Stop eating before you read this story. It’s a bit stomach-turning.
The Cleveland-Lloyd Dinosaur Quarry is a dense deposit of Jurassic-age theropod dinosaurs, mostly Allosaurus fragilis. What caused this mass death of 46 allosaurs (and some 25 other dinosaurs)? Why were there so few other kinds of typical fossils like crocodilian teeth or turtle shells? The bones were not scavenged. What happened here?
Hypotheses included that the place was a death trap where animals became mired in mud. Or, that the animals were killed by some toxin in the environment. A recent study suggests that the location was an ephemeral water body that was the final resting place for animals that died nearby.
Periodic floods washed the corpses into this low area creating, as the author describe, “significant numbers of rotting dinosaurs in a body of standing water” creating “hypereutrophic” conditions. Yuck!
This hypothesis explains the accumulation and condition of the remains and why there are few other vertebrate remains present. Additional evidence to support this putrid pond idea are as follows:
Sediment geochemistry. The deposition area is enriched in heavy metals and sulfide minerals which are not present in the surrounding formation or in other fossil bone beds. The presence of sulfides and calcite/barite nodules suggest that hypereutrophic conditions were present resulting in a concentration of heavy metals as the animals decomposed.
High rates of organic matter decay would have led to hypoxia or anoxia and the subsequent formation of sulfide minerals and the calcareous soaps required to form the calcite nodules.
Bone fragment abrasion patterns. Characteristics of the bone fragments in the quarry deposit were compared to other bone assemblages. There was a wide range of degree of abrasion in this particular quarry. Some bones had been exposed to environmental weathering longer than others. This variation, along with an examination of the matrix within which the larger bones were fossilized, supports the idea that there were separate events that formed the deposit as periodic flooding and drying occurred, possibly over a range of 10-20 years.
The physical characteristics of the bone fragments of CLDQ suggest variable taphonomic histories among the fragments; angular fragments suggest weathering or pulverization followed immediately by burial while rounded fragments suggest prolonged exposure and re-working.
Finally, using the evidence about the climate conditions of the time, it appears that this area in Utah was subjected to periods of dryness interspersed with “weak monsoons and sub-humid conditions during stronger monsoons, similar to climates seen in modern savannahs”. This supports the idea that the carcasses accumulated during flood events and then periodically dried out, leaving a horrible pit of rotting flesh in a toxic pool.
Read the entire study here:
New data towards the development of a comprehensive taphonomic framework for the Late Jurassic Cleveland-Lloyd Dinosaur Quarry, Central Utah by Joseph E. Peterson , Jonathan P. Warnock, Shawn L. Eberhart, Steven R. Clawson, and Christopher R. Noto
published June 6, 2017. PeerJ.
Thanks to Dr. Thomas Holtz for notice of this news story.
Read More from Spooky Geo:
“For inducing fear and unease, dead things are big-time spooky. Geological factors can result in recording death in particularly captivating ways, freezing the animals’ death throes across enormous stretches of time.” From Death scenes, geologically preserved