Marmosa jansae, that rings a bell?

A new mouse opossum species named after the Bell’s curator of mammals Sharon Jansa

Published06/24/2021 , by Emily Dzieweczynski

Marmosa jansae—if that sounds familiar, it’s not because it’s a well known species—instead, it’s a new species of mouse opossum named after the Bell Museum’s curator of mammals Sharon Jansa! In a recent paper by Rob Voss and Tom Giarla, titled, “A revision of the didelphid marsupial genus Marmosa. Part 3, A new species from western Amazonia, with redescriptions of M. perplexa Anthony, 1922, and M. germana Thomas, 1904,” the researchers identify a new species of mouse opossum and use the opportunity to recognize Sharon’s role in this research .

Sharon first learned of the honor after receiving an email on the day the paper was published, which happened to be April Fool’s Day (Coincidence? We think not.), with the paper attached. After the initial surprise, she recalled feeling incredibly honored, as the paper was authored by two of the scientists she admires most.

A person, Sharon Jansa, with a skull

Sharon Jansa, curator of mammals

Having a new species named after you is quite the honor—but this honor is the result of decades of work and dedication. Sharon first started working with Rob, the curator of mammals at the American Natural History Museum, roughly 20 years ago when they launched an initiative to understand opossum diversity and evolutionary history. This was no small endeavour, as there are over 100 known opossum species throughout North and South America—many that look extremely similar. Additionally, classifying and documenting new species of opossum requires a high standard for evidence. The species must be genetically and morphologically distinct, and this must be demonstrated using multiple types of data. Sharon and Rob turned out to be the perfect people for the job. With Rob possessing a keen eye for morphometrics and Sharon with an expertise in genetics, they offered the combined knowledge and compatible skill sets to take on this unique challenge. In fact, they recently published a book on this research.

Tom, on the other hand, is a tenured professor at Siena College in upstate New York where he teaches biology, but Sharon and him go way back, too. Tom recalls the great interpersonal connection that developed on a frigid January day in 2007, when he met Sharon during his search for doctoral programs. Soon, he became one of Sharon’s first graduate students at the University of Minnesota. Tom explained that Sharon offered him, along with many other students, a dedicated and caring mentorship that inspired them as young mammalogists.

“I have memories of her grading and reading all our long papers and offering thorough feedback—not something many professors do. She always wanted to connect me with people and helped me get in touch with collaborators. She was the type of advisor that I needed, when I didn't know what I needed… She has a no-nonsense attitude that is great for when you’re trying to get science done, that, coupled with support and loyalty towards you, made her a great advisor,” Tom shared.

A group of scientists

From left to right: Eliecer Gutierrez, Tom Giarla, Sharon Jansa, Rob Voss, and Juan Diaz-Nieto.

All these connections fostered not only Sharon receiving the honor but also the discovery itself—which is an important and fascinating one, to say the least. Documenting and describing biodiversity is so important because it allows us to uncover patterns of life on Earth. For example, some regions—like Amazonia—are extremely species-rich; others—like northern Minnesota—not so much. Understanding why these patterns exist is one of the main goals of evolutionary biology. Describing species is useful, too, for conservation policy—in order to understand what species are at stake and what we can do to help them, we need to know what’s out there and be able to identify it. Rob and Sharon’s work specifically has been on South American marsupials—a little-known group of mammals that were in need of such focused scientific attention. Their careful work has revealed that there are far more species of opossum than we originally thought.

Sharon is driven by the fact that there is so much work to be done in this area—so much more to discover. Sharon explains that, when it comes to science, you’ll always be traversing the unknown.

What is a species?

Scientists classify the diversity of life using a hierarchical system invented by Carl Linnaeus in 1735. This system sorts organisms into nested sets—Kingdom, Phylum, Class, Order, Family, Genus, Species—called a taxonomy. Ideally, this taxonomy should reflect the evolutionary history of life on Earth, such that all species in a genus are closely related to each other, a family contains a set of closely related genera, and so on up the hierarchy. In this system, organisms are given a scientific name, which is a unique identifier that combines the genus and species names. Thus, all modern humans are Homo sapiens, and we are members of the Family Hominidae, Order Primates, Class Mammalia, Phylum Chordata, and Kingdom Animalia.

Most biologists think that the lowest rank in that hierarchy—the species—is more than just an organizational category and has real biological meaning. Yet, scientists disagree on exactly how to define species. Some define species as a group of organisms that can interbreed and produce fertile offspring, but that definition is hard to apply to asexual organisms, or fossils, or really anything where we can’t observe reproduction directly. Others recognize species as distinct evolutionary lineages that maintain their identity over space and time, which is a fairly heady concept that can be difficult to apply. Generally, though, we agree that species are formed when populations become isolated from each other and diverge until they can no longer exchange genes. When that divergence is accompanied by changes in phenotype (what an organism looks like), we can then identify species as genetically isolated units that look different from other such units.

“Going in, you never know what you might find. For example, we found an opossum species that can eat venomous snakes and indicators that there may have been a large scale extinction event in opossum history,” she exclaimed.

A grouping of three Marmosa jansae specimens

Marmosa jansae, M. perplexa, and M. germana

Sharon also hopes that there are more dedicated and curious individuals who want to take this research further. She hopes to encourage more young mammalogists who want to develop the expertises, keen eyes, and curious minds that will make the next strides in mammalian discoveries. Tom shared that one of the most important things for him as a budding mammalogist was having access to museum collections.

“Doing research at a university that has a museum was a great experience for me… many people conduct research through field work, but a lot more of my work was based on museum collections. If you’re interested in mammalogy, being associated with the Bell Museum was great,” Tom shamelessly plugged the Bell.

If you’re considering a career in mammalogy, you may be interested in reading more about Sharon’s lab. If you want to read more about the research that Sharon, Rob, Tom and others have done on opossums, you can read the recently published book or the study mentioned in this article.

Congratulations, Rob and Tom, on the incredible discovery of a new mouse opossum species, and to Sharon for receiving this honor! We hope that you can one day meet Marmosa jansae!