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A Study of Egg Porosity and Incubation Environment in Extinct Taxa Frankie Jackson The origin of avian reproductive behaviors such as parental care and egg brooding remain controversial in the literature. Most hypotheses rely on attributes of living birds, rather than evidence from fossil specimens. This is understandable since the fossil record until recently provided little evidence in this area. However, recent discoveries of eggs with embryos, feathered theropods, and an oviraptorid in an avian-like brooding over unhatched eggs shed new light on the origins of avian reproduction. A recent study of gas conductance in dinosaur eggs, however, argues against brooding in theropods, based on gas conductance values that are 2-5 times greater than those of living birds. The author concludes that all dinosaur eggs were incubated in the manner of modern reptiles. However, his calculated values for Troodon eggs equal those of modern birds and not reptiles, thus the conclusions warrant further investigation. All previous dinosaur egg gas conductance studies were calculated on specimens lacking embryonic remains that are essential for definitive identification. My objective, therefore, is to calculate gas conductance for three definitively identified Late Cretaceous fossil eggs: the theropod Troodon, a titanosaur sauropod, and a terrestrial turtle. The fossil turtle egg represents the first analysis of any fossil non-dinosaurian taxon. This is important since Mesozoic turtles most likely occupied similar ecological niches as living members of the clade. Furthermore, this study combines site taphonomy, assessment of diagenesis, and trace fossil nests to provide a more rigorous test of egg incubation hypotheses. This information will provide a better understanding of embryonic metabolism and provide a phylogenetic context for further examination of the origin of avian reproductive behaviors. ©2006 - 2001 Evolving Earth Foundation. All rights reserved |
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