Nov. 9 (UPI) -- Under the right conditions, a dinosaur's soft tissue can be transformed and preserved, enabling fossilization. The process features chemical transformations similar to those that characterize browned or burnt toast.
Scientists have long debated whether soft tissue can be preserved within dinosaur bones. While hard tissue -- bones, eggs, teeth, scales -- can survive for more than 100 million years, most studies suggest the proteins that form blood vessels, cells and nerves are fully degraded after 4 million years.
And yet, paleontologists have regularly found organic structures similar to cells and blood vessels inside 100-million-old dinosaur bones.
To better understand this paradox, researchers at Yale, the American Museum of Natural History, the University of Brussels and the University of Bonn set out to identify the chemical process that make protein fossilization possible.
"We tested 35 samples of fossil bones, eggshells and teeth to learn whether they preserve proteinaceous soft tissues, find out their chemical composition, and determine under what conditions they were able to survive for millions of years," Yale paleontologist Jasmina Wiemann said in a news release.
In oxidative environs, like sandstones and shallow, marine limestones, scientists found proteins can be converted into more stable compounds called Advanced Glycoxidation and Lipoxidation end products, or AGEs and ALEs.
The end products are more resistant to degradation and decay and are structurally similar to the compounds that form on the outer layers of bread browned in the toaster. Brownish colors also stain soft tissue converted to AGEs and ALEs.
Scientists used a variety of advanced imaging techniques, including microspectroscopy, to observe the transformation of soft tissues inside decalcifying fossils.
Researchers say their findings -- published this week in the journal Nature Communications -- could help paleontologists know where to look when searching for preserved soft tissue.
"Our results show how chemical alteration explains the fossilization of these soft tissues and identifies the types of environment where this process occurs," said Derek Briggs, a professor of geology and geophysics and curator at the Yale Peabody Museum of Natural History. "The payoff is a way of targeting settings in the field where this preservation is likely to occur, expanding an important source of evidence of the biology and ecology of ancient vertebrates."