Fossil Ghosts of a Lizard's Teeth, Via High-Speed X-Ray

A souped-up x-ray scanning fluorescence technique is letting paleontologists peer into the chemical hearts of ancient fossils to reveal hidden details and change the way we see animals that lived and died tens of millions of years ago.

A new study from the U.K.’s University of Manchester describes how synchrotron rapid scanning x-ray fluorescence (SRS-XRF) can unmask minute deposits of atoms that were part of the living animal. The resulting maps show details like the tiny phosphorus deposits that were once lizard teeth and the copper clusters that mark melanosomes (the organelles that store melanin, giving cells their pigmentation). The group’s previous work includes analyzing colors on petrified feathers and mapping proteins in ancient lizard skins.

The research—by Manchester’s Nicholas Edwards and other member’s of lead investigator Phillip Manning’s “Chemical Ghosts” team—took advantage of new facilities at the Stanford Synchrotron Radiation Lightsource (SSRL). The system includes a beefed-up x-y rastering stage that quickly steps big samples (measuring up to one meter square and weighing as much as 50 pounds) through increments of 80 to 100 micrometers. While scans like this have been done before, the Stanford SRS-XRF covers about two square centimeters a minute—some 3000 times faster than previous systems (which managed about one square centimeter a day). The SRS-XRF can also examine much larger regions—up to 60 by 30 centimeters—than previous instruments. Thus, paleontologists can for the first time thoroughly examine macroscopic fossils of significant size. The SRS-XRF can scan in two regimes: a high-intensity, high-energy beam delivering 10¹⁰ to 10¹¹ photons per second at either 12 or 13.5 kiloelectron volts stimulates emissions from heavier elements like calcium, barium, manganese, iron, copper zinc, and nickel; and a lower-energy beam of about 10⁹ photons per second at about 3 keV detects lighter silicon, phosphorus, sulfur, and chlorine.

The sitter for one of the first SRS-XRF portraits was a 50-million-year-old lizard, about 8 centimeters long, found in the Green River sediments of the Western U.S. (The smaller figure at left in the photo above.)  The fossil was ambiguous. It appeared to be just a lizard’s hide: it preserved the scales in minute detail, but showed no hard tissues like bone or teeth. Paleontologists were not sure whether it was a sloughed skin or the remains of a whole animal.

SRS-XRF scans for copper and sulfur clearly showed the outlines of the scales, but the surprise came from the scans for phosphorus (shown above right). The maps of emissions from the lizard’s head showed two dotted lines—showing what were once the lizard’s teeth. (The red outlines show teeth from one jaw; the blue show teeth from the other; it is no possible yet to say which is the upper and which the lower.) Just as dental x-rays help modern forensic examiners identify a body, the unconventional SRS-XRF maps make it easier to narrow down the fossil. (For the taxonomically inclined, it appears to be a shinisaurid, possibly related to Bahndwivici ammoskius.)

For more on the analysis of ancient fossils, see Manning’s blog, Dinosaur CSI.

Images: Phillip Manning, School of Earth, Atmospheric & Environmental Sciences, University of Manchester, Manchester, U.K.