Sciencemag is reporting that plesiosaurs, the large marine reptiles that lived at the same time as dinosaurs, may have given birth to a single baby, instead of laying eggs. After spending twenty years in a basement, this fossil has given F.R. O’Keefe and L.M Chiappe insight into the maternal habits of the Cretaceous behemoth.
The image above shows the fossil, with the yellow-highlighted bones showing the position of the smaller animal. The researchers say that the smaller skeleton was probably not eaten by the adult plesiosaur because the bones did not show any bite marks.
If the study’s assumptions are correct, that this is a single large embryo within a pregnant female, it would suggest that plesiosaurs follow a K-selected reproduction strategy – that is, they give birth to a single large infant and care for it until it becomes independent (like humans). The alternative, R-Selection, is a reproduction strategy followed by animals such as turtles, most fish and insects – they produce many young and do not expend parental resources on raising them. R/K-selection is a trade off between quantity and quality of offspring.
Of course, these findings are speculative, especially the authors statement that plesiosaurs may have been social and cared for their young after birth. As it has been said before, behaviour does not fossilise, and it will take many more finds such as this one to fill in our understanding of these ancient creatures.