As a scientist, laboratory work can sometimes become monotonous. However, in 2017, while I was doing my doctorate. When I was a paleobiology student at the University of Bristol in the United Kingdom, I heard a joyful exclamation from across the room. Kirsty Penkman, head of the North East Amino Acid Racemization laboratory at the University of York, had just read the data printed from the chromatograms and was practically jumping up and down.
The device detected traces of ancient amino acids in the eggshell. Amino acids are the building blocks that form protein sequences in living organisms. But this wasn’t just any eggshell; It was a fossil of a titanosaur, a giant herbivorous dinosaur that lived about 70 million years ago.
Not much organic matter survives for millions of years, limiting scientists’ ability to study the biology of extinct organisms compared to modern organisms whose proteins and DNA can be sequenced. These amino acids were extraordinary, as Penkman’s enthusiasm demonstrated.
In fact, this result came unexpectedly during our team’s efforts to test claims that nearly intact protein was preserved in dinosaur bone. I had brought various fossil bones to Penkman, but the results showed that no original amino acids were preserved and were even contaminated by microbes from the environment in which they were buried.
Testing eggshell fossils wasn’t even in our original research plan.
Orphan fossil fragments
But I had just seen that my colleague Beatrice Demarchi, Penkman, and their team had identified short protein sequences in 3.8 million-year-old bird eggshells. I guessed that if dinosaur eggshells didn’t preserve any of the original protein, their bones probably wouldn’t preserve any either, and I wanted to see if that was the case. Luckily we had a supply of dinosaur egg shells.
Around 2000, many eggshell fragments were illegally exported from Argentina to the commercial market. As a fossil-obsessed kid, I was even gifted a dime-sized piece from a mineral depository in the US. Penkman and I tested this piece as well as another piece purchased from the gift shop of a European museum.
Since these fossil pieces do not belong to any museum collection, they have gained scientific value in a way. We didn’t have to worry about damaging them during analysis. Surprisingly, we had a rare opportunity to examine the ancient organic remains of a dinosaur.
Amino acids in eggshell
Building on this initial discovery, our large international team analyzed further dinosaur egg shells from Argentina, Spain and China using a wide range of techniques. Although some eggshells preserve amino acids much better than others, the evidence overall suggests that these molecules are old and original, probably ranging from 66 million to 86 million years old.
Proteins that helped calcify the eggshell throughout life were trapped inside the mineral crystals. However, the remaining amino acids we detected consisted of free molecules that broke off from protein chains by reacting with water. We have identified only a few of the most stable amino acids. The less stable ones did not exist because they were broken.
The amino acids still preserved were what chemists call racemic. Amino acids can occur in left- or right-handed configurations. Living organisms arrange their amino acids so that they appear almost entirely in a left-handed configuration. After the organism dies, amino acids can rotate between hands until they reach a 50-50 mix of both configurations.
A 50-50 mixture is known as racemic and indicates that the amino acids were separated from the protein chains a long time ago.
Calcite, an amino acid archive
Our dinosaur eggshell results showed more extreme degradation than that seen in younger bird eggshell and mollusk shell fossils. Our results also matched those from experiments that exposed eggshells to heat in the laboratory and simulated deterioration over thousands or millions of years.
Organisms strengthen these shells with a type of calcium carbonate mineral called calcite. Unlike the calcium phosphate that forms bone, calcite can act as a closed system by trapping the products of proteins involved in calcification as they break down, including free amino acids that are separated from protein sequences. This closed system allowed us to monitor amino acids in our analyses.
In fact, bird egg shells are among the best materials for finding preserved protein sequences in fossils, let alone free amino acids. Demarchi’s team identified short, intact sequences of amino acids still connected in a chain from bird egg shells that are at least 6.5 million years old.
Other researchers claimed to have found more extreme and less likely claims of conserved protein sequences as well as older amino acids. However, our study uses a broader range of methods and reports the best signal for stable molecules in a tissue that we now know preserves molecules well.
Our dinosaur amino acids may hold the record as the oldest protein-related material ever found; It can be said that the evidence for this is very strong and that it is the first clear evidence of a Mesozoic dinosaur.
Using calcite to look back in time
Ultimately, the genetic sequence in DNA expressed in proteins provides a source code for organisms that scientists can study. But if only a subset of amino acids are preserved in the fossil, this is like removing all but five letters from a book; little literary analysis is possible. So what messages from ancient life might survive in these calcite time capsules?
A biologically informative signal may contain stable isotopes, which are atoms of the same element with different masses. Scientists can look at stable isotope ratios of carbon, oxygen, or nitrogen to learn about the animal’s sources, such as its diet. Because eggshell calcite is a closed system, the stable isotope ratios in its amino acids are more likely to come directly from the dinosaur rather than from outside contamination.
In future research, our team will use the fossils to probe even further back in time. Organisms other than egg-laying dinosaurs strengthened their tissues with calcite. For example, marine arthropods called trilobites that lived more than half a billion years ago had calcite in their eyes.
Studying older remains can help scientists understand molecular changes that occurred in fossils over long periods of time. A calcite fossil, Earth’s molecular time capsule, could send faint tales of long-lasting life to researchers to better understand their biology.
The orphaned eggshells we used in our initial analysis had a happy ending. They eventually gained a new home at Argentina’s Museo Provincial Patagonico de Ciencias Naturales, a natural science museum in Patagonia, and were returned to the only province known to produce this type of eggshell microscopic structure.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and authoritative analysis to help you understand our complex world. Written by: Evan Thomas Saitta, University of Chicago
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This research was supported by the University of Bristol Bob Savage Memorial Fund and Leverhulme Trust (PLP-2012-116).