Synapsid/mammal evolution

[delboy]

My understanding is that mammals are now not to be considered as evolved from within reptiles. So synapsids must have branched off the amniote line before the reptile common ancestor. What does the group they branched from lack (or have) that means they are not considered reptile? And does the group have a name? I think reptiliomorphs date back a bit further and are more amphibian like.

EDIT - I may have partly answered my question - just found a reference to reptiles/birds having beta-keratin and mammals having alpha-keratin.

 

If alpha-keratin is softer than beta, maybe that means mammal-like reptiles didn't have such a rigid skin as reptiles?

Edited April 13, 2014 by delboy

[Moontanman]

My understanding is that mammals are now not to be considered as evolved from within reptiles. So synapsids must have branched off the amniote line before the reptile common ancestor. What does the group they branched from lack (or have) that means they are not considered reptile? And does the group have a name? I think reptiliomorphs date back a bit further and are more amphibian like.

I am not trying to be pedantic but you answered your own question... Synapsids, Some people call them the mammal like reptiles but synapsids is the correct label, turtles on the other hand are Anapsids, reptile is no longer a useful term in this context..

Edited April 13, 2014 by Moontanman

[delboy]

I am not trying to be pedantic but you answered your own question... Synapsids, Some people call them the mammal like reptiles but synapsids is the correct label, turtles on the other hand are Anapsids, reptile is no longer a useful term in this context..

 

I'm not sure what you're saying there. I didn't phrase it very well - I'm asking if there is a name for a group before synapsids/anapsids/diapsids?

[Moontanman]

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

 

labyrinthodonts I think would be what you are looking for..

From fish to amphibians[edit]


Acanthostega, a fish-like early labyrinthodont.
The first jawed vertebrates appeared in the latest Ordovician and became common in the Devonian, often known as the "Age of Fishes".[20] The two groups of bony fishes, the actinopterygii and sarcopterygii, evolved and became common.[21] The Devonian also saw the demise of virtually all jawless fishes, save for lampreys and hagfish, as well as the Placodermi, a group of armoured fish that dominated much of the late Silurian. The Devonian also saw the rise of the first labyrinthodonts, which was a transitional between fishes and amphibians.

Mesozoic vertebrates[edit]
The reptiles appeared from labyrinthodonts in the subsequent Carboniferous period. The anapsid and synapsid reptiles were common during the late Paleozoic, while the diapsids became dominant during the Mesozoic. In the sea, the bony fishes became dominant. The dinosaurs gave rise to the birds in the Jurassic.[22] The demise of the dinosaurs at the end of the Cretaceous promoted expansion of the mammals, which had evolved from the therapsids, a group of synapsid reptiles, during the late Triassic Period.

 

Amphibians are not in the direct ancestry of reptiles but are an offshoot...

[delboy]

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

 

labyrinthodonts I think would be what you are looking for..

 

 

Amphibians are not in the direct ancestry of reptiles but are an offshoot...

 

Thanks, I'll have a read. I didn't know that about amphibians/reptiles.

[Ringer]

Well, not all synapsids are in the mammalian line (pelycosaurs). The line therapsids are thought to be mammalian ancestors though. As Moontanman said, reptile isn't a good category depending on if you include crocs, turtles, birds, sauropods, etc. A way to (somewhat) easily define if you are looking at a mammalian ancestor is the articulation of the jaw. Mammals articulate at the dentary and squamosal bones while other vertebrates articulate at the quadrate and articular.