Biomedical Ephemera, or: A Frog for Your Boils

Mammalian Woodpeckers

Did you know that there are not one, but two mammalian woodpeckers? Well, they fill the same ecological niche as woodpeckers, at least!

The striped possum (Dactylopsila trivirgata) is a close relative of the Sugar Glider and lives throughout New Guinea, while the Aye-Aye is a proto-lemur (Daubentonia madagascariensis) that lives on the island of Madagascar.

Both of these creatures are percussive hunters. That is, they use parts of their body to tap on a surface (in this case, tree trunks) in order to locate their prey, which they then dig into the surface of the tree to extract.

While the woodpecker uses its beak to percuss, the aye-aye and striped lemur use their fingers, and the aye-aye is especially adapted for the job! Their long, thin middle fingers are full of far more nerves than other fingers, and they can often feel a grub's vibrations before they hear it. The extensive network of nerve endings means that the middle fingers require a large bloodflow to be effective, and as such, they're not "warmed up" until the aye-aye decides that it's time to hunt.

While the stripped possum is less adapted than the aye-aye to its particular niche (supplementing its diet with many free-wandering bugs and having good eyesight), its small ears betray its extremely sensitive hearing, and its prehensile tail allow it to reach where other vertebrates of the area cannot.

Images:

Proceedings of the Zoological Society of London. Illustrations by Joseph Wolf in 1908 and 1863.

Top: Common Opossum - Didelphis marsupialis Bottom: Virginia Opossum - Didelphis virginiana

Stay in the pouch, kids! We can't stop here; this is bat country!

Even though several marsupial families lived in the Americas before the last ice age, opossums are the only ones still remaining. Thanks to their opportunistic omnivorous diet and high rate of reproduction, opossums have survived in their current form for millenia, even despite their extremely low encephalization quotient. While rote brain volume does not in and of itself determine intelligence of an animal, mammals with smaller encephalization quotients tend to be more specialized and quickly speciated when hardships are encountered (such as ice ages). Opossums in the Americas generally have an EQ around 1/5 that of the raccoons.

Didelphidae (Western hemisphere opossums) have very short lifespans, generally living less than two years in the wild, which is very unusual for a mammal of their size (up to the size of a large housecat). However, they can generally produce two successful litters of up to 13 young each in their short lives.

Australian opossums, while distantly related to those in the Americas, have furry tails, larger brains, and are much less urbanized. They also bear fewer young, live at least twice as long, and are less than half the size of the largest North American opossums.

Dictionnaire Universel d'Histoire Naturelle. Charles d'Orbigny, 1849.

"Koalo" (Koala - Phascolarctos cinereus)

Sure, it lives its life in trees, dines almost exclusively on a plant genus that is incredibly non-nutritive and toxic to most animals (Eucalyptus), and the males have a two-pronged penis, but the koala has more in common with humans than you might think.

For one, they have lots of problems with venereal diseases, including one that's so closely related to the human strain it can be transmitted across species - chlamydia. However, in koalas, chlamydia is present even in most healthy animals, and it's only when the animal gets stressed or otherwise weakened that it manifests as disease. There's currently a huge uptick in the numbers of koalas infected with chlamydia, causing mass sterility and, in many cases, death.

On a less dire note, koalas are the most distantly-related mammal to display "dermatoglyphes" - fingerprints with ridged loops and whorls, like humans have. In fact, it's almost impossible to tell the difference between the two under a microscope. As Homo sapiens and Phascolarctos cinereus diverged over 70 million years ago, it's clear that this is a case of convergent evolution, developed to help the koala grip onto branches and tree trunks.

Aracana, or, The museum of Natural History. George Perry, 1811.

Dide[l]phis derbiana (now Caluromys derbianus) - Derby's Opossum

This Paraguayan and Central American opossum was named in honor of the 13th Earl of Derby.

This particular specimen lived in the Zoological Society's Gardens, and would viciously attack anyone who came near her when she had young who were not yet on their own. When she was not with her young, she was shy, but not eager to attack.

Biologia centrali-americana: Mammalia. Edward Richard Alston, 1882.

"Dog-headed thyloeinus"

This is either a miniature thylacine, or a damn giant of a platypus...thylacines ranged from 40-70 lbs (20-30 kg) as adults (they were about the size of a small greyhound, but built more for stamina than speed), and platypuses are considered BIG if they reach 6 lbs (2.6 kg).

Roosevelt's Thrilling Experiences in the Wilds of Africa Hunting Big Game. Marshall Everett, 1909.*

*No, this scene is not from Africa. It is from an account of another explorer later in the book, who went to Tasmania

Aboriginal art at Ubirr

This ~2200 y.o. drawing of a thylacine is on a cave rock in Ubirr, an aboriginal holy site in the Kakadu National Park, in the Northern Territory of Australia. There is art depicting indigenous wildlife, local spirits, and the aborigines themselves. Since approximately 40,000 years ago, the many rock outcroppings at Ubirr have been painted and re-painted, but the pigment used on this illustration has been dated to (roughly) 200 B.C.E. 

The thylacine is known to have been extinct in this area for over 2000 years.

Kakadu National Park and Aboriginal Culture

Thylacoleo ("marsupial lion") skull fragments

Richard Owen received and described these skull fragments in 1859. The extraordinary difference in one of the teeth presented to him led him to question the initial proposition that this was simply another extinct placental mammal. Comparing the mandibular structure and tooth structure to dasyures and thylacines versus the mandibular structure of the placental lion showed him that this was a marsupial mammal.

On the Fossil Mammals of Australia Part I. Richard Owen, 1859.

The Tasmanian Tiger - Thylacinus cynocephalus

The Mammals of Australia. Krefft, from photographs by Victor A. Prout, 1869.

Thylacinus cynocephalus

So I was reading more about the thylacine, and it turns out that conservation measures WERE actually made law regarding them!....except, they were made law in 1936, after Benjamin died. :| 

Proceedings of the Scientific Meetings of the Zoological Society of London. 1850.

The last thylacine ever, in Hobart, Tasmania. His name was Benjamin.

The thylacine jaws could open over 120 degrees, but were not particularly strong. Actually, compared to other carnivores (like the Tasmanian Devil), they had quite weak jaws. I wonder why they could open so wide, but not chomp down? I mean, I'm sure the two traits go together (the longer the muscle, the more it takes to make it strong), but I wonder about the origin of the traits.

Thylacines at Beaumaris Zoo in Hobart, Tasmania

This photograph was taken in 1910. The thylacines in this photograph are siblings, and I think they were the last litter ever born.