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Carnegie Museum of Natural History

One of the Four Carnegie Museums of Pittsburgh

Paleolab

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Fossil Matrix Under the Microscope

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.

fossil matrix on a sorting tray
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.

Container of fossil matrix with a person holding it.
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 in a clear plastic container with a paper label
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.

Patrick McShea works in the Education and Visitor Experience department of Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

Related Content

The Bromacker Fossil Project Part III: Fossil Preparation

Pebble or Jaw?

Mesozoic Monthly: Nemicolopterus

Carnegie Museum of Natural History Blog Citation Information

Blog author: McShea, Patrick
Publication date: August 27, 2021

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Badwater 20: Not So Bad After All

by Lauren Raysich

small fossil

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.)

small fossil next to a penny for scale

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.

Lauren Raysich is an undergraduate student at the University of Pittsburgh who volunteers in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences working at the museum.

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Mastodon Restoration

Dan Pickering working on mastodon restoration

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.

You can watch Dan and other Scientific Preparators at work on the mastodon in PaleoLab.

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Clues

By Amy Henrici

Collection Managers often solve fossil mysteries, and sometimes we have only a few clues to assist us. A recent mystery involved some rib fragments prepared by PaleoLab volunteers. Individual packages containing rib fragments found in an old cardboard box stashed in a Vertebrate Paleontology storage room proved to be perfect for PaleoLab volunteers to hone their preparation skills.

My task as Collection Manager is to catalog and integrate these ribs into the fossil mammal collection. Fortunately, most of the rib packages contained field labels, which are used to record information when the specimen is collected. My first clue came from the Description category of a field label with one of the rib packages, and it indicated that the rib connected with a block (which consists of fossil and rock). Because there are no blocks of unprepared fossil mammals in storage, I had to assume that this block had been prepared and the specimen was cataloged. The field label lacked a catalog number (Department No. on the label) and any locality information, which would normally assist in locating the rest of the specimen.

old label for a museum specimen

This field label must have been printed for an expedition to Brazil, and the left overs were used by all museum expeditions until they ran out.

The only clue that I had to link the rib to a cataloged specimen in the Section’s computerized database was the block number (Blk. 11/1931), which are entered in the field number category of the database. A search of the database retrieved two specimens with this field number, CM 6425 and CM 36355. Both were brontotheres, formerly known as titanotheres, which are large, extinct rhinoceros-like herbivores. I located the specimens in the collections, and both included incomplete ribs. The field label shown here mentioned that the rib made contact with a “…portion in block indicated by letter D”. Amazingly, I found the letter D written on the broken end of a rib cataloged as CM 6425, and the rib fragment associated with the field label connects to it. I was able to fit all of the rib pieces prepared in PaleoLab onto other ribs cataloged as CM 6425.

two parts of a rib bone being held together
The rib piece held in the left hand fits onto a piece stored in this drawer. Both have the letter D written on them at the point where they join. (Photograph taken by Norm Wuerthele)

 

black and white image of a large mamal skelleton
Archive image showing the skeleton of the brontothere, Brontops dispar, CM 767, which can be seen on exhibit in Cenozoic Hall.

Amy Henrici is the Collection Manager for Vertebrate Paleontology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences of working at the museum.

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Ask a Paleontologist

Diplodocus carnegii dinosaur fossil

In January, Carnegie Museum of Natural History paleontologist Dr. Matt Lamanna talked from the Big Bone Room of Carnegie Museum of Natural History on Facebook Live and answered questions from viewers and schools across the country. Matt received more than 75 questions! Here’s one he wasn’t able to answer live. New episodes featuring different scientists are live streamed every month. Follow us on Facebook!

How old is the Diplodocus in our museum?

“Our Diplodocus carnegii fossils are about 150 million years old. If you’re asking how old the animals were when they died, unfortunately we don’t know that (at least for the moment).”

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Paleo Field Tools

By Patrick McShea

Although work gloves, rock hammers, chisels, and protective goggles remain standard field equipment for fossil field work, electronic devices have become critical search tools. In both the Elko Hills and South Egan Wilderness, Vertebrate Paleontology Collections Manager Amy Henrici regularly referred to her iPad’s topographic map app which utilized a GPS function to provide accurate on-screen tracking of our movement across the landscape.

Other sometimes overlooked field tools are described below.

Reliable Transportation

Jeep Wranlger on a rugged dirt path

A rented Jeep Wrangler proved to be an indispensable field tool. Unlike the high speed off-road travel depicted on television commercials, during a steep ascent from sage brush flats to the zone of pinyon and juniper we climbed in a low gear crawl. (Above) In places where the track crossed dry stream washes, it was sometimes necessary to scout routes into and out of the deeply eroded channels.

Fields Notes

Field notebooks

Field notes add a layer of documentation to scientific fossil collecting. Details about localities, the field crew, the vegetative cover, and even the weather might prove to be important information for a future paleontologist re-examining a particular set of fossils.

As an educator, the field work journal I kept doesn’t have direct association with particular fossils. Instead the duct tape-bound notebook, which bears the label of a Nevada-brewed IPA, serves as portable file, holding hand-written notes, related maps, brochures, and reports.

Place-related Information

field with mountain range in the distance
Nevada’s Ruby Mountains from the hills outside Elko.

 

Because western scenery differs so much from that of east, a guide to the contrasts is useful tool, even for visitors focused on finding fossils. Observations by author Wallace Stegner aid in the appreciation of western landscapes.

In a dry land the brinks of hills will be clifflike, not rounded; valleys will often be canyons; hills are likely to be buttes and mesas and barerock movements; the coloration will not be the toned greens of wetter regions but the red and ochre and tan and gray and black of raw rock, the gray of sagebrush, the yellow of dry grass.

– Wallace Stegner “Why I Like the West” Marking the Sparrow’s Fall Henry Holt and Company, New York, 1998

Patrick McShea is a museum educator who is traveling through Nevada with Vertebrate Paleontology Collections Manager Amy Henrici to search for frog fossils. He frequently blogs about his experiences.