A university study into the incubation behavior of modern birds is shedding new light on the type of parental care carried out by their long extinct ancestors.
The study, by researchers at George Mason University and University of Lincoln (United Kingdom), aimed to test the hypothesis that data from exisiting birds could be used to predict the incubation behaviour of Theropods, a group of carnivorous dinosaurs from which birds descended.
The paper, out today in Biology Letters, was co-written by Geoff Birchard from the Department of Environmental Science and Policy at Mason and Charles Deeming and Marcello Ruta from the University of Lincoln's School of Life Sciences.
A 2009 study in the journal Science suggested that it was males of the small, carnivorous dinosaurs Troodon and Oviraptor that incubated their eggs. However, by taking into account factors known to affect egg and clutch mass in living bird species, the authors found that shared incubation with mature young was the ancestral incubation behavior rather than male-only incubation, which had been claimed previously for these Theropod dinosaurs.
"The previous study was carried out to infer the type of parental care in dinosaurs that are closely related to birds," said Birchard. "That study proposed that paternal care was present in these dinosaurs and this form of care was the ancestral condition for birds. Our new analysis, based on three times as many species as in the previous study, indicates that parental care cannot be inferred from simple analyses of the relationship of body size to clutch mass. Such analyses have to take into account factors such as shared evolutionary history and maturity at hatching.
The group decided to repeat the Science study with a larger data set and a better understanding of bird biology because other palaeontologists were starting to use the original results to predict the incubation behavior of other dinosaur species.
"Irrespective of whether you accept the idea of Theropod dinosaurs sitting on eggs like birds or not, the analysis raised some concerns that we wanted to address," said Deeming. "Our analysis of the relationship between female body mass and clutch mass was interesting in its own right, but also showed that it was not possible to conclude anything about incubation in extinct distant relatives of the birds."
The project has helped in understanding the factors affecting the evolution of incubation in birds. More importantly it is hoped that the new analysis will assist palaeontologists in their interpretation of future finds of dinosaur reproduction in the fossil record.