Oldest Fossil Terrestrial Vertebrate Embryos Found! (they're dinosaurs too...)

Found in South Africa, the fossilised eggs date back to the Jurassic, 190 million years ago, and are a dinosaur known as Massospondylus, a prosauropod. They were discovered during preparation, which required high powered microscopes to achieve. Their exceptional preservation allowed for full reconstruction, giving incredible insight into dinosaur ontogeny. The almost hatchlings show how much of the skeleton had become bone and show that dinosaurs began life much like we do - with odd proportions. They had disproportionally large heads and walked on all fours, whereas their older form used bipedal locomotion to get around. They also had shorter necks and this data suggests that their necks and hind limbs grew faster than their heads and forelimbs during their life.

They also lacked teeth, which when combined with the awkward body proportions suggests that they received parental care after hatching (unlike pterosaurs which could fly soon after hatching). If so, then this is not only the oldest example of terrestrial vertebrate embryos and of dinosaur embryos, but also the oldest record of parental care. 

For more, see this press release.