Platypi and echidnae don't.
Actually, do marsupials have navels? They don't have much of a gestation period...
Anything with an umbilical cord has a navel...
a hoola hoop with a nail in it is a navel destroyer
Looks like marsupials and platypi don't:
Quote:A. Monotremes - primitive mammals represented by the duck-billed platypus (so unusual that museum personnel in London believed that the first specimen they received from Australia was a fake) and the echidna; females have mammary glands with external pores but no nipples; oviparous (like reptiles).
B. Marsupials - young born very altricial; reared in a pouch called a marsupium; originated in Australia and South America before Australia became isolated (no placental mammals are native to Australia; all introduced by settlers; all niches were filled, however compare the now extinct marsupial wolf to the N. American timber wolf - this illustrates the evolutionary theory of convergence: animal species in different geographic but similar areas "converge" on an optimal body type for those habitats; other examples: dolphins, sharks and ichthyosaurs (extinct) in the oceans).
1. Many marsupial species in South America are believed to have become extinct the last time the Central American land bridge (isthmus) formed; placental mammals from N. America migrated southward and out-competed, preyed upon, gave diseases to the marsupials living there. The only exception is the opossum which has successfully colonized N. America (can be found on the Belmont campus and as far north as the Canadian border).
C. Placentals - young develop in the uterus each with an umbilical cord attached to a placenta which serves as an organ of respiratory gas and nutrient/waste exchange; placenta(s) are usually delivered a few minutes after viviparous partuition (live birth; did your Dad get to cut the umbilical cord???).
This, about the short-tailed opossum, would seem to indicate that they do, though it does contain some disturbing information about male marsupial anatomy.
Quote:Males have the usual marsupial placement of testicles, between the navel and the penis.
Sorry, dys -- have got phenomenally off-topic here...
Hmmmm... gotta have a word with this guy about pseudo-possa navels -- and perhaps about testes, as well.
back to horticulture please
Hey! You can't make me drink!
Where were we?
oops, did I say that?
The platypus and echidna probably don't have them since they're egg laying mammals.
Note:
The name Monotremata means "one hole," a reference to the single anal opening (cloaca) which these mammals share with reptiles, amphibians, and fishes. They were named by Etienne Geoffroy Saint-Hailaire, an early French scientist who embraced the new science of evolution. He wanted to establish monotremes as a new class of vertebrates, separate from mammals.
The order Monotremata includes just three species, the platypus and the short- and long-nosed echidnas. Home base for monotremes is Australia?-an island continent famous for its weird animals. They are also found on some nearby islands except for the long-nosed echidna, which is found only on the island of New Guinea.
Monotremes are the world's only egg-laying mammals. Or are they? Some scientists have suggested that they're living fossils that only resemble mammals. They thought monotremes might actually be primitive reptiles known as therapsid reptiles.
Other scientists suggested that monotremes are living fossils AND mammals. They thought they could be related to multiberculates, a group of plant-eating mammals that evolved towards the end of the Age of Dinosaurs and became extinct early in the Age of Mammals.
Below are lists of some of the features monotremes share in common with mammals and reptiles:
Like Reptiles
Like mammals
just one anal opening that combines the posterior end of the intestine, the ducts of the excretory system, and the genital ducts, a common chamber known as the cloaca
lay shelled eggs that are hatched outside the body of the mother
resemble reptiles in some anatomical details, such as the structure of the eye and the presence of certain bones in the skull, reptilian pectoral or shoulder girdle, and some features of ribs and vertebrae
covered with hair
four-chambered hearts
nurse their young with milk secreted by specialized glands
warm-blooded (though the body temperatures averages lower than that of other mammals, about 30-32 degrees Centigrade)
three middle ear bones, among other mammal similarities in skeletons
Like Monotremes
Monotremes bear horny spurs on their ankles. In platypuses, these spurs are used to inject a poisonous secretion.
So what do you think?-are monotremes reptiles or mammals?
Well, scientists decided to classify them as mammals. But what kind of mammals?
Monotremes have "marsupium" bones, the bones that gave marsupials their name. But scientists decided monotremes were just too unique to find a home even among marsupials. So they created a new order, Monotremata. Ironically, this name comes from a reptilian feature?-the single anal opening.
Thus, we have three major groups of living mammals?-eutherians (a group that includes everything from cats, horses, and humans to bats and whales), marsupials (most of which live in Australia), and the egg-laying, toothless monotremes.
Toothless? That's right, monotremes do not have any teeth. Well, platypuses do when they're young, but they don't even penetrate the gums. Fossils reveal that at least some prehistoric monotremes did have teeth.
* * * * * * * * * *
Taxonomists just can't deal with those intermediate forms.
Like - did anyone ask the MONOTREMES what they wanted to be?
Their hearts are mammalian - let us leave it at that!
Oops, did i say that?
I knew bunnies could be provoked. Is the opposite convoked as in the opposite of progress is congress.
Dinosaurs had (and hence birds have) four-chambered hearts, and crocodiles and alligators and their ilk either do or very nearly do. It's a natural progression from the inefficient amphibian version.
Leave the smegging convokes out of this!
haven't they suffered enough?
Hey! I got to hug a marsupial today! A little Red Kangaroo whose mummy got run over was being cared for by a client who is a wild-life rescue volunteer. Very calm little feller - mostly they are a bit worried by strangers - not this one.
Didn't check for an umbilicus.
dlowan wrote:Like - did anyone ask the MONOTREMES what they wanted to be?
Monotremes don't care. They just go on about the business they've been at for millions of years. It's us people who've started to go about in our mincing hairless way and
classify everything. It's pathological.
