A mouse with heart

There are basically two types of rodents in South America: caviomorph rodents and sigmodontine rodents. (Squirrels, pocket gophers, and kangaroo rats can also be found in the extreme north of the continent, but they are newcomers and include relatively few species.)

Caviomorphs, literally the guinea pig-like rodents, include a stunning diversity of rodents of unusual size (for a rodent) that pertain to a dozen families: the water-loving capybara, the bunny-like chinchilla, the long-legged mara, and porcupines with grasping (prehensile) tails, just to name a few. They have been in South America for more than 40 million years, having rafted there from Africa, and they are the only rodents found at fossil sites older than about 5 million years. As a consequence, I am generally much more interested in caviomorphs than other groups of South American rodents.

That being said, the other main group of South American rodents, the sigmodontines, are pretty impressive in their own right. Although most of them are small, and they have been in South America for a far shorter period of time than caviomorphs (somewhere between 4 and 10 million years), they have evolved into many more species: some 400 species are alive today (depending on which groups are included) compared to about 250 for caviomorphs. They are generally referred to as New World rats and mice, as they are found exclusively in the Americas.

Fig. X Sigmodontine Teeth.jpg
Upper (left) and lower (right) molars of several species of living sigmodontine rodents. The red arrows indicate molars in the shape of an “s” (albeit a backwards one), the feature that gave sigmodontines their name. (Sigmodon essentially means “s-tooth”.) Modified from Barbiere et al. 2016:fig. 4.

Sigmodontines are part of a larger family, Cricetidae, which includes rodents like hamsters, voles (not to be confused with moles, which are relatives of shrews rather than rodents), lemmings, and the muskrat. The nearly 600 species of that family make it the second-largest family of living mammals. The largest family, at more than 700 species, is Muridae, which includes the house mouse (Mus musculus), lab and sewer rats (Rattus spp.), and many other species native to the Old World.

Put another way, there are A LOT of small rodent species in the world, and a significant proportion of those are sigmodontines. If you want to read a bit more about sigmodontines, check out this Tetrapod Zoology blog, which provides a nice introduction to them. Today, I’m just going to mention one extinct species with which I have a personal connection: Chukimys favaloroi.

First, the facts: Chukimys favaloroi was a mouse-sized species that was named late last year based on an upper jaw with three molars and a single lower molar, probably from the same individual. The fossils were collected from the Bochero Formation in the province of Córdoba in north-central Argentina and are thought to be close to 3 million years old (Pliocene in age).

Why did this paper catch my eye? It wasn’t because of its scientific content, but rather the name the authors selected for the new species. To be exact, it was the specific epithet – the second part of its two-part name – that I noticed: favaloroi.

If you have ever had coronary artery bypass surgery, or had a friend or loved one who has, the man you should thank is a René Favaloro. Favaloro essentially invented the procedure in 1967 when he was working at the Cleveland Clinic, having traveled there from his home country of Argentina to advance the field of cardiothoracic surgery. He returned to Argentina several years later and established the Favaloro Foundation, whose mission is to promote medical teaching and research. He suffered a tragic death in 2000, and it is this Favaloro after which this little sigmodontine is named.

The monument to René Favaloro in La Plata, which is located in the same park as the natural history museum, across the street from the planetarium. Photo from the web site of Favaloro’s soccer club, the Club de Gimnasia y Esgrima La Plata.

My personal connection to René Favaloro isn’t via the procedure he pioneered, but rather through the citizens of his home country and the town where he grew up, La Plata. I had the good fortune to spend several months in La Plata last fall (which is springtime in La Plata), and there were few days I did not see or hear something of Dr. Favaloro. Sometimes a reference to Dr. Favaloro would come after I mentioned I was from Cleveland, as his connection to the Cleveland Clinic is common knowledge there. The park where the natural history museum is located bears a prominent monument to Dr. Favaloro, who attended medical school at the Universidad Nacional de La Plata, and I would often pass by it when walking from one faculty to the next. The husband of the couple from whom I rented my La Plata apartment turned out to be a protégé of Dr. Favaloro’s and past president of the Federación Argentina de Cardiología. He was instrumental in bringing a traveling exhibit about Dr. Favaloro to fruition that premiered in La Plata just last month. When I came across a paper about an extinct species named after Dr. Favaloro, I clearly could not pass it up.

Favaloro Aficha.jpg
Flyer for the traveling exhibit about René Favaloro.

Dr. Favaloro was a humble man despite his fame. I think it is quite appropriate that an unassuming little mouse was named after him rather than a more flamboyant mammal.


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