# Darwin's Black Box **URL:** \ **Category:** Great Debates\ **Created:** [June 10, 2003, 2:56am UTC](https://boards.straightdope.com/t/darwins-black-box/180769 "2003-06-10T02:56:45Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [June 10, 2003, 6:48pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/41 "2003-06-10T18:48:17Z")
> [@](#): > > \*Originally posted by Drabble \* > \*\*Basically my main point is that monotremes were around first, then marsupials, then placentals. Your trees show that, and you had argued they evolved at the same time and existed together from the very beginning. That would be like saying h0m0 sapiens evolved when australopithecans did, and we existed together…that’s not the case. They are our ancestors…like therapsids with montreme characteristics (egg laying) were monotremes’ ancestors. > > Just like fish were around first, and mammals much later. Just like australopithicus was here before h0m0. > > You can see the traits evolving in the ancestors from reptilian (egg laying) to modern mammals with a uterus. Right? This is evolution, and you can trace the traits changing as you go up the ‘tree’. > > You didn’t have mammals with uteruses evolving early on with therapsids. You see egg laying first…and uteruses way up on the tree. Even marsupials have an “egg” that sustains the young in their reproductive tract. The young is not attached by an umbilical cord. > > You have to see the clear evolution of traits…from egg to puch to uterus,it very intersting. > > That’s what I’m trying to say. \*\* You have to be careful about drawing conclusions about evolution solely from extant species. Just because two groups appear to have common traits does not mean that the “more advanced” group evolved from the “more primitive” group. It is quite possible that both had a common ancestor that shared some of the traits of both but was, in fact even more “primitive” than either. The common ancestor of monotremes and placetals might have been neither a monotreme nor a placental, but something else altogether. I would agree, however, that the common ancestor was an egg layer. More to the point, it is not at all clear that marsupials represent some intermediate (living missing link) between monotremes and placentals. They might easily be a seperat side branch. It’s like saying chimps represent an intermediate between humans and monkeys, which is absolutely false. Yes, our common ancestor might have looked more like a chimp than a human, but it wasn’t either a chimp or a human. It was something else altogether. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [June 10, 2003, 6:50pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/42 "2003-06-10T18:50:36Z")
The last sentence in the first paragraph should have read: “I would agree, however, that the common ancestor was **most likely** an egg layer.” My mistake. ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 6:51pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/43 "2003-06-10T18:51:11Z")
Cladogram SYNAPSIDA | Therapsida |–Biarmosuchia `--+--Dinocephalia | |--Anteosauria | `–Tapinocephalia `--+--Anomodontia | |--Venyukovioidea | `–Dicynodontia `--Theriodontia |--Gorgonopsia `–±-Therocephalia `–CYNODONTIA but the Cretaceous was a melting pot of mammalian sub-classes most of which do not survive to today However, therapsids are known as the first mammals, and they did lay eggs. The Triassic Period of the Mesozoic Era 250 to 205 million years ago -when therapsids appeared Triassic Period–Therapsids, cynodonts, and the first mammals So they had a 100 million years before the first placental appeared. Phanerozoic Mesozoic Triassic Late Triassic Middle Triassic Early Triassic (Scythian) Jurassic Early Jurassic (Lias) Middle Jurassic (Dogger) Late Jurassic (Malm) Cretaceous Early Cretaceous (Neocomian) Mid Cretaceous (Gallic) Late Cretaceous (Senonian) Cretaceous is Waaaayyyyy after triassic ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [June 10, 2003, 6:51pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/44 "2003-06-10T18:51:22Z")
> [@](#): > > They are our ancestors…like therapsids with montreme characteristics (egg laying) were monotremes’ ancestors. > [@](#): > > You have to see the clear evolution of traits…from egg to puch to uterus,it very intersting. _ **IF** _ I understand these two comments, then I’m afraid you are wrong. The fact that monotremes may have preceded marsupials and placentals chronologically does _not_ make them ancestors–ancestor implies that placentals descended through monotremes and marsupials. There is no evidence for that. There is no “evolution of traits” that proceeds “from egg to puch to uterus” even if it is true that pouch was _earlier_ than uterus (since uterine mammals did not descend from marsupials) or that eggs were _earlier_ than pouches (since marsupials did not descend from monotremes). [This paper on monotreme evolution viewed through DNA](http://teach.biosci.arizona.edu/462aH2002/phamm/mhcreview2.pdf) (Adobe required) discusses the cladistics on pages 11 and 12, noting that the traditional division separates monotremes from the other therian-descended groups, then shows marsupials and placentals dividing as sister groups (meaning neither gave rise to the other). It then notes that a counter hypothesis suggests that placentals divergd first, leaving monotremes and marsupials as sister (not parental) groups. So, the use of the word _ancestor_ (which implies descent) when discussing the relationship of monotremes, marsupials, and placentals is clearly wrong. ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 6:52pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/45 "2003-06-10T18:52:27Z")
[http://www.uky.edu/KGS/education/Triassic.htm](http://www.uky.edu/KGS/education/Triassic.htm) ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 6:56pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/46 "2003-06-10T18:56:19Z")
> [@](#): > > The common ancestor of monotremes and placetals might have been neither a monotreme nor a placental, but something else altogether. I would agree, however, that the common ancestor was an egg layer. Marsupials and placentals also have a common ancestor…and marsupials evolved first and claimed the planet for a while before placentals took over. That much is observable, so no conclusions really need to be drawn. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [June 10, 2003, 6:56pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/47 "2003-06-10T18:56:27Z")
> [@](#): > > However, therapsids are known as the first mammals, and they did lay eggs. > . . . > So they had a 100 million years before the first placental appeared. However, you appear to be confusing “egg-laying” with “monotreme.” While monotremes lay eggs, they are _not_ in line of descent with marsupials or placentals. There is more to the identification of montreme than simply their laying of eggs. ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 7:02pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/48 "2003-06-10T19:02:27Z")
Okay, therapsids with montreme characteristics first appeared…making that a common ancestor for all mammals…from an egg laying ancestor. Then marsupials appeared with marsupial characteristics…evolving closely to the same time as placentals? I’m checking to see what period marsupials appeared in. Therapsids…laying eggs like monotremes were in the triassic…and we don’t see placentals until cenozoic? ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 7:08pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/49 "2003-06-10T19:08:18Z")
I’m not trying to say they are all on the same branch…so I’m not saying anything about direct line of decent. I’m talking about the beginnings of branches. Therapsids are shown at the beginning of the whole mammalian line…making it a common ancestor of all mammals. ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 7:31pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/50 "2003-06-10T19:31:51Z")
Okay, the textbook says the monotremes and placentals branched from a common ancestor 80-100 million years ago, and the ancestry is obscure. Did the common ancestor have more marsupial traits than placental though? That’s my question…or was it equal in traits of both? Or did it have more monotreme traits than anything, in fact, was it just a monotreme that is considered the common ancestor? If it was completely monotreme it would mean there is no transition from marsupial to placental…only from monotreme to both marsupial and placental. (you have to look at all bone structures, and other parts of anatomy, not just uterus vs no uterus). If the ancestor was more marsupial then there is a link from monotreme to marsupial to placental. If it was more placental then it went monotreme-placental-marsupial. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [June 10, 2003, 7:41pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/51 "2003-06-10T19:41:16Z")
> [@](#): > > If the ancestor was more marsupial then there is a link from monotreme to marsupial to placental. If it was more placental then it went monotreme-placental-marsupial. Of course, if there is no connection among the three of them, then neither of these scenarios is valid. I have never seen any evidence that either marsupials or placentals evolved from monotremes and the literature is quite consistent that neither placentals nor marsupials evolved from the other. You appear to continue to equate “egg-laying” with “monotreme,” but I have seen no evidence that the therapsids, in general, are legitimately called monotremes. > [@](#): > > (you have to look at all bone structures, and other parts of anatomy, not just uterus vs no uterus). True. So where is your evidence? In addition to bones to examine, we have genetic analysis (to which I have already provided a link) that denies that any of the three groups under discussion gave rise to either of the others. ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 7:52pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/52 "2003-06-10T19:52:25Z")
Just like this dilemma of finding which ‘transition’ animal is actually reptile or mammal: > [@](#): > > Fossil synapsid reptiles from the Periman period 250 million years ago, show many skeletal features of mammals, but not all. Thrinaxodon at the base of the Triassic period 245 million years ago, has a secondary palate and teeth that can be divided into incisors, canines and molar-like teeth. Thrinaxodon was a meat eater and had long canines to slice into its prey. But what makes it a reptile is that had articular and quadrate bones as part of the jaw joint. Most books refer to these fossil synapsid reptiles as mammal-like reptiles, mostly because paleontologists debate where to draw the line between reptile and mammal. I’m sure there are marsupials or monotremes ‘on the edge’ between each other…and then the same between the common ancestor between marsupials and placentals… Or is that the monotreme at the end of the monotreme line is more of a placental/monotreme? Then there would be the animals that are placental/marsupial. which is it? ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 8:02pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/53 "2003-06-10T20:02:24Z")
no, I equate egg laying as a montoreme trait. Just like it is also a reptilian trait…and then as shown as above…the evolution of montremes from reptiles. I never said therapsids are montremes…rather a link from therapsid from reptile to monotreme, or maybe therapsids are monotremes. Or you’re saying that the three mammal groups each have their own reptilian ancestor? That’s the only way they would not have common ancestors and no connection. That’s not so, because the marsupials and placentals have a common ancestor. The literature clearly states a common ancestor for marsupials and placentals…so that common ancestor would have to be connected. tomndebb, are you a creationist? If so, I don’t care to discuss this anymore because the discussion will never end. It will always be an argument about ‘truth’ and transitions, and the sides of creation vs evolution are divided in such a way that discussion is pointless My theory will continue to be that marsupials and monotremes have a common ancestor, and it has already been stated in literatue that marsupials and placentals have a common ancestor…whether that ancestor be more placental or marsupial…I have to find out. ---
**Author:** ![Drabble](https://avatars.discourse-cdn.com/v4/letter/d/8491ac/32.png) [@Drabble](https://boards.straightdope.com/u/Drabble)\ **Post date:** [June 10, 2003, 8:06pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/54 "2003-06-10T20:06:26Z")
Okay, therapsids are ancestors are monotremes > [@](#): > > They retain many characters of their therapsid ancestors (for example, a complex pectoral girdle, laying of eggs rather than bearing live young, limbs oriented with humerus and femur held lateral to body, and a cloaca). The skulls of monotremes are almost birdlike in appearance, with a long rostrum and smooth external appearance. Modern monotremes lack teeth as adults; sutures are hard to see; the rostrum is elongate, beak-like, and covered by a leathery sheath; and lacrimal bones are absent. Monotremes have several important mammalian characters, however, including fur (but they lack vibrissae), a four chambered heart, a single dentary bone, three middle ear bones, and the ability to lactate. [http://animaldiversity.ummz.umich.edu/chordata/mammalia/monotremata.html](http://animaldiversity.ummz.umich.edu/chordata/mammalia/monotremata.html) So I can see where marsupials and placentals could branch from therapsid instead of monotremes…but I don’t think that is as likely as a branch from monotremes to marsupials and placentals. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [June 10, 2003, 8:33pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/55 "2003-06-10T20:33:56Z")
> [@](#): > > \*Originally posted by Drabble \* > \*\*My theory will continue to be that marsupials and monotremes have a common ancestor, and it has already been stated in literatue that marsupials and placentals have a common ancestor…whether that ancestor be more placental or marsupial…I have to find out. \*\* Your theory does not agree with any current phylogeny of the three groups. Marsupials and monotremes do not share any common ancestor that does not also include eutherians. Marsupials and eutherians do share a most recent common ancestor (and are collectively known as Theria), and the most recent common ancestor of Theria with monotremes would be the primeval mammal. The questions you should be asking are not, “Is the common ancestor more marsupial-like or more placental-like?” - that’s putting the cart before the horse. Both groups retain [primitive characters which were present in their common ancestor](http://www.palaeos.com/Vertebrates/Units/430Mammalia/430.500.html#Theria). Both groups have derived characters _not_ present in that ancestral group. Marsupials may or may not retain their reproductive arrangement from that ancestor, but doing so simply means that that character is “primitive”, with respect to that ancestor, not that the ancestor is “more marsupial-like”. Not that any of this has anything to do with Behe, of course… ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [June 10, 2003, 8:44pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/56 "2003-06-10T20:44:47Z")
My position is that the following is a valid statement: > [@](#): > > My theory will continue to be that marsupials and monotremes have a common ancestor, and it has already been stated in literatue that marsupials and placentals have a common ancestor but that when you continue on with: > [@](#): > > …whether that ancestor be more placental or marsupial…I have to find out. you are echoing your still earlier statement, which is not valid: > [@](#): > > If the ancestor was more marsupial then there is a link from monotreme to marsupial to placental. If it was more placental then it went monotreme-placental-marsupial. Mammals arose from cynodont therapsids, but there is no reason to assume that Protherians (Triconodonts, Docodonts, Monotremes, and Multituberculates) gave rise to Therians (Pantotherians, Marsupials, and Eutherians) or that within Theria, Marsupials or Eutherians gave rise to each other (or to Pantotherians). You may not like the conclusion, but all the current evidence argues against your preference to line them up in descent. ---
**Author:** ![amarone](https://avatars.discourse-cdn.com/v4/letter/a/e0b2c6/32.png) [@amarone](https://boards.straightdope.com/u/amarone)\ **Post date:** [June 10, 2003, 10:59pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/57 "2003-06-10T22:59:18Z")
Can we get this back to the OP? ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [June 10, 2003, 11:28pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/58 "2003-06-10T23:28:19Z")
I second that. This hijack has gone on far enough. Drabble refernces have been provided showing your hypithesis to be wrong on numerous grounds. Can you please start another thread concerning mammalin evolution, one which I would love to join. But contimuing the hijack of this thread is really bad manners. ---
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [June 11, 2003, 9:42pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/59 "2003-06-11T21:42:03Z")
I third that. I’m finding the discussion of Behe quite fascinating and illuminating. I’m finding the discussion of monotreme evolution repetitive and pointless. Just my pair of pennies. ---
**Author:** ![Ben](https://avatars.discourse-cdn.com/v4/letter/b/df788c/32.png) [@Ben](https://boards.straightdope.com/u/Ben)\ **Post date:** [June 11, 2003, 10:31pm UTC](https://boards.straightdope.com/t/darwins-black-box/180769/60 "2003-06-11T22:31:53Z")
> [@](#): > > \*Originally posted by Cervaise \* > \*\*I third that. > > I’m finding the discussion of Behe quite fascinating and illuminating. > > I’m finding the discussion of monotreme evolution repetitive and pointless. > > Just my pair of pennies. \*\* Any thoughts on my “What Is Science” page? [Previous page](https://boards.straightdope.com/t/darwins-black-box/180769.md?page=2)