Talk:Morganucodon

What Defines a Mammal

The three distinct bones of the middle ear is the hallmark of the mammalian species. The jaw joint is only a consequence of that in that they are correlated, but it is not what defines a mammal. —Preceding unsigned comment added by 152.13.72.89 (talk) 19:23, 2 May 2008 (UTC)

I have to disagree on this - the formation of the mammalian jaw joint, i.e. a joint between the dentary and the squamosal, has and is still being used to define a mammal, and is being used as such in some of the most influential publications in the field. Another potential definition that has been used is the absence of ANY postdentary bones in the lower jaw, though I would say that the jaw joint definition is the more widely accepted definition. Granted, all this is very theoretical as it is just a labelling exercise with no real consequences for the biology of this mammal. —Preceding unsigned comment added by 79.64.209.23 (talk) 00:06, 7 June 2008 (UTC)

Grandma Morgie

When I searched the web for references to the nickname "Grandma Morgie", I got only 9 hits, and about half of those were creationist sites. Is this really a nickname given by the AMNH? TomS TDotO (talk) 10:41, 12 March 2009 (UTC)

File:100_1887.JPG may be deleted

I have tagged File:100_1887.JPG, which is in use in this article for deletion because it does not have a copyright tag. If a copyright tag is not added within seven days the image will be deleted. --Chris 07:05, 27 April 2009 (UTC)

Must have been done since file is indicated as non existent. Retained this message for those who give importance to such matters J.H.McDonnell (talk) 21:55, 13 September 2010 (UTC)

Mammals, not reptiles or amphibia

Morganucodon is either a mammal or a protomammal, not a reptile or an amphibian. To eliminate the confusion I've gone ahead and deleted the references to those irrelevant taxa on this page. J.H.McDonnell (talk) 21:48, 13 September 2010 (UTC)

You didn't go nearly far enough! There's repeated talk of mammalian jaw structure evolving from reptilian jaw structure, which reads like something out of the 1930s. Let's get it straight. Mammiliaforms evolved from earlier Synapsids, which are not reptiles, and both Synapsids and Sauropsids evolved from early amniotes. Neither group evolved from the other. The passages in question should reflect this. Macdonald-ross (talk) 06:04, 18 November 2010 (UTC)

It does depend on what systematics you are using. From a purely phylogenetic nomenclature POW there is no such as a reptile at all (they are either synapsids, sauropsids or stem amniotes). From a traditional Linnaean or evolutionary taxonomy POW there are reptiles, and mammals evolved from them. If you want to follow Michael Benton, there's yet another system, where mammals evolved from synapsids which themselves evolved from reptiles. Take your pick. Despite cladistians commonly claiming they are the only show in town, other systems are in use, and Wikipedia being a general encylopedia should cater to them all. Petter Bøckman (talk) 21:49, 12 January 2011 (UTC)

Not entirely true, Reptilia is a phylogenetically defined clade with an identical definition to Sauropsida, and actually predates the modern phylogenetic definition of Sauropsida. If an alternate system is in wide use in the technical literature it should be discussed, but you'll have to point out the source. I haven't personally seen a vert paleo paper in any sub-field use any Linnean type system since the '90s. Which current workers are using the alternate systems, and in which papers? I nkow about Benton, but that's only in the appendix to a textbook. Any in use in active research? MMartyniuk (talk) 00:00, 13 January 2011 (UTC)

I think Zofia Kielan-Jaworowska and Jørn Hurum (bout of whom have been working on early mammals) use a more or less Linnaean nomenklatur (e.g. Kielan-Jaworowska, Z., & Hurum, J.H. (2001). "Phylogeny and systematics of multituberculate mammals". Palaeontology 44: pp 389–429 and Kielan-Jaworowska, Z., Cifelli, R.L., Zhe-Xi, L. (2004): Mammals from the age of dinosaurs : origins, evolution, and structure. New York: Columbia University Press. ISBN 0231119186.). A traditional Linnaean approach is also found in any number of entry level university textbooks and almost universal in paleoanthropology (which really is a vert paleo subfield), so claiming the system is not in use is untrue. Reptilia as a phylogenetic unit identical to Sauropsida is also a new and as far as I have seen far from universally accepted proposal and far less commonly used than let's say Benton (wouldn't the name Sauropsida have priority for this group anyway?). I think we again are in a situation where our perspectives are coloured by where we work, my office is just down the hall from Hurum's. The same argument we have gone over on the reptile discussion goes here too: Wikipedia is a general encylopedia and should not only cater to the experts in the field, and we have room to present bout views.Petter Bøckman (talk) 08:43, 13 January 2011 (UTC)

I agree we write for an interested but non-professional group of users, although I don't suppose anyone arrives at this article without biological education! I had thought about the same issues Petter raises, but came to a different conclusion.
In my experience almost no-one rids themselves of childhood learning, such as reptiles = snakes & lizards (and these days, dinosaurs). That is, unless they actually study vertebrate palaeontology. Consequently, the use of the word 'reptile' to describe huge tracts of tetrapods way back to amphibia is counter-productive. It means the word is too elastic and slippery as an instrument of communication.
Also, and here I don't think it a matter of opinion, it is wrong educationally as well as scientifically to call the ancestor of mammals 'reptiles'.
I don't think it cladistic to have terms like sauropsid, synapsid, therapsid, cynodont... which can be defined, and which fit what we know about the evolution of vertebrates. Macdonald-ross (talk) 09:45, 15 March 2011 (UTC)

I work as an educator at the local nat.hist. museum. In the understanding of the word "reptile" I meet among the general public, it is a catch-all phrase for anything cold-blooded and scaly. Should anyone meet a dragon (the mythical beast, not genus Draco), it would rather unhesitantly be labelled a reptile. Perhaps it is a cultural or linguistic differences at work here. I am not a native English speaker. I do however fail to see how using the world reptile as it has been used for the last century or so in English speaking litterature makes it failing as a tool of communication. Romer and Carroll, both excellent comunicators, seem to never have had any problems with it. Neither do I. How is the traditional use of the word reptile "elastic and slippery"? The definition of "reptile" is perfectly clear.

There's nothing wrong with sauropsid, synapsid, therapsid, cynodont though, they are just not commonly known (I'm fairly certain you will find more people able to tell you what a "mammal-like reptile" is than people who can do the same for "synapsid"). I have never suggested we should somehow stop using such names. It does on the other hand not stop us from using the more vernacular "mammal-like reptile" too.

A far greater problem with this article is that it has several sections devoted to phylogeny, and only two sections about the animal itself. It seems petty discussions on rather incosequential details of labelling has taken priority over the critter itself. Petter Bøckman (talk) 10:50, 15 March 2011 (UTC)

This was probably just a live-bearing shrew-like mammal. That's what it looks like from all appearances. If we found a fossil like this in higher rock layers, we would certainly assume it is just a typical small vivaporous mammalian creature. The egg-laying is unsupported speculation and wishful thinking because it makes for a better story. 72.73.109.8 (talk) 02:00, 20 January 2014 (UTC)

"from all appearances"? "assume"? These terms don't belong is science. There's a thing called comparative anatomy we can use to say this is not a crown mammal. MMartyniuk (talk) 11:53, 20 January 2014 (UTC)

Pronunciation

Anyone know how to pronounce the name of this animal? /ˌmɔːrɡənˈjuːkəˌdɒn/? /ˌmɔːrɡəˈnʌkəˌdɒn/? /mɔːrˈgɑnəkəˌdɒn/? Peter M. Brown (talk) 18:07, 17 January 2011 (UTC)

Ovipary

How does Morganucodon 's phylogenetic position near the very base of the mammalian lineage provide reason for supposing it oviparous? Is it a matter of phylogenetic bracketing between dinosaurs and monotremes? While I am very far from regarding about.com as a reliable source for anything, it does say "Paleontologists believe Cynognathus. . .may have given birth to live young (rather than laying eggs)" and Cynognathus is more basal than Morganucodon. How to dispute this? After all, there are viviparous fish. Peter Brown (talk) 15:26, 29 May 2013 (UTC)

Cynognathus laying eggs??? Oh my! Lot's of interesting stuff on that page, but having them "sport a thick coat of hair" is rather dubious (non of them show the dent in the skull for the harderian gland, a trait used to interfere the presence of fur (see Evolution_of_mammals#Hair_and_fur).

Ovipary is the primitive condition in all amniotes. Monotremata still lay eggs. Anything predating the Prototheria/Theria split should be egg-laying, unless one want to argue that the eggs in Monotremata is an atavism. I don't really think anyone seriously entertain this idea, but I may be wrong. If so, it would be WP:fringe. Our friend Morganucodon, being an outside-the-crown-group mammal or a mammaliform if you wish, it's split from the extant stock must necessarily predate the Prototheria/Theria split. The only way it could be live-bearing is if it evolved that trait independently (which of course is possible, which is why the article say "likely"). Petter Bøckman (talk) 20:38, 29 May 2013 (UTC)

I would be interested in your evidence that ovipary is the primitive condition in all amniotes. An alternative would be for vivipary to be the original condition, with ovipary developing in the sauropsid line after the divergence from the synapsids. Monotreme ovipary would then be homoplastic, not atavistic.

Regardless, I think that the tie between phylogeny and ovipary, however valid, requires more background than Wikipedia expects of its readers. We can't assume that they know any mammals to be oviparous; without that background, Morganucodon's being a basal mammal has no more relevance to ovipary than Cynognathus's being a basal eucynodont or Zhangheotherium's being a basal trechnotherian. Shall we just say that Morganucodon probably laid eggs? Peter Brown (talk) 23:51, 29 May 2013 (UTC)

My personal preference would be "Morganucodon probably laid small, leathery eggs, a condition still found in monotreme mammals (platypus and echidnas)." Would that do?

As for evidence amniotes primitively laid eggs, it is sort of an WP:BLUE situation. We know vivipary has evolved once among extant mammals, and multiple times in squamats, but there is no recorded instance of a reversal of this trait, indicating that regaining ovipary is evolutionary very difficult. It is also extremely difficult to see how returning to ovipary would have been advantageous for primitive sauropsids, considering how many anatomically and ecologically similar species are now evolving the other way. Here's a 2002 paper quite univocally stating eggs were the original condition in synapsids.Petter Bøckman (talk) 07:29, 30 May 2013 (UTC)

While we could use Oftedal as a reliable source if we need one, you make a much better case than he does, appealing, as you do, to irreversibility. Peter Brown (talk) 16:48, 30 May 2013 (UTC)

Thank you! We do not know if the trait is irreversible, but so far it seems to be. The problem with eggs as the primitive condition for amniotes is as I said a WP:BLUE-kind of problem, but at least authorities working with the rise of amniotes as diverse as Alfred Romer, Robert L. Carroll and Michel Laurin all assumes this to be the case. I think (i.e. noting we can cite) that much of the uncertainty around just this and related topics these days is a result of the phylogenetecists wanting to get out of the idea that "mammals have evolved from reptiles". While I guess the shake up was necessary to some degree, it has also served to throw out some perfectly fine biological understanding on how animals work in the process. Then again, uncertainty leads to new research, so I guess it's all good. Petter Bøckman (talk) 20:40, 31 May 2013 (UTC)

Also,about the viviparous fishes argument for the reversibility, isn't it easier for a fish egg to be developed inside the body, facilitating the reversibility of the process than on an amniote? 95.136.94.20 (talk) 15:30, 2 August 2014 (UTC)MilhoVerde

References

Teeth

I see you want the teeth section better explained.

The idea is that tetrapods that grows slowly (i.e reptiles) continue to grow in maturity. Both the steadily increasing size of the jaws and the wear and tear imposed by a long life dictate continued change of teeth. Mammalian teeth being complex, replacing teeth requires quite a bit of resources, and as anyone having children of pre-school age can attest to, it is also a lot of bother (try eating an apple without your front teeth!). Thus, for the fast-living, high energy demanding life of insectivorous mammals, tooth replacement is kept to an minimum (i.e two setts, a trait retained in their descendants). How do you propose going about explaining it without making it a disproportionally large part of the article? Or is it so important it should be a large part? Petter Bøckman (talk) 20:52, 29 May 2013 (UTC)

Horses are also diphyodont and, according to the article Horse teeth, that animal has all its permanent teeth within five years of birth; according to Horse#Lifespan and life stages, it can expect to live until the age of 20 in the wild. Its permanent teeth, therefore, are good for 15 years. Why cannot a morganucodon be expected to live 15 years after it acquires its permanent teeth? Did its diet produce that much more wear per unit area than that of a horse?

I don't see that the article has to discuss teeth at all. According to Blueweiss et al. (1978, Table 1), the average life span of a mammal weighing W grams is 630 W^0.17 days; small mammals don't live long. A morganucodon was about the size of a modern chipmunk, with a life expectancy of 15 months. :Peter Brown (talk) 23:16, 29 May 2013 (UTC)

Indeed, small mammals live fast, but small reptiles do not. Your average lizard can live for 20 years, and so can a frog or salamander. A toad can live to 50, and I guess I don't need to mention turtles. The change from a long lifespan with continuous growth and (where applicable) teething to a short lifespan with arrested growth and only a single change of teeth is in itself an extremely interesting topic, and the change is one of those parameters that separate mammals from other tetrapods. The sources I have cited typically mention the change from several to two sets of teeth, as this seems to have taken place just around where Morganucodon & Co branches off. That is the reason I believe it is relevant to this article. It might on the other hand be more suited to the evolution of mammals, with only a short mention here. Petter Bøckman (talk) 06:53, 30 May 2013 (UTC)

It is surely no coincidence that arrested growth, precise dental occlusion, diphyodonty, a Blueweiss-style mass-longevity correlation, and prismatic enamel all appeared at much the same time. There has to be a common cause. If you can direct me, in particular, to discussions of why the mammalian mass-longevity relation is so distinctive, I will be most grateful.

My problem with the article remains: the implication that a pattern of rapid growth and permanent teeth indicate a short life. I introduced the horse as a counterexample. Peter Brown (talk) 13:34, 30 May 2013 (UTC)

I guess you can ad extremely small size, high obligatory metabolism (if monotremes are secondarily bradymetabolistic, which seem to be the majority approach these days), a full coat of fur, short juvenile stage, early maturity, possibly a dash of neoteny and a high reproductive output per pregnancy to your list. Essentially we see the evolution of the a whole slew of traits typical of small short-lived mammal insect-eaters like shrews and marsupial mice. The problem here is that we don't really know what is case and what is effect. All we have to go on is the extremely fragmented remains of a handful shrew-sized critters, usually only a dentary. If you ask me to speculate, I would say the driving force is early reproduction: Get those babies out of the nest fast, before the next Coelophysis comes around! We do know that there is a correlation though, whatever is cause or effect. I'll see if I can dig up a suitable reference.

The horse may appear long lived to us, but as almost all mammals it is actually quite short lived. 20 years, perhaps 30 if taken good care of, for a critter that weigh in at half a ton? That's really not impressive. It is about the same as a monitor lizard or an ostrich, the latter who weighs in at around 100kg. Even a duck or a puffin beat a horse for longlivety. A reptile the the same size as a horse (a very large crocodile or turtle) is expected to outlive it at least three times over if not prematurely made into a belt. A Latimeria will just have reached maturity by the time a horse goes to the eternal grazing grounds. To answer your question, horse molars has open roots and continue to grow, so the horse does not spend 15 years with the same teeth. And notice horses are really pushing it: Anyone working with horses know their growing teeth causes all kinds of problems and often need the attention of a veterinary with a file. Elephants too suffer the same diphyodonty fate, only it goes through one pair of molars at a time, all through life. Eventually it runs out of teeth, what kills old elephants is hunger. We mammals aren't built to last, and it's probably spending about a 170 million years with our physiology being fine tuned to live as critters like Morganucodon that is to blame. Petter Bøckman (talk) 21:27, 31 May 2013 (UTC)

You really prefer {{reflist}} to {{harvtxt}} on talk pages? {{harvtxt}} allows the references to stay with the section rather than being collected at the end, which may be many pages later.

You may think that an animal living 20 years is "short lived", but I don't think most readers told that Morganucodon "lived a fairly short life" are likely to think in terms of 20 years. Rapid growth and permanent teeth do not indicate a fairly short life in the sense of "short" that readers will assume.

If horses don't work, how about American bison? M₁ emerges fully in the first year of life and all permanent teeth are in place by its fifth birthday; the lifespan is 15 years, meaning that the teeth function 10–14 years. Unless Morganucodon teeth are markedly inferior to Bison teeth (per unit area, of course), tooth wear should not limit its lifespan to a couple of years.

I agree that early reproduction is probably an important driving force, but I doubt that the point is predator avoidance. As Hone and Benton have noted, "a longer generation time gives a slower rate of evolution and, consequently, a reduced ability to adapt to sudden change".

Peter Brown (talk) 01:08, 1 June 2013 (UTC)

Are there any sources specifying the dental formula? (the number of incisors, canines, premolars, and molars, on each side, top and bottom.)

Lifespan

(Dividing this up for ease of editing, sorry for the wall-o-text)

{{harvtxt}} - yours is the first mention of it I have seen (I'm not particularly tech-savvy). I just wanted all references to be in the same formate. Please, go ahead and put the refs in what format you feel is best. Could you also include a link explaining how to use harvtext, it might come in handy?

Bison and teeth - I think the bison exemplifies much of our problem here. From a zoological view, an animal closing in on a metric ton lasting a mere 15 years is a ridiculously short lifespan. However, diphyodonty seems more to be the effect than the cause. Mammals simply don't last long, so no need to invest in expensive poliphyodonty, when the complex mammalian teeth (and particularly the tribosphenic kind like Morganucodon had) are a hassle to grow and replace. I think we'll need to expand a bit on this topic, something to the effect of "... had a lifespan more typical of mammals,(ref. I'll find one on Monday) which for a mammal this size was is very short, around a year.(ref. Blueweiss & al.)"

Should this go here at all? - I would argue yes. The very similar and closely related Sinoconodon grew reptile style, had multiple changes of teeth and probably did not suckle. Thus, if this is to be mentioned in Wikipedia at all, here (and/or Evolution of mammals) is the place.

Cause and effect - I suggested predation as a reason for a short lifespan above, but there is more. Are you familiar with the concepts of r- and K-selected species? Small animals, let's say mosquitoes, are more at the mercy of wind and frost than let's say a moose. The mosquitoes can't weather out a windy night with frost, most will die. When going is good, the survivors will reproduce as much and as fast as possible, before the weather turn sour again. Being killed by the millions by the next night frost, such animals are rarely limited by carrying capacity (I shudder to imagine it), but rather by their reproductive rate (r), hence they are said to be r-selected. The moose population at the other hand, will mostly weather the frosty night and expand to the point where food will be a limiting factor, hence they are limited by carrying capacity (K). For them, it pays to delay reproduction to a point where they have enough resources to bring forth a healthy offspring able to effectively compete for food.

Small mammals like mice and shrews are typically r-selected, they grow up fast (thanks to lactation), have short gestation and large litters and limited parental investment in each offspring. They live intense, fast and very dangerous lives. Of the perhaps 30-70 offspring a successful female mouse bears, on average only two survive to maturity. They may not all be killed by Coelophysis (hawks and crows these days), but killed they are, by predators, bad weather or bad luck. The thing is, Morganucodon seem to fall into the r-selected category, while Sinoconodon (or a similarly sized lizard) do not. Whatever the reason, the change of pace between the two seems to involve a basic change in life history-parameters.

Now, all wee need a source for the correlation between diphyodonty and short (mammalian) lifespan, and we're all set.

Benton - Benton's argument can't be turned on it's head and read like short lives are an adaptive benefit in a changing environment, because it would violate one of the most fundamental rules of evolution: You can't select for something your descendants can use, you must have a benefit from that trait for it to be selected. "Increased ability to adapt to sudden change" would be a happy by-product of a trait evolved for some other purpose.

Petter Bøckman (talk) 22:35, 1 June 2013 (UTC)

Cause and effect: You suggest that Sinoconodon was K-selected. Its closest known relative, though, was Morganucodon. It seems entirely possible that Morganucodon inherited that K-selectivity from their common ancestor. How heritable is K-selectivity? Might it not overpower other factors like body size?

Benton: No, genetic plasticity is not selected for. Nor is mutation. Both can arise, though, and be heritable. Then, after vast climatic and tectonic changes, it would be unsuprising to find that the creatures with less genetic flexibility had gone extinct while the more flexible live on in a wide diversity of ecological roles. Mammals and squamates, I suggest, possess this sort of flexibility, which is why they now constitute two-thirds of the extant tetrapod species outside of the birds and why such an explosive radiation happened after the demise of the dinosaurs. The persistence of this heritable flexibility is assured by the fact that a lineage that loses it is likely to become extinct. Peter Brown (talk) 00:08, 2 June 2013 (UTC)

Cause and effect: (sorry for the wall-o-text ... again) Being r- og K-selected is about a host of traits, some which can change easily and others that are more conservative. Exactly what traits were variable and what were more constant in early mammals is very hard to say.

The concept of r- and K-selection was typically minted on mammals, and to some extent birds, and like many such concepts does not translate too well to animals like reptiles and amphibians. Today most researchers use life history theory, which looks at the composition of traits that typify a species, rather than lumping them in with r- or K-selection. So what about Sinoconodon? It appears to have grown through life, which indicate it was somewhat long lived (like a lizard perhaps?). Also, thanks to its continuously growing jaw, it did not have perfect occlusion, so we can assume it was a less effective eater than Morganucodon. Chances are it did not suckle—see Dykes (2004)—which means no therapsids suckled either, if we assume non-reversibility, something I think is a safe bet in this case. This would mean less resource available for rapid and large scale reproduction and rapid growth. All in all, while Sinoconodon was small, insectivorous and probably nocturnal, it was likely not your average r-selected shrew like critter. Morganucodon, with it's diphyodont, well occluding teeth and likely suckling appears to fit that bill though.

I have thought long about which of the many traits we have discussed would have been cause and which would be effects. First off, the benefit of rapid and large-scale reproduction to small tetrapods is obviously high. Holding back the evolution of such traits was possibly the lack of effective means of getting enough calories, i.e. reptilian occlusion, forcing a more relaxed growth pattern. Reducing the number of teeth changes would be beneficial, Sinoconodon had sort of a halfway situation. With suckling, the young would grow up faster, and enabling the evolution of drastically lower number of teeth changes, to just two. This again also allowed for mammalian occlusion, which then would allowed for the animals to be even smaller, quicker and more r-selected. I believe suckling is the culprit in the evolution of mammalian life history traits. We can't put my speculations in Wikipedia though.

Try Kielan-Jaworowska, Cifelli, and Luo (2004), p. 148, which discusses, with references, the relationship between skull growth, lactation, and diphyodonty in much the way you do. The authors even suggest that the pattern of dental replacement provides evidence for lactation.

Peter Brown (talk) 23:26, 4 June 2013 (UTC)

Benton: I believe you are spot on!

Petter Bøckman (talk) 22:01, 4 June 2013 (UTC)

References

• Dykes, Trevor (2004). "Mammals of the Mesozoic: The least mammal-like mammals". Retrieved June 4, 2013.
• Mammals from the Age of Dinosaurs. Columbia University Press. 2004. {{cite book}}: Cite uses deprecated parameter |authors= (help)

References

Recent edits

It seems we disagree over content again, Dinoguy2. Discussion before editing? Petter Bøckman (talk) 10:58, 30 August 2013 (UTC)

Sure. I question the utility of using a completely unrelated analogue as an example photo which is as misleading as using a photo of a Hoatzin in the article on archaeopteryx. They are only superficially similar at best, and there's already a life restoration of the actual animal. This perpetuates the myth that all small mammals and mammal-like mammaliaforms are basically the same and breeds misinformation. Also, we do not use the manual taxobox on, say, Castorocauda, which would also be a mammal under a typological definition. This could be discussed in the text, but is it really "controversial" enough to warrant such hedging for this particular species when all mammals are in the same boat?

The consensus of the automatic taxobox system, and the article Mammal itself, seems to be to limit Mammalia to the crown group and discuss alternatives in the text. Why single this article out for a different system? If you're issue is with this practice in general, best top bring it up on the talk page for Mammal. MMartyniuk (talk) 11:47, 30 August 2013 (UTC)

Source is king. There is ample sources to Mammalia being used in the inclusively to cover these critters, it is not a small minority view. Thus I believe it is relevant to have this in the taxobox. The shrew was included to give an idea of what the animal looked like which the illustration do not convey. I see your point of the dangers of using modern animals as stand-ins for extinct ones, ideally I'd like new illustration rather than a comparison. I do however object to your statement that comparing ecologically and anatomically similar species necessarily breeds misinformation. In you filed (doinos) you may be right, because there's really nothing comparable around today, but not in the case of anatomically basal insectivorous mammals. Petter Bøckman (talk) 12:42, 30 August 2013 (UTC)

The Mammal article is not slanted toward the crown-group definition; it maintains fairly strict neutrality on the issue, as Wikipedia policy requires.

• The "Temporal range" specification provides the ranges under both the traditional and the crown-group interpretation.
• The first body section is an impartial discussion of the different approaches.
• The second section, Distinguishing features, lists characteristics common to all mammaliaforms. The only exception, the three-ossicle middle ear, is listed with an explicit qualification: "In crown-group mammals. . . ."
• Under Classification, Simpson's classification (which includes Morganucodon as a mammal) is discussed first, prior to the presentation of the McKenna–Bell classification that excludes it. In the interest of neutrality, perhaps a fuller classification under the traditional conception should be presented.
• Castrorocauda, which was not a crown mammal, is mentioned in the section The mammals appear with the explict qualification that the paragraph is concerned with mammals "in Kemp's sense".
• Earliest appearance of features mentions both Castorocauda and Hadrocodium but remains ambiguous as to whether they were mammals.

Much of the rest of the article is concerned with extant mammals, where there is of course no distinction to be drawn. Peter Brown (talk) 13:49, 30 August 2013 (UTC)

Synonymous with Eozostrodon?

Does anyone know if Morganucodon is even a valid name? Apparently Jenkins and Crompton (1979) (see "Taxonomic Opinions") synonymized all species of Morganucodon with Eozostrodon, which was named earlier. The Paleobiology Database lists Eozostrodon watsoni as an "alternative combination" of M. watsoni. "Eozostrodon" is mentioned in Linzey's 2012 Vertebrate Biology text here (p. 273) in a passage that resembles the discussion here. --Animalparty-- (talk) 08:15, 17 December 2013 (UTC)

Kielan-Jaworowska & Luo (Mammals from the age of dinosaurs, 2004) consider them distinct and valid genera, see Google books. Petter Bøckman (talk) 10:39, 18 December 2013 (UTC)