Mammal Or Reptile?

[Doughboy]

It has always been assumed all dinosaures such as Brontosaurus, triceratops and others like these were reptiles and they couldn't have been mammals because they lay eggs and no mammals were around back then. Well for a while now scientists have been debating this since they do have more mammal traits than reptiles and there are mammals today that do lay eggs. I found this article online by a Dr. Velikovsky and the article appeared in the KRONOS Journal in about 1978. R.Solàrion. I would quote it for you but instead here is the link for it.

 

My link

 

and it's not the only link I have found that have suggested these animals were mammal not reptile and it makes since to me, I think the only reason scientists always claimed them to reptiles is because mammals weren't suppose to be around then, but who are they to say when something is or isn't suppose to be around after all the aforementioned article says that there mammals with dinosaurs, and also that they lay eggs, as do the platypus and echidna

[Ringer]

Actually mammals were around at the time of the dinosaurs (depending on which time frame you are referencing) they just weren't the prevalent species. If you want to know what mammals lived in the Jurassic that we are aware of here you go.

 

Now how we know what animals mammals are descended from comes more from the shape of their hip/leg joints and their skulls than they way they give birth. Indeed the placentals and marsupials came along after mammals that laid eggs.

 

 

 

 

On a side note Brontosaurus is a lie.

 

[edit]Spelling[/edit]

Edited July 19, 2011 by Ringer

[Arete]

A problem I see with your hypothesis is that the presence of extant egg laying mammals (monotremes) and a large number of viviparous reptiles (boas, vipers, Egernia etc) renders egg laying an uninformative character for splitting mammals and reptiles. The placement of the sauropods in Reptilia is based on other morphological characters which are as I understand, pretty extensive.

[michel123456]

Velikovsky is a very controversial author. Edited July 19, 2011 by michel123456

[Doughboy]

Velikovsky is a very controversial author.

 

 

yeah that's what I liked about his article he wasn't afraid to ask the questions no one else would

[Ringer]

Being controversial and making things up are totally different.

 

Velikovsky's ideas have been almost entirely rejected by mainstream academia (often vociferously so) and his work is generally regarded as erroneous in all its detailed conclusions. Moreover, scholars view his unorthodox methodology (for example, using comparative mythology to derive scenarios in celestial mechanics) as an unacceptable way to arrive at conclusions. The late Stephen Jay Gould^[34] offered a synopsis of the mainstream response to Velikovsky, writing, "Velikovsky is neither crank nor charlatan — although, to state my opinion and to quote one of my colleagues, he is at least gloriously wrong ... Velikovsky would rebuild the science of celestial mechanics to save the literal accuracy of ancient legends."

[Moontanman]

It's actually not proper to say Dinosaurs were reptiles any more than it is proper to say mammals are reptiles. Both animal groups evolved from reptiles through various intermediate forms. Dinosaurs and mammals split from the reptiles at approxamately the same time, dinosaurs pretty much domionated mammals and through this domination/competition the mammals we see today evolved. Many ancient animals that are commonly thought of as dinosaurs were not and were more closely related to mammals.

 

http://en.wikipedia.org/wiki/Dimetrodon

 

If not for the dinosaurs mammals would have no doubt never evolved into the forms we see today and might have more closely resembled the dimetrodon.

[Arete]

If not for the dinosaurs mammals would have no doubt never evolved into the forms we see today and might have more closely resembled the dimetrodon.

 

Phylogenetic analysis disagrees - the dinosaur lineages are nested within extant reptile lineages and as such did not give rise to mammalian taxa.

 

e.g.

 

with one caveat

 

 

[Moontanman]

Exactly where did i suggest mammals evolved from dinosaurs?

[Arete]

The phylogenetic placement disputes this:

It's actually not proper to say Dinosaurs were reptiles any more than it is proper to say mammals are reptiles.

 

Archosaurs are indeed reptiles by phylogenetic placement.

 

And this:

Many ancient animals that are commonly thought of as dinosaurs were not and were more closely related to mammals.

 

Pterosaurs, and theropods and sauropods - your classic dinosaur taxa are nested within extant reptile lineages and thus have much closer affinities to reptiles than mammals. Other extinct animals indeed bear closer relation to mammals, but these aren't typically considered dinosaurs.

 

 

The caveat of course is that phylogenetically, birds are reptiles too. In hindsight I should have quoted the more relevant portions of your post.

Edited July 30, 2011 by Arete

[Moontanman]

Again, where did I suggest that mammals evolved from dinosaurs?

 

Both archosaurs and mammals evolved from reptiles, a similar crude phylogeny could be made with mammals and reptiles.

[Arete]

Both archosaurs and mammals evolved from reptiles, a similar crude phylogeny could be made with mammals and reptiles.

 

While any scientific conclusion acknowledges that it may be incorrect, that "crude" phylogeny is supported by a large body of scientific evidence. I chose the image because of its simplicity and relatively low level of assumed knowledge.

 

 

Blow up Diapsida:

 

 

There's the Archosaurs! a well and truly derived group within Reptilia (along with Aves, the aforementioned caveat).

 

 

http://tolweb.org/tr...ial_Vertebrates is a more complete summation of the current phylogenetic understanding of the group.

 

In addition almost all studies show that the split between Mammalia and Reptilia is basal in relation to the internal split between the Archosaurs and the rest of Reptilia, so this:

Dinosaurs and mammals split from the reptiles at approxamately the same time

is also in contradiction to current best knowledge.

 

So in summary my point was: phylogenetically speaking - the dinosaurs are considered reptiles, they arose considerably after the Mammalia did and none of the organisms one would classically or technically consider to be dinosaurs bear closer affinities to mammals than reptiles.

Edited July 30, 2011 by Arete

[Moontanman]

You seem to be thinking that mammals emerged from reptiles fully formed as mammals when in fact (and yes you are correct mammals in this sense did indeed evolve before archosaurs did but not by much)

 

http://genesispanthesis.tripod.com/fossils/rept_mam.html

 

The mammal like reptiles were the first of the mammalian line Dimetrodon was not a dinosaur, it was on of the first mammal like reptiles from which all mammals derived. Dimetrodon was not a direct ancestor of modern mammals but they are related as much as crocodiles are to dinosaurs. later mammal like reptiles like Tetraceratops had more mammalian characteristics but were not modern mammals any more than crocodiles are birds or ancestral to birds. Your mistake is equating the mammals that emerged at the end of the dinosaurs as the only mammals but the mammal like reptiles were ancestral to mammals as we know them and if they were still around we would classify them as mammals not reptiles and if not for the rise of the dinosaurs these mammal like reptiles would have dominated and it's doubtful that mammals as we see them would ever have evolved. mammals as we see them now are just a tiny branch of the mammal like reptiles just like all the dinosaurs including birds are just branches of archosaurs. a great many dinosaurs even the really large ones more not the reptilian beasts we imagine but were covered with feathers and the living animals would have born as little similarity to a lizard as a chicken does an iguana. BTW, reptilian like scales occur in some mammals as well so the idea that mammals have no connection to reptiles because they have fur and not scales is as inaccurate as saying dinosaurs didn't a connection because some of them had feathers.

 

The animals we call mammals had deep roots, every bit as deep as dinosaurs, quite possibly deeper if you count the mammal like reptiles but the first mammals were not tiny harry creatures hiding from dinosaurs, they were large animals every bit as large and impressive as the first dinosaurs but the dinosaurs won the evolutionary lotto, at least the first few of them...

[Arete]

You seem to be thinking that mammals emerged from reptiles fully formed as mammals

 

Quite simply, no. This assumption was never made.

 

Dimetrodon was not a direct ancestor of modern mammals but they are related as much as crocodiles are to dinosaurs.

 

The phylogenetic placement shows this is simply not true. Look at the tree - Dimetrodon was a basal Synapsid. Crocodilians and dinosaurs are Archosaurs. As such, Crocodiles are considerably more closely related to dinosaurs than Synapsids. You'd need a radically different phylogeny to support your statement.

 

Your mistake is equating the mammals that emerged at the end of the dinosaurs as the only mammals but the mammal like reptiles were ancestral to mammals as we know them and if they were still around we would classify them as mammals

 

Synapsids are again, not Archosaurs and relatively distantly related to Archosaurs in comparison to extant reptile taxa. It seems you might be making an error in assuming that the basal Synapsidae are Archosaurs (dinosaurs) which they are not.

 

not reptiles and if not for the rise of the dinosaurs these mammal like reptiles would have dominated and it's doubtful that mammals as we see them would ever have evolved.

 

If organismal evolution hadn't progressed the way it happened to progress the entire biota of the planet would by definition, be distinct from what is observed today. Determining which lineages would and wouldn't have succeeded given a hypothetical change in historical events is ludicrously speculatory.

 

A great many dinosaurs even the really large ones more not the reptilian beasts we imagine but were covered with feathers and the living animals would have born as little similarity to a lizard as a chicken does an iguana.

 

Yes. Aves - a phylogenetically reptilian lineage has feathers. Under a biological species concept, the generally accepted vertebrate species concept since Mayr 1942, birds would rightfully be reptiles. The caveat I've now mentioned three times

 

BTW, reptilian like scales occur in some mammals as well so the idea that mammals have no connection to reptiles because they have fur and not scales is as inaccurate as saying dinosaurs didn't a connection because some of them had feathers.

 

No one ever stated that Synapsidae did not share a common ancestor with Reptilia - the argument is a straw man. The issue is that Archosaurs are nested within modern Reptilian lineages, Synapsidae are basal to all of the modern reptile lineages. There's simply no way to argue that the dinosaurs could share more affinities with mammals than reptiles, unless you reject the phylogeny altogether, in which case you'd need evidence of an alternative scenario which outweighs the evidence supporting the current one.

[Moontanman]

I never said archosaurs were ancestral to mammals, I never said that dinosaurs shared more affinities with mammals than reptiles, why do you keep saying this?

 

I simply said that both dinosaurs and mammals were descended from reptiles, I did not say mammals were decended from dinosaurs. If i wanted to draw a crude phylogeny, as you did of archosaurs and thier relationship with dinosaurs, of mammals I would show the mammal like reptiles as being similar in their relationship to mammals as archosaurs were to dinosaurs. Again, i did not ever, not even once, suggest that mammals descended from archosaurs or dinosaurs.... and the demitrodon was not an archosaur, it was a mammal like reptile.

 

Dinosaurs were no more reptiles than birds are lizards, yes they shared common ancestors but dinosaurs were not just big reptiles any more than crocodiles are just big lizards.

[Arete]

I never said archosaurs were ancestral to mammals, I never said that dinosaurs shared more affinities with mammals than reptiles, why do you keep saying this?

You state:

It's actually not proper to say Dinosaurs were reptiles any more than it is proper to say mammals are reptiles.

 

Which is clearly proven false by the phylogenetic placement. Dinosaurs are much more reptiles than mammals are reptiles. Synapsidae - the ancestral mammalian lineage is a monophyletic, evolutionarily independent lineage basal to extant Reptilia. Archosauria - which contains the crocodiles, birds and dinosaurs is nested within extant Reptilian lineages and is thus, phylogenetically speaking, much more closely allied with extant reptiles than it is with extant mammals.

 

You then counter with a suggestion of an alternative phylogeny:

If i wanted to draw a crude phylogeny, as you did of archosaurs and thier relationship with dinosaurs, of mammals I would show the mammal like reptiles as being similar in their relationship to mammals as archosaurs were to dinosaurs.

 

I'm wondering what you would base an alternative phylogeny on in the face of the bulk of scientific evidence supporting the arrangement in the figure I posted:

 

http://www.tandfonline.com/doi/abs/10.1080/02724634.1991.10011426

http://www.sciencemag.org/content/283/5404/998.short

http://jpaleontol.geoscienceworld.org/cgi/content/abstract/75/6/1185

http://www.jstor.org/stable/4523513

http://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2009.00918.x/full

etc ad infinitum.

 

All reconstructions of the vertebrate phylogenetic tree of life place Synadspids as basal to Reptilia and Archosaurs as well and truly nested within. The crudeness of the diagram comes from the lack of nodal support values and branch length scaling, not the placement of lineages.

 

Dinosaurs were no more reptiles than birds are lizards, yes they shared common ancestors but dinosaurs were not just big reptiles any more than crocodiles are just big lizards.

 

This is a false dichotomy. Aves and Squamata are reciprocally monophyletic as are Crocodilia and Squamata. Archosauria IS NESTED WITHIN REPTILIA. It's like saying "Ostriches are no more birds than parrots or robins are hawks."

[Moontanman]

So, you are saying that mammals in general are somehow less related to reptiles than birds are related to reptiles? Are you saying that mammals somehow appeared with no basil forms? Are you saying that mammal like reptiles are basil to achosaurs but not mammals? Mammal like reptiles were not basal to archosaurs by any definition of the idea. One group of reptiles evolved in one direction and another evolved in another direction (I am sure there were more groups that went no where in an evolutionary way and much more complexity but as you said earlier we are being crude here)

 

Mammals as we know them did not spring into existence, they had precursors just like dinosaurs did. If not for the ecological pressures of dinosaurs the mammal like reptiles would never have given rise to the animals we see as mammals today. It's like you are trying to say humans are related to apes but not monkeys. (humans are both apes and monkeys by definition) Archosaurs, specifically dinosaurs dominated the mammal like reptiles not due to chance but do to real superior adaptations that the mammal like reptiles simply didn't have, like an upright stance, bipedal, better respiratory systems, the mammal like reptiles, even the more advanced ones we would have seen as more mammalian couldn't compete and were driven to extinction by the competition of dinosaurs.

 

Only those mammal like reptiles that had evolved to fill the niches occupied by small creatures survived. This evolutionary pressure changed them drastically from their ancestors but the connection is still there. I honestly do not see how you can separate mammals from reptiles so completely when they obviously evolved from reptiles at some point in their evolutionary past as did archosaurs, yes most archosaurs do superficially resemble reptiles more than most mammals but that is due to the more reptilian mammals having been eliminated by competition with the dinosaurs. Can you honestly say that crocodiles are reptiles with no caveats?

 

Compare a Komodo Dragon with a Crocodile, not the same type of creature, they only superficially resemble each other and their evolutionary connection is just as distant as the distance between a Komodo Dragon and a Lion. An alligator is no more a lizard than a bird is a lizard, some mammals not only lay eggs but lack both the upright stance of most mammals and also lack efficient thermo-regulatory systems. In our modern world none of the more basil mammals have survived, the three types of mammals that do survive are quite different from each other, some would say as different as crocodiles from dinosaurs at least. Either I am stupid which is of course entirely possible or we do not understand each other very well.

[Arete]

So, you are saying that mammals in general are somehow less related to reptiles than birds are related to reptiles?

 

Exactly - there's a more extensive phylogeny on the tree of life webpage I posted earlier. It seems like you're not all that familiar with phylogenetic trees, so I'll explain in basic terms and apologize in advance if it's too simple, but think of the tree in terms of a human genealogy - obviously with a huge number of extinct terminals and unrepresented intermediates.

 

Mammals and reptiles share an ancestor deep in the phylogeny - like a great great great grandfather, but went off on their own branch of the family tree long ago. Turtles are a long lost uncle to the rest of the reptiles. Squamates are the first cousins of the Archosaurs. The lineages within Archosauria - Crocodiles, Sauropods, Therapods, Ornithscians and Pterosaurs are all siblings, the birds of today are the children of the Theropods. In this sense, the Archosaurs, including the birds of today are considerably more closely related to each other than they are to any extant or extinct mammal lineage, and they are a clan nested within the rest of the reptiles. In contrast, the mammals are a group which went on it's own evolutionary way long ago.

 

Are you saying that mammals somehow appeared with no basil forms?

 

Not at all.

 

Are you saying that mammal like reptiles are basil to achosaurs but not mammals?

 

Synapsids - the "mammal like reptiles" evolved into mammals, but not Archosaurs. After this split, the ancestral reptile went through several intermediate stages resulting in many extinct taxa (see tree of life link) and the extant turtles. In the Permian, an Ancestral Saurian - which was uncontroversially a reptile, gave rise to the Archosaurs and the Lepidosaurs. As such, Archosaurs - which contains the dinosaur lineages came along much further down the Retilian lineage than the Syndapsidae and thus bears much more Evolutionary relation to extant reptiles than mammals.

 

 

Mammal like reptiles were not basal to archosaurs by any definition of the idea. One group of reptiles evolved in one direction and another evolved in another direction

 

Yes. Synapsids evolved into extant mammals, but did not evolve into Archosaurs.

 

Mammals as we know them did not spring into existence, they had precursors just like dinosaurs did. If not for the ecological pressures of dinosaurs the mammal like reptiles would never have given rise to the animals we see as mammals today.

 

Self evident and irrelevant to phylogenetic placement.

 

It's like you are trying to say humans are related to apes but not monkeys. (humans are both apes and monkeys by definition)

 

No. Humans are not monkeys and apes, that is a miscarriage of the Linnaean system of classification. Humans, monkeys and apes are all animals, vertebrates, mammals and primates. Humans and apes are Homonids - sharing a common ancestor, the old world monkeys are not. Old world monkeys are all Cercopithecoids sharing a common ancestor, humans and apes are not.

 

In the same sense, Mammals and reptiles and birds are all Amniotes, sharing a common ancestor. the Archosaurs and the extant Squamates are also in the subclades Reptilia, Diapsidae and Suaria, indicating a much longer period of common ancestry between extant reptiles and Archosaurs than between the mammals and the Archosaurs.

 

 

Can you honestly say that crocodiles are reptiles with no caveats?

 

Well unless you reject the entire system of Linnaean classification, by common ancestry, crocodiles are a linneage within Reptilia, sharing a common ancestor with the rest of the Reptiles and are therefore classified as reptiles.

 

 

Compare a Komodo Dragon with a Crocodile, not the same type of creature, they only superficially resemble each other and their evolutionary connection is just as distant as the distance between a Komodo Dragon and a Lion. An alligator is no more a lizard than a bird is a lizard, some mammals not only lay eggs but lack both the upright stance of most mammals and also lack efficient thermo-regulatory systems. In our modern world none of the more basil mammals have survived, the three types of mammals that do survive are quite different from each other, some would say as different as crocodiles from dinosaurs at least. Either I am stupid which is of course entirely possible or we do not understand each other very well.

 

Convergent evolution may make classification difficult in some cases, but what we generally base classification on is common evolutionary history. Phenotypic divergence is irrelevant. Komodo dragons and crocodiles share more common ancestry than either do with lions, ergo crocodiles and komodo dragons are reptiles, lions are mammals. Dinosaurs shared more common ancestry with reptiles than they did with mammals and are similarly, considered to be reptiles.

Edited August 3, 2011 by Arete