Why dinosaurs probably evolved to birds?

[delboy]

 

Could you quote the related passage from your reference? From my understanding, alpha-keratin is indeed a mammalian distinction but not one we are currently able to determine relative to ancestral reptiles from the fossil record. Is it, perhaps, a hypothesized distinction considered probable based on separate, more solid anatomical links to mammals from the fossil record of ancestral synapsids; e.g., jawbone?

 

 

The article was about how to read a phylogenetic tree so not detailed about reptiles/mammals. This is the quote. Sorry I can't seem to quote the tree diagram but it's the basic tetrapod tree.

 

I think you're right, the distinction must be inferred from the fact that all extant mammals have alpha keratin and all reptiles (inc birds) have beta keratin.

 

 

The next thing you need to know is that characters are depicted at their point of origin on a phylogenetic tree. So, on this tree you can see that (1) the amniotic egg originated in ancestor 1 and was passed on to all of its descendants (mammals, ancestor 2, turtles, ancestor 3, ancestor 4, crocodiles, birds, ancestor 5, tuataras, and lizards plus snakes). In evolutionary terms, the amniotic egg is a unique trait that is shared only by ancestor 1 and all of its descendants; (2) a special type of skin protein (β keratin) originated in ancestor 2 and was passed on to all of its descendants (turtles, ancestor 3, ancestor 4, crocodiles, birds, ancestor 5, tuataras and lizards plus snakes). β keratin is a unique trait shared by the group called “Reptilia”; and (3) a breakable tail originated in ancestor 5 and was passed on to all of its descendants (tuataras, lizards plus snakes). A breakable tail is a unique trait shared by members of the group tuataras + lizards + snakes.

[DrmDoc]

Although not found in the fossil record, as I now understand, the keratin distinctions we find presently certainly infers an evolutional divergence between species that is significant as those distinctions we find anatomically. Thanks for the quote.

[sethoflagos]

I think your problems are more semantic than real.

 

If you recognise the term 'reptile' as a valid classification, then the first Amniote was a reptile and we are descended from reptile stock. Though since we are excluded from the definition of 'reptile', that becomes a paraphyletic group and apparently that is a bad thing now.

 

Better to drop the term 'reptile' completely and talk about Series Amniota (https://en.wikipedia.org/wiki/Amniote - based on egg structure) and its split into Synapsida and Sauropsida (based predominantly on the temporal fenestrae, but also a few other features).