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Home > True Science > Preserving a Perfect Dinosaur
How Nature Preserves a Perfect Dinosaur Skeleton by Bob Simon

Bob Simon CamarasaurusDuring the summer of 2007, we found and excavated a Camarasaurus skeleton at the digsite. This magnificent specimen is now on display at the Fukui Prefectural Dinosaur Museum in Japan. The Camarasaurus was almost perfectly articulated when found and over 95% complete. There were no other bones from different dinosaur species found associated with this specimen, and there was no evidence of scavenging by predators.

So, how did this occur? How could such a complete skeleton be preserved like this? While it is impossible to absolutely know the mechanisms that produced this result, it is possible to postulate the processes based on the dinosaur itself and the matrix or rock in which it was entombed.

The area in which the dinosaur was found is believed to be within a large meandering river system that existed throughout the area about 145 million years ago, during the Jurassic Period. At this time (Morrison Formation), the overall area was a large basin with some static rivers systems and many ephemeral rivers and streams. The topography was most likely flat, with undulations due to the changing or meandering of the river channels over time.

What does the rock strata or rock sequences tell us?

The Camarasaurus was mostly found within a fine-grained grey siltstone, devoid of any larger pebbles and with very minor plant material. Below this layer was a plant-rich zone that contained multitudes of carbonized plant remains interbedded with silt and sandy layers. Underneath this zone was a very hard sandstone, which appears to have been a former channel of the current river that had migrated laterally over time. This basal sandstone unit appears to have created a slight topographic high during the Morrison time, as plant-rich layers as well as more marshy layers seem to have been onlapping its edges.

What does the positioning of the dinosaur tell us?Camarasaurus femur

The dinosaur was almost perfectly articulated when found. The neck and the tail sections curved up and over the body, almost touching one another in a closed ‘horseshoe’ appearance. Some paleontologists call this a classic death position. The skull was detached from the end of the neck and nestled within the arc created by the tail and neck, against the major portion of the body. Also, it could be noted that there was a slight shift in some of the leg bones, indicating drift in one direction prior to final and ultimate burial and preservation.

What does the dinosaur itself tell us?

Camarasaurus arm boneThe bones themselves were very well preserved (see bone map). Many of the bones were encased in thin to thick calcareous concretions. This may have been a result of diagenetic effects of the interaction of organic material (soft tissues such as muscle, fat, tendons, etc.) having been attached to the bones prior to and during burial. Chemical reactions involving these tissues, the surrounding matrix, and mineral-laden groundwater may have led to the generation of these concretionary masses.

Putting it all together!

Using the information from the surrounding rock sequences, the positioning of the dinosaur, and the bones themselves, we can generate a hypothesis as to how the dinosaur came to rest and was preserved throughout time.

It appears the Camarasaurus died, probably somewhere not too distant from its final resting place. An intense storm or weather event created a flood in the area. Most likely - as the topography was gentle and areas outside the channel system were semi-arid - a large-scale mudflow was generated. This mudflow picked up volumes of fine-grained silty sediment and followed subtle lows in the area. The mudflow need not be a huge flood, but of enough magnitude and velocity to pick up a decaying and possibly bloated carcass in a laminar flow regime (not turbulent or destructive).

This mudflow would have continued to carry the dinosaur until a slight topographic obstruction was found and the dinosaur body was ‘stuck’ in place. The mudflow could have continued and detached the skull from the neck, the skull stopping when it encountered the body. Also, some of the leg elements may have been moved with the flow, but with enough soft tissue attachment in place to keep the elements intact.dinosaur bones in dig site

The mudflow may not have entirely covered the dinosaur remains, and further desiccation/decay occurred that created the so-called death pose of the tail and neck. Finally, other weather processes such as subsequent floods or wind-blown sedimentation could have covered the entire specimen for ultimate burial.

Lack of any predation or scavenging seems to indicate that the topographic high on which the Camarasaurus finally rested may have been isolated by water or thick, impassable mud for enough time to negate any scavengers being able to feed on the carcass. 

It can also be postulated that the flow direction of the flood during the transport of the Camarasaurus carcass was from the northeast to the southwest. Evidence of this is seen in the preservation of the skull, which detached from the neck yet nestled against the main body, thereby preserving it. Also taken into consideration is the slight movement of the leg elements in a singular direction similar to the skull movement.

Camarasaurus skeletonIt is always fun and interesting to speculate why a dinosaur is found and preserved. While we can posit explanations based on facts in the fossil/rock record, we must also understand that any conclusion is only a hypothesis. Too many variables are not preserved in the record of the rocks, so making absolute statements are to be avoided.

See Camarasaurus Bone Map.

Learn more about the digsite and digsite geology.

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