Embryology of Early Jurassic dinosaur from China with evidence of preserved organic remains

Analysis of an Early Jurassic dinosaur bone bed reveals the rapid early growth stages of sauropodomorph embryos as well as the earliest evidence of in situ organic remains from a terrestrial vertebrate. Jurassic embryology Fossil dinosaur embryos are extremely rare, and mainly restricted to the Late Cretaceous period. Hence the interest in a newly uncovered bone bed of Lower Jurassic sauropodomorph embryos from China, which at about 190–197 million years old is the oldest assemblage of such bones ever found. A three-year multinational programme of excavation and research has yielded a treasure trove of embryonic bones, and the oldest known evidence of organic remains. Study of bones preserved at various developmental stages indicates that these large dinosaurs had a short incubation time and flexed their muscles while still in the egg, preparing the growing skeleton for life in the outside world. Fossil dinosaur embryos are surprisingly rare, being almost entirely restricted to Upper Cretaceous strata that record the late stages of non-avian dinosaur evolution 1 , 2 . Notable exceptions are the oldest known embryos from the Early Jurassic South African sauropodomorph Massospondylus 3 , 4 and Late Jurassic embryos of a theropod from Portugal 5 . The fact that dinosaur embryos are rare and typically enclosed in eggshells limits their availability for tissue and cellular level investigations of development. Consequently, little is known about growth patterns in dinosaur embryos, even though post-hatching ontogeny has been studied in several taxa 6 . Here we report the discovery of an embryonic dinosaur bone bed from the Lower Jurassic of China, the oldest such occurrence in the fossil record. The embryos are similar in geological age to those of Massospondylus and are also assignable to a sauropodomorph dinosaur, probably Lufengosaurus 7 . The preservation of numerous disarticulated skeletal elements and eggshells in this monotaxic bone bed, representing different stages of incubation and therefore derived from different nests, provides opportunities for new investigations of dinosaur embryology in a clade noted for gigantism. For example, comparisons among embryonic femora of different sizes and developmental stages reveal a consistently rapid rate of growth throughout development, possibly indicating that short incubation times were characteristic of sauropodomorphs. In addition, asymmetric radial growth of the femoral shaft and rapid expansion of the fourt