Conventional wisdom has always been that fossils are impressionistic: although they can tell us a lot about the morphology of a great variety of organic structures, it has been assumed that all but the most recent of fossil remains contain none of the original material that made up the fossilized organism. A recent article in Scientific American by Mary H. Schweitzer (“Blood from Stone“) calls into question this conventional wisdom.
In this well-written article, Schweitzer explains how she serendipitously discovered the remains of red blood cells in the well-preserved fossil of a Tyrannosaurus rex. While this initial discovery made scientific waves, it has taken Schweitzer and other researchers looking at similar fossil phenomena nearly two decades to dislodge the common belief that biological remains and compounds are too fragile to ever be preserved in the fossil record.
Schweitzer’s depiction of her scientific travels provide a really nice overview of how paleontologists go about testing their hypotheses. Sometimes, a lot of creativity is involved: Schweitzer wanted to show that the compounds she was isolating from her fossils were indeed biologically significant, so she injected them into mice, who produced antibodies against these foreign biological molecules. This technique (along with protein-sequencing) also allowed her to eliminate a competing explanation for the presence of biomolecules in these fossils: bacterial contamination. The molecules recovered from Schweitzer’s dinosaur bones resemble those produced by modern-day birds, but are not produced by bacteria. In the article, Schweizer suggests that maybe there was more skepticism of her findings than was scientifically warranted, but she also makes a compelling case for the fact that deliberate investigation eventually elevates the best hypothesis.
That ancient fossils might still contain proteins, DNA, and other biomolecules offers new hope to evolutionary biologists who seek to understand major evolutionary transitions. The possibility of understanding the metabolic and physiological processes of extinct organisms opens up all sorts of new opportunities to understand where each organism fits on the tree of life. Rather than having to infer from phylogenies where and when key innovations emerged, Paleontologists now have the potential to directly observe the evidence needed to establish the existence of particular adaptations.
In addition to providing a compelling account of this important new area of paleontology, the article also provides a nice graphic box summarizing the basic taphonomic processes that lead to fossil preservation and discovery.
Paleonotology, Taphonomic Processes