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

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.

Allometric wing growth links parental care to pterosaur giantism

“…The allometric growth patterns ( figure 2 and table 1 ; electronic supplementary material, table S1) recovered by our multivariate approach are consistent with previous reports of allometry that used bivariate methods. These reports conclude that: (i) the ontogeny of Rhamphorhynchus shows near-isometry in wingspan, negative allometry in humerus, radius and metacarpal IV and positive allometry in WP2–3 relative to body length [ 16 ]; (ii) large specimens of Pterodactylus have significantly longer necks and skulls, and the metacarpal IV and proximal wing phalanges show positive allometry relative to the antebrachium and to distal wing phalanges [ 15 ]; (iii) sinopterine pterosaurs share isometry in the ulna, metacarpal IV and WP1–2, and positive allometry in the femur [ 29 ]; and (iv) Pteranodon shows negative allometry in tibia relative to femur and positive allometry in metacarpal IV relative to radius/ulna and to WP1 [ 14 ].…”

“…Measurements of 13 key skeletal dimensions were collected for allometric analysis: 1, skull length; 2, neck length; 3, tail length; 4, humerus length; 5, ulna or radius length; 6, wing metacarpal length; 7-10, lengths of WP1-4, respectively; 11, femur length; 12, tibia length; 13, wingspan (= combined length of humerus + ulna/radius + metacarpal IV + WP1-4) × 2.1) [26]. Measurements of Rhamphorhynchus muensteri (sensu Bennett [27]), Pterodactylus antiquus (sensu Bennett [15] and Vidovic & Martill [28]), Sinopterus dongi (sensu Pêgas et al [29]) and Pteranodon (sensu Bennett [14]) were taken from Hone et al [16] (88 specimens), Wellnhofer [30] (22 specimens), Pêgas et al [29] (and references therein; 10 specimens) and Bennett [14,31] (59 specimens), respectively (see electronic supplementary material, data S1 for detailed measurements for each specimen). Measurements of Pteranodon include two species, Pteranodon sternbergi and Pteranodon longiceps, because they do not differ in their postcranial skeletal anatomy [14] and only postcranial measurements are included in this analysis.…”

“…Measurements of Rhamphorhynchus muensteri ( sensu Bennett [ 27 ]), Pterodactylus antiquus ( sensu Bennett [ 15 ] and Vidovic & Martill [ 28 ]), Sinopterus dongi ( sensu Pêgas et al . [ 29 ]) and Pteranodon ( sensu Bennett [ 14 ]) were taken from Hone et al . [ 16 ] (88 specimens), Wellnhofer [ 30 ] (22 specimens), Pêgas et al .…”

“…[ 16 ] (88 specimens), Wellnhofer [ 30 ] (22 specimens), Pêgas et al . [ 29 ] (and references therein; 10 specimens) and Bennett [ 14 , 31 ] (59 specimens), respectively (see electronic supplementary material, data S1 for detailed measurements for each specimen). Measurements of Pteranodon include two species, Pteranodon sternbergi and Pteranodon longiceps , because they do not differ in their postcranial skeletal anatomy [ 14 ] and only postcranial measurements are included in this analysis.…”