Using light to describe the ancient world

Archive for April, 2013

#Organic traces in dinosaur embryos

Robert Reisz and colleagues have described dinosaur embryos in a Letter published in Nature. The embryos are from a sauropodomorph dinosaur, “…probably Lufengosaurus…”, and were collected from Early Jurassic sediments (Sinemurian, 190–197 million years old) in the Yunnan Province of China. The tiny embryonic bones are impressive and the microstructural detail (i.e. histology) is astounding. The thing that caught my eye, though, was the evidence for organic molecules.

Thin sections of the tiny dinosaur bones were analysed at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan. The researchers were interested in the wavelengths of infrared light that would be absorbed by the fossils (the synchrotron was their light source). Infrared absorbance is an excellent method for identifying molecules in a sample. Atoms bind together to form molecules – the type of atoms and the way they are bound controls the wavelengths of light that a molecule will absorb. More specifically, a molecule can be identified from the wavelengths of light it absorbs. The researchers presented the results from one bone: infrared wavelengths were directed at 120 points (150 × 180 µm, one spectrum collected every 15 µm), and the spectrum of wavelengths absorbed from each point was mapped.

Organic remnants in a dinosaur bone. Infrared absorption in the amide I and amide II regions provides strong evidence for a peptide bond, the ‘backbone’ of proteins, including collagen. Light microscope images show section of fossil bone that was analysed (left), colored maps show the distribution of apatite, amide I and a carbonate (middle), and spectra were collected from points highlighted with a red cross (right). Reprinted by permission from Macmillan Publishers Ltd: Nature. RR Reisz et al. Nature 496, 210-214 (2013) doi:10.1038/nature11978, copyright (2013).

Organic remnants in a dinosaur bone. Infrared absorption in the amide I and amide II regions provides evidence for a peptide bond, which are found in proteins. Light microscope images show section of fossil bone that was analysed (left), colored maps show the distribution of apatite, amide I and a carbonate (middle), and spectra were collected from points highlighted with a red cross (right). Reprinted by permission from Macmillan Publishers Ltd: Nature. RR Reisz et al. Nature 496, 210-214 (2013) doi:10.1038/nature11978, copyright (2013).

Some of wavelengths absorbed by the dinosaur bones would also be absorbed by the proteins of living animals. The basic structure of a protein involves a set of small molecules (amino acids) linking together to form a long chain (peptide). The ‘linking together’ forms a peptide bond, which has a characteristic infrared absorption. The characteristic absorptions of a peptide bond appear at very specific regions in an infrared absorption spectrum – two of those regions fall between 1500 and 1700 cm-1 and are termed ‘amide I and amide II’. The embryonic dinosaur bones absorb infrared light in the amide I and amide II regions, suggesting the presence of a peptide. Bone is a mixture of mineral (bioapatite) and protein (collagen), so it might be possible that the peptide traces in the fossil are remnants of collagen. The authors state that “…Previous reports of preserved dinosaur organic compounds, or ‘dinosaurian soft tissues’, have been controversial because it was difficult to rule out bacterial biofilms or some other form of contamination as a possible source of the organics. Our results clearly indicate the presence of both apatite and amide peaks within woven embryonic bone tissue, which should not be susceptible to microbial contamination or other post-mortem artefacts….”

Remnant collagen from a 190 million year old dinosaur embryo? Might well be.

Reisz, R R et al. 2013. Embryology of Early Jurassic dinosaur from China with evidence of preserved organic remains. Nature 496, 210-214.

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