Fossil of the Week

11/18/10 – Ultraviolet Cone

This week’s fossil is a cone snail from the Plio-Pleistocene of Florida (5.3 to 1.8 million years ago). It is shown here under ultraviolet light, which reveals the original color pattern of the bleached shell that looks chalky white under normal light. The PRI collections are particularly rich in shells such as this from the Pliocene and Pleistocene epochs of the Gulf and Atlantic Coastal Plains.

There are approximately 500 living species of cone snails recognized today. Another 1,000 fossil species have also been named, dating back to the Eocene (approx. 55 million years ago). They are fascinating animals – active predators that capture prey by stinging them with a poisoned harpoon-like tooth before engulfing them for internal digestion. Prey ranges from worms to fish, and those cones that specialize on fish use very powerful neurotoxins (called conotoxins – needed to quickly subdue a fish), so powerful that they can be deadly to humans too. Although all cone snails can sting, the really dangerous ones are restricted to the Indo-Pacific region of the globe.

Cone snails are also among the most beautiful of gastropods, and their color patterns are varied and intricate. These color patterns make them popular with shell collectors and are important in identifying cone species. Yet cone snails have poor eyesight themselves, and spend most of their days hiding under rocks or below the surface of the sand (called “infaunal”). Some also hide their color patterns under a thick, dark organic layer called periostracum (note: all snails have periostracum – critical in producing the shell – but it is thin and nonpersistent in many species).

So of what use are these colors? That’s a difficult question to answer. Some researchers have proposed that the patterns are the result of the excretion of waste products, stored in the shell – but there are no proven examples to support this conclusion. Another explanation says that pigment strengthens the shell, so the color patterns might serve a structural function. Color, aligned as it often is with spiral or axial sculpture, can strengthen the shell against crushing predators such as crabs. Thicker shells might serve the same purpose, but color might be more energy efficient to produce. The same explanation is often used to explain the colorful interiors of clam shells.

This image appeared on the cover of American Paleontologist, May 2003.








Text by Paula Mikkelsen

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?

PRI at GSA

The big blue bear at the Colorado Convention Center peers in at the 2010 annual Geological Society of America convention in Denver. More than 6,000 participants are giving about 3,700 presentations over 4 days. 56 associated societies (including PRI), 17 GSA divisions, and 160 exhibitors add to what will be a very busy week. Six PRI staff members are here, presenting, learning, meeting with colleagues, and selling PRI publications and plush trilobites at the PRI booth in the Exhibition Hall.