How to Make a Dinosaur Bonebed

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It is often assumed that dinosaur paleontologists are interested only in getting the fossils they discover out of the ground as quickly as possible. This is not true. Paleontologists generally take great care to document and catalogue every fossil removed from a dig site, because the position and surroundings of those fossils may say something about where the animal lived and how it died. This can be especially important when multiple skeletons are found together. Were the animals part of a herd? Did they die at the same time? Were their bones washed to the same place by a river? Did scavengers pick at the bones?

Paleontologists studying the Dalton Wells bone beds near Moab, Utah, have grappled with such questions for a long time. Dated to the Early Cretaceous, about 127-98 million years ago, the site contains the remains of at least 67 individual dinosaurs of eight different genera. Bones from sauropods, ankylosaurus, Iguanodon-like herbivores and the predatory Utahraptor are all mixed together, and many of them appear to have been trampled. What happened?

In a new study published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, researchers led by Brooks Britt of Brigham Young University try to envision how the massive bone bed was formed.  As scientists excavated the bone bed, they found not a collection of articulated skeletons, but a heap of bits and pieces jumbled together. This suggested that the dinosaurs did not die all at once in an event that covered up the bones en masse, but that the bodies probably accumulated over a relatively short span of time, maybe as the result of a drought, and were subjected to the elements. The bones show little sign of scavenging by predatory dinosaurs, but they were extensively damaged from being scattered by water, trampled by other dinosaurs and eaten by insects. Eventually, the dinosaur graveyard was covered with sediment and preserved for tens of millions of years.

Given the damage to the bones, it’s surprising that there is a bone bed to study at all. Anyone who has spent a lot of time on the African savanna can tell you that the skeletons of even large animals, such as elephants, can be reduced to splinters within a relatively short time if they are not covered up. Scavengers, insects and the trampling feet of herbviores can soon turn a full skeleton into bone shards. This fact makes every fossil important, and at places like the Dalton Wells bone bed, even heavily damaged bones can provide us with a window into the distant past.

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