It wasn't just herds of bison that migrated across the vast plains of North America in the past. Giant sauropod dinosaurs such as Camarasaurus had seasonal migration too, according to scientists reporting in the journal Nature today.
Camarasaurus teeth from Dinosaur National Monument that were used in the study. Oxygen isotopes laid down in the tooth enamel give a record of what they drank and thus the landscape they occupied.
By studying fossil teeth from Camarasaurus specimens, scientists led by Henry Fricke from Colorado College, USA, discovered these dinosaurs migrated long distances of up to 300km out of their usual habitat, and back again. This is the first evidence for dinosaur migration.
Around 150 million years ago in the Late Jurassic, Camarasaurus roamed the river floodplains of the Morrison basin in western North America. These huge herbivores, with their long necks and tails, were common in this area, despite the annual dry seasons when resources became scarce.
It has been a puzzle how populations of Camarasaurus survived when they would have needed vast amounts of plants and water to eat and drink all year round.
This new research helps explain how - the animals moved out of their area seasonally. They may have migrated when there was drought, moving to places where food and water was more plentiful. But whether this was the incentive for the animals to move, or they did it instinctively whether resources were scarce or not, is not yet known.
The team studied the ratio of oxygen isotopes in Camarasaurus teeth. The oxygen comes from the surrounding soil, lakes and wetlands and the isotope ratios are specific to a particular area.
The isotopes are laid down in the enamel as the tooth grows. The oldest enamel is at the tip, and youngest at the base. So, the isotopes recorded in the enamel becomes a timeline, like the growth rings of a tree, for example.
By comparing the oxygen isotope ratios in the tooth enamel with those in the animal's surroundings, scientists can tell where the animal was living at particular times.
The team found that at seasonal points, the isotope ratios in the Camarasaurus teeth differed from those in their home habitat. Instead, it corresponded to those from highlands 300km away.
This meant that Camarasaurus left their home and moved huge distances to higher, and probably more fertile, areas, the team says. However, the fact that their teeth are found in the basin means they returned to their homeland, maybe when conditions improved in the wet season.
Natural History Museum dinosaur and fossil expert (palaeontologist) Paul Barrett comments on this research, ‘This work provides convincing evidence that at least some of the gigantic sauropod dinosaurs migrated considerable distances, probably in order to maintain a constant fuel supply to provide the energy for their enormous bodies.’
‘It builds on work that showed similar patterns for some other more recently extinct animals, such as mammoths, and raises the possibility of doing many more similar studies on dinosaurs and other long-extinct animals.’
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