Fossil of the Week

11/10/10 – K-Pg Boundary Samples


The PRI collections are full of fossil specimens, many of which are from groups that are entirely extinct. This is just one piece of evidence that life on Earth has changed through time, sometimes gradually and sometimes rapidly and catastrophically. Part of what paleontologists do is try to work out what triggers such changes by studying both the fossils and the rock in which the fossils are found, to reconstruct what the environment was like and how it changed over time. So the collections at PRI and other museums contain both fossil specimens and lots of things that you might not consider to be paleontological at first glance.

This Fossil of the Week “specimen” is one example of something that doesn’t look particularly fossil-like, but which is really useful. This is part of a bulk sample (PRI accession no. 1541), which is a sample that includes the actual rock or matrix rather than just individual fossils. In fact, in some cases there might not be fossils at all in the sample, but that doesn’t mean that it isn’t valuable. Multiple samples are often collected from one outcrop in small increments up a sequence – they form a series through time so that changes over a period of time can be studied in detail.

What makes this perhaps-not-very-inspiring sample of rock really cool is its location and time frame: it was collected from the K-Pg boundary on Seymour Island in Antarctica. [K-Pg is short for Cretaceous-Paleogene – an important boundary between two geological time periods, 65 million years ago. It was formerly called the K-T (Cretaceous-Tertiary) boundary, until the name “Tertiary” was discouraged by the International Commission on Stratigraphy.] Seymour Island has one of the largest exposures of the boundary in the world and has been important in helping to figure out what was happening before, during, and after the extra-terrestrial impact that seems to have caused the mass extinction that killed off the dinosaurs, ammonites, and many other groups. Sedimentary layers all over the world at the K-Pg boundary are unique in containing a concentration of the element iridium many times greater than normal.

These samples were donated to PRI in 2009 by Professor William Zinsmeister of Purdue University as part of a much larger collection of material from Antarctica*. Because of this gift, PRI now has one of the most extensive collections of Antarctic fossils in the country.

Text by Ursula Smith (reprinted from “Fossil Focus” in American Paleontologist, Winter 2009).

*For more about the Zinsmeister Antarctic collection, see Fossil of the Week 10/13/10 – Tropical Antarctica?