Fossil Atlas guide
Paleontologists usually do not date the bones themselves. They date the rocks around them, using radiometric dates from volcanic layers, index fossils, stratigraphic position, and magnetic signatures to estimate when the fossil-bearing layer formed.
Method 1
Radiometric dating measures radioactive decay in minerals from datable rock layers, especially volcanic ash. If an ash bed above a fossil-bearing layer and another below it can be dated, the fossil age can be bracketed between them. This is one of the strongest ways to anchor a fossil-bearing formation in time.
Method 2
Index fossils are species that are useful time markers because they were widespread, recognizable, and limited to a particular slice of geological time. Marine fossils, pollen, and other correlated records can help place non-marine dinosaur-bearing rocks into a broader timescale when direct radiometric dates are limited.
Method 3
Earth's magnetic field has flipped polarity many times. Some rocks preserve the magnetic direction from when they formed. Geologists can compare those polarity patterns with the global geomagnetic polarity timescale, especially in long rock sequences where other dating anchors are available.
On Fossil Atlas
Fossil Atlas specimen profiles and hotspot pages usually report ages as ranges. For example, a page may use the age range of a formation rather than a specimen-level date. This is conservative: the actual fossil horizon may be narrower, but the broader formation age is safer unless a more precise published date is available.
FAQ
Usually, no. Dinosaur bones are fossils, and the original material has typically been altered or replaced by minerals. Paleontologists usually date the rocks around the fossil instead. If datable volcanic ash layers occur above and below a fossil-bearing bed, the fossil age can be bracketed between those dates. Carbon-14 dating is not useful for non-avian dinosaur fossils because it only works for much younger material.
Radiometric dating measures the decay of radioactive isotopes in minerals to estimate when a rock formed. For dinosaur-age rocks, useful methods include uranium-lead dating of zircon crystals in volcanic ash and argon-based dating of volcanic minerals. These methods date the rock layers, not the dinosaur bone itself, and are strongest when combined with careful stratigraphy.
Index fossils are species that were widespread, abundant, and short-lived in the geological record. Because they only appear in rocks of a narrow age range, finding an index fossil tells you the approximate age of the rock layer. For dinosaur paleontology, marine index fossils like ammonites and foraminifera are especially useful because they evolve rapidly and are found worldwide. When a dinosaur fossil is found in a rock layer that also contains a known index fossil, the dinosaur's age can be correlated to the established marine timescale.
Fossil Atlas usually reports age ranges based on the geological formation or published literature for each record. These ranges describe the estimated age of the rock unit, not necessarily the precise death date of an individual animal. Some formations have finer dating than others, so age ranges should be read as current best estimates rather than exact specimen ages.
Sources
Source links show where Fossil Atlas gets record and curation context. They do not make this page an exhaustive scientific bibliography.
Caveat
This page provides a simplified overview of fossil dating methods. Geochronology is complex, and individual specimen ages can change as new stratigraphic or dating studies are published. Fossil Atlas age ranges should be read as current best estimates.