Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators - PubMed (original) (raw)

Neck biomechanics indicate that giant Transylvanian azhdarchid pterosaurs were short-necked arch predators

Darren Naish et al. PeerJ. 2017.

Abstract

Azhdarchid pterosaurs include the largest animals to ever take to the skies with some species exceeding 10 metres in wingspan and 220 kg in mass. Associated skeletons show that azhdarchids were long-necked, long-jawed predators that combined a wing planform suited for soaring with limb adaptations indicative of quadrupedal terrestrial foraging. The postcranial proportions of the group have been regarded as uniform overall, irrespective of their overall size, notwithstanding suggestions that minor variation may have been present. Here, we discuss a recently discovered giant azhdarchid neck vertebra referable to Hatzegopteryx from the Maastrichtian Sebeş Formation of the Transylvanian Basin, Romania, which shows how some azhdarchids departed markedly from conventional views on their proportions. This vertebra, which we consider a cervical VII, is 240 mm long as preserved and almost as wide. Among azhdarchid cervicals, it is remarkable for the thickness of its cortex (4-6 mm along its ventral wall) and robust proportions. By comparing its dimensions to other giant azhdarchid cervicals and to the more completely known necks of smaller taxa, we argue that Hatzegopteryx had a proportionally short, stocky neck highly resistant to torsion and compression. This specimen is one of several hinting at greater disparity within Azhdarchidae than previously considered, but is the first to demonstrate such proportional differences within giant taxa. On the assumption that other aspects of Hatzegopteryx functional anatomy were similar to those of other azhdarchids, and with reference to the absence of large terrestrial predators in the Maastrichtian of Transylvania, we suggest that this pterosaur played a dominant predatory role among the unusual palaeofauna of ancient Haţeg.

Keywords: Azhdarchids; Biomechanics; Cretaceous; Maastrichtian; Pterosaurs.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1

Figure 1. Giant azhdarchid cervical vertebra referred to Hatzegopteryx sp. (A–D) line drawings of EME 315 in anterior (A) right lateral (B) ventral (C) and dorsal (D) views; (E) proportions of EME 315 compared to other azhdarchid cervicals: note atypical combination of length/width ratio (l:w) and length compared to other azhdarchid cervicals, and especially against the only other known giant cervical, Arambourgiania (UJA RF1).

Light shading indicates damage; dark shading indicates filler. Abbreviations: co, cotyle; hy, hypapophysis; nc, neural canal; nsa; neural spine (anterior region); nsp, neural spine (posterior region); pnf, pneumatic foramen; prz, prezygapophysis; poz, postzygapophysis; vprzt, ventral prezygapophyseal tubercle (fused cervical rib). Scale bar is 100 mm.

Figure 2

Figure 2. Characteristics of azhdarchid vertebrae across their cervical series, demonstrated by several azhdarchid taxa.

(A) Azhdarcho lancicollis cervical III (ZIN PH 131/44), left lateral aspect; (B–C) Quetzalcoatlus sp. cervical III (TMM 41544.16) in dorsal (B) and left lateral (C) aspect; (D) A. lancicollis cervical IV (ZIN PH 144/44), left lateral aspect; (E) Q. sp. cervical V (TMM 41455.15), left lateral aspect; (F) Arambourgiania philadelphiae cervical V (UJA VF1), dorsal aspect; (G–H) A. lancicollis cervical VI (ZIN PH 147/44) in left lateral (G) and posterior (H) aspect (note especially large neural spine); (I) A. lancicollis cervical VII (ZIN PH 138/44), dorsal aspect; (J) Phosphatodraco cervical VII (OCP DEK/GE 111), left lateral aspect; (K) A. lancicollis cervical VIII (ZIN PH 137/44), dorsal aspect. Abbreviations as for Fig. 2, also with con; condyle; ex, exapophysis; ns, neural spine. (A, D, G–H) and (K) after Averianov (2010); (F) after Frey & Martill (1996); (J) after Suberbiola et al. (2003).

Figure 3

Figure 3. Relationships between azhdarchid cervical vertebrae to cervical III–VII length.

Figure 4

Figure 4. Metrics and cross sections used in estimates of bending strength analysis.

(A) EME 315 in dorsal view showing line of modelled section (dotted line) and projected 300 mm length; (B) UJA VF1 in dorsal view showing line of section and projected 770 mm length (Frey & Martill, 1996); (C) cross section and dimensions of EME 315; (D) cross section of UJA VF1. Note difference in shape and bone wall thicknesses in (C) and (D).

Figure 5

Figure 5. Measured and estimated azhdarchid pterosaur neck lengths against approximate wingspans.

Figure 6

Figure 6. Speculative skeletal reconstructions of Hatzegopteryx sp. and Arambourgiania philadelphiae (estimated wingspans ≥10 m—Frey & Martill, 1996; Buffetaut, Grigorescu & Csiki, 2003) to show discrepancy in neck length alongside a ‘typical’ azhdarchid body plan.

(A) Hatzegopteryx skeleton in lateral aspect; (B) dorsal view of EME 315 and FGGUB R1083 jaw elements, proportionate to actual size, suggesting Hatzegopteryx bore a wide, as well as relatively short, neck construction (soft-tissue outline in black). Jaw width after Buffetaut, Grigorescu & Csiki (2003); (C) reconstructed Arambourgiania philadelphiae cervicals III–VII in lateral aspect; (D) 4.6 m wingspan Q. sp. skeleton in lateral aspect; (E) Q. sp. cervical vertebrae III–V and skull in dorsal view; Note how the neck length of Hatzegopteryx is similar to this much smaller pterosaur. H. thambema holotype (FGGUB R1083) and undescribed referred elements are shown in (A); known elements of A. philadelphiae (UJA JF1) indicated in white shading in (C). Scale bar represents 1 m.

Figure 7

Figure 7. Azhdarchid craniocervical skeleton compared to those of some other tetrapods.

(A) Tanystropheus cf. longobardicus; (B) reconstruction of Zhejiangopterus linhaiensis cervical skeleton, vertebral morphology adapted from Averianov (2010); (C) Giraffa camelopardalis; (D) Camelus dromedarius; (E) Odocoileus virginianus. Note that the mid-series vertebrae of all taxa—even those with highly complex, strongly-muscled neck skeletons—have reduced features compared to those at the posterior and anterior: the fact that azhdarchid mid-series cervicals have reduced features does not necessarily reflect underdeveloped cervical soft-tissues. (A) reconstructed from fossils illustrated by Rieppel et al. (2010); (B) reconstructed from Cai & Wei (1993) and Averianov (2010); (C–E) after Goldfinger (2004). Images not to scale.

Figure 8

Figure 8. Azhdarchid disparity in cranial and limb anatomy.

(A) ZIN PH 112/44, rostral fragment of Azhdarcho lancicollis showing concave dorsal skull margin (after Averianov, 2010); (B) anterior skull and mandible of TMM 42489-2, unnamed azhdarchid from the Javelina Formation, USA; (C) restored skull of Quetzalcoatlus sp. (based 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: car, 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. Scale bars represent 100 mm, except for A (10 mm).

Figure 9

Figure 9. Diversity in predicted life appearance and ecologies for giant azhdarchid pterosaurs.

(A) two giant, long-necked azhdarchids—the Maastrichtian species _Arambourgiania philadelphiae_—argue over a small theropod; (B) the similarly sized but more powerful Maastrichtian, Transylvanian giant azhdarchid pterosaur Hatzegopteryx sp. preys on the rhabdodontid iguanodontian Zalmoxes. Because large predatory theropods are unknown on Late Cretaceous Haţeg Island, giant azhdarchids may have played a key role as terrestrial predators in this community.

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