus is slender, with the deltopectoral crest well distal to the humeral head. The deltopectoral crest is short, broad, and subrectangular, with weak constriction; warping of the deltopectoral crest is weakly developed. The humeral head has large ventral pneumatic fossa and foramen/foramina. Small pneumatic foramina are proximal to the lateral condyle. The bones of the antebrachium are slender—130% of the humerus’s length. The femur is 85% of the humerus’s length, with a slender shaft and a moderately developed greater trochanter. Description. The type (Fig 11) preserves parts of the left and right mandible. There is a small cotyle posteriorly; ahead of this, the jaw becomes deeper and plate-like, with a thick ventral margin and a sharp occlusal margin. The dorsal margin is gently concave, indicating that the upper and lower jaws were upcurved as in other nyctosaurids. A single cervical is preserved. It is proportionately short and broad, as in other nyctosaurids [35] and pteranodontids. The scapulocoracoid is preserved in medial view. It resembles other nyctosaurids, being a boomerang-shaped element with the robust scapula and coracoid meeting at an angle of 60°. The 2 elements are fused, suggesting skeletal maturity [51]. The humeral head has a semicircular dorsal margin and a concave anterior ventral. The humeral shaft (Figs 11A and 12) is long and slender and sigmoidal in anterior view. The deltopectoral crest is distally placed relative to the humeral head, unlike Alcione but as in Nyctosaurus [35]. The deltopectoral crest is constricted at midlength and distally expanded to give it the characteristic hatchet shape. However, the deltopectoral crest is unusually short and broad. The distally expanded tip, which gives nyctosaurids the distinctive hatchet-shaped crest, is weakly developed, a primitive feature. In anterior view, the crest is slightly warped. This feature is very weakly developed compared to pteranodontoids such as Pteranodon but better developed than in other nyctosaurids. Ventrally, there is a prominent ventral pillar running from the apex down the shaft. Anterior to this is a muscle scar, running obliquely to the distal prong of the deltopectoral crest. The ventral surface of the humeral heads bears a large pneumatic fossa, with either a foramen or several small foramina. The presence, size, and position of this foramen are unique to Barbaridactylus among nyctosaurids. The ulnar crest is well developed and subtriangular in shape; it projects ventrally. Distally, there is an enlarged supracondylar process as in other nyctosaurids. There is a depression between the medial and lateral condyles, with a pneumatic foramen inside the depression, beneath the lateral condyle. A pair of small, elongate pneumatic foramina are present proximal to the lateral condyle, which appear to be unique to Barbaridactylus among nyctosaurs. The antebrachium resembles that of Nyctosaurus [35]. The ulna is relatively slender, in contrast to the robust ulna of Alcione, and weakly expanded at either end. The radius is about two-thirds of the diameter of the ulna. The femur resembles other nyctosaurids and pteranodontids [35] in having a sigmoidal shaft with a strong dorsal projection of the humeral head and a weakly developed greater trochanter. In contrast to Nyctosaurus [35] and Alcione, the femur lacks the strong distal expansion of the shaft. The end of the shaft is more gently expanded, as in Pteranodon [35]. Comments. Barbaridactylus is referred to Nyctosauridae on the basis of the deltopectoral crest, which is hatchet-shaped, with a ventral pillar, and weakly curved rather than warped in end view. It is distinguished from other nyctosaurids by its large size, long and slender humerus, quadrangular deltopectoral crest, and foramen/foramina on the anterior surface of the humerus below the deltopectoral crest. The pneumatic foramen is variable in Barbaridactylus, and it differs in size and morphology in all the individuals studied; in some individuals, it is developed as a single foramen, and in others, it is developed as a pair of foramina. Nevertheless, this feature is seen, where exposed, in all specimens referred to Barbaridactylus and is absent in other nyctosaur material. Barbaridactylus resembles “N.” lamegoi from the Campanian-Maastrichtian of Brazil [22] in terms of size and the broad deltopectoral crest and the proximally shifted ventral pillar. These affinities are supported by phylogenetic analysis (see below). However, it lacks the strongly pointed proximal prong of the deltopectoral crest seen in “N.” lamegoi, indicating that the 2 are distinct. Azhdarchoidea Kellner 2003 [46] Neoazhdarchia Kellner 2003 [46] Azhdarchidae Nessov 1984

Phosphatodraco mauritanicus Pereda-Suberbiola et al. 2003 [43] Referred material. FSAC-OB 12 (Fig 13), cervical vertebra C5, and FSAC-OB 13, cervical vertebra. PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 13. FSAC-OB 12 P. mauritanicus cervical vertebra. In (A), dorsal view, (B) ventral view, (C) left lateral view; (D) anterior view; (E) posterior view. Abbreviations: cot, cotyle; hyp, hypapophysis; nsp, neural spine; pex, postexapophysis; poz, postzygapophysis; prz, prezygapophysis. https://doi.org/10.1371/journal.pbio.2001663.g013 Description. The centrum of the referred cervical vertebra (Fig 13) measures 190 mm, and the maximum length of the vertebra is 210 mm. These measurements closely compare with cervical 6 of P. mauritanicus, which measures 196 mm and 225 mm, respectively [43]. The cervical is long and slender, as typical of Azhdarchidae [21]. The length of the vertebra is approximately 400% the width across the prezygapophyses, matching the proportions of cervical 6 of the holotype of Phosphatodraco, OCP DEK/GE 111 [43]. The centrum lacks lateral pneumatic foramina, as in other azhdarchids. Prominent postexapophyses project ventrolaterally. As in other Azhdarchidae, a hypapophysis projects anteriorly beneath the cotyle [21]. The anterior cotyle is flanked by grooves beneath the prezygapophyses, implying that the cervical ribs had not fused to the centrum to form transverse foramina. The animal may have been near maturity but was not skeletally mature. The neural arch is reduced and confluent with the body of the centrum. The prezygapophyses project anterodorsally, while the postzygapophyses project almost laterally. The neural spine is reduced as in other azhdarchids [21]; it forms small anterior and posterior blades, but between the 2 blades, the neural spine is not developed. Comments. The azhdharchid P. mauritanicus has previously been described from the phosphates [43]. The vertebra described here is consistent with Phosphatodraco in size and proportions, supporting referral to that taxon.

Azhdarchidae aff. Quetzalcoatlus Material. FSAC-OB 14, cervical vertebra C5 (Fig 14). PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 14. FSAC-OB 14, aff. Quetzalcoatlus cervical vertebra. In (A), dorsal view, (B) ventral view; (C), left lateral view, and (D), anterior view. Abbreviations: dlr, dorsolateral ridge; hyp, hypapophysis; nsp, neural spine; pex, postexapophysis; poz, postzygapophysis; prz, prezygapophysis; pzl, prezygapophyseal laminae; vfo, ventral fossa. https://doi.org/10.1371/journal.pbio.2001663.g014 Description. The cervical vertebra comes from a small azhdarchid; the centrum measures 153 mm. However, the surface bone lacks vascularization, and the cervical ribs are fused to the centrum. These features indicate that despite the animal’s small size, it was somatically mature [51]. The centrum is typical of Azhdarchidae in being elongate and lacking pneumatic foramina piercing the lateral surfaces. The elongate proportions of the vertebra indicate that it comes from the middle of the neck. Based on comparisons with Quetzalcoatlus [58], the vertebra is probably C4 or C5, most likely C5 given the similarities in shape. Centrum length is 440% of the width across the prezygapophyses, more elongate than the C5 of Phosphatodraco [43], where length is 356% of the prezygapophyseal width. The centrum differs from Phosphatodraco in being broad anteriorly but very narrow posteriorly; however, this feature is typical of Quetzalcoatlus [59]. Posteriorly, the centrum bears a deep ventral depression; a similar depression is present but much more weakly developed in Phosphatodraco. Lateral to the depression, a pair of prominent, subtriangular postexapophyses project laterally. Those of Phosphatodraco are more weakly developed. As in other Azhdarchidae, the neural arch is confluent with the centrum, with no clear separation between them. Anteriorly, the prezygapophyses are long and narrow, while those of Phosphatodraco are shorter and more ovoid. Two laminae extend from the prezygapophyses to the neural spine, forming a “V.” A similar feature is seen in Phosphatodraco, but here the ‘V’ extends further back so that the dorsal surface of the centrum is broadly exposed, which does not occur in Phosphatodraco. A pair of faint ridges extend back from the prezygapophyses onto the dorsal surface of the vertebra. Postzygapophyses are laterally projecting and shifted anteriorly. The neural spine is highly reduced as in other azhdarchids. Anteriorly, it forms a low ridge, which then becomes shallower posteriorly until near the middle of the centrum it forms a faint line running along the dorsal surface of the centrum. Comments. The new azhdarchid is smaller than Phosphatodraco but exhibits fusion between the cervical ribs and centrum and an avascular surface bone texture. This suggests that it is mature [51] and not a juvenile Phosphatodraco. The new azhdarchid also differs from P. mauritanicus in the strong tapering of the centrum posteriorly, the deep ventral fossa on the posterior end of the centrum, and the larger postexapophyses. These are derived features that are shared with Quetzalcoatlus [59] to the exclusion of Phosphatodraco and suggest affinities with that genus. Phylogenetic analysis places this azhdarchid as sister to a clade including Zhejiangopterus linhaiensis, Arambourgiania philadelphiae, Hatzegopteryx thambena, and Quetzalcoatlus spp.

Sidi Chennane Azhdarchid Material. FSAC-OB 203, left ulna missing proximal end (Fig 15). PPT PowerPoint slide

PowerPoint slide PNG larger image

larger image TIFF original image Download: Fig 15. FSAC-OB 203, giant azhdarchid (?Arambourgiania) ulna. Middle shaft and distal end of the left ulna, in posterior view. Abbreviations: ut, ulnar tubercle; vp, ventral process. https://doi.org/10.1371/journal.pbio.2001663.g015 Description. The ulna comes from a very large pterosaur. The preserved part of the bone, comprising the distal end and the middle of the shaft, measures 362 mm in length and may have been 600–700 mm long when complete. The shaft is 40 mm in diameter at its narrowest and 65 mm at its distal end. These proportions suggest a wingspan approaching 9 m. Overall, the shaft is proportionately long and slender. The shaft is broad proximally, narrows distally, and then gradually expands towards its distal end. The distal end bears a broad tubercle, as in Azhdarcho [21]. The ventral margin bears a long, low flange, again as in Azhdarcho. There is an articular surface dorsal to the tubercle, separated by a notch. Comments. The broad tubercle and low, proximodistally elongate ventral crest support azhdarchid affinities; the tubercle of Pteranodontidae is smaller, the ventral crest is much more pronounced, and the ulna is proportionately shorter and broader. Affinities with either Phosphatodraco or aff. Quetzalcoatlus appear unlikely given that the bone texture of both indicates that they are somatically mature. Affinities with or referral to the giant azhdarchid A. philadelphiae seem more likely given that both are known from late Maastrichtian deposits of the Tethys sea [37], but more complete material is needed to test this assignment. The animal approached Quetzalcoatlus in size, but it was much more lightly built and presumably weighed much less. These proportions presumably indicate a distinct flight mode and ecological niche, suggesting that giant pterosaurs occupied a range of niches.