The "Re-Os" bit indicates that it was Rhenium-Osmium dating of black shale (a sedimentary rock commonly found on paleo-coastlines) in the formation.

One of the major differences between the paleontologists and archaeologists is their opinion of shale and other mudstones. Paleontologists love the stuff, archaeologists hate it.

Geologists and paleontologist usually use multiple methods to estimate age. Carbon works well for young deposits. Uranium dating can be used for much older materials. As AlotOfReading mentioned Rhenium-Osmium. Sometimes they can use Oxygen ratios in inclusions in Zircon crystals. There are other more specialized measures. Using multiple methods can help calibrate each other.

Thanks everyone, very interesting and probably worth further reading!