Formation specimen TMM 42489-2), and gracile forms with elongate rostra

(A) ZIN PH 112/44, rostral fragment of Azhdarcho lancicollis showing concave dorsal skull margin (following Averianov, 2010); (B) anterior skull and mandible of TMM Erior (H) aspect (note specially {large 42489-2, unnamed azhdarchid from the Javelina Formation, USA; (C) restored skull of Quetzalcoatlus sp. Scale bars represent 100 mm, except for a (10 mm).thick-walled cervicals of Hatzegopteryx, too as its typically reinforced bones and wide jaws (Buffetaut, Grigorescu Csiki, 2002; Buffetaut, Grigorescu Csiki, 2003), look much better suited to tackling bigger, more potent prey, or for utilizing greater force and violence when getting meals, than azhdarchid species with thin-walled bones, extended, gracile necks and narrow skulls. Undescribed fossils probably referable to Hatzegopteryx (like added skull and limb components that can't be described here) show that robust construction was consistent across its physique. The higher resistance to bending stresses and indications of significant cervical muscle tissues in Hatzegopteryx are consistent with this idea, as would be the inverse findings for Arambourgiania. Modern research on azhdarchid foraging behaviour recommend that they were terrestriallyforaging generalists (Witton Naish, 2008; Witton Naish, 2015; Carroll, Poust Varricchio, 2013; Witton, in press). What tiny is identified of giant azhdarchid anatomy is similar enough to that with the smaller sized, superior recognized azhdarchids to assume that in addition they foraged terrest.Formation specimen TMM 42489-2), and gracile forms with elongate rostra and slender jaws (Quetzalcoatlus sp.; Zhejiangopterus; Alanqa). Some azhdarchids also seem to possess somewhat slender rostra, as indicated by the concave dorsal skull margin of Azhdarcho (Fig. 8A, Averianov, 2010). A third category issues the wing skeletons: we note that the reasonably abbreviated metacarpal IV and proximal wing phalanx from the diminutive azhdarchid Montanazhdarcho minor contrasts markedly together with the elongate distal forelimb elements of Quetzalcoatlus sp. and Zhejiangopterus (McGowen et al., 2002). It has been speculated that azhdarchids could be roughly grouped into `robust' and `gracile' forms based on these variations (Witton, 2013). It certainly appears suitable to consider types like Hatzegopteryx `robust' and others--e.g., Quetzalcoatlus and Zhejiangopterus--`gracile', but some taxa show `mixed' anatomies (e.g., Montanazhdarcho has proportionally stocky wing bones, but elongate neck bones (McGowen et al., 2002)), suggesting these categories have to be considered loose. Azhdarchid physique plans may have been rather a lot more varied than imagined previously. Our assessment of vertebral mechanics in Hatzegopteryx and Arambourgiania suggests that azhdarchid necks had drastically distinctive functional capabilities. We presume that cranial and cervical disparity reflects distinct foraging habits and prey preferences, with robust azhdarchids tackling somewhat larger prey than their gracile counterparts. The stout,Naish and Witton (2017), PeerJ, DOI 10.7717/peerj.20/Figure 8 Azhdarchid disparity in cranial and limb anatomy. (A) ZIN PH 112/44, rostral fragment of Azhdarcho lancicollis showing concave dorsal skull margin (soon after Averianov, 2010); (B) anterior skull and mandible of TMM 42489-2, unnamed azhdarchid in the Javelina Formation, USA; (C) restored skull of Quetzalcoatlus sp. (depending on Kellner Langston Jr, 1996); (D) skull of Zhejiangopterus linhaiensis (based on Cai Wei, 1993); (E) MOR 69I, Montanazhdarcho minor holotype pectoral girdle and left forelimb (note stunted metacarpal IV); (F) M1323 postcrania of Z. linhaiensis. Abbreviations: vehicle, carpals; cer, cervical vertebrae; cor, coracoid; fem, femur; hum, humerus; mcIV, metacarpal IV; pt, pteroid; rad, radius; tib, tibia; ul, ulna; wpI, wing phalanx I.