Thylacine Opens a World

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Animal Phyla

Introduction

A 1600 Work I

Thylacine Opens a World

Bill Long 12/9/08

Classifying/Understanding This Among the Mammals

Thylacine was one of the words given (and missed) at the Portland spelling bee last night. I think I would have misspelled it, too, and so I owe it to myself to track it down. When I did, I discovered that there was a tremendous "subculture" of people interested in this extinct (only since the 1930s) Australian marsupial. Here, for example, is a whole web site devoted to the thylacine or tasmanian wolf (the word thylax is Greek for "pouch," and cyne is Greek for "dog"). The purpose of this essay is to show how biologists struggled to classify this beast and to explicate some of these classification terms. It is popularly known as the Tasmanian wolf, though other terms, like the "Zebra-wolf" or "Thylacine Dasyure" have been popular.

Though there were several native terms for this animal (picture here), the first Europeans to study it focused on the animal's head and in 1808 named the species Didelphis cynocephala-- or "dog-headed opposum." But a better translation is "two-wombed dog-headed (animal)," for the word opossum, which means "doglike animals" is derived from Virginia Algonquian (I wonder if that is the branch with the drawl....) while the word "two-wombed" is a literal translation of "didelphis" (di is Greek for "two" and delphus is a "womb").

Generic Classifications of Mammals

In the early days of "modern" classification (early 19th century), the Didelphia were synonymous with the Marsupialia, or "marsupial implacental mammals" and constituted one of the three subclasses of the Mammalia. By the way, the word marsupial comes from the Latin word meaning "pouch." The other two old terms for the "subclasses" of mammals were Monodelphia ("one womb") and Ornithodelphia ("bird womb"). The subclass terminology for mammals changed in the late 1870s when TH Huxley, probably the greatest naturalist of his time, suggested different language. The three terms he chose, still in use today, are Prototheria (first beasts--the egg-laying ones); Metatheria (those beasts that come next--the marsupials) and Eutheria (the "true beasts").

But here is where the terminology and credit for it is not fully clear. Most online sources attribute the name Prototheria to Gill in 1872, even though the first apparent usage of it in a narrative description was by Huxley in 1880. "It will be convenient to have a distinct name, Prototheria, for the group which includes these, at present, hypothetical embodiments of that lowest stage of the mammalian type, of which the existing Monotremes are the only known representatives. A monotreme (words had been used since the 1820s) has "one" (mono) "hole" (trema) and is so called because these egg-laying mammals have a "common opening for the urogenital and digestive system." The only extant members of this contemporary order are the platypus (Ornithorhynchus anatinus--this means "bird-beaked duck." The word anatine--AN a tin--in English means "resembling a duck or duck-like) and two species of echidna. So, I think the Ornithodelphia gave way to the Prototheria.

The second category, Didelphia, gave way to the Metatheria. The OED likewise credits Huxley with the first usage of Metatheria, and there is apparently no previous use of it by Gill or anyone else. Also from his work in 1880: "An intermediate type between that of the Prototheria and that of the higher mammals, which may be termed that of the Metatheria." The OED calls these an "infraclass" of mammals, comprising the single order Marsupialia. Now we see how current taxonomists are tied up in terminology. Is it an "infraclass" or, like the Prototheria, a "subclass"? I think the complexity of classification is so extreme now that we are almost to the point of constant "clade wars." A thousand years ago it was "clan wars." Now we have moved up to the "clades."

The third classic category, the Monodelphia has been replaced by the term Eutheria, or "true beast." As the OED says in its definition of Monodelph: "A mammal of the former subclass Monodephia (now usually regarded as the infraclass Eutheria), comprising those whose females have a single uterus and vagina (the placental mammals)." Now, this is interesting from a number of angles. Now the third of the "big three" categories "under" Mammalia is called an "infraclass." So two of the three categories under the Mammalia are called "infraclass" in the OED, while the third is called a "subclass." No wonder students have difficulties. And, to top it off, the word Eutheria, which occurs as the important word in the OED definition of Monodelph, doesn't have an entry in the OED! What do we have instead? We have eutherian, again attributed to Huxley in 1880: "An undifferentiated Eutherian." But then, the OED tells us that TN Gill used the term Eutheria first in 1872. The Wikipedia article says that Huxley proposed Metatheria and Eutheria in 1880, but the latter term isn't attributed by the OED to Huxley (it was to Gill in 1872), and the OED says that Huxley was the first to used Prototheria (which the Wikipedia article doesn't mention) in 1880. I have no euphoria over eutheria, or any other term, as a result.

To make things worse, this 1913 History of Land Mammals in the Western Hemisphere, says that the "class Mammalia" is divided into two sub-classes of very unequal size (so apparently the three-fold system of Huxley hadn't fully caught on even a generation after it was developed). These two are Prototheria and Eutheria. But the apparent dumbness of this should have been apparent to all. What is the point of dividing up classes into subclasses that have, on the one hand, 2 and, on the other hand, about 500 species? No point at all. But then, the author says that the second subclass, Eutheria is divided into Didelphia and Monodelphia. I think there are more chances for confusion than enlightenment here, don't you?

Moving to the Genus Names

Well, as I said above, at first the thylacine was called Didelphis cynocephale and classified with the rest of the marsupials. But then, its genus name began to change. The year after G.P. Harris had named it a Didelphis, the Parisian zoologist Etienne Geofffroy Saint-Hilaire assigned the thylacine to the genus Dasyurus along with the martens or quolls. But further investigation of this animal (which actually was last sighted in the 1930s) led Conrad Jacob Temminck to create, in 1824, the genus name that is still in use today--Thylacinus. He kept Harris' species name, and there you have an explanation of Thylacinus cynocephalus.

Let's conclude with some contemporary terminology, rough as it still is. We know that most zoologists will now speak of three "subclasses" or "infraclasses" of mammals: Prototheria, Metatheria, Eutheria. Very neat. The Prototheria comprises only the monotremata (platypus and echidna). The Metatheria now comprises about 250 species in seven orders, where there was previously only the one--Marsupialia. These are the animals with a pouch, and the young are born, walk around, and then climb back into the pouch for a while. I could go into the names of these orders (names such as Didelphimorphia---"two-womb form" or Peramelemorphia-- "pouched badger," the Greek work pera is a pouch or pocket), but I think we have more than enough words for now. Language, which can often be our friend and take us right to the heart of the phenomena we study, can also be a sort of daunting prospect for us. I am afraid it is when you want to learn all the names of animals in the world. But this takes us one tiny step closer...

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