The exceptionally well-preserved fossils belong to the ancient aquatic reptiles mesosaurs and suggest the animals were either viviparous -- giving birth to live offspring -- or that they laid eggs in advanced stages of development, scientists said.
The discovery was made by an international team including Michel Laurin from the Centre de Recherche sur la Paleobiodiversite et les Paleoenvironnements, or CNRS, in France.
In Brazil, the team uncovered a fossil specimen in gestation, suggesting the reptiles were probably viviparous.
The same researchers unearthed 26 adult mesosaur specimens in Uruguay, all of which were associated with embryos or very young individuals, suggesting young animals were looked after by at least one of the parents, pointing to the existence of parental care, a CNRS release said Thursday.
The research reveals the first examples of embryo retention -- and perhaps viviparity -- pushing back this reproductive mechanism by some 60 million years from what has previously been believed, the researchers said.