Short Life, Long Journey

Around 70 million years ago, a giant female hadrosaur from the species Saurolophus angustirostris lay several eggs beside a riverbank in what is now the Gobi Desert in Mongolia. The eggs and embryos within them developed, but may or may not have hatched. The babies were already dead by the time they were buried by river sediment during the wet summer season. As dinosaurs will do, over the next tens of millions of years, they were further buried and turned into fossils until the entire site, known as the Dragon’s Tomb in the Nemegt Formation, was discovered in 1947.

The Dragon’s Tomb site yielded many dinosaur fossils and became a target for poachers, who took the “nest” of fossilized Saurolophus angustirostris eggshells and perinatal specimens and sold them to private collectors in Japan. The fossils were later sold to other private collectors in Europe, where scientist François Escuillié discovered them and convinced the collectors to donate them to the Royal Belgian Institute of Natural Sciences in 2013. More recently, the fossils were returned to Mongolia, where they will stay, catalogued for future study.

That’s a long trip for potentially short-lived dinosaurs! Belgian and Mongolian scientists studied the well-traveled, still fairly well-preserved fossils and discovered three-to-four perinatal dinosaurs or babies, and two associated eggshell fragments. The team found that the skull length (about six centimeters, just over two inches) of these Saurolophus was around 5% that of the largest known S. angustirostris specimens, indicating that these specimens were in the earliest stages of development. The perinatal bones already displayed S. angustirostris characteristics, including the upwardly directed snout, but the specimens did not yet have the characteristic cranial crest at the top of the head. Particular areas of the skull—the cervical neural arches—were not yet fused, which had not been documented in hadrosaurs before, though this fusion is common in present-day mammal development.

Despite these findings, the scientists are still unsure whether the individuals were still in the eggs or had just hatched when they died, but either way, they believe these specimens document the earliest developmental stages of the giant hadrosaur. The study was published this week in PLoS ONE.