Published on July 1st, 2019 | by David Marshall Episode 101: Organic Preservation of Dinosaur Bone
Fossilisation of organic material was long thought to result in the complete loss of original content. However in the last 20 years, several high-profile publications reported the discovery of proteins, blood vessels, blood cells and even DNA. But for as long as these arguments have existed, so too has a counterargument as to the validity of the discoveries.
In this episode, we’re joined by Dr Evan Saitta of the Field Museum of Natural History, Chicago, lead author of a recent paper seeking to discover and evaluate the preservation of putative original organic materials within dinosaur bones.
Organic content from the demineralisation of Centrosaurus bone. Such structures as these have previously been interpreted as organically-preserved blood vessels.
To determine the validity of these claims, Dr Saitta led a study to collect and analyse ‘fresh’ samples of dinosaur bone.
Ridge on which Centrosaurus samples were collected. Looking East at mouth of Jackson Coulee, Dinosaur Provincial Park, Alberta, Canada.
Here many specimens of Centrosaurus have been discovered, with bone fragments commonly found littering the surface.
Having removed the overlying sediments, samples were taken of freshly-exposed bone and surrounding sediments.
A Centrosaurus tibia (lower leg) analysed in this study.
Whilst it would be impossible to collect the fossils in a sterile manner, aseptic techniques were used to minimise modern contaminants.
The samples of dinosaur bone were ‘demineralised’ in acids, leaving behind just the organic tissues, and their chemical composition was compared to that of a similarly-demineralised sub-fossil shark tooth and recent chicken bone. Whilst the organic structures seen in the dinosaur bones (D & E) superficially resemble blood vessels, their chemical composition (H – K) was different: the shark (B,F,L) and chicken (C,G,M) organics possessed more Carbon, Oxygen, Nitrogen and Sulphur. This suggests that the dinosaur ‘vessels’ are relatively inorganic in composition and were chemically consistent with a mineralised biofilm.
The organics originating from within the dinosaur bones were also stained with propidium iodide, a chemical which makes DNA glow red under UV flourescence. Interestingly, the concentration of DNA was 50x higher in the dinosaur bone than in the surrounding sediments. The source of the DNA was however modern.
A comparison of the microbial communities of freshly-exhumed Centrosaurus bone and adjacent sediments (mudstone) with two analyses per sample.
16S rRNA gene amplicon sequencing revealed the predominance of Actinobacteria and Pro-
teobacteria in subterranean Centrosaurus bone. Nitriliruptoria and Deltaproteobacteria were more abundant than in adjacent sediments or even the surface scrapings from the bone itself. This is evidence that bone, even in pristine conditions must be considered an ‘open system’, and even cultures its own unique microbial community.
Whilst these results cast serious doubt over previous claims of the preservation of original organic content in dinosaur bones, it is good news for microbiologists who can now learn more about this exciting new microbial habitat.