Comparisons between experimental and morphometric water vapor conductance in the eggs of extant birds and crocodiles: implications for predicting nest type in dinosaurs

Abstract

Estimates of water vapor conductance for the eggs (i.e., diffusive capacity of eggshell; Gh2o, mg H2O·day−1·Torr−1) of extinct archosaur species have been used to infer their nest type (i.e., covered vs. open) because experimental Gh2o values for living archosaur species appear to reflect nest type. The methods used to derive Gh2o for fossil eggs (eggshell morphometrics) differs from that for extant eggs (experimental measurements), and it remains unknown if these two methods are comparable or if morphometric Gh2o values correspond to nest type. Although previous studies assumed that Gh2o values derived from the two methods were comparable, this assumption has not been statistically evaluated in a large sample size that includes both crocodiles and birds. Here, Gh2o values for over 100 species of living archosaurs for both morphometric and experimental methods were compiled and compared using statistical analyses. Results showed that although experimental and morphometric Gh2o values are significantly correlated, there is disagreement between the methods particularly apparent in small eggs, likely due to systematic errors. These results suggest that morphometric and experimental Gh2o of living species are not necessarily comparable, although the reason for the discrepancy remains uncertain. Thus, direct comparisons between morphometric Gh2o of dinosaurs and experimental Gh2o of living species should be avoided when inferring the nest type for dinosaurs.