Talk:Evolution of mammals

older entries

Epipubic bones also found in males, both with and without pouches.

Kudos!

Very impressive article, folks - one of the best I've seen on Wikipedia in the last year or so. Thanks! -- Writtenonsand (talk) 13:18, 17 November 2007 (UTC)

Evolution as "experimenting". Tweak?

"Multituberculates ... are a fine example of how evolution was "experimenting" in the Mesozoic." --- I suggest that we tweak this sentence, as IMHO even with the scare quotes on "experimenting" it tends to re-inforce the popular misconception that evolution is conscious or teleological rather than stochastic. -- Writtenonsand (talk) 13:34, 17 November 2007 (UTC)

I certainly don't want to encourage misconceptions that evolution is conscious or teleological. But I couldn't think of an alternative phrasing which was not much longer, and the article is rather long already. If you can think of an alternative that adds no more than a handful of words to the length, that would be good.Philcha (talk) 16:41, 17 November 2007 (UTC)

Section "Expansion of ecological niches" - add further taxonomic clarification?

The section Expansion of ecological niches in the Mesozoic lists "mammaliforms and true mammals" -- I suggest that we add in a note on the relevent order for each item listed, in order to give readers a better sense of the taxonomic picture. E.g., "Castorocauda (order Docodonta), which lived in the mid Jurassic ..." -- Writtenonsand (talk) 13:44, 17 November 2007 (UTC)

I'm not happy with this idea as it would increase the length and complexity of a long, complex article. IMO: the general reader doesn't need it and wouldn't understand it; specialists know the taxonomic context already; intermediate readers can get the taxonomic context from the linked articles on the animals mentioned.Philcha (talk) 16:44, 17 November 2007 (UTC)

clade template

Great article! Have you ever used the Clade template before? It'll preserve formatting of the cladograms regardless of page size or resolution, and it looks cleaner because it's not set aside in a box, with individual "---"s. For comparison, here's your first tree:

--Tetrapods--------------------------------------------------
      |
      +-- Amphibians ---------------------------------------
      |
      `--Amniotes-----
             |
             +--Sauropsids------------------------------------
             |
             `--Synapsids------
                    |
                    `--Pelycosaurs----
                           |
                           `--Therapsids-----
                                  |
                                  `--Mammals------------------

And here is a quick conversion to Clade template:

Tetrapods	Amphibians  Amniotes  Sauropsids  Synapsids  Pelycosaurs  Therapsids  Mammals

If you're interested, I could convert them for you (not right now, though), or if you'd like to do them yourself, I have a few examples here. J. Spencer (talk) 15:21, 17 November 2007 (UTC)

Intersting idea. I tried reducing the browser window width and your clade template behaved better than the "ASCII art". How would it work for something more complex, e.g. Fossil-based_family_tree_of_placental mammals? Philcha (talk) 16:54, 17 November 2007 (UTC)

Hmm... the extra information makes it look trickier, but I'll give it a shot. J. Spencer (talk) 00:15, 18 November 2007 (UTC)

Unless there's something I don't understand (which is entirely possible), doesn't the clade graph imply that Therapsid and Pelycosaur are sister clades. Would this be more correct:

Tetrapods	Amphibians  Amniotes  Sauropsids  Synapsids   Pelycosaurs   Therapsids  Mammals

Ennisj (talk) 09:32, 14 December 2009 (UTC)

How's this? I had to flip some clades to make the appearance better, so the order is not exactly the same.

Eutheria

Xenarthra (Paleocene) (armadillos, anteaters, sloths) <font color="white">unnamed Pholidota (early Eocene) (pangolins  Epitheria  some extinct groups X <font color="white">unnamed Insectivora (Late Cretaceous) (hedgehogs, shrews, moles, tenrecs) <font color="white">unnamed <font color="white">unnamed Anagalida Zalambdalestidae X (late Cretaceous) <font color="white">unnamed Macroscelidea (late Eocene) (elephant shrews) <font color="white">unnamed Anagaloidea X Glires (early Paleocene) Lagomorpha (Eocene) (rabbits, hares, pikas) Rodentia (late Paleocene) (mice & rats, squirrels, porcupines  Archonta  <font color="white">unnamed Scandentia (mid Eocene) (tree shrews)  Primatomorpha  Plesiadapiformes X Primates (early Paleocene) (tarsiers, lemurs, monkeys, apes, humans) <font color="white">unnamed Dermoptera (late Eocene) (colugos) Chiroptera (late Paleocene) (bats) <font color="white">unnamed Ferae (early Paleocene) (cats, dogs, bears, seals)  Ungulatomorpha (late Cretaceous)   Altungulata  Hilalia X <font color="white">unnamed <font color="white">unnamed Perissodactyla (late Paleocene) (odd-toed ungulates: horses, rhinos, tapirs) Tubulidentata (early Miocene) (aardvarks)  Paenungulata ("not quite ungulates")  <font color="white">unnamed Sirenia (early Eocene) (manatees, dugongs) Proboscidea (early Eocene) (elephants) Hyracoidea (early Eocene) (hyraxes)  Eparctocyona (late Cretaceous)  <font color="white">unnamed Arctostylopida X (late Paleocene) <font color="white">unnamed Mesonychia X (mid Paleocene) (predators/scavengers, but not closely related to modern carnivorans)  Cetartiodactyla  Cetacea (early Eocene) (whales, dolphins, porpoises) Artiodactyla (early Eocene) (even-toed ungulates: pigs, hippos, camels, giraffes, cattle, deer) (some extinct groups) X

J. Spencer (talk) 02:02, 18 November 2007 (UTC)

Thanks for trying, but I prefer to stick with the "ASCII art". I run my screen at 800x600 because I have poor eyesight, and at 800x600 the template causes a lot of horizontal scrolling. With the "ASCII art" one can mitigate that by reducing the insets. Is there any way to reduce horizontal scrolling when using the template? Also in this particular case I find the "ASCII art" version easier to read because most modern mammals are descended from the Epitheria.

I've just had a rather wild idea, which I'm surprised I didn't think of before. Could cladograms be represented by expandable / collapsible trees, similar to those used for folders by Windows Explorer and many email programs? The same approach is also used in some Web pages, using DHTML. Could that be made to work in Wikipedia, and would it be acceptable? Philcha (talk) 18:18, 21 November 2007 (UTC)

I have no clue how one would include DHTML, but if it could be made to work (the now-absent Josh Grosse created the clade template), I don't see why not. J. Spencer (talk) 22:36, 21 November 2007 (UTC)

I've posted the suggestion at Wikipedia talk:Village pump (proposals) Philcha (talk) 16:32, 24 November 2007 (UTC)

There is a problem here... Pholidota is shown as quite separate from Ferae, but Ferae (as it is currently defined) is a clade containing Carnivora and Pholidota. If the connection between Pholidota and Carnivora is rejected, then shouldn't Ferae in this diagram be replaced by Carnivora?

Lactation / suckling and neck ribs

Someone added to the section "Lactation"

“ One can infer the possession of mammary glands in from a fossil by seeing if ribs are present in the neck bone. If the animal possessed these ribs, they would not have had the necessarily flexibility required for suckling, which would suggest that mammary glands where not present in the species. ”

This is an interesting idea, but the way it is currently presented has major weaknesses:

• No citations.
• Ambiguity. Would neck ribs prevent the mother from producing milk or the baby from taking it? I expect the latter but then the phrasing could be a lot clearer. I'd also like more explanation of why neck ribs are such an obtacle.
• Logic. If correct, the presence of neck ribs would imply no suckling but absence of neck ribs would no imply suckling - in fact one would expect to find (eventually) transitional forms with no neck ribs but without suckling.
• Position - at present it breaks the flow of the text.

I hope the person who added this material will respond here or by editing that part of the article. Otherwise I'll remove it in 2 weeks. Philcha (talk) 14:56, 15 December 2007 (UTC)

I've removed the remarks about neck ribs. Philcha (talk) 18:12, 29 December 2007 (UTC)

Great work!

Great work, Philcha! My compliments, you assembled a great article! DaMatriX (talk) 00:00, 22 December 2007 (UTC)

Agreed. May I make a suggestion that the article Evolution of mammalian auditory ossicles could use some of the same hand. Especially, the drawings of the jaw-to-middle ear transitional forms. TomS TDotO (talk) 11:20, 29 February 2008 (UTC)

Hair/fur helping mammals survive K-T extinction

I've removed from the end of "(earliest evolution of) Hair / fur" the following sentence: "The possession of such insulation is thought to be one of the several reasons that mammals triumphed the K-T extinction." It provides no refs to support it, and I've never seen any such suggestion from a credible source. Philcha (talk) 18:35, 29 December 2007 (UTC)

Timeline

To improve accessibility, could we have a timeline similar to {{Permian graphical timeline}} in the article? This would give an overview of development of key features with approximate dates, and would be more meaningful for readers who aren't familiar with the eras and their dates.-gadfium 20:21, 14 April 2008 (UTC)

Good article nomination

This article ought to be nominated at Wikipedia:Good article nominations. Cheers! Wassupwestcoast (talk) 01:07, 19 April 2008 (UTC)

Placenta

There is a press release which reports about research on the origins of the mammalian placenta. Should something about this be included as one of the distinctively mammalian features which evolved?

Stanford University Medical Center (2008, April 17). Clues To Ancestral Origin Of Placenta Emerge In Genetics Study. ScienceDaily. Retrieved April 19, 2008, from Clues To Ancestral Origin Of Placenta Emerge In Genetics Study TomS TDotO (talk) 13:13, 19 April 2008 (UTC)

Perhaps, if we can get the peer-reviewed article and it actually covers the same ground ("news" articles often contain off-the-cuff comments and personal opinions that the researchers did not include in the the peer-reviewed article). The news article is wrong on at least 1 point, where it says, "the placenta initially evolved through repurposing genes the early mammals inherited from their immediate ancestors when they arose more than 120 million years ago." If these genes are "in common with birds and reptiles" they were inherited from the last common ancestor of mammals and reptiles (possibly a basal amniote) over 320M years ago.

Please keep suggesting things! It's like football (soccer or gridiron) - most moves break down, but eventualy you SCO-O-O-O-O-ORE. Philcha (talk) 14:54, 19 April 2008 (UTC)

Evolution of Man - A Different View

THE EVOLUTION OF MAN -A DIFFERENT VIEW

Abstract

A hypothesis is proposed that mammals evolved directly from amphibians rather than from reptiles. Also, how paedoneogenesis and sexual selection could account for man’s attributes including a larger brain relative to other mammals.

Paper

It is usually assumed and taught that mammals including man have evolved from reptiles, which in turn evolved from amphibians.

Reptiles have a vascular system that has developed from the right aortic arch. A similar system appertains in birds, which have an accepted evolution from reptiles (ornithischian dinosaurs). They appeared in the Cretaceous period (145 million years ago).

Mammals have a vascular system that has developed from the left aortic arch. Reptiles have a skull whose jaw is derived from several bones. Mammals have a bony separation of the swallowing and breathing passages. Mammals have functional differentiation of teeth. Reptiles’ teeth are usually all similar and replaceable. The limbs are lateral in reptiles but evolved ventrally in mammals. These differences are to be seen over the millennia.

To determine the origin therefore of mammals one must search further back in time for an ancient amphibian with bilateral aortic arches that could have allowed the left aortic arch to become dominant. The progenitors of the amphibia are the lung fish (dipnoae), which have many affinities to the amphibia such as lungs and an ability to respire partially through the integument.

It is probable that primitive lungs developed in Devonian times (400 million years ago) in fish that lived in pools that were drying out. Nasal pouches in fish have an olfactory function, but in the lungfishes nostrils appear with associated skull changes and the fish is able to breathe bypassing the mouth. Lungfish have fleshy fins with skeletal support that have the beginnings of jointed limbs and radiating terminations. The ancient lungfishes had now the opportunity to develop the tetrapod gait and ability to utilise the atmosphere direct for respiration.

In Devonian times the first amphibia, the Stegocephalia appeared. An example was Eryops, a crocodile like animal about six feet long which was adapted to both aquatic and terrestrial environments. Reptiles lay eggs on land whereas amphibia lay their eggs in water. These shell less eggs could have been retained in the oviduct whilst development proceeded and this way the evolution of placentae could occur. The placenta is thought to have evolved from the allantois of the egg, which is an umbilical extension of the gut.

The Reptilia evolved from stem reptiles called cotylosaurs that in turn evolved from amphibia. Dimetrodon being an example. Reptiles started to make their appearance in the Carboniferous era, (360 million yeas ago). The first reptiles were the lizard like cotylosaurs. The stem reptiles gave rise to two great groups, the archosaurs (dinosaurs and crocodiles) and the lepidosaurs (lizards and snakes).

In the later Permian (290 million years ago) animals with mammalian features appear. For example Cynognathus had a differentiated dentition with a secondary palate and the limbs supported the body ventrally.

In the Triassic (245 million years ago) it is thought these early mammals became viviparous, that is gave birth to their shell less young. By the Cretaceous (145 million years ago) mammals had started to differentiate into the marsupials and placentals which suckled their young. These appear to have mainly been small active rodent like animals. If like present-day rodents they were nocturnal it would have necessitated being homoeothermic (warm blooded), aided by a furry coat.

These early mammals are thought to have been insectivores and from arboreal species the early progenitors of the primates evolved in the Paleocene (65 million years ago).

Originally it was thought that man evolved from tree climbing primates, but many now believe that man evolved from ground living free roaming animals with a lifestyle similar to baboons. Rather like ‘Lucy’ the hominid, one of whose relative’s footprints have been left to posterity in the Oldivai gorge.

Important evolutionary features developed; binocular vision to scan the horizon aided by bipedal gait to see over the savannah. The upper limbs could now become manipulative.

In the Miocene about 14 to 20 million years ago primitive apes (Dryopithecines) branched into two groups. One of which gave, rise to the early tree dwelling apes about 7 million years ago, whilst the other group lived in open country. This latter group gave rise to Australopithecus, which includes ‘Lucy’, who had a true bipedal gait, but with features of both hominids and apes.

In the Pleistocene about 1.5 to 3 million years ago Homo habilis (‘the tool maker’) made an appearance to be followed by Homo erectus, to be supplanted by Homo sapiens.

A mystery that has never been explained is why man among the apes is relatively hairless. I would suggest that this is due to sexual selection of juvenile characteristics, which when associated with the ability to reproduce is termed paedoneogenesis.

This would explain the disappearance of the heavy brow and the less prominent jaw. The young of mammals have a relatively larger brain compared with the adult. Retention of this attribute could explain the superior intelligence of man over other apes.

Thus, in my opinion the evidence indicates that man and the rest of the mammalia evolved direct from an amphibian ancestor and not by way of reptiles, which independently arose from the amphibia. Dr t c mayer (talk) 14:50, 2 July 2008 (UTC)

First, that's nice, but original research. We can't use it unless you submit it to a journal and get published.

Second, your research is a bit redundant, as a majority of modern researchers agree that mammals did not evolve from reptiles, they evolved from a common tetrapod ancestor that was not reptile (Sauropsida), but what would be generically called and "amphibian" (though that name is formally restricted to the modern group containing frogs and salamanders). Derived characteristics of reptiles are absent in mammals and stem-mammals: dry skin, scales, etc. In fact skin impressions from early synapsids show "fishapod" style dermal scales instead of reptilian scales. Your paper doesn't appear to cite any other sources. More research of relevant lit might be useful in demonstrating this view is not new ;) Dinoguy2 (talk) 01:55, 3 July 2008 (UTC)

Are all modern Afrotheria from Africa and South America?

The article (Family tree of placental mammals according to molecular phylogenetics section) says:

The grouping together of the Afrotheria has some geological justification. All surviving members of the Afrotheria live in South America or (mainly) Africa.

This statement isn't true - one of the surviving species of this group is Elephas maximus, also known as the Asian Elephant, lives (as the name suggests) in Asia. 194.90.113.98 (talk) 11:45, 27 July 2008 (UTC)

Good point! Does anyone know the evolutionary history of Proboscidea? For example if the fossil record showed that the earliest Proboscidea were African, the Afrotheria hypothesis remains viable — otherwise it could be in trouble. I know that Afrotheria is a clade based on DNA, not on bones. But DNA analysis can't tell us when or where earlier members of the clade lived, which is IMO essential in order to do a good job of incorporating 194.90.113.98's point into the article. -- Philcha (talk) 13:55, 27 July 2008 (UTC)

I found the following statement in Amebelodon:

Amebelodon is a member of a diverse group of primitive proboscideans called gomphotheres, a group that also gave rise to the modern elephants and their close relative the mammoth. Amebelodon first appeared in the Great Plains and Gulf Coast regions of North America during the late Miocene, roughly between 9 and 8 million years ago...

This would seem to mean that modern elephants evolved from a North American species from 8-9 million years ago, which means that the point about Afrotheria seems not to be true. 194.90.113.98 (talk) 08:29, 11 August 2008 (UTC)

Scientists map elephant evolution says the African and Indian elephant lineages diverged about 7.6 MYA, in Africa. However I don't know the earlier history of the elephant lineage. -- Philcha (talk) 23:40, 11 August 2008 (UTC)

Where are humans?

Just to point out I couldn't see humans anywhere in the definition of a mammal Phthinosuchusisanancestor (talk) 19:01, 22 October 2008 (UTC)

Humans are mammals, so they "inherit" all the defining features of mammals. OTOH specifically human characteristics can't be used in defining "mammal" as they would not apply to the vast majority of mammals. -- Philcha (talk) 19:06, 22 October 2008 (UTC)

Evolution of Vivipary?

This is a glaring omission for me. How and when did synapsids move from an egg-laying model to giving birth to live young? How did vivipary evolve? —Preceding unsigned comment added by Captainsiberia (talk • contribs) 03:08, 2 April 2009 (UTC)

While researching for the work on this article I did a while ago, I found nothing on the subject - so I guess it's a glaring omission for the scientists too. The best evidence would be a fossil of a pregnant mammal, but fossilisation is rare and probably most animals that were fossilised have not been discovered.

OTOH the earliest known marsupial, Sinodelphys, and the earliest known eutherian, Eomaia, date from about 125 million years ago, so it's a reasonable bet that viviparity appeared before then. However stating that in the article would be original research, which WP forbids. If you find a good source for info on this, please include it in the article or post it in the Talk page.

BTW viviparity is more common among animals than you might think - some sponges (!), all scorpions, platyctenid ctenophores, some sharks and probably several other animals I don't know about. --Philcha (talk) 07:18, 2 April 2009 (UTC)

Eotherapsid hypothesis for the origin of Monotremata

Ivakhnenko, Mikhail F. (2009). "Eotherapsid hypothesis for the origin of Monotremata". Paleontological Journal. 43 (3): 237–250. Aleksey (Alnagov (talk) 09:25, 23 June 2009 (UTC))

Cladogram Template (Palaeos.com) Inconsistency

This might just be nitpicking, but i noticed the cladogram (morphological) under the section 'Evolution of major groups of living mammals' is very slightly different to the original over at Paleos.com. In particular, there are quite a few extra '+' signs on the one reproduced here. As i understand the system used by Palaeos.com, the '+' signs represent missing or unnamed clades. Therefore, i'm not too sure what the following part of the cladogram means:

--Eutheria

   |
   +--Xenarthra (late cretaceous)
   |  (armadillos, anteaters, sloths)
   |
   `--

If you replace the '+' sign with a name, you get the following:

--Eutheria

   |
 (Unnamed)
   | 
   |--Xenarthra (late cretaceous)
   |  (armadillos, anteaters, sloths)
   |
   `--

This doesn't make much sense as you have two clades name (both Eutheria and unnamed) that unite the two following clades.

Please can someone knowledgable on this or maybe a member of palaeos.com take a look at this? Many thanks.

Darkuser999 (talk) 17:12, 12 October 2009 (UTC)

So there's another problem with the cladogram. This one is about the location of culogos, bats, plesiadapiforms and primates in relation to one another.

If one visits the plesiadapiform entry or looks at some other cladograms on Wikipedia and elsewhere (although the conflict within wikipedia is far more relevant), culogos are positioned differently with respect to the others (bats separate from all, culogos as a sister clade to primatamorphs). I have seen a number of statements to the effect that new research supports this latter formulation, but I am not a biologist and don't keep up with research to that degree of specificity. If it hits Nature, etc., I'll have probably read it. Otherwise, it's outside my specialty and out of sight out of mind.

Still, the evolutionary relationships of major clades within vertebrata and the radiation of bilaterians are quite interesting to me so I would like very much if someone could look at this cladogram & the one on (for example) the plesiadapiform entry & determine which is most correct given research (or, if possibly both are in error when compared to current research).

I understand that there are significant periods when theories are hashed out when it is not clear which is the best interpretation. That's fine. Perhaps pages that deal with finer-grained cladograms in other entries need to have multiple options spelled out there and this one left until the science is more clear. But as long as WP has internal inconsistencies, we should try to either fix or explain them so non-scientists don't look at them and take it as evidence that we don't know what we're doing.

And, y'know, to pass on the best info possible. That too.

Thanks folks.

Dating the Platypus-Echidna split

Under the Monotremes heading, the article says that the finding that Teinolophos was a Cretaceous platypus shows that the platypus and echidna lineages diverged earlier, but that seems to contradict a recent finding that implies that they split only about 19-48 million years ago.

http://www.pnas.org/content/106/40/17089

Doesn't that seem like it needs to be included here? —Preceding unsigned comment added by 70.167.51.34 (talk) 21:25, 14 October 2009 (UTC)

Go for it. Looks like there are 2 competing views to be summarised: (a) T. was a basal monotreme, before the platypus and echidna lineages diverged, possibly quite recently; and (b) T. was a platypus, and the platypus and echidna lineages diverged before T. Please add the citation for the paper you mentioned. --Philcha (talk) 22:09, 14 October 2009 (UTC)

Akinesis

A great article! There's one omission for me though - akinesis. Most amniotes have kinetic skulls apart from mammals, which is an important character of mammals. In Kardong (Vertebrate Evolution), he explains that the primary reason for Akinesis is because of the formation of a secondary palate, which prevents movement relative to the braincase; the secondary palate is required for suckling in infants. I might add this in a couple of weeks (after my exams!), although it has to be said I would have thought akinesis would have been unnecessary anyway due to the strength of the dentary-squamosal joint and the associated lateral mobility of the jaw. But I guess you can't really disagree with Kardong. Oliverjknevitt (talk) 14:29, 22 May 2010 (UTC)

You may also want to write the akinesis article. It currently is a redirect to hypokinesia. - UtherSRG (talk) 14:43, 22 May 2010 (UTC)

It's a little more complex when you look at how amniotes originates in the Late Carboniferous and almost split. The major groups of are:

• Sauropids, which include lizards (Late Carboniferous), crocodilians (Triassic), dinosaurs (Triassic), and birds (Late-ish Jurassic). Most sauropids have kinetic skulls, except for birds. I haven't researched this but guess that the evolution of birds' large brain forced the braincase to expand and dominate the skull, making it rigid.
• Synapsids developed rigid skulls very quickly. Their only living members are mammals.
• Anapsids may have 1 ancestor or more - paleologists are divided. Most died out in the Permian-Triassic extinction event, but 1 group survived into the Triassic.
• Testudines (turtles, tortoises, etc.) are the greatest puzzle to paleologists. The anapsid skull looks "primitive", but the eariest fossil testudines, in the Triassic, already have the legs inside the ribcage

Controversial phylogenetics?

"One often feels compelled to try to explain the evolution of features that do not appear in fossils. This endeavor often involves Molecular phylogenetics, a technique that has become popular since the mid-1980s but is still often controversial because of its assumptions, especially about the reliability of the molecular clock."

The wording of this is quite odd. "compelled" by whom? Also, molecular phylogenetics is used by thousands of studies (the phrase is in about 30,000 articles, according to Google Scholar), so I don't think it is still "controversial". Like any method, it must be used appropriately. The molecular clock assumption is often violated, which is true, but 1) molecular phylogenetic methods to infer a topology or even tree with branch lengths do not depend on a clock, and 2) there are methods that can provide dates even in the absence of a molecular clock.

--Bcomeara (talk) 20:55, 19 August 2010 (UTC)

I created this article in 2007 or 2008, because Mammal was very inaccurate. At the time molecular phylogenetics was regarded as poor at dating. In 2009-2010 a combination of more powerful computers and more advanced software provide more accurate dating - although a run usually takes 4 to 6 weeks. --Philcha (talk) 22:05, 19 August 2010 (UTC)