Migrating herds of sauropods once travelled the American West

[n2doc]

By Scott K. Johnson


Sauropods (such as the iconic Apatosaurus) are among the very biggest creatures that ever lived. Their fossils have been found in the American West, preserved in the famous Jurassic-aged Morrison Formation and uncovered at places like Dinosaur National Monument. The geologic record tells us that this region was a seasonally dry floodplain at the time when sauropods roamed across it.

Many paleontologists have suggested that they would have had to migrate elsewhere to find food and water during the dry summer months. This week, a paper published in Nature presents geochemical evidence indicating that this migration did, indeed, take place.

Their method measures stable isotopes in water (16O and 18O, specifically), which vary geographically due primarily to fractionation during evaporation and condensation. Since 18O (which has two more neutrons than 16O) has slightly more mass, it’s a little more difficult to evaporate, and a little easier to condense. One consequence of that is that the ratio of 18O to 16O in rain water changes along storm tracks, as the 18O preferentially rains out more quickly.

The oxygen in that rain water is incorporated into carbonate that precipitates in lake sediment and soils, leaving a geologic record of this process. Analysis of oxygen isotopes in carbonate from the floodplain region of the Morrison Formation shows that it differs from the volcanic highlands that were once to the west (this is prior to the formation of the Rocky Mountains).

more
http://arstechnica.com/science/news/2011/10/migrating-herds-of-sauropods-in-the-american-west.ars

[byronius]

1. This is a great mental image. And thanks for everything you do.

I read more of your posts than any other person's. Edifying.

[Enthusiast]

2. Fascinating!