Gerald Grellet-Tinner, Suzanne Lindsay & Mike Thompson (2016)
The biomechanical, chemical, and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs.
PeerJ Preprints 4:e2100v1
Megapodes are galliform birds endemic to Australasia and unusual amongst modern birds in that they bury their eggs for incubation in diverse substrates and using various strategies. Alectura lathami and Leipoa ocellata are Australian megapodes that build and nest in mounds of soil and organic matter. Such unusual nesting behaviors have resulted in particular evolutionary adaptations of their eggs and eggshells. We used a combination of scanning electron microscopy, including electron backscatter diffraction and energy-dispersive X-ray spectroscopy, to determine the fine structure of the eggshells and micro-CT scanning to map the structure of pores. We discovered that the surface of the eggshell of A. lathami displays nodes similar to those of extinct titanosaur dinosaurs from Transylvania and Auca Mahuevo egg layer #4 (AM L#4). We propose that this pronounced nodular ornamentation is an adaptation to an environment rich in organic acids from their nest mound, protecting the egg surface from chemical etching and leaving the eggshell thickness intact. By contrast, L. ocellata nests in mounds of sand with less organic matter in semiarid environments and has eggshells with weakly defined nodes, like those of extinct titanosaurs from AM L#3 that also lived in a semiarid environment. We suggest the internode spaces in both megapode and titanosaur species act as funnels, which concentrate the condensed water vapor between the nodes. This water funneling in megapodes through the layer of calcium phosphate reduces the likelihood of bacterial infection by creating a barrier to microbial invasion. In addition, the accessory layer of both species possesses sulfur, which reinforces the calcium phosphate barrier to bacterial and fungal contamination. Like titanosaurs, pores through the eggshell are Y-shaped in both species, but A. lathami displays unique mid-shell connections tangential to the eggshell surface and that connect some adjacent pores, like the eggshells of titanosaur of AM L#4 and Transylvania. The function of these inter-connections is not known, but likely helps the diffusion of gases in eggs buried in environments where occlusion of pores is possible.
Also, non-dino, but may be of interest:
Jing Lu, Min Zhu, Per Erik Ahlberg, Tuo Qiao, You’an Zhu, Wenjin Zhao and Liantao Jia (2016)
A Devonian predatory fish provides insights into the early evolution of modern sarcopterygians.
Science Advances 2(6): e1600154
Crown or modern sarcopterygians (coelacanths, lungfishes, and tetrapods) differ substantially from stem sarcopterygians, such as Guiyu and Psarolepis, and a lack of transitional fossil taxa limits our understanding of the origin of the crown group. The Onychodontiformes, an enigmatic Devonian predatory fish group, seems to have characteristics of both stem and crown sarcopterygians but is difficult to place because of insufficient anatomical information. We describe the new skull material of Qingmenodus, a Pragian (~409-million-year-old) onychodont from China, using high-resolution computed tomography to image internal structures of the braincase. In addition to its remarkable similarities with stem sarcopterygians in the ethmosphenoid portion, Qingmenodus exhibits coelacanth-like neurocranial features in the otic region. A phylogenetic analysis based on a revised data set unambiguously assigns onychodonts to crown sarcopterygians as stem coelacanths. Qingmenodus thus bridges the morphological gap between stem sarcopterygians and s and helps to illuminate the early evolution and diversification of crown sarcopterygians.