Soft tissue preservation in fossils does not seem to depend upon the species, age or burial environment of the fossils in question, according to new research from North Carolina State University. The work provides further evidence for the preservation of soft tissues and structures through deep time and could also serve as a methodological framework for other researchers interested in pursuing these questions.
“We wanted to test several hypotheses with this work – the first one being whether we would be able to retrieve these tissues from different dinosaur species,” says Mary Schweitzer, professor of biology emeritus at North Carolina State University and research curator at the North Carolina Museum of Natural Sciences. “The other questions followed from that one – do the age or the depositional environment make a difference in our ability to retrieve soft tissue from these specimens?”
The research team began by demineralizing bone fragments from six fossils – four Tyrannosaurus rex specimens, one Brachylophosaurus canadensis and one ceratopsian. The specimens ranged in age from around 65 to 80 million years old.
“Some of the enduring questions around this work are how to distinguish actual tissues, like blood vessels, from bacteria, fungus or potential contaminants,” Schweitzer says. “Over the years we’ve developed a suite of analytical tools that are best suited to helping us answer these questions.”
The researchers began by imaging – using transmitted light microscopy, scanning electron microscopy, transmission electron microscopy, and nano computed tomography to obtain extremely high-resolution images of the vessels.
Next, they used several analytical techniques to characterize these tissues at different levels, including immunofluorescence, immunogold labeling, lactophenol cotton blue staining and time-of-flight ion mass spectrometry to identify what the molecules were.
“It’s like starting with a big funnel and working your way down, eliminating and identifying everything we see so that we can distinguish original structures and molecules from bacterial or fungal growth,” Schweitzer says. “And since we don’t have a living control to compare the results to, we use ostriches, which are dinosaurs’ closest living relative, to get an idea of how these tissues should respond to our analyses if they are endogenous.”
The researchers were able to retrieve vessels from all six specimens, though they varied in quality. They also found evidence of peptides and proteins that were not microbial in origin, suggesting that they could be original preserved molecules.
Overall, they found that the depositional environment – where the fossils fossilized, in other words – did not seem to have much impact on their ability to retrieve the vessels, although the sample from one T. rex found in mudstone was not as pristine as the others, which were retrieved from both mudstone and sandstone.
“It seems as though the preservation of vessels through deep time is not that uncommon,” Schweitzer says. “But the work still must be done on a case-by-case basis, because so far there isn’t any evidence that a particular preservation environment is best. So don’t rule out a fossil because of depositional environment or age. Those factors don’t seem to matter.
“We also hope that our techniques can be used to establish a methodological framework for this research going forward, so that we can give better answers to the ongoing question of what may preserve through deep time.”
The research appears in Scientific Reports and was supported by Lynn and Susan Orr, Vance and Gayle Mullis (Mullis Analytics), and the Swedish Research Council. Adam Hartstone-Rose, professor of biology at NC State, along with former lab manager Wenxia Zheng and former post-doc Edwin Dickinson, are NC State co-authors. Peter Sjövall of RISE Institutes of Sweden and Johan Lindgren of Lund University, Sweden, also co-authored the work.
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