Marsupial evolution

If you were not arguing ALL other traits, please provide for us the proper interpretation of this statement (particularly the bold part): Furthermore, you've still failed to address the fact that the dental formula, the reproductive system, the various skull features in Arachnophobia's skull photographs, and the genetics nicely correlate to the grouping of bears and wolves with horses, rodents and bats, and to the grouping of thylacines with kangaroos, Tasmanian devils, sugar gliders and opossums (the link on "genetics" is an example of the many studies done to determine the phylogenetic relationships of the thylacine: this one allies it to the marsupial order Dasyuromorphia, which includes numbats, quolls and the Tasmanian devil).If anything, the similarity between wolves and thylacines provides a wonderful proof of evolution: otherwise, you've got an Intelligent Designer who used two different methods and constructions to make a dog-like animal, and chose to make the "dog" of each region similar to the other animals of that region on all taxonomic fronts.

---

Darwin loves you.

Randman, I haven't seen anybody claim that the environment is responsible for the convergence between thylacine and wolf. In fact, I'm quite sure they said it was their ecological niche. The thylacine family (yes, they have their own separate family) evolved alongside large herbivores that were probably not ecologically very different from ungulates. So, thylacines likely evolved to hunt things that are very similar to the things wolves evolved to hunt. Doesn't it make sense that these two animals would evolve similarities based on similar life history traits?

---

Darwin loves you.

Has it yet dawned on you that you are the only one here using the word “same?” I have often had people tell me that I look a lot like someone they know. Once, a girl kept insisting that I was this person named “Jacob” (that’s not my name), and thought I was only teasing her by pretending that I was someone else. I have also seen many people who look like other people that I know, despite having no known relation to one another. You wouldn’t expect random birthing events to produce two individuals that superficially resemble one another, yet this phenomenon can be readily observed. What’s your problem with that? So now, instead of two look-alike mammalian carnivores, you think there should be three? Just because two animals came up with similar solutions to similar problems, doesn’t mean another group can’t come up with something different. Why shouldn’t they? You seem to think evolution is an intelligent designer that makes perfect matches between morphology and ecology. If two things happen to look like one another, and neither is at a disadvantage for this, how could natural selection undo it? ToE is not entirely adaptationist, you know.The lack of perfection is beautiful evidence for evolution.Edited by Bluejay, : Added final line.

---

Darwin loves you.

(1) Evolution is not a random process.(2) Mutation is not evolution.(3) I have provided a rebuttal to this your “no random duplications” reasoning. Rolling a certain combination of numbers on a set of dice does not render it impossible to roll the same set again later. This shows that it is perfectly within the bounds of probability that random processes can repeat themselves, which falsifies the basis for your line of reasoning, which is “there is no reason to expect a random process to repeat itself.”(4) You still haven’t made the case that the thylacine and the wolf are all that similar, anyway. All you have is, “they look a lot alike.” I showed you that people can often “look a lot alike,” even when they’re not related, which undermines your point that “looking alike” is in any way meaningful for determining relationships.

---

Darwin loves you.

Hello, hadar288. Welcome to EvC! Well, I think more care is needed here, too: all these traits are most likely also convergent. Kangaroos belong with koalas, Australian possums (not American opossums) and wombats in the order Diprotodontia, whereas the thylacine belongs in with devils, quolls, numbats and marsupial mice in the order Dasyuromorphia (note that none of these animals I've listed are known to have these hopping traits). Given this (which is well-supported by genetic and morphological studies), it's highly unlikely that the hopping traits listed by iceage are actually shared between thylacine and kangaroo.If they were shared, it would imply that all Dasyoromorphs and Diprotodonts evolved from a hopping ancestor, which, to me, sounds very dubious, if even possible (note that I haven't studied this thoroughly enough to completely rule it out, though).

---

Darwin loves you.

There are just so many problems with superficial resemblance. Randman has insisted that scientists have not analyzed all features available, yet, he doesn't seem to understand that the reason for the current classification of thylacines as marsupials is because just such deep analyses have been done. I provided a genetics study upthread, and Arachnophilia's skull photos are really still irrefutable.In a way, randman does have part of a point somewhere, though: he likes to call everything we do in evolutionary biology "assumptions." Some of these things, in fact, are assumptions. But, he doesn't grasp that it doesn't take exhaustive data to uncover a pattern (such as the pouch, double uteri and forked penis of marsupials, as well as the dental formula and the other skull features Arachnophilia presented).Once you've established the pattern (using, say, fifty marsupial species), all you have to do is look for the hallmarks of the pattern, and you're pretty much guaranteed to be right. And, to lessen the probability of errors, anatomists have done comprehensive studies on key organisms (translation: organisms that people think are important or interesting), and the pattern is built upon and upheld by such studies.----For new users:EvC uses quote boxes to separate what you write from what you quote. There are a few types of quote boxes. Push the "peek" button at the bottom of any post to see the dBcodes you can use to make quote boxes like these: and

quote:

---

This one is good for quoting reference materials.

---

URLs for sources and stuff: Message #76, upthread, from me. Note, while you're peeking, that, in the "url=" part for a particular post you are referencing, it's best to make the last two numbers (separated by the "#") the same.

---

Darwin loves you.

Hi, Carl. Welcome to EvC! So, I'm an entomologist, but paleontology and marsupials are two topics I like to read about a lot.Like Ned said, not much is known about the common ancestor. The primary distinguishing features are reproductive, and those don't fossilize well. So, the fossil record will must likely never tell us much about when marsupials developed the marsupium (pouch) or when placentals developed the placentum.Obviously, milk glands predate live birth, because monotremes produce milk but still lay eggs. Most likely, the common ancestor retained the eggs inside itself until just before they hatched (ovovivipary), and eventually, simply did away with the "shell" and membranes of the egg, because these were no longer really needed.Alternatively, the common ancestor may have simply lost the ability to create "shell" and membranes, and the young simply developed on a yolk without a protective shell. This seems highly unlikely to me, though.But, in the end, we'll have to wait until paleontology and genetics develop the tools (and funding agencies develop the interest) to learn how it really happened.

---

I'm Bluejay.Darwin loves you.

Hi, Carl. Well, they probably also didn't have a marsupium (pouch), so wouldn't that make them more like a placental mammal?I think it's going to take a lot more traits than just the reproductive structures to actually find the answer to your question. Likely, the best paleontologists will ever be able to do is compare bone structures, such as dental formulas and the relative shapes and sizes of various bones (as Arachnophilia provided in Message 16 of this thread, but using pre-placental/marsupial mammals for comparison).I think the consensus so far is that the evidence is ambiguous. Maybe someday a brilliant paleontologist and/or a brilliant geneticist will be able to resolve the question with better tools and more information than we have today.

---

I'm Bluejay.Darwin loves you.