Location: Cuenca, Spain
Age: Barremian (Lower Cretaceous)
The Las Hoyas Lagerstatte preserves many types of fossil well. This is largely because a lacustrine environment is one of the best terrestrial environments for fossil preservation. The lake sediments are finely laminated showing it was a low energy environment. Continuous fine grained carbonate sedimentation provides a good chance to preserve organisms. The low energy means organisms were not physically broken up after death, and continuous sedimentation allows quick burial preserving the organism well.
The bottom of the lake was probably anoxic as shown by the trace fossil evidence, so there were no benthic organisms that could destroy or decompose dead organisms on the lake floor. Again, good conditions for preservation. The trace fossils also show evidence of mild turbidite flows which kill living organisms, and bury both living and dead organisms quickly. This also increases their preservation potential.
Leaf fossils at Las Hoyas are so good because many leaves fell straight into the lake so never became dehydrated or mechanically broken down before they were buried. The leaves therefore remained intact, anoxic and water-saturated until extracted providing high quality samples. They contained little evidence of post-depositional (diagenetic) change. The tiny leaf fragments were primarily deposited into fluvial environments which caused mechanical breakdown due to the high energy environment. These leaf fragments settled out of suspension once the high energy river water entered the low energy lake. Despite being broken down, once they entered the lake, they were preserved well.
Las Hoyas preserves the mineralized soft tissue of the dinosaur Pelecanimimus. It is only the second discovery like it. Mineralized Pelecanimimus skin and muscle are replicated in iron carbonate and preserved at cellular level. The soft tissues are preserved as a microbial mat. It is now mineralised in apatite consisting of thin layers of coccoids. This shows that microbial mats are important in soft tissue preservation.
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