550: Embryos of an Early Jurassic Prosauropod Dinosaur and Their Evolutionary Significance -- Reisz et al. 309 (5735): 761 -- Science

Embryos of an Early Jurassic Prosauropod Dinosaur and Their Evolutionary Significance -- Reisz et al. 309 (5735): 761 -- Science:

Articulated embryos from the Lower Jurassic Elliot Formation of South Africa are referable to the prosauropod Massospondylus carinatus and, together with other material, provide substantial insights into the ontogenetic development in this early dinosaur.

The fossils are roughly 200 million years old. Examining dinosaur eggs and embryos lets scientists understand the development of dinos, and how the development evolved. This is new data to test evolutionary hypotheses.

The combination of the body proportions and poorly developed dentition suggest that the hatchlings may have required parental care (21). The diminutive ventral elements of the pelvic girdle, small caudal vertebrae, and relatively enormous head of the Massospondylus embryos suggest it would have been difficult for the hatchlings to move around efficiently. The virtual absence of teeth in these embryos is another indicator of altricial behavior. Only a single possible tooth fragment is preserved in the two skulls, whereas other delicate, loosely attached elements were preserved largely undisturbed. Even if most of the teeth were poorly mineralized or lost postmortem, they were not well suited for feeding. If this interpretation is correct, these embryos provide early evidence of altricial behavior in a nonavian dinosaur.

"Altricial" means the parents cared for the offspring.