Baby dinosaurs are hard to find. While the bones of large, adult dinosaurs were often sturdy enough to survive the processes involved in fossilization, the bones of young dinosaurs were small and delicate and have rarely made it into the fossil record. In many cases we just don't know what baby dinosaurs looked like. Now a pair of well-preserved eggs has allowed paleontologists a rare look into the early growth of one species.
The eggs in question were part of a clutch found in the approximately 200-million-year-old, Lower Jurassic rock of South Africa. They were discovered in 1976, but the tiny skeletons inside two of the eggs were found only during more recent preparation of the fossils. The analysis of these tiny dinosaurs was published late last year in the Journal of Vertebrate Paleontology.
Although the species of dinosaur that laid the eggs cannot be known with absolute certainty, the most likely candidate is Massospondylus carinatus. This was one of the long-necked sauropodomorph dinosaurs which were early cousins to later giants such as Apatosaurus. Based on the anatomy of the newfound embryos, though, these dinosaurs underwent some major changes between hatching and adulthood.
Compared to skeletons seen in other dinosaur eggs, the Massopondylus embryos were well-developed and were probably close to hatching. They did not look very much like their parents. Instead of being long and slender, these baby dinosaurs were relatively short and squat. Their heads were huge compared to their body size, and their eye sockets were proportionally quite large. They also probably started life walking around on all fours—only later did they gain the ability to switch between walking on two legs and all four.
In fact, many dinosaurs appear to have undergone major changes during their lives. Baby dinosaurs were not just smaller copies of adults. As dinosaurs grew, their proportions changed, and thanks to finds like these paleontologists are beginning to understand how these impressive animals got their start in life.
Reisz, R., Evans, D., Sues, H., & Scott, D. (2010). Embryonic skeletal anatomy of the sauropodomorph dinosaur Massospondylus from the Lower Jurassic of South Africa Journal of Vertebrate Paleontology, 30 (6), 1653-1665 DOI: 10.1080/02724634.2010.521604