Whenever paleontologists dig up dinosaur bones from one site or another, the fossils are welcomed with great excitement by the scientific community. In some rare cases, the ancient bones even manage to preserve soft tissue samples — such as blood vessels, cells, and nerves — which renders these discoveries all the more thrilling.
The problem with soft tissue is that it doesn’t endure time. Unlike hard tissue, which is able to survive the process of fossilization quite well, soft tissue is mostly made up of proteins, which can only last for so long before they completely degrade.
The general consensus is that the proteins in soft tissue take about four million years to fully deteriorate. Past that point, scientists believe that it’s virtually impossible for soft tissue samples to still cling to fossilized bones.
Meanwhile, dinosaur fossils have stuck around for tens of millions of years and even longer than that. Some dinosaur bones date back to roughly 100 million years and still manage, on occasion, to retain organic structures similar to cells and blood vessels.
This gives rise to a paradox that scientists have long struggled to explain. How can soft tissue proteins, which only last for a maximum of four million years, still turn up within 100-million-year-old dinosaur bones?
At long last, a team of researchers led by Yale University has finally figured out the answer. And, believe it or not, it’s all somehow connected to burnt toast, reports Science Daily.
— Yale University (@Yale) November 9, 2018
In order to crack the mystery of the long-lasting proteins, the scientists investigated a series of dinosaur fossil samples — including bones, eggs, teeth, and enamel scales — known to have preserved soft tissue. The team used a sophisticated technology known as Raman microspectroscopy to unravel the chemical composition of both the hard, bony tissue and the soft tissue encased within it.
As Yale University points out, this method is non-invasive and allowed the researchers to safely examine the precious samples without destroying them.
“We took on the challenge of understanding protein fossilization,” said team leader Jasmina Wiemann, a paleontologist at Yale. “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.”
Writing in the journal Nature Communications, her team explain that these puzzling discoveries only occur in specific types of geological environments. According to their analysis, only oxidative environments — such as sandstones deposited from rivers, dune sands, and shallow marine limestones — can yield dinosaur fossils that still contain soft tissue samples.
Due to the specific condition found in these environments, the dinosaur bones that remain frozen in time in these types of locations all go through a special oxidation process — that mirrors what happens to burnt toast.
This oxidation turns the proteins in their soft tissues into a certain type of polymers which are water- and decay-resistant. Known as AGEs and ALEs (Advanced Glycoxidation and Lipoxidation end products), these compounds can withstand the normal effects of water and prevent bacteria from consuming the soft tissue samples.
The strange thing about these polymers is that they share a common trait with burnt toast. AGEs and ALEs are “structurally comparable to chemical compounds that stain the dark crust on toast” and “are characterized by a brownish color that stains fossil bones and teeth that contain them,” explain Yale officials.
Study co-author Derek Briggs, Yale professor of geology and geophysics and a curator at the Yale Peabody Museum of Natural History, believes that these findings could help pinpoint the location of paleontological sites that could contain fossilized bones with soft tissue still clinging to them.
“Our results show how chemical alteration explains the fossilization of these soft tissues and identifies the types of environment where this process occurs. 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.”