A fossil reptile embryo from the Middle Triassic of the Alps.

The first nothosaur (Neusticosaurus sp.) embryo, one of the very few fossil embryos known, provides a rare glimpse at reproduction in extinct reptiles. The specimen from the southern Alpine Middle Triassic (about 230 million years ago) was recognized as an embryo in comparison with an exceptionally large and well-understood sample of juvenile and sexed adult Neusticosaurus sp. The skeleton shows many embryonic features and may well be the smallest fossil reptile known (body length 51 millimeters). It reached only 22% of mean adult length whereas modern reptiles of this size do not hatch before they reach about 30% of mean adult length. The question of ovipary versus vivipary in pachypleurosaurs is discussed in light of the embryo.