Though it is highly likely that burial of fossils for millions of years destroys any trace of their DNA the massive bones of large creatures can preserve cell material. A near complete 67 Ma old Tyrannosaurus rex, fondly known as ‘Big Mike’ has revealed blood cells in thin sections of its bone (Schweitzer, M.H. 2010. Blood from stone. Scientific American, v. 303 (November 2010), p. 38-45). Her article also covers traces of blood vessels, and collagen of similar antiquity. The research involved positive reaction of antibodies against proteins, thereby proving the materials to be organic and not products of biomineralisation formed during the process of fossilisation. Potentially such forensic work can tease out relationships among animal groups whose fossils preserve organic materials, in a similar way to indications of the rise of prokaryote groups by biogeochemical marker molecules in carbonaceous shales. Indeed, sequences of fossil proteins from dinosaurs closely resemble that of modern birds. One of the great surprises of the late 20th century was the growing evidence that the stem-line for birds was dinosaurian, specifically the theropod group. This is nicely summarized by another review article (O’Donoghue, J. 2010. Flight of the living dead. New Scientist, v. 208 (11 December 2010), p. 36-40) that addresses the certainty of birds’ evolution from dinosaurs; which of the fossils is bird, which feathered dinosaur and when did they separate; and why did birds survive the end-Cretaceous mass extinction while dinosaurs famously succumbed – probably a matter of breeding; its pace, that is. The two articles together suggest a fruitful way forward for palaeobiologists.
Further material about biochemical relics in fossils and methods used to detect and analyse them can be found in Hecht, J. 2011. Waking the dead. New Scientist, v. 209 (22 January 2011 issue), p. 43-45.