Palaeobiological Implications of the Bone Histology of Pterodaustro guinazui

Abstract

This study provides a comprehensive investigation of the bone microstructure of multiple bones of the Early Cretaceous filter-feeder, Pterodaustro guinazui, from the Largacito Formation of Central Argentina. We provide information regarding the bone histology of multiple elements from single skeletons, as well as a variety of bones from different individuals. In addition, we analysed changes in bone microstructure through ontogeny in growth series of several long bones of the taxon. Our investigation of skeletal and ontogenetic variation in Pterodaustro gives insights into the developmental growth dynamics of this unusual ctenochasmatid pterodactyloid from early ontogeny through to adulthood and also provides information pertaining to histological variability within and between bones of individuals. This study also documents the presence of what appears to be medullary bone tissue within the medullary cavity of a large femur of Pterodaustro. This suggests that, like birds, reproductively active female pterosaurs may have deposited a special bone tissue (medullary bone) to cope with the demand of calcium during eggshelling. Our study supports the hypothesis that small Jurassic pterodactyloids took several years to reach adult body size. More specifically, we provide data that suggests that Pterodaustro attained sexual maturity at about 2 years of age, and continued to grow for a further 3-4 years doubling in size before attaining skeletal maturity.

Medullary bone-like tissue in the mandibular symphyses of a pterosaur suggests non-reproductive significance

“…Although found in different anatomical locations, based on the description of Chinsamy et al 30 these tissues have very similar histological characteristics in Pterodaustro and Bakonydraco, which speaks for a common tissue type. The justness of referring to them as medullary bone is harder to judge.…”

“…Among more than 30 investigated specimens of the Early Cretaceous pterodactyloid pterosaur, Pterodaustro guinazui, Chinsamy et al 30 reported a single femur (V 382), the largest known for the taxon, that showed a considerable amount of endosteally derived bone tissue in the mid-diaphyseal region, which they proposed could represent medullary bone. However, for reasons not mentioned in their work, the authors were not entirely convinced (20).…”

“…Other abbreviations as in Fig. 2. www.nature.com/scientificreports SCIENTIFIC REPORTS | 4 : 6253 | DOI: 10.1038/srep06253about the true nature of this tissue 30 . Unfortunately, we could not properly identify the fine characteristic details on the provided images, either.…”

“…Therefore the calcium content of eggshells and hence the calcium demand for their formation in pterosaurs must have been lower than that of the thicker, heavily calcified shells characterizing the eggs of archosaurs and turtles 56,57 or even the rigid-shelled gecko eggs 56 . Although Chinsamy et al 30 argued that the egg of Pterodaustro was shown to have had hard shell 50 , and therefore this genus may have required medullary bone during egg-laying 30 , it is still valid that the eggshell of Pterodaustro was also extremely thin (30 mm) 50 . Thus, pterosaurs apparently would not have needed medullary bone for eggshell production 58 .…”

“…Recently, with the discovery of medullary bone in different non-avian dinosaurs, the occurrence of medullary bone has proven to be phylogenetically more widespread and is considered as further evidence for the close relationship between birds and theropod dinosaurs 21,[27][28][29] . Apart from dinosaurs, there has been only one report on the presence of an extensive, endosteally derived bone structure in a single femur of the Early Cretaceous pterosaur Pterodaustro that was tentatively interpreted as medullary bone 30 . Since it has been found in theropod 21,27,29 as well as in ornithopod 27,28 dinosaurs but not in extant alligators 31,32 , medullary bone has been suggested to have first appeared in the ornithodiran lineage of archosaurs after its divergence from crocodilians 27,32 .…”