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A tiny start for the giant Saurolophus

Gigantic skeletons of dinosaurs often draw the biggest crowds at museums, but the elusive remains of baby dinosaurs are breathtaking in their own way. Beyond the “cute” factor, tiny bones from the youngest animals help document the immense physical changes that occurred as a dinosaur transformed from hatchling to adult. Today, a report in PLOS ONE reveals the earliest life stages of the crested herbivorous dinosaur Saurolophus. [Full disclosure: I was the handling editor for this paper.]

Dewaele and colleagues document a compact blob of rock, scarcely a foot long, that holds the skeletons of at least three baby dinosaurs. The little critters were scarcely six inches tall at the hip when alive, and well under two feet in total body length. Their small size, as well as associated eggshell fragments, suggest that the animals were probably just out of the egg when they met their untimely demise. The bony anatomy identifies the critters as hadrosaurs (colloquially known as ‘duck-billed dinosaurs’), and details of the skull, such as the shape of the beak, were consistent with the hadrosaur Saurolophus. Although the exact locality for the fossils is unknown, circumstantial evidence shows they are almost certainly from the Nemegt Formation of Mongolia. Saurolophus just happens to be one of the most common dinosaurs there, with nice specimens known from all life stages. However, the newly described fossils are by far the smallest yet reported.

Tiny Saurolophus skeletons in the rock, from Dewaele et al. 2015. CC-BY.
Tiny Saurolophus skeletons in the rock, from Dewaele et al. 2015. CC-BY.

Adult Saurolophus are easily spotted by a spike-like crest jutting from the top of the skull. The babies notably lack that feature, though. This is consistent with a large body of evidence showing that dinosaurs often added their headgear later in life. Nonetheless, other skull bones show shapes and relationships quite similar to those in adult Saurolophus, but lacking in other hadrosaurs. This means that paleontologists can have some confidence in the the babies’ identity, even if the overall skull shape is quite different.

Adult <i>Saurolophus</i>, life restoration by L. Xing and Y. Liu, from Bell 2012.
Adult Saurolophus, life restoration by L. Xing and Y. Liu, from Bell 2012. CC-BY.

The fossils themselves had a complicated history of discovery and study, as documented in the paper. Illegally looted from rocks in Mongolia, the tiny fossils made their way via Japan to a European collector. From there, the fossils were donated to the Royal Belgian Institute of Natural Sciences, which in turn arranged for the repatriation of the fossils to Mongolia. The remains are now housed at the Institute of Paleontology and Geology of the Mongolian Academy of Sciences, and a team of paleontologists from France, Belgium, and Mongolia collaborated on the study. Although precise geological and geographic data were lost during the illegal collection of the fossil, the ultimate (and legal) return to their homeland is still a fairly happy ending for the little Saurolophus.

Dewaele L, Tsogtbaatar K, Barsbold R, Garcia G, Stein K, Escuillié F, et al. (2015) Perinatal Specimens of Saurolophus angustirostris (Dinosauria: Hadrosauridae), from the Upper Cretaceous of Mongolia. PLoS ONE 10(10): e0138806. doi:10.1371/journal.pone.0138806

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