At https://phys.org/print460957896.html … the discovery of what looks very much like soft tissue of dinosaurs preserved in rocks in recent years has obviously perplexed scientists as they have now come up with an explanation that seems to have a lot of merit. Hard tissue such as bones, eggs, teeth and enamel scales are able to survive the process of fossilisation but soft tissue such as blood vessels, cells, and nerves, which are located inside hard tissue, are more delicate and should degrade and decay rapidly after death. These soft tissues are composed mostly of proteins which are thought to competely degrade within 4 million years (a calculation). Yet dinosaur remains date back to 100 million years ago and they occasionally preserve organic structures similar to cells and blood vessels etc. Researchers from Yale University say soft tissue preserved in oxidative environments such as sandstones and marine limestones are transformed into Advanced Glycoxidation and Lipoxidation which themselves are resistant to decay. In other words the soft tissue has suffered from chemical alteration.