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Linsly Church

January 8, 2021 by wpengine

A Visit to the Mammoth Site, Hot Springs, SD

Did you know that not all museums display their fossil specimens mounted in life-like poses? At The Mammoth Site of Hot Springs, South Dakota, visitors view fossils “in situ,” or as they were discovered, and because excavation continues year-round, this unique museum is also an active dig site.

brown sign that says The Mammoth Site
A sign welcomes visitors to The Mammoth Site of Hot Springs, South Dakota.

Instead of being held in place by the fabricated support structures that are so crucial to traditional fossil displays, bones at The Mammoth Site rest on sediment and appear in the same orientations in which they were found. The remains of more than 60 Columbian mammoths (Mammuthus columbi) have been documented here to date, comprising the world’s most extensive collection of skeletons of these Ice Age elephant relatives.

The Mammoth Site was discovered in 1974 when the landowner decided to build a housing development on the 14-acre plot. While the heavy machine operator was bulldozing a small hilltop, he found tusks and bone. Construction stopped and officials at four colleges were contacted, but none expressed interest in the find. Fortunately, the son of the heavy machine operator, who had taken geology and archaeology courses in college, was able to gain interest from one of his former professors, who was then conducting fieldwork in Arizona. When the professor arrived at the site a few days later he recognized the exposed bones of four to six individual mammoths and the potential for more nearby. He arranged for a field crew to salvage and stabilize the visible bones, teeth, and tusks, and returned the next summer with a group of students to do more excavating. A complete skull with tusks attached was the prize find of these more organized recovery efforts, and by the end of the summer the landowner had decided the tract’s highest value was as a place for scientific study.

mammoth skulls in situ
Mammoth skulls with tusks attached at The Mammoth Site. Notice the sediment supporting the fossils.

I recently had the opportunity to visit The Mammoth Site, which is located in the Black Hills, a scenic region of green pine trees and deep red earth. Once you purchase your admission, you are directed to a theater where a looped video introduces the relevant geologic history. The site is the result of a sinkhole that developed when groundwater dissolved the limestone layers through which it flowed. Subterranean water-filled caverns were an early product of this process, but as the water table lowered the caverns weakened and collapsed, resulting in a deep sinkhole with a chimney-like shaft, through which a warm artesian spring percolated to the surface. In three phases over a period of 750 years, the sinkhole refilled with sediment and the remains of mammoths and other creatures before it was eventually reduced to a mud wallow.

photo of geologic map
Geologic map of the beautiful Black Hills area of South Dakota and Wyoming.

After the theater, the bonebed is the next stop. The museum has a special app that can be listened to with headphones for a tour of the bonebed. The bonebed room is very large and naturally lit and has a high beam ceiling with windows at the top of one wall. There is a crane attached to the rafters that is used to move any specimens that need to be permanently removed from the ground. Because a large tusk can weigh over 100 pounds, and skulls far more than this, this overhead crane is an essential tool.

complete mammoth skeleton
The most complete mammoth skeleton or “model mammoth,” found in the deep end of the bonebed. It is used to compare to the remains of others to determine attributes such as age, size, and sex.

How, you ask, do researchers know there are over 60 individuals in the sinkhole? For every mammoth or person or other critter with a skeleton, there are a certain number of each bone in the body. Because mammoths have two tusks it is possible to count the number of tusks in the bonebed, 123, and divide by two to calculate the presence of at least 62 individuals.

bonebed at Mammoth Site
How many tusks can you find in this section of the bonebed?

Determining the sex of a mammoth is possible when its pelvis is well-preserved with minimal crushing or distortion. By measuring a specific spot on the pelvis and the width of the pelvic canal at a certain area, and comparing these two measurements, it can be determined whether the pelvis belonged to a male or female mammoth. This calculation is possible because males are generally larger than females, and also because females had a proportionally larger pelvic canal to aid in giving birth. Mammoth remains recovered at The Mammoth Site have all been male. Although the presence of more than 60 males but no females at the site may seem surprising, studies have shown that “natural death traps” such as The Mammoth Site captured many more males than females. This may be because, rather than living in herds led by a knowledgeable matriarch, relatively inexperienced male mammoths typically traveled alone, making them more likely to get stuck in these kinds of traps.

It is also possible to age a mammoth using growth rates of bones and the state of fusion of the epiphyses (the ends of the limb bones); however, it is most accurate to age these animals by measuring their teeth. The length and width of the occlusal (= chewing) surface is then used to verify which of their six sets of teeth they were using at the time of death. Generally, a mammoth’s life span could be as long as 60 to 80 years, an age when the animal would be relying upon its sixth set of teeth. When these teeth wore down, starvation would follow. Dental comparisons at The Mammoth Site indicate that most of the remains represent mammoths that were between 15 and 29 years old when they died, with a few in their late forties or early fifties.

mammoth skull fossil in situ
An upside-down mammoth skull shows holes at the front where the tusks attach. Two sets of molars are also visible (I think).

When you next visit Carnegie Museum of Natural History, be sure to head to Pleistocene Hall, where we have our very own mounted Columbian mammoth skeleton on display!

mounted mammoth fossil
The mounted Columbian mammoth at Carnegie Museum of Natural History.

And please remember to keep a tusk-length apart! (Social distancing the mammoth way.)

Linsly Church is a Curatorial Assistant in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum staff, volunteers, and interns are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Early Bats: Ancient Origins of a Halloween Icon

Specimen Carnegie Museum (CM) 62641, the holotypic, or name-bearing, right dentary (lower jaw bone) of the tiny fossil bat Honrovits tsuwape in lingual (= internal) view, still partially encased in ~50-million-year-old rock of the Wind River Formation of west-central Wyoming. Note the length of the scale bar, only 1 cm (less than half an inch)!

Did you know that bats have been around for at least 55 million years? In 1992, several fossils in the Carnegie Museum of Natural History collection, including the lower jaw bone shown above, were described as representing a new genus and species of ancient bat, Honrovits tsuwape—Shoshone for “bat” and “ghost,” respectively—by a team that included two former curators in the museum’s Section of Vertebrate Paleontology, Christopher Beard and Leonard Krishtalka, both now of the University of Kansas. Honrovits dates to the early part of the Eocene Epoch of the Cenozoic Era (the ‘Age of Mammals’), about 50 million years ago, and is a member of a now-extinct bat group called the Onychonycteridae.

Replica of a beautifully preserved fossil skeleton of Onychonycteris finneyi, a close relative of Carnegie Museum of Natural History’s own Eocene-aged bat Honrovits tsuwape, on display at Fossil Butte National Monument in Wyoming. Photo by Matthew Dillon.

Interestingly, Honrovits shares dental characteristics with a mammal group known as insectivores, which includes today’s hedgehogs, shrews, and moles, and in that sense, it differs from the condition in most other bats. However, bat teeth possess distinctive diagnostic features, so although Honrovits is known only from a few tooth-bearing jaw bones and a skull fragment, there’s no doubt that the diminutive beast was indeed an early bat. The fragmentary nature of its fossils means that we don’t know for sure what Honrovits looked like in life, though it’s a good bet that it bore a close resemblance to other onychonycterid bats, such as Onychonycteris finneyi, which is known from exquisitely preserved skeletons (such as the one shown above).

Flesh reconstruction of the ~50-million-year-old bat Onychonycteris finneyi. There’s an excellent chance that Honrovits tsuwape would have looked like this. Art by Nobu Tamura.

The incompleteness of the Honrovits fossils is, unfortunately, the norm rather than the exception when it comes to prehistoric bats. Fossils of these creatures are exceedingly rare because most bats have very small, light skeletons and achieve their greatest diversity and abundance in areas that have low potential for fossil preservation, such as tropical forests. Occasionally, complete skeletons such as those of Onychonycteris are found, but not nearly as often as fragments.

So, this autumn, if you happen to catch a glimpse of a bat silhouetted against the evening sky, acrobatically wheeling and plunging in pursuit of flying insects, pause and reflect on the history of these extraordinary flying mammals whose ancestry dates nearly to the time of the dinosaurs.

Linsly Church is a Curatorial Assistant in the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum staff, volunteers, and interns are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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January 17, 2019 by wpengine

Preserving Fossil Treasures: Eocene Fishes from Monte Bolca, Italy

by Linsly Church

In 1903, Carnegie Museum of Natural History purchased an enormous private fossil collection from the Baron Ernest de Bayet of Brussels, Belgium. Over a 40-year period the Baron had amassed a collection comprising tens of thousands of individual fossils. At age 65 he married a much younger woman and sold the collection to fulfill her dream of having a house on the shore of Italy’s Lake Como. Within the collection are fossils from all over Europe. Fossils from Italy include the Monte Bolca fish collection, which contains about 290 beautifully-preserved specimens that date to about 50 to 49 million years ago, early in the Eocene Epoch.

map of Italy highlighting the province of Verona
The province of Verona (in red) in Italy, where the Monte Bolca site is located.

One quarry at Monte Bolca has been owned by the same family for almost 400 years. It is known as the Pesciara, meaning the fishbowl, because many of the marine fossils found there are those of fishes. Because the preservation is so good in some layers of limestone, the site is considered a Lagerstätte. A Lagerstätte is a site that contains exquisitely-preserved fossils, typically representing a diversity of organisms. At Monte Bolca, some fishes and other creatures have preserved internal organs and even skin pigmentation, the result of an anoxic (oxygen-poor) environment that hindered decay and scavenging. The fossil site also differs from most others in that it is an underground mine with tunnels instead of a typical open quarry.

fish fossil
fish fossil
Two of Carnegie Museum of Natural History’s most spectacular ~50 million-year-old fossil fishes from Monte Bolca, Italy. Top: specimen number CM 4369, belonging to the moonfish Mene rhombea. Bottom: specimen CM 4467, belonging to the spadefish Exellia velifer. Note the dark stains in the eye sockets, which are vestiges of the original eye pigments of these ancient fishes.

Carnegie Museum of Natural History’s collection of fishes from Monte Bolca is currently undergoing conservation. In the past, the museum’s Vertebrate Paleontology collection was housed on open shelves in rooms with poor air filtration systems, resulting in soot from the local steel industry building up on the fossils. In recent years, the museum has installed an HVAC system in the Vertebrate Paleontology collection rooms, which has greatly reduced the particulates that make it into these rooms and onto the specimens. In the years since these measures were taken, we in Vertebrate Paleontology have commenced a general cleaning of our specimens, starting with our fishes from Monte Bolca.

To clean the specimens, we use a soot sponge (or chemical sponge), which is also used by restoration companies to clean after fires. “Chemical sponge” is a slightly misleading name because there are no chemicals added to the sponge. It is made of vulcanized rubber and has tiny pores on its surface that collect fine soot particles without depositing chemicals on the fossil. Therefore, there is no need for water or additional solvents when using these sponges. Wet cleaning of soot can cause staining on the surface that is being cleaned so it is very important to use dry cleaning methods such as chemical sponges. In some cases, the soot on the specimens is so dense that it is obvious where cleaning has taken place.

clean soot sponges
dirty soot sponges
Before and after: clean soot sponges, prior to use (top); dirty soot sponges, after use (bottom) (with the source of the soot—a newly cleaned fossil fish from Monte Bolca—in the background).
fish fossil
fish fossil
fish fossil
Evolution of a fish, roughly 50 million years after the fact. From top to bottom, the same fossil fish specimen from Monte Bolca (CM 4530, Carangopsis dorsalis) in four successive stages of cleaning.

Once the specimens have been cleaned, repairs are made as needed and labels are reattached if they are delaminating from (or falling off of) the specimen. Then, storage mounts are created for specimens as needed using archival materials. These materials are made specifically to be as neutral or inert as possible so as not to give off gases that could react harmfully with the specimens. Storage mounts are important because they reduce the amount of times someone needs to touch the specimen—which, in turn, reduces breakage—and protect the specimen from vibration when the compactors in which it is housed are opened and closed. These measures will help to protect the integrity of the specimens for years to come.

A drawer full of recently-cleaned Monte Bolca fishes in their new storage mounts.
A drawer full of recently-cleaned Monte Bolca fishes in their new storage mounts.

Linsly Church is the curatorial assistant for the Section of Vertebrate Paleontology at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

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Carnegie Museum of Natural History Blog Citation Information

Blog author: Church, Linsly
Publication date: January 17, 2019

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Filed Under: Blog Tagged With: fossils, Linsly Church, Vertebrate Paleontology

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