Dake W. Greenwalt
Remnants of Ancient Life: The New Science of Old Fossils
Princeton, 2022. 278pp.
Like DNA, this book folds a great deal of information into a
compact space (228 pages of text plus a good reference section). Greenwalt is a
scientist at the Smithsonian, specializing in fossil insects, and here he
covers the highlights of the new frontier of paleontology: retrieving chemical
signatures, proteins, and biomolecules from fossils. There are chapters on
pigments, biometals, and the indicators of fibers and feathers on our friends
the dinosaurs.
Greenwalt became famous for a paper reporting the presence
of hemoglobin in a mosquito 46 million years old. What animal it fed on can’t
be determined, though Greenwalt suspects it was a bird. Greenwalt takes us back
to the beginnings of life: a claim of isotopic evidence 4.2 billion years (BY)
old, stromatolites 3.7 BY, and then the great leap to the first known multicellular
animals at 1.6BY. A singular moment in detecting biomolecules came later: Dr,
Kliti Grice isolated molecules including a “cholesterol-like” one in a
crustacean 380 million years old. Chlorophyll? Found in still-green fossil
leaves in the stomach of a German mammal fossil 46MY old.
Greenwalt explains the function of individual molecules and
why we find them in the creatures we do. Melanin is not just a skin pigment: it
evolved as an antioxidant and is used in many places in nature, including
serving as a clotting factor for an injured insect. It turns
up in a dizzying array of creatures up to 300 MY old. Phosphorus molecules are
markers showing the presence of bones that rotted away before fossilization.
Copper can help us determine the color of an ancient creature.
Greenwalt examines the use of molecular clocks, a useful if
imperfect way of using changes in the genes of a protein tracing relationships
and estimates the time a group emerged. He offers an example everyone has heard
of, the enormous ape Gigantopithecus. He describes the work of Chinese anthropologist
Wei Wang in excavating wonderfully preserved Giganto molars 1.9 MY old, whose
enamel yielded partial sequences from six proteins. This was matched with other
evidence to prove the theory Giganto was a hominid closely related to the
orangutan (sorry, Bigfoot fans.)
He celebrates the countless recent discoveries, including
thought-impossible finds like collagen sequences from a T. rex, which
some scientists argue are impossible: other labs reported they could not
replicate it and there must have been contamination. We revisit the iceman,
Otzi, and learn what we know so far of prehistoric humans and our close
relations. Greenwalt explores the mechanics and limits of preservation in amber
and goes into the oft-overlooked topic of molecular clues in plants.
It’s all clearly explained: I’ve no chemistry background,
but I understood everything.
Greenwalt tackles two side topics. He sees no chance for
bringing back dinosaurs, On the mammals, he asks whether the effort to create
something resembling a mammoth, if possible, would be the best use of the
enormous resources involved. He also takes a look at the quest for
biosignatures on Mars. Based on the finds at the time of publication, he
doesn’t think we have the evidence but offers hope we may yet find it. He mixes
in stories of discoveries and fieldwork that make the topic about scientists as
well as science. Onne section walks us through the exhaustive efforts needed in
a laboratory to isolate the desired clues while avoiding contamination. The
illustrations (photographs and drawings, like phylogenetic trees) are good, but
I wanted more diagrams of the structures and molecules he was writing about.
An interesting idea I’d never read elsewhere is using extant creatures including “living fossils” to gain some insight into elements of a long-vanished common ancestor’s genome. As an aficionado of Dunkleosteus terrelli, I wondered if we could “triangulate” genetic information bony fishes (the placoderms’ descendants), and coelacanths: that’s likely a step too far, but it shows the kind of imagination this book sparks in readers taking a new look at a lost world.
Matt Bille is a writer, historian, and naturalist living in Colorado Springs. He can be reached at mattsciwriter@protonmail.com. Website: www.mattbilleauthor.com.
