Could mammals have evolved from birds?

[Dremmer]

It's is believed by scientists that they came from reptiles, but could they have come from birds? A primitive mammal, the platypus closely resembles a bird. It can lay eggs. Could hair have evolved from feathers?

 

[SW VandeCarr]

It's is believed by scientists that they came from reptiles, but could they have come from birds? A primitive mammal, the platypus closely resembles a bird. It can lay eggs. Could hair have evolved from feathers?

Could have? Who knows? It's very unlikely that they actually did. Do you have a reference for this interesting hypothesis?

 

[Borek]

That would require mammals to be younger than birds, as far as I know, they are older.

 

[Dremmer]

That would require mammals to be younger than birds, as far as I know, they are older.

The fossil record however is not complete. New discoveries found could lead to some surprises.

 

[Borek]

I don't think it is THAT incomplete. Plus, phylogenetic tree is not based only on fossils, also on measurements of genetic distance.

 

[Dremmer]

Could have? Who knows? It's very unlikely that they actually did. Do you have a reference for this interesting hypothesis?

Here is an article that talks about the hypothesis.

http://www.evolutionem.co.uk/page9.html

I'm not saying I believe it happened, but there are some things that may support the idea.

 

[bobze]

It's is believed by scientists that they came from reptiles, but could they have come from birds? A primitive mammal, the platypus closely resembles a bird. It can lay eggs. Could hair have evolved from feathers?

No, if you compare mammals and birds, then birds and "reptiles" either through comparative anatomy, gene or protein data, the clustering of similar traits is too statistically significant for it be an error and for birds to belong to a mammalian nested set.

Edit: Not monotremes and birds both "lay eggs" (and other early mammals to boot) because of a commonality in ancestry. However, when you look at monotreme eggs and bird eggs, they are very dissimilar. The word "egg" here is being used too generally. Fish also lay eggs, as do insects, as do mollusks. That doesn't indicate that birds are the direct descendants of fish, insects of mollusks. It can however, be indicative of a very basal feature for modes of reproduction.

 

[Dremmer]

There are many features that birds and mammals share that do not exist in reptiles.

 

[Drakkith]

There are many features that birds and mammals share that do not exist in reptiles.

Such as?

 

[bobze]

There are many features that birds and mammals share that do not exist in reptiles.

Such as?

I'd be interested in hearing them too.

Also as a quick note, remember that homology does not necessarily indicate common ancestry.

For the classic example, can you pick out the wolf skull and thylacine skull without cheating?

 

[Proton Soup]

http://en.wikipedia.org/wiki/Great_white_shark"

 

[paleobarbie]

Why yes, I could, but this view is difficult (perhaps intentionally?) The thylacine is the upper skull as it clearly lacks the enlarged carnassial tooth (fourth premolar) of the wolf, as seen in all placental mammals in the order Carnivora (unless secondarily modified, as in the panda). The thylacine also has the marsupial pattern of 3 premolars and 4 molars. The wolf has at least 4 premolars that we can see in this view (unlike any known marsupial)

If we had other views, we could see many more differences. For example, the number of incisors. A total of six above and six below in the wolf (as in most placentals) as opposed to 10 above and 8 below in the thylacine (as in most marsupials).

If we were to view the lower jaw from the back, we would see that the thylacine had a distinct inturned flange on the base of the jaw, a distinctive feature of all marsupials, lacking in all placentals.

If we were to view the skulls from the palate (i.e., the top part of the skull turned upside down) we would see that the thylacine had holes in the palatal bones, typical of marsupials, not seen the wolf.

If we were to look in detail at the way that the bone arching below the eye was formed at the point of the jaw articulation, we would see that a certain bone (the jugal) formed part of the articulation for the jaw, as in all marsupials, but not in the wolf, as typical for placentals. (Actually you can see this if you look carefully)

If we viewed the skull from above we would see that the nasal bones of the thylacine formed a diamond shape at their posterior border, typical of marsupials, as opposed to the rectangular shape in the wolf typical of placentals.

Oh, I could go on and on, and I haven't even started yet on the postcranial skeleton or the internal anatomy. "Homology does not necessarily indicate common ancestry?" Get an education in science rather than cut and pasting from creationist factoid websites

PS. Things that birds and mammals share (to the exclusion of reptiles) are clearly convergences due to both being warmblooded, no problem there. (E.g., single aorta, but on the left in mammals, the right in birds, clearly derived independently.)

 

[Drakkith]

Oh, I could go on and on, and I haven't even started yet on the postcranial skeleton or the internal anatomy. "Homology does not necessarily indicate common ancestry?" Get an education in science rather than cut and pasting from creationist factoid websites

I think the person you quoted would agree with everything you said. Are you sure you read that post correctly?

 

[Greg Bernhardt]

Oh, I could go on and on, and I haven't even started yet on the postcranial skeleton or the internal anatomy. "Homology does not necessarily indicate common ancestry?" Get an education in science rather than cut and pasting from creationist factoid websites

Of course, because you are clearly an expert in the area. I think bobze (who is a med student!) is speaking towards the non-expert populace.

 

[bobze]

Why yes, I could, but this view is difficult (perhaps intentionally?) The thylacine is the upper skull as it clearly lacks the enlarged carnassial tooth (fourth premolar) of the wolf, as seen in all placental mammals in the order Carnivora (unless secondarily modified, as in the panda). The thylacine also has the marsupial pattern of 3 premolars and 4 molars. The wolf has at least 4 premolars that we can see in this view (unlike any known marsupial)

If we had other views, we could see many more differences. For example, the number of incisors. A total of six above and six below in the wolf (as in most placentals) as opposed to 10 above and 8 below in the thylacine (as in most marsupials).

If we were to view the lower jaw from the back, we would see that the thylacine had a distinct inturned flange on the base of the jaw, a distinctive feature of all marsupials, lacking in all placentals.

If we were to view the skulls from the palate (i.e., the top part of the skull turned upside down) we would see that the thylacine had holes in the palatal bones, typical of marsupials, not seen the wolf.

If we were to look in detail at the way that the bone arching below the eye was formed at the point of the jaw articulation, we would see that a certain bone (the jugal) formed part of the articulation for the jaw, as in all marsupials, but not in the wolf, as typical for placentals. (Actually you can see this if you look carefully)

If we viewed the skull from above we would see that the nasal bones of the thylacine formed a diamond shape at their posterior border, typical of marsupials, as opposed to the rectangular shape in the wolf typical of placentals. Oh, I could go on and on, and I haven't even started yet on the postcranial skeleton or the internal anatomy.

Yes I am aware to the student of CVA or someone who is more than passingly familiar with gross anatomy, that such differences are many.

I'd echo Drakkith and Greg's posts though, perhaps you should read the topic from the beginning--Rather than jumping to conclusions and making assumptions (you know the whole ***/you situtation? )

The topic we were talking (again from the OP) was why mammals didn't evolve from birds, because the both lay "eggs"?

Specifically the post I was replying to was: "There are many features that birds and mammals share that do not exist in reptiles." Hence, highlighting this with the example to the poster; that to the untrained and the "layman" to biology--"Homology" (or better, "they look the same!") is a poor way to establish relatedness. You know, the reason we've collectively invested so much money in comparative genomics.

"Homology does not necessarily indicate common ancestry?" Get an education in science rather than cut and pasting from creationist factoid websites

Yes, have a couple thank you. And that is true statement for the reasons you elucidate below. Convergent traits fooled many a amateur and professional biologist. That is why, when using homology as a null hypothesis, one must be careful to ensure they are not constructing polyphyletic trees--Least our evolved disposition toward "seeing is believing" lead us astray. In fact a classic illustration of this mistake (and to keep this on-topic) is a avian/mammalian polyphyletic tree;

Which I'm sure you are aware, would be from not accounting for convergent traits--The OP however, didn't seem to be aware of this...

PS. Things that birds and mammals share (to the exclusion of reptiles) are clearly convergences due to both being warmblooded, no problem there. (E.g., single aorta, but on the left in mammals, the right in birds, clearly derived independently.)

Yarp, got it thanks