A giant soft-shelled egg from the Late Cretaceous of Antarctica

Legendre, Lucas J.; Rubilar-Rogers, David; Musser, Grace; Davis, Sarah N.; Otero, Rodrigo A.; Vargas, Alexander O.; Clarke, Julia A.

doi:10.1038/s41586-020-2377-7

Cited by 12 publications

(34 citation statements)

References 24 publications

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“…While not the focus of Legendre et al. (2020), these results suggested that there may be different scaling relationships between eggshell thickness and mass in different subclades of dinosaurs, and some may be marked between volant and non‐volant taxa. However, these studies did not include the dense taxonomic sampling germane to specifically assessing evolutionary patterns in dinosaurian eggshell thickness: it did not densely sample eggs of non‐avian dinosaurs closely related to crown birds, which could help understand if potential differences in scaling relationship were influenced by the acquisition of flight.…”

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confidence: 84%

“…(2019), identified another significant relationship between egg mass and eggshell thickness specific to hard‐shelled eggs (Legendre et al. 2020). This study also performed ancestral state reconstructions for all species in its sample, and preliminarily identified dinosaur subclade‐specific trends; sauropods and secondarily‐flightless paleognath birds shared low values of relative eggshell thickness (i.e.…”

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confidence: 99%

“…ratio eggshell thickness/egg mass), while volant extant birds presented much higher values (Legendre et al. 2020). While not the focus of Legendre et al.…”

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confidence: 99%

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Shifts in eggshell thickness are related to changes in locomotor ecology in dinosaurs

Legendre

Clarke

2021

Evolution

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Birds share an array of unique characteristics among extant land vertebrates. Among these, external and microstructural characteristics of extant bird eggs have been linked to changes in reproductive strategy that arose among non‐avian theropod dinosaurs. More recently, differences in egg proportions recovered in crown birds relative to other dinosaurs were suggested as possibly linked to avian flight, but dense sampling close to its proposed origin was lacking. Here we assess the evolution of eggshell thickness in a targeted sample of 114 dinosaurs including birds, and test the relationship of eggshell thickness with potential life history correlates and locomotor mode using phylogenetic comparative methods. Only egg mass and flight are identified as significant predictors of eggshell thickness. While a high correlation between egg mass and eggshell thickness is expected, that relationship is much stronger in flying taxa, which show a significantly higher slope and lower residual variance than flightless species. This suggests stabilizing selection of eggshell thickness among theropods, as recovered for other traits in extant birds (e.g. genome size, metabolic rate). Within living birds, Eufalconimorphae present an apomorphic increase in relative eggshell thickness which remains unexplained, as few morphological synapomorphies of this clade have been identified.

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confidence: 84%

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confidence: 99%

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Shifts in eggshell thickness are related to changes in locomotor ecology in dinosaurs

Legendre

Clarke

2021

Evolution

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“…By contrast, soft-shelled eggs, such as those of most lizards and snakes, have leathery outer coverings that decay rapidly and thus are only rarely preserved. Now, Norell et al 1 (page 406) and Legendre et al 2 (page 411) describe multimillion-year-old softshelled eggs that might alter the prevailing view of dinosaur reproduction, and possibly also change current thinking about ancient marine reptiles.…”

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confidence: 99%

“…This finding challenges the generally accepted view that dinosaur eggs were always hard-shelled, in turn suggesting that the earliest eggs laid by dinosaurs were soft-shelled. Legendre et al 2 report the discovery of a huge originally soft-shelled egg in Antarctica, a specimen they call Antarcticoolithus, that is about 68 million years old. Legendre and colleagues hypothesize that this might have been laid by a marine reptile.…”

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Hard evidence from soft fossil eggs

Kear

2020

Nature

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Evolution of eggshell structure in relation to nesting ecology in non‐avian reptiles

D’Alba

Goldenberg

Nallapaneni

et al. 2021

Journal of Morphology

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Amniotic eggs are multifunctional structures that enabled early tetrapods to colonize the land millions of years ago, and are now the reproductive mode of over 70% of all terrestrial amniotes. Eggshell morphology is at the core of animal survival, mediating the interactions between embryos and their environment, and has evolved into a massive diversity of forms and functions in modern reptiles. These functions are critical to embryonic survival and may serve as models for new antimicrobial and/or breathable membranes. However, we still lack critical data on the basic structural and functional properties of eggs, particularly of reptiles. Here, we first characterized egg shape, shell thickness, porosity, and mineralization of eggs from 91 reptile species using optical images, scanning electron microscopy, and micro computed tomography, and collected data on nesting ecology from the literature. We then used comparative analyses to test hypotheses on the selective pressures driving their evolution. We hypothesized that eggshell morphology has evolved to protect shells from physical damage and desiccation, and, in support, found a positive relationship between thickness and precipitation, and a negative relationship between porosity and temperature. Although mineralization varied extensively, it was not correlated with nesting ecology variables. Ancestral state reconstructions show thinning and increased porosity over evolutionary time in squamates, but the opposite in turtles and crocodilians. Egg shape, size, porosity and calcification were correlated, suggesting potential structural or developmental tradeoffs. This study provides new data and insights into the morphology and evolution of reptile eggs, and raises numerous questions for additional research.

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A giant soft-shelled egg from the Late Cretaceous of Antarctica

Cited by 12 publications

References 24 publications

Shifts in eggshell thickness are related to changes in locomotor ecology in dinosaurs

Shifts in eggshell thickness are related to changes in locomotor ecology in dinosaurs

Hard evidence from soft fossil eggs

Evolution of eggshell structure in relation to nesting ecology in non‐avian reptiles

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