New work on an ancient mammal

June 9, 2009 • 5:39 am

With her usual journalistic panache, Natalie Angier reports today in the New York Times on new work on the echidna, otherwise known as the spiny anteater (there are four species in the genera Zaglossus and Tachyglossus). The species is bizarre because, like the platypus, it is one of the two groups of mammals that lay eggs — the monotremes.  And, like the  platypus, echidnas are found in Australia, but also in New Guinea. They are toothless, and, unlike other mammals except the platypus, the females produce milk not through teats, but through a hairy patch on the belly from which milk is lapped up by the young (this may represent the primitive state of mammary glands from which modern breasts evolved).  Unlike other mammals (but like birds), they have a single hole for excretion, sex, and egg-laying: the cloaca.

A paper by Muse Opiang in the Journal of Mammalogy reports on the long-beaked echidna from New Guinea, Zaglossus bartoni.  Several individuals were captured (no easy feat for these reclusive beasts: it took 500 man-hours just to find the first one!) and radiotracked to determine home range size.  Although the results — that home range size is variable among individuals, ranging from about 10 to 170 hectares (0.1 to 1.7 square kilometers) — aren’t terribly exciting to the nonbiologist, they are valuable in contributing to our knowledge of this rare animal.   Angier livens things up by telling the tale behind the paper:

Muse Opiang was working as a field research officer when he became seized by a passion for the long-beaked echidna, or Zaglossus bartoni, which are found only in the tropical rain forests of New Guinea and a scattering of adjacent islands. He had seen them once or twice in captivity and in photographs — plump, terrier-size creatures abristle with so many competing notes of crane, mole, pig, turtle, tribble, Babar and boot scrubber that if they didn’t exist, nobody would think to Photoshop them. He knew that the mosaic effect was no mere sight gag: as one of just three surviving types of the group of primitive egg-laying mammals called monotremes, the long-beaked echidna is a genuine living link between reptiles and birds on one branch, and more familiar placental mammals like ourselves on the next. . .

.. . . Reproductively, monotremes are like a VCR-DVD unit, an embodiment of a technology in transition. They lay leathery eggs, as reptiles do, but then feed the so-called puggles that hatch with milk — though drizzled out of glands in the chest rather than expressed through nippled teats, and sometimes so enriched with iron that it looks pink.

Monotreme sex determination also holds its allure. In most mammals, a single set of XX chromosomes signifies a girl, a set of XY specifies a boy. For reasons that remain mysterious, monotremes have multiple sets of sex chromosomes, four or more parading pairs of XXs and XYs, or something else altogether: a few of those extra sex chromosomes look suspiciously birdlike. Another avianlike feature is the cloaca, the single orifice through which an echidna or platypus voids waste, has sex and lays eggs, and by which the group gets its name. Yet through that uni-perforation, a male echnida can extrude a four-headed penis.

When I was a graduate student, I had the good fortune to encounter one of these creatures — an adult named Francis who lived in the Museum of Comparative Zoology at Harvard.  I used to walk downstairs to pet it on the non-spiny parts,  and found, as Angier notes, that it was a friendly and peaceful beast.

Enrich your world by reading Angier’s article!


baby echidna

Damn!  P.Z. has posted a cat again! I see him a cat and raise him a panda:


17 thoughts on “New work on an ancient mammal

  1. My point is nippled teats ARE modified sweat glands, so what’s the distinction being made? I’m sure there is one, it’s just not clear from the description.

    1. There simply is no teat to suckle at. The milk just flows out into a shallow – like a cup or spoon.

  2. This time, the cat isn’t my fault — my wife picks some cute animal for me to post on Mondays, and she never seems to favor the slimy protostomes I prefer.

  3. A 4-headed penis – imagine that! Makes opossums with their bifurcate penis (something I recall from either my embryology or comparative anatomy text from eons ago) sound ordinary.

    Interesting that multi-heads turn up in both monotremes & marsupials. Other examples? Adaptive significance?

    One online ref says that opossum sperm travel in pairs. Perhaps echidna sperm travels in tetrads??

  4. For reasons that remain mysterious, monotremes have multiple sets of sex chromosomes, four or more parading pairs of XXs and XYs, or something else altogether

    It should be pointed out that the X’s and Y’s in monotreme sex determination are not related to the X’s and Y’s in eutherian sex determination.

    Monotremes do have a chromosome related to the human x-chromosome (from which the y-chromosome evolved), but it is not a sex chromosome.

    Glen Davidson

  5. The echidnas are just awesome – you should see how quick they burrow to get at ants/termites/other bugs on its menu. They’re very shy and curl up into a ball (making it somewhat difficult to touch without being pricked), but the non-prickly part (mostly the underside) is nice and soft. Unfortunately they’re not good at dodging traffic on the roads.

  6. Great post, Gerry. Getting links to other brilliant stuff is definitely one of the best features of a blog. Only ONE, of course. But how can you miss out on such an opportunity to get another contest going?

    That photo of the panda is crying out for a caption.

    And just in case you start a contest, I’ll kick off with this feeble effort:

    “Don’t shoot me, I’m only the piano player!”

  7. “- – not through teats, but through a harry patch on the belly – -“. I’m sure glad this is not a pleisomorphic characteristic that was retained in humans. Or, if it were; would I now think that?

Leave a Reply