Excavations in Argentina reveal that dinosaurs lived in herds as early as 193 million years ago
Researchers from Argentina, the United States and South Africa have found evidence of herding in sauropodomorphs, a group of dinosaurs, as early as the early Jurassic, about 193 million years ago. The article of scientists was published in the journal Scientific Reports.
Since 2013, paleontologists have unearthed more than 100 eggs and about 80 skeletons of young and adult Mussaurs – herbivorous sauropodomorphs, the distant ancestor of sauropods such as Diplodocus and Argentinosaurus – during excavations of the Laguna Colorada Formation in southern Patagonia. Most of the former were grouped into clutches of eight to 30 eggs. X-ray imaging at the ESRF synchrotron in Grenoble showed that all eggs contained Mussaur embryos. Moreover, it turned out that they were all grouped in two or three rows inside specially dug “trenches”, which indicates the presence of a nest.
Paleontologists analyzed the size and age of the bone tissue of Mussaur skeletons in order to determine their age. In addition, they analyzed the formation itself: the fossils were found in different horizons at the same place, which suggests that Mussaurs came to the same point over many mating seasons. It turned out that the fossils were grouped by age – eggs and newly hatched individuals were found in one place, the skeletons of young animals in another. Researchers managed to isolate a cluster of 11 individuals less than a year old – which indicates the existence of “schools”. Skeletons of adults – alone or in pairs – were found separately, but within the same area about a square kilometer in size. All this led the researchers to assume that Mussaurs lived in herds, but tried to group by age.
In order to determine the age of the fossils, the researchers analyzed samples of volcanic ash. They contained zircons – minerals, according to the ratio of the isotopes of uranium and lead, scientists were able to determine that the age of the fossilized Muszaurs is 193 million years. Most likely, the herd died during the flood, and then was covered in ash from the eruption. This is the oldest evidence of complex social behavior in dinosaurs – 40 million years older than previously discovered.