A skeleton from the Middle Jurassic of Scotland illuminates an earlier origin of large pterosaurs

New insights into pterosaur cranial anatomy: X-ray imaging reveals palatal structure and evolutionary trends

Among the least studied portion of the pterosaur skeleton is the palate, which tends to be poorly preserved and commonly only visible from one side (the ventral portion). Even in well-preserved specimens, the bones tend to be fused, with the limits of individual palatal elements obscured. To shed new light on this region, we employed advanced X-ray imaging techniques on the non-pterodactyloid Kunpengopterus (Wukongopteridae), and the pterodactyloids Dsungaripterus (Dsungaripteridae), Hongshanopterus (Istiodactylidae), and Hamipterus (Hamipteridae). Our analyses revealed the presence of sutures between palatal bones in Dsungaripterus and Kunpengopterus, which resulted in different interpretations of the relation between palatine, ectopterygoid, and pterygoid, leading to a new identification of the palatal openings. Furthermore, our study shows six main observations such as the variation of the angle between the palatine rami and the variation in the relative sizes of the palatal openings. We also point out that the presence of a maxillopalatine fenestra (previously identified as postpalatine fenestra), is unique within Diapsida. Although much more work needs to be done, we showed that advanced X-ray imaging techniques open a window for understanding pterosaur cranial anatomy and provide a new perspective for investigating the evolutionary history of these flying reptiles.

A new gnathosaurine (Pterosauria, Archaeopterodactyloidea) from the Late Jurassic of Portugal

An incomplete, yet remarkably-sized dentated rostrum and associated partial cervical vertebrae of a pterosaur (ML 2554) were recently discovered from the Late Jurassic (Late Kimmeridgian-Early Tithonian) Lourinhã Formation of Praia do Caniçal, of central west Portugal. This specimen exhibits features such as a spatulated anterior expansion of the rostrum, robust comb-like dentition, and pronounced rims of the tooth alveoli, indicating gnathosaurine affinities. Based on its further unique tooth and dentary morphology, a new genus and species, Lusognathus almadrava gen. et spec. nov., is proposed, making this the first named pterosaur species found within Portugal. The presence of this taxon adds yet another element to the fluvio-deltaic lagoonal environment that has been suggested as representative of the Lourinhã Formation in the Late Jurassic, further contributing to the diversity and distribution of gnathosaurines worldwide.

Allometric wing growth links parental care to pterosaur giantism

Pterosaurs evolved a broad range of body sizes, from small-bodied early forms with wingspans of mostly 1-2 m to the last-surviving giants with sizes of small airplanes. Since all pterosaurs began life as small hatchlings, giant forms must have attained large adult sizes through new growth strategies, which remain largely unknown. Here we assess wing ontogeny and performance in the giant Pteranodon and the smaller-bodied anurognathids Rhamphorhynchus, Pterodactylus and Sinopterus. We show that most smaller-bodied pterosaurs shared negative allometry or isometry in the proximal elements of the fore- and hindlimbs, which were critical elements for powering both flight and terrestrial locomotion, whereas these show positive allometry in Pteranodon. Such divergent growth allometry typically signals different strategies in the precocial-altricial spectrum, suggesting more altricial development in Pteranodon. Using a biophysical model of powered and gliding flight, we test and reject the hypothesis that an aerodynamically superior wing planform could have enabled Pteranodon to attain its larger body size. We therefore propose that a shift from a plesiomorphic precocial state towards a derived state of enhanced parental care may have relaxed the constraints of small body sizes and allowed the evolution of derived flight anatomies critical for the flying giants.

Complex macroevolution of pterosaurs

Pterosaurs, the earliest flying tetrapods, are the subject of some recent quantitative macroevolutionary analyses from different perspectives.^1-2 Here, we use an integrative approach involving newly assembled phylogenetic and body size datasets, net diversification rates, morphological rates, and morphological disparity to gain a holistic understanding of the pterosaur macroevolution. The first two parameters are important in quantitative analyses of macroevolution, but they have been rarely used in previous pterosaur studies.^{1,3,4,2,5,6,7,8,9,10,11,12} Our study reveals an ∼115-Ma period-from Early Triassic to Early Cretaceous-of multi-wave increasing net diversification rates and disparity, as well as high morphological rates, followed by an ∼65-Ma period-from Early Cretaceous to the end of the Cretaceous-of mostly negative net diversification rates, decreasing disparity, and relatively low morphological rates in pterosaur evolution. Our study demonstrates the following: (1) body size plays an important role in pterosaur lineage diversification during nearly their whole evolutionary history, and the evolution of locomotion, trophic, and ornamental structures also plays a role in different periods; (2) birds, the other major flying tetrapod group at the time, might have affected pterosaur macroevolution for ∼100 Ma; and (3) different mass extinction events might have affected pterosaur evolution differently. Particularly, the revealed decline in pterosaur biodiversity during the Middle and Late Cretaceous periods provides further support for the possible presence of a biodiversity decline of large-sized terrestrial amniotes starting in the mid-Cretaceous,^13,14 which may have been caused by multiple factors including a global land area decrease during these periods.