#paleolab

by Pat McShea

Museum visitors who approach the broad window of PaleoLab encounter an array of large fossilized bones. If not for the pair of microscope workstations positioned against the lab’s right wall, it would be easy to misinterpret the enormous jaws, ribs, vertebrae, and limb bones as evidence of a size bias in the science of vertebrate paleontology.

A scoop of fossil-bearing matrix on a sorting tray.

Small fossils have certainly made mighty contributions to our understanding of life during ancient time periods. Such fossils, which include loose teeth, small bones, and bone fragments, are the primary focus of some paleontological research. In other projects, where considerably larger fossilized creatures are the focus of study, the fossils of smaller creatures add information about species diversity, food webs, and even the climate conditions of ancient ecosystems. The sorting of fossil-bearing matrix that occurs under PaleoLab’s microscopes ensures that important discoveries will continue to occur.

The term matrix refers to the natural rock surrounding a fossil. In the case of fossil bones encased in rock, the matrix consists of the loose sediments that originally buried the bones, sediments that were later transformed into rock over long stretches of time by the pressure of other sediment layers deposited above them. When fossil-bearing rock layers erode, however, and loosened fossils are transported by water, wind, or other forces, the unconsolidated mix of surrounding materials in which the fossils eventually settle is also termed matrix.

In the field, paleontologists sometimes collect and screen loose matrix on site, using water to both separate floatable bits of plant debris and wash away soil, then sun-drying the resulting sludge for later screening. In the case of the matrix currently being sorted in PaleoLab, material eroded from a more than 50 million-year-old rock unit near Meridian, Mississippi was collected in bulk by CMNH paleontologists and brought back to Pittsburgh for washing and drying at the museum.

Unsorted fossil-bearing matrix.

During a recent visit to PaleoLab, Scientific Preparator Dan Pickering pulled two containers from a shelf as “before” and “after” sorting examples. In the “before” container, a quart-sized plastic jug that once held ground coffee, a black, dime-sized shark tooth resting atop similar-sized irregular gray rock fragments hinted at the possible rewards for future sorting efforts. The considerably smaller and lighter “after” container bore not just an array of small marine fossils, including shark teeth and skate tooth plate fragments, but also the name and working notes of the sorter, CMNH volunteer Jason Davis.

Fossils picked from matrix, with volunteer Jason Davis’ notes revealing that the material is from the lowermost Eocene (~55 million-year-old) Tuscahoma Formation of Mississippi.

Dan termed the recent finds typical for the current operation, but he also noted a now decades-old exciting discovery in matrix screened from a different, but adjacent Mississippi rock unit. In a scientific paper published in 1991, then-CMNH paleontologists K. Christopher Beard and Alan R. Tabrum described a tooth and jaw fragment from an early primate. The fossil was the first record of an early Eocene mammal in eastern North America, and because of its association with well-studied marine fossils, the find helped to better calibrate existing separate biochronologies of terrestrial and marine fossils.

by Lauren Raysich

Although many people are familiar with fossilized bones of dinosaurs and other large extinct creatures, some fossils can be so small that a microscope is needed to see them. In Carnegie Museum of Natural History’s PaleoLab, volunteers like me use microscope stations to search for tiny fossils in different sediments collected from sites all over the world. Sediment from the Badwater 20 locality in Wyoming interests me more than any other. Sediment from this site dates to a time known as the Eocene Epoch. The middle of three epochs in the Paleogene Period, the Eocene lasted from 56 to 33.9 million years ago. Many fossils found from the Eocene belong to some of the oldest known members of modern mammal groups. Studying these fossils helps scientists trace the evolutionary histories of mammals we know today.

After searching through the Badwater 20 sediment for nearly two weeks, I had found only fragments of bones and teeth. Then, surprisingly, I came across a small, complete bone. It is not common to find complete fossil bones that are this tiny because they can be broken easily, whether by erosion or by being crushed by scavenging animals or water currents. Fossils are not immune to human-induced hazards either. After I found the bone, I was so excited that I accidentally dropped it on the floor of the lab and had to use a magnifying glass to relocate it! (Thankfully, it didn’t break.)

This bone interested me more than any other because it was the first bone I’d found from the Badwater 20 site that wasn’t fractured in some way. Since the bone is so small, I figured it had to have come from a tiny mammal. Through research and the help of other museum volunteers and staff, I have concluded that this bone is a phalanx (finger or toe bone) of an Eocene rodent. The mouse-like animal to which it belonged most likely lived in a tree, a burrow, or the undergrowth more than 37 million years ago! Although, to some people, this little bone may not be as exciting as those of, say, Tyrannosaurus rex, it thus has an important story to tell in the history of life on our planet.

What does a Scientific Preparator do? Part of Dan Pickering’s really cool job is carefully restoring museum specimens. In this photo he’s working on our mastodon specimen, one of Andrew Carnegie’s first acquisitions for the museum.

After having 120 years of “stuff” put on it to “preserve” it while it was on display, it needed significant restoration work.

All of this “stuff” was applied to the mastodon specimen over time:

·     Shellac

·     Varnish

·     Paint

Plus, cracks, cavities, and broken and missing areas were kept up with:

·     Plaster

·     Putty

·     Bondo

·     Glue

·     Epoxy

·     Wood

·     Chicken wire

·     Metal pins

On top of all that, soot built up on the mastodon when the museum was free and the doors were kept wide open.

Everything from shellac to soot must be removed or corrected to modern standards to restore this historically valuable specimen.

However, not all of these materials can be removed because most fossils are found as partial skeletons. When work is complete, you shouldn’t be able to see which parts are real bones and which parts were added – the skeleton should look cohesive. But if you look closely (from within five feet or so), different tones, colors, and textures will reveal real bones vs. elements added during restoration.