The fossilized offspring of a family of gigantic duck-billed dinosaurs has been found in a Mongolian excavation site known as the Dragon’s Tomb. Paleontologists have uncovered an extremely young group of Saurolophus angustirostris (meaning “lizard crest”), part of the visually arresting hadrosaurid group, within this small area of the Gobi Desert. The researchers, from Ghent University and the Royal Belgian Institute of Natural Sciences, report their findings this week in the journal PLoS One.
The Dragon’s Tomb – an inarguably wonderful name for an excavation site – is famous among paleontologists for discoveries of non-flying dinosaurs from the Late Cretaceous, a period of geological time ending with the 65-million-year-old extinction event that wiped them out. Remarkably, researchers have now uncovered three or four extremely young species of hadrosaur here, so young in fact that they could be described as “babies.”
Two associated eggshell fragments were also recovered from the site, indicating that the babies had possibly just been born or were still in their eggs before they were buried. The authors think that it is likely all four specimens were part of the same nest originally located on a sandy river bank, which at one point overflowed and smothered them all during a wet summer season.
One of the crushed, fossilized baby hadrosaurs found at the site. Image credit: Dewaele et al./PLoS One
Well-preserved and complete skeletal fossils of S. angustirostris have been found in the region before, but a find like this, containing up to four newly born dinosaurs, is far rarer. Their tiny skulls are only 5% of the length of the fully-grown adult specimens.
The herbivorous hadrosaurs are often referred to as “duck-billed,” as their heads somewhat visually resemble the aforementioned modern-day water fowl. Their flattened, beak-tipped snout would have been ideally suited for cutting vegetation away from branches. This name may be somewhat of a missed opportunity, however, as their cranial ornamentation is by far their most distinguishing feature. Their crest varies between subfamilies but is undoubtedly a prominent physical characteristic in all of them. The Lambeosaurinae subfamily generally have hollow crests, which paleontologists suggest might have been used to produce unique sounds, whereas the Saurolophinae lacked any such air chamber.
In any case, the fossils of these baby specimens, with their poorly developed crests, demonstrate that crest growth begins before they even hatch from their eggs. The eggshells in question closely resemble those found from S. angustirostris relatives found elsewhere in Mongolia.
One of the most well-preserved and complete fossilized hadrosaur specimens was excavated from the Hell Creek Formation in North Dakota. The preservation of the fossil is immaculate, with skin, ligaments, tendons and fragments of internal organs all still intact, along with the majority of the skeletal features. Dakota, as the fossil was named, was essentially a mummified dinosaur. By looking at the preserved muscle mass, paleontologists managed to work out that it probably had the ability to outrun predators, including the infamous Tyrannosaurus rex.
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