mammals

March 7, 2023 by Erin Southerland

March Mammal Madness 2023: Learn and Win

by Patrick McShea

What chance does a giant water bug have in a battle with a wolverine? During the next few days participants in the online tournament known as March Mammal Madness will attempt to predict the outcome for this theoretical encounter plus 31 others. “Play” in this single elimination series of antagonistic animal matches begins with a wild card qualifying battle on March 13, and concludes, four well-spaced rounds of competition later, with a championship match on April 5. This now decade-old annual activity, which was created and continues to be directed by Professor Katie Hinde, of Arizona State University, has a well-earned reputation as a fun interactive educational event.

The website for March Mammal Madness (MMM) describes the proceedings as “inspired by (but in no way affiliated with or representing) the NCAA College Basketball March Madness Championship Tournament.” Like the basketball tournament, MMM relies upon a branching four-division bracket listing qualifying competitors and their ranking number to both record predictions and track the tournament’s progress. There are, of course, significant bracket differences. In place of the small print note where some sport tournament brackets announce the chart’s purpose as “For Amusement Only,” the MMM document bears the disclaimer, “MMM includes many non-mammal species.” Also, in the front and center position, where an NCAA, media sponsor, or gaming corporation’s logo would normally appear, is instead the MMM guiding motto: “If you’re learning, you’re winning!”

The clearest explanation of how the competition unfolds, and how willingness to learn is a condition of fandom, is on the MMM website:

The organizers take information about each combatant’s weaponry, armor, fight style, temperament/motivation, and any special skills/consideration and estimate a probability of the outcome and then use a random number generator to determine the outcome. This is why there are upsets in the tournament.

Another thing that can happen is if a species has to battle in an ecology that is really bad for it – for example, if a cold adapted species is battling in a tropical forest, it can dangerously overheat- changing the outcome probabilities. Sometimes an animal gets injured or snaps a canine in a previous round that carries over into the next round- just like an injury of a star player totally changes a basketball team’s outcome. Also hiding or running away counts as a forfeit.

In the early rounds the battle location is in the preferred habitat of the better-ranked combatant in the battle, and ecology can play a huge role in what happens.

I kept all of this in mind as I considered the first-round water bug versus wolverine battle. On the museum’s second floor, a giant water bug is an invertebrate detail in the Hall of Botany’s bog diorama. On the first floor, an encased wolverine taxidermy mount flanks the interactive space Discovery Basecamp. If both creatures mysteriously came to life and met on a back stairway landing, the insect would certainly be flattened or swallowed whole. Like a sports bettor double-checking a basketball team’s bench depth, foul-shooting percentage, or dependable three-point shooters, I conducted a brief internet search for wolverine vulnerabilities.

Details in a summary of the Western States Wolverine Conservation Project revealed this large member of the weasel family as a species highly sensitive to climate change. The long-clawed and densely furred carnivore, whose common name has been used by various corporations to create brands for action heroes, rugged footwear, and all-terrain vehicles, requires large territories with persistent spring snow cover. In the four U.S. states where resident populations of wolverines are known to occur (Washington, Montana, Idaho, and Montana), locations with heavy spring snow cover provide ample “refrigerated” space for the catching of prey, as well as safe denning sites for pregnant females.

I still picked the wolverine to beat the giant water bug, but I won’t be surprised if it doesn’t happen. Highways were mentioned in some research summaries as barriers to wolverine movements, raising the possibility of a forfeited match. Despite a reputation for ferocity, a no-show wolverine could send a giant water bug to the MMM second round.

Patrick McShea is an Educator at Carnegie Museum of Natural History.

World Pangolin Day 2023 – The Mysterious Brain Bone

by John Wible

The third Saturday in February marks World Pangolin Day, celebrating the scaly anteater that is sometimes called the pinecone mammal. Pangolins are covered with scales made of keratin, the same stuff in your fingernails and hair. Because some traditional medicines mistakenly impart curative powers to their scales, pangolins have become the most heavily illegally trafficked animal on the planet. Pangolins lack teeth and live exclusively on social insects, like ants and termites, which they catch with their very long sticky tongue. Today, there are eight species of pangolins, four in Asia and four in Africa. The fossil record reveals greater diversity and geographic distribution for these unusual creatures, including Europe and North America.

I study the evolutionary relationships of mammals, building family trees based on the anatomy of living and extinct species. In the 1800s and 1900s, pangolins were grouped with other mammals that are toothless or have very reduced teeth, such as anteaters, aardvarks, sloths, and armadillos, in the aptly named Edentata (think edentulous, or “toothless”). In the last 25 years, the study of DNA has revealed a totally different set of relationships for these edentate mammals. Aardvarks are in an African group with elephants, elephant shrews, tenrecs, and hyraxes; anteaters, sloths, and armadillos are in a South American group; and pangolins are most closely related to Carnivora (dogs, bears, cats, hyaenas, raccoon, etc.). It is hard to imagine that the gentle, toothless pangolins are close kin to the ferocious meat-eater lineage that includes lions, tigers, and saber-toothed cats.

Although DNA supports relationships of pangolins and carnivorans, we are hard pressed to find anatomical features that link the two groups. One unusual feature shared by both and, therefore, hypothesized to be present in their common ancestor is the os tentorium or brain bone! A typical mammalian brain is composed of three parts delimited by deep grooves, termed sulci, the fore-, mid-, and hindbrain, which correspond respectively to the olfactory bulbs, cerebrum, and cerebellum.

*This brain of the African white-bellied tree pangolin,* Phataginus tricuspis, is modified from Iman et al. (2018: Journal of Comparative Neurology 256: 2548-256), courtesy of Paul Bowden, Carnegie Museum of Natural History.

The human brain is dominated by its greatly enlarged cerebrum with tiny olfactory bulbs; pangolins and carnivorans have a much better sense of smell with well-developed olfactory bulbs and relatively smaller cerebrum. The brain in mammals is encased in a fluid-filled space surrounded by layers of connective tissue and within the bony braincase of the skull. One of the connective tissue layers, the dura mater, has a fold called the tentorium cerebelli (meaning the tent of the cerebellum) that fits in the deep sulcus between the cerebrum and cerebellum. In pangolins and carnivorans, the connective tissue tentorium has a layer of bone in it, creating a partial bony separation between the cerebrum and cerebellum. In pangolins and carnivorans, the os tentorium is not a single bone, but is made up of contributions from three or four skull bones. There are other mammals that independently have evolved an os tentorium, including horses, but it is not as extensive as that in pangolins and carnivorans.

*Chinese pangolin,* Manis pentadactyla, CT scan data. Top, whole cranium; middle, sagittally sectioned cranium with brain added; bottom, sagittally sectioned cranium with blue indicating os tentorium.

Okay, so we have a nice anatomical feature allying pangolins and carnivorans. However, we are left with one very large unanswered question. Why? If it is such a good thing to partially separate the cerebrum and cerebellum by bone, why don’t all mammals do it? The os tentorium is said to be “protective” of the brain, but protective how? Did a random mutation some 60 million years ago in the common ancestor of pangolins and carnivorans lead to the formation of the brain bone in the living forms? Is the brain bone somehow linked to another innovation that is strongly selected for? Is there some function to the brain bone that our brains cannot fathom? As an anatomist, I can study the structure and distribution of the brain bone in living and extinct mammals but to get at the “why” question may require a deep dive into molecular biology. Understanding the genetics behind the os tentorium may be the only path forward on cracking this mystery.

John Wible is Curator of Mammals at Carnegie Museum of Natural History.

Groundhog Day 2023

by John Wible

January 21, 2023 was Squirrel Appreciation Day! With Groundhog Day, which commemorates our most famous squirrel, Punxsutawney Phil, right around the corner, I thought it appropriate to celebrate squirrels with this blog.

Rodents are the most diverse lineage of living mammals with more than 2,500 species, which represents nearly 40% of the species diversity of living mammals. Squirrels (Sciuridae) are one of 36 families of living rodents. There are nearly 300 species of squirrels found in the Americas, Eurasia, and Africa; a few squirrels have been introduced into Australia by humans. Broadly speaking, there are three main types of squirrels: tree, ground, and flying. Tree and ground are descriptive of their main habitats; flying squirrels also inhabit trees but are so called because of their unique locomotory pattern, which actually isn’t flying but gliding! Regarding their evolutionary relationships, all flying squirrels are more closely related to each other than to other squirrels, supporting a single origin of gliding in their common ancestor. The tree and ground squirrels do not show the same pattern; all ground squirrels are not each other’s closest relatives and the same is true of all tree squirrels. The fossil record (see text below) supports tree life as the earliest squirrel habitat, with multiple episodes of ground invasion from the trees.

In Pennsylvania, we are fortunate to have seven native species of squirrels (two ground, three tree, and two flying). You can learn more about Pennsylvania mammals at our website: https://mammals.carnegiemnh.org/pa-mammals/

Allegheny County has six of the seven PA squirrel species: the two ground squirrels (the Eastern chipmunk, Tamias striatus, and the groundhog, Marmota monax); the three tree squirrels (the gray squirrel, Sciurus carolinensis, the fox squirrel, Sciurus niger, and the red squirrel, Tamiasciurus hudsonicus); and one of the two flying squirrels (the Southern flying squirrel, Glaucomys volans). Depending on where you are in Allegheny County, you may see all six squirrels, although the Southern flying squirrel is likely the most elusive because of its nocturnal (nighttime) activities.

Squirrels have a long evolutionary history. The oldest fossils identifiable as squirrels first appeared around 34 million years ago in western North America, all showing adaptations to tree life. One of these, Protosciurus, is on display at the Smithsonian in Washington, D.C. (see below). Its skeleton is remarkably like those of living gray squirrels, both in size and morphology. Given that this remarkable similarity occurred over 30 million years of geological time, scientists consider our gray squirrel and tree-adapted relatives to be living fossils, that is, not dramatically changed compared to their very ancient relatives.

*Reconstruction of the skeleton of* Protosciurus on display at the Smithsonian’s National Museum of Natural History in Washington, D.C. *Image credit: Claire H. from New York City, USA, CC BY-SA 2.0 https://creativecommons.org/licenses/by-sa/2.0, via Wikimedia Commons*

Most rodents are small mammals; think mice and their relatives. Punxsutawney Phil is the second largest living squirrel; his cousin, the hoary marmot, Marmota caligata, from the Pacific Northwest is slightly larger, with adult males typically over 20 pounds. There was a larger ground squirrel that lived in western North America between 10 and two million years ago, Paenemarmota, a Latin name that translates to “almost a marmot.” Some of my colleagues have called it the “giant marmot,” which should be taken with a gigantic grain of salt! Below is an image of four ulnae, one of the two bones in the forearm. On the left is the living groundhog and next to it is the “giant marmot.” Anatomically, the bones are nearly identical, with one a little larger than the other. Weight estimates for the “giant marmot” are around 35 pounds. Yes, that is big for a squirrel, but not compared to some truly giant rodents. Next to the “giant marmot” is the ulna of the largest living rodent, the semiaquatic Central and South American capybara, Hydrochoerus, which translates to “water pig.” Capybaras, which can grow to nearly 150 pounds, are related to guinea pigs! But wait, there is more. Capybaras pale in comparison to the largest rodent that ever lived. The 8-million-year-old Proberomys from Venezuela was estimated to be the size of a large African antelope at 300 to 550 pounds. Yikes, now that is a giant guinea pig.

*Ulna (forearm bone) of select living and extinct rodents.*

Recently, one of my colleagues, Ornella Bertrand from the Universitat Autònoma de Barcelona, Spain, and coauthors have studied the evolution of the brain in squirrels. From CT scans of fossil skulls (see images below), they were able to recreate various parameters of the brain, including the relationship between brain size and body size. They found that squirrels living in trees had larger brains to their body size than other squirrels, that life in the complex arboreal environment was a driver of brain evolution in squirrels. The result of this evolutionary story for us may be that we will always be hard pressed to build a bird feeder that those big-brained tree squirrels can’t get into!

*Images courtesy of Ornella Bertrand. Middle, skull taken from CT scans of the 32-million-year-old fossil squirrel* Cedromus wilsoni from Wyoming with the blue indicating the reconstructed brain, shown separately to the right; left is Ornella’s reconstruction of the animal’s head. For 3D models made by Ornella Bertrand and more, see https://ornellabertrand.wordpress.com/3d-models/

John Wible, PhD, is the curator of the Section of Mammals at Carnegie Museum of Natural History.

GETTING FROM THE FERN HOLLOW BRIDGE TO THE FRICK FAMILY

by Lisa Miriello

*A view of Forbes Avenue bridge crossing over Fern Hollow in Frick Park, 1914. Pittsburgh City Photographer Collection, University of Pittsburgh.*

After the Fern Hollow Bridge collapse on January 28, 2022, many commuters found themselves experiencing some traffic headaches as they scrambled to find different ways to and from work or school. My new route takes me past The Frick Pittsburgh, a museum complex in the Point Breeze section of Pittsburgh that includes Clayton, the former home of industrialist Henry Clay Frick.

As someone who works in the Section of Mammals, my thoughts while passing the stately grounds often turn to Frick’s son Childs (1883-1965), who grew up here exploring the woods surrounding the estate and attending Sterrett School (now Sterrett Classical Academy), less than a third of a mile away.

*Photographer unknown, American,* Sterrett School, c. 1900, gelatin silver printing-out paper print, H: 7 1/2 in. x W: 10 5/8 in., Carnegie Museum of Art, Pittsburgh, Second Century Acquisition Fund, 1999.34.2, Photograph © 2021 Carnegie Museum of Art, Pittsburgh.

As Childs grew older his early interest in the natural world turned to more scientific pursuits, and he embarked on a series of collecting expeditions in North America followed by visits to Africa, first in 1909 and again in 1911. But Childs wasn’t looking for “trophies.” By collecting animals at different life stages his goal was to further the knowledge of the lifestyle and habitats of these unfamiliar animals. Many of these specimens were gifted to the Carnegie Museum, and as the shipments arrived from overseas the staff taxidermists had their hands full.

Led by brothers Remi and Joseph Santens these skilled artisans created expressive animal likenesses rather than the static displays that were seen in most museums at the time. Both Santens even visited zoos in New York and Washington, DC, to study the movements of living animals. Preserved plant life from Africa provided even more authenticity to the displays. The African Buffalo (Syncerus caffer) group was especially notable in how it was depicted. The animals appear to be spattered with mud and tramping through brush, a display then-Director W. J. Holland believed to be the first instance in which exhibition specimens had been accurately placed within their supporting environment. In the Carnegie Museum’s 1913 Annual Report he wrote that the group “may possibly provoke comment and criticism, but it is believed to be a step in the right direction, and will likely be followed by the leading taxidermists of the future.“ You can see the African Buffalo, along with other specimens collected by Frick, in the museum’s Hall of African Wildlife.

*Carnegie Museum of Natural History, photo by Mindy McNaugher*.

While Childs enriched the collection of the natural history museum, other family members left an impact on the city of Pittsburgh as well. His father, Henry Clay Frick (1849-1919), bequeathed 151 acres of land that would become Frick Park. Expanded by hundreds of acres over the years, it’s now the largest of the city’s parks.

Childs’ sister, Helen Clay Frick (1888-1984), was an art collector like her father and helped establish the Henry Clay Frick Fine Arts Library at the University of Pittsburgh. She later had the Frick Art Museum constructed on Clayton’s grounds to showcase her collection of art. This cultural resource opened to the public in 1970.

At the end of the day, as my car inches past the peaceful grounds of Clayton, I imagine traffic must have looked a little different over a hundred years ago when “horseless carriages,” horse-drawn vehicles, trolleys, and bicycles all shared the same road in a free-for-all. Today, with traffic signals and defined lanes, at least it’s more of an ordered chaos.

A view of a portion of Grant Boulevard populated with a mixture of automobiles, a horse with buggy, and a bicycle in the background. Grant Boulevard was renamed Bigelow Boulevard in 1916. Thomas Mellon Galey Photographs, Detre Library & Archives, Senator John Heinz History Center
*Grant Boulevard | Historic Pittsburgh*

Museums and parks can provide welcome relief in a chaotic world, and the Frick family’s contributions to these sanctuaries of art, science, and nature will be enjoyed for generations to come.

Lisa Miriello is the Scientific Preparator for the Section of Mammals.

Do Any Mammals Lay Eggs?

by Dr. John R. Wible

Scientists recognize three major types of living mammals: placentals, marsupials, and monotremes, all of which produce milk to nourish their young. Of the 6,495 mammal species recognized in 2018 (Burgin et al., Journal of Mammalogy vol. 99), 6,111 are placentals, 379 are marsupials, and 5 are monotremes.

Placentals and marsupials are viviparous, meaning they give birth to live offspring. Marsupials, such as kangaroos, koalas, and our local Virginia opossum, give birth to very immature, embryo-like offspring that complete their development outside the womb usually attached to a nipple in a pouch. In contrast, placentals, such as dogs, cats, and humans, give birth to more developed offspring and have no pouch. Both marsupials and placentals have a placenta that nourishes the developing offspring in the womb, but this organ is more efficient in placental mammals than in marsupials.

But what about monotremes? The five species of living monotremes include the duck-billed platypus found only in eastern Australia, the short-beaked echidna found in Australia and New Guinea, and the three species of the long-beaked echidna found only in New Guinea. Echidnas are also known as spiny anteaters.

In contrast to the viviparous marsupials and placentals, monotremes are oviparous, a word that means they “give birth to eggs”. Unlike the hard-shelled eggs of birds, monotreme eggs have a leathery exterior, like those of most reptiles. The platypus has one mating season per year and produces one to three eggs with an average of two. Pregnancy lasts about 21 days and incubation of the hatched egg in a nest of wet vegetation is about 10 days. The lima bean-sized platypus newborn or puggle (or platypup to some) is embryo-like, but more advanced than a newborn joey (kangaroo). It crawls onto the mother’s belly in search of milk, which oozes from the skin surface, as monotremes don’t have nipples.

On a recent research trip to Edinburgh in the United Kingdom, I visited the mammal collection of the National Museum of Scotland. There I came across a model of the egg of a platypus, which was the inspiration for this blog. This three-quarter-inch-long egg will hatch and grow into a house cat-sized animal. Given that monotremes, most reptiles, and all birds are oviparous, the common ancestor of mammals is thought to have been an egg-layer as well. This primitive mode of birth was retained in living monotremes, but evolved into live birth in the common ancestor of placentals and marsupials.

Platypus egg in a box with a label next to it that says "Egg of the duck-billed platypus, Ornithorhynchus anatinus, East and South-East Australia and Tasmania."

John Wible is the Curator of Mammals at the Carnegie Museum of Natural History.

Early Placental Mammal Evolution Prioritized Brawn over Brains

*Crania and virtual endocasts inside the translucent cranium of the Paleocene mammal Arctocyon (left) and the Eocene mammal Hyrachyus (right). Credit: Ornella Bertrand and Sarah Shelley.*

An international research team, including scientists from Carnegie Museum of Natural History (CMNH), authored a new study published this month in the prestigious journal Science finding that early placental mammals developed bigger bodies before developing proportionally bigger brains after the extinction of the dinosaurs. Modern mammals have the largest ratio of brain to body size, or encephalization, among vertebrates, and it has long been contended that this ratio emerged in the early stages of mammalian evolution. The study, “Brawn before brains in placental mammals after end-Cretaceous extinction,” finds that mammals prioritized increased body size to enhance survival in the first 10 million years following dinosaur extinction.

CMNH research associate Dr. Sarah Shelley and curator of mammals Dr. John Wible contributed to the study, led by Dr. Ornella C. Bertrand, postdoctoral fellow at the University of Edinburgh. The team analyzed CT scans on newly discovered fossils from the Paleocene, the epoch 10 million years after the mass extinction. The team learned that relative brain sizes of mammals initially decreased because their body sizes increased at faster rates. Their findings also suggest that mammals in this period retained advanced senses of smell, leaving the other senses—including vision—to adapt later, suggesting that size and smell were more important for survival than intelligence.

“Because modern mammals are so intelligent, many assumed that large brains enabled mammalian survival after the extinction,” said Wible. “However, it appears our modern brain is much more recent than we anticipated, arriving on the scene in the Eocene epoch, another 10 million years later. It’s very possible that large brains might have proven impediments to survival in the post-dinosaur world.”

Illustration of two prehistoric mammals. — Reconstruction of the Eocene mammal Hyrachyus modestus, a rhinoceros-tapir ancestor (left) and the Paleocene mammal Arctocyon primaevus, a carnivorous predator most closely related to the group including living pigs, sheep and other even-toed ungulates (right).Credit: Sarah Shelley.

In the Eocene, about 54.8 to 33.7 million years ago, multiple placental mammal lineages independently developed larger relative brain sizes as extinction survivors filled niches vacated by departed species. Brains continued to grow as competition surged in crowded ecosystems.

Timeline

66 million years ago: Cretaceous ends with mass extinction, including dinosaurs.
66 million-56 million years ago: Paleocene. Placental mammals evolve larger bodies, but not larger brains.
55 million-34 million years ago: Eocene. Most modern mammal lineages appear, including ones with larger relative brain sizes.

Shelley and Wible were involved in all aspects of the study, including CT scanning of fossils, data analysis, and writing. Shelley contributed original art to the accompanying illustrations and figures.

About Science

Science has been at the center of important scientific discovery since its founding in 1880—with seed money from Thomas Edison. Today, Science continues to publish the very best in research across the sciences, with articles that consistently rank among the most cited in the world. In the last half century alone, Science published the entire human genome for the first time, never-before seen images of the Martian surface, and the first studies tying AIDS to human immunodeficiency virus.

March Mammal Madness 2023: Learn and Win

by Patrick McShea

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Groundhog Day 2023

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GETTING FROM THE FERN HOLLOW BRIDGE TO THE FRICK FAMILY

by Lisa Miriello

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Do Any Mammals Lay Eggs?

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