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A taxonomic revision of the Sinopterus complex (Pterosauria, Tapejaridae) from the Early Cretaceous Jehol Biota, with the new genus Huaxiadraco - PubMed

  • ️Sun Jan 01 2023

A taxonomic revision of the Sinopterus complex (Pterosauria, Tapejaridae) from the Early Cretaceous Jehol Biota, with the new genus Huaxiadraco

Rodrigo V Pêgas et al. PeerJ. 2023.

Abstract

Tapejarids are edentulous pterosaurs particularly abundant in the Chinese Jiufotang Formation, counting with over 10 described specimens and dozens of undescribed ones. A total of seven nominal tapejarid species (within two genera) have been proposed, though it is disputed how many of those are valid instead of sexual or ontogenetic morphs of fewer, or a single, species. However, detailed revisions of the matter are still lacking. In the present work, we provide a specimen-level survey of anatomical variation in previously described Jiufotang tapejarid specimens, as well as of six new ones. We present qualitative and morphometric comparisons, aiming to provide a basis for a taxonomic reappraisal of the complex. Our results lead us to interpret two Jiufotang tapejarid species as valid: Sinopterus dongi and Huaxiadraco corollatus (gen. et comb. nov.). Our primary taxonomic decisions did not rely around cranial crest features, which have typically been regarded as diagnostic for most of these proposed species albeit ever-growing evidence that these structures are highly variable in pterosaurs, due to ontogeny and sexual dimorphism. However, a reassessment of premaxillary crest variation in the Sinopterus complex reveals that while much of the observed variation (crest presence and size) can easily be attributed to intraspecific (ontogenetic and sexual) variation, some of it (crest shape) does seem to represent interspecific variation indeed. A phylogenetic analysis including the species regarded as valid was also performed.

Keywords: Allometry; Jiufotang Formation; Linear morphometrics; Ontogeny; Osteology; Phylogeny; Pterosaur; Taxonomy.

© 2023 Pêgas et al.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Sinopterus dongi holotype (IVPP V 13363).

(A) Skeleton overview; (B) left metacarpus; (C) left foot; (D) skull (right lateral view). (E–H) Respective schematic drawings. Abbreviations: ca, carpus; co, coracoid; cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; epi, epiphysis; etp, extensor tendon process; f, frontal; fe, femur; fpc, frontoparietal crest; h, humerus; ios, interorbital septum; l, left; lpt, lateral proximal tarsal; m, maxilla; mc, metacarpal; mt, metatarsal; n, nasal; naof, nasoantorbital fenestra; pm, premaxilla; ph, phalanx; pt, pteroid; ti, tibia; ul, ulna; r, right; rad, radius; sca, scapula; st, sternum. Scale bars: A, 50 mm; E, 50 mm; F, 20 mm; G, 10 mm; H, 20 mm.

Figure 2
Figure 2. Sinopterus gui holotype (BPV-077).

(A) Skeleton overview; (B) skull (left lateral view). (C and D) Respective schematic drawings. Abbreviations: co, coracoid; cv, cervical vertebra; d, dentary; dvs, dorsal vertebral series; f, frontal; fe, femur; fi, fibula; fpc, frontoparietal crest; h, humerus; is, ischium; j, jugal; l, left; mc, metacarpal; mt, metatarsal; n, nasal; naof, nasoantorbital fenestra; or, orbit; pt, pteroid; pu, pubis; prap, preacetabular process; ti, tibia; ul, ulna; r, right; rad, radius; sca, scapula. Scale bars: C, 50 mm; D, 50 mm.

Figure 3
Figure 3. Huaxiapterus jii holotype (GMN-03-11-001).

(A) Skeleton overview; (B) skull (left lateral view, slightly ventrolateral). (C and D) Respective schematic drawings. Abbreviations: ca, carpus; co, coracoid; cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; dv, dorsal vertebra; epi, epiphysis; fe, femur; h, humerus; j, jugal; l, left; mc, metacarpal; pm, premaxilla; ph, phalanx; pp, prepubis; pt, pteroid; ti, tibia; ul, ulna; r, right; rad, radius; sca, scapula; st, sternum. Scale bars: C, 50 mm; D, 20 mm.

Figure 4
Figure 4. Huaxiapterus corollatus holotype (ZMNH M813).

(A) Skeleton overview; (B) skull (right lateral view); (C) left metacarpus. (D–F) Respective schematic drawings. Abbreviations: ca, carpus; co, coracoid; cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; fe, femur; fpc, frontoparietal crest; h, humerus; l, left; m, maxilla; mand, mandible; mc, metacarpal; mt, metatarsal; n, nasal; naof, nasoantorbital fenestra; pm, premaxilla; ph, phalanx; pt, pteroid; ti, tibia; ul, ulna; r, right; rad, radius; sca, scapula; sk, skull. Scale bars: A, D, 100 mm; E, F, 10 mm.

Figure 5
Figure 5. Specimen D2525.

(A) Skeleton overview; (B) right foot; (C) right metacarpus. (D–F) Respective schematic drawings. Abbreviations: co, coracoid; cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; dsc, distal synpcarpal; etp, extensor tendon process; f, frontal; fe, femur; fpc, frontoparietal crest; gas, gastralia; h, humerus; ios, interorbital septum; is, ischium; l, left; lpt, lateral proximal tarsal; mc, metacarpal; mt, metatarsal; pc, preaxial carpal; ph, phalanx; poap, postacetabular process; pp, prepubis; prap, preacetabular process; psc, proximal syncarpal; pt, pteroid; pu, pubis; ti, tibia; ul, ulna; r, right; rad, radius; ri, rib; sca, scapula; st, sternum. Scale bars: D, 50 mm; E, 10 mm; F, 50 mm.

Figure 6
Figure 6. Huaxiapterus benxiensis holotype (BXGM V0011).

(A) Skeleton overview; (B) left metacarpus; (C) skull (left lateral view). (D–F) Respective schematic drawings. Abbreviations: cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; f, frontal; fe, femur; fpc, frontoparietal crest; h, humerus; ios, interorbital septum; j, jugal; l, left; m, maxilla; la, lacrimal; mc, metacarpal; mt, metatarsal; naof, nasoantorbital fenestra; np, nasal process; pm, premaxilla; ph, phalanx; pt, pteroid; ti, tibia; ul, ulna; r, right; rad, radius. Scale bars: 50 mm.

Figure 7
Figure 7. Sinopterus lingyuanensis holotype (JPM-2014-005).

(A) Skeleton overview; (B) right foot; (C) skull (left lateral view). (D–F) Respective schematic drawings. Abbreviations: art, articular; ca, carpus; cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; fe, femur; fpc, frontoparietal crest; h, humerus; ios, interorbital septum; j, jugal; l, left; lpt, lateral proximal tarsal; mc, metacarpal; mt, metatarsal; naof, nasoantorbital fenestra; np, nasal process; pm, premaxilla; ph, phalanx; pt, pteroid; pv, pelvis; t, tarsus; ti, tibia; ul, ulna; r, right; rad, radius; sca, scapula; sv, sacral vertebrae. Scale bars: D, 50 mm; E, 10 mm; F, 50 mm.

Figure 8
Figure 8. Huaxiapterus atavismus holotype (XHPM 1009).

(A) Skeleton overview; (B) skull (left lateral view). (C and D) Respective schematic drawings. Abbreviations: ca, carpus; cv, cervical vertebra; co, coracoid; d, dentary; d1–d4, digits 1–4; fe, femur; fpc, h, humerus; mand, mandible; mc, metacarpal; mt, metatarsal; pmc, premaxillary crest; ph, phalanx; ti, tibia; ul, ulna; r, right; rad, radius; sk, skull. Scale bars: 50 mm.

Figure 9
Figure 9. New specimen D4019.

(A) Skeleton overview; (B) skull (left lateral view). (C and D) Respective schematic drawings. Abbreviations: ca, carpus; cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; fpc, frontoparietala crest; h, humerus; j, jugal; m, maxilla; mc, metacarpal; mt, metatarsal; naof, nasoantorbital fenestra; pm, premaxilla; pmc, premaxillary crest; ph, phalanx; ti, tibia; ul, ulna; r, right; rad, radius; ri, rib; sk, skull. Scale bars: 50 mm.

Figure 10
Figure 10. New specimen BPMC 103.

(A) Skeleton overview; (B) skull (left lateral view); (C) metacarpus, distal region. (D–F) Respective schematic drawings. Abbreviations: cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; fpc, frontoparietala crest; h, humerus; j, jugal; m, maxilla; mc, metacarpal; mt, metatarsal; naof, nasoantorbital fenestra; pm, premaxilla; pmc, premaxillary crest; ph, phalanx; ti, tibia; ul, ulna; r, right; rad, radius; ri, rib; sk, skull. Scale bars: D, 50 mm; E, 20 mm; F, 10 mm.

Figure 11
Figure 11. New specimen BPMC 104.

(A) Skeleton overview; (B) skull (left lateral view); (C) left pelvis; (D) right femur; (E) right metatarsus; (F) right pelvis; (G) left metacarpus. (H–N) Respective schematic drawings. Abbreviations: cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; etp, extensor tendon process; fe, femur; h, humerus; il, illium; is, ischium; m, maxilla; mc, metacarpal; mt, metatarsal; naof, nasoantorbital fenestra; pfo, pneumatic foramen; pm, premaxilla; ph, phalanx; pp, prepubis; pu, pubis; pv, pelvis; ti, tibia; ul, ulna; r, right; sca, scapula; sk, skull; ti, tibia. Scale bars: H, 50 mm; I, 50 mm; J–N, 10 mm; G, 50 mm.

Figure 12
Figure 12. New specimen BPMC 105.

(A) Skeleton overview; (B) skull (left lateral view); (C) detail of right manus. (D–F) Respective schematic drawings. Abbreviations: ca, carpal; etp, extensor tendon process; h, humerus; j, jugal; l, left; mand, mandible; mc, metacarpal; naof, nasoantorbital fenestra; or, orbit; pm, premaxilla; pmc, premaxillary crest; ul, ulna; r, right; ra, radius; rap, retroarticular process; sca, scapula; sk, skull; ti, tibia. Scale bars: A, D, 50 mm; B, C, E, F, 20 mm.

Figure 13
Figure 13. New specimen BPMC 106.

(A) Skeleton overview; (B) skull (right lateral view). (C and D) Respective schematic drawings. Abbreviations: art, articular; cv, cervical vertebra; h, humerus; j, jugal; mc, metacarpal; np, nasal process; pm, premaxilla; po, postorbital; pt, pteroid; ul, ulna; rad, radius; sca, scapula; sk, skull. Scale bars: A, C, 50 mm; B, D, 10 mm.

Figure 14
Figure 14. New specimen BPMC 107.

(A) Skeleton overview; (B) skull (right lateral view); (C) left humerus; (D) sternum; (E) left foot; (F) right pelvis. (G–L) Respective schematic drawings. Abbreviations: art, articular; ca, carpus; cv, cervical vertebra; d, dentary; d1–d4, digits 1–4; dpc, deltopectoral crest; f, frontal; fe, femur; fpc, frontoparietal crest; h, humerus; il, illium; is, ischium; l, left; mc, metacarpal; mt, metatarsal; naof, nasoantorbital fenestra; pmc, premaxillary crest; ph, phalanx; poap, postacetabular process; pt, pteroid; pu, pubis; ti, tibia; ul, ulna; r, right; rad, radius; sca, scapula; st, sternum; uc, ulnar crest. Scale bars: A, B, G, H, 50 mm; I–K, 10 mm; L, 30 mm.

Figure 15
Figure 15. Resulting dendrogram of the UPGMA analysis.

Species names represent their holotypic specimens. Red indicates Morphotype I. Blue indicates Morphotype II.

Figure 16
Figure 16. Results of the PCA analyses.

(A) Graph based on components 1 and 2 of the analysis using mean values imputation for the missing data. (B) Graph based on components 1 and 2 of the analysis using iterative imputation for the missing data. Species names represent their holotypic specimens. Red indicates Morphotype I (polygon represents convex hull; ellipse represents the 95% confidence ellipse). Blue indicates Morphotype II (polygon represents convex hull; ellipse represents the 95% confidence ellipse).

Figure 17
Figure 17. Anatomical variation in the skull and wing in the Sinopterus complex.

(A) Schematic representation of skull and metacarpus + wing digit of Morphotype I (S. dongi). Based mainly on the holotype of S. dongi (IVPP V 13363), except for the premaxillary crest (based on the holotype of H. jii; GMN-03-11-001). (B) Schematic representation of skull and metacarpus + wing digit of Morphotype II (H. corollatus). Based mainly on the holotype of H. benxiensis (BXGM V0011). (A) and (B) are not to scale, but are both proportionately scaled to the same metacarpal IV length. Numbers indicate features that vary between S. dongi and H. corollatus (see text): (1) orbit shape; (2) quadrate reclination; (3) nasal process shape; (4) nasoantorbital fenestra length/height ratio; (5), premaxillary crest shape; (6) rostrum deflection; (7) metacarpal I length; (8) wing phalanx 4 length.

Figure 18
Figure 18. Nemicolopterus crypticus holotype (IVPP V-14377).

(A) Skeleton overview, and (B) schematic drawing. (C) Skull (right lateral view), and (D) schematic drawing. Abbreviations: cdv, caudal vertebrae; co, coracoid; cv, cervical vertebra; d1–d4, digits 1–4; f, frontal; fe, femur; h, humerus; hy, hyoid; il, illium; is, ischium; j, jugal; l, left; la, lacrimal; mand, mandible; mc, metacarpal; mt, metatarsal; naof, nasoantorbital fenestra; or, orbit; pa, parietal; pm, premaxilla; ph, phalanx; ti, tibia; r, right; sca, scapula. Scale bars: A–B, 100 mm; C–D, 5 mm.

Figure 19
Figure 19. Eopteranodon lii holotype (BPV 078).

(A) Counterpart; (B) main part. (C and D) Respective schematic drawings. Abbreviations: cv, cervical vertebra; co, coracoid; d1–d4, digits 1–4; fe, femur; fi, fibula; h, humerus; j, jugal; mand, mandible; mc, metacarpal; pmc, premaxillary crest; pe, pelvis; ph, phalanx; ti, tibia; ul, ulna; rad, radius. Scale bars: C, 50 mm; D, 10 mm.

Figure 20
Figure 20. Eopteranodon lii holotype (BPV 078) details.

(A) Close-up of the specimen’s main part, and (B) schematic drawing. Abbreviations: art, articular; d, dentary; h, humerus; m, maxilla; naof, nasoantorbital fenestra; pmc, premaxillary crest; ppm, posterior premaxillary process. Scale bars: 50 mm.

Figure 21
Figure 21. Time-calibrated strict consensus tree.

The two species of the Sinopterus complex here regarded as valid are indicated in dark red. 1: Tapejaromorpha. 2: Thalassodromidae. 3: Tapejaridae. 4: Caupedactylia. 5: Tapejarinae. 6: Sinopterinae. 7: Azhdarchomorpha. 8: Chaoyangopteridae. 9: Alanqidae. 10: Azhdarchidae.

Figure 22
Figure 22. Life reconstruction of the Jiufotang tapejarids.

The coexistence between Sinopterus dongi and Huaxiadraco corollatus comb. nov. in the Jiufotang paleoenvironment. Art: courtesy of Zhao Chuang.

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This work was supported by FAPESP (#2019/10231-6), the Hokkaido University DX Doctoral Fellowship (#JPMJSP2119), the Deep Time Peter Buck Postdoctoral Fellowship from National Museum of Natural History, Smithsonian Institution, the Fund from the Key Laboratory of Stratigraphy and Palaeontology, Ministry of Natural Resources (#KLSP2101). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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