Post by B13 on Oct 26, 2013 7:11:33 GMT 1
So according to number 9 Pigeons and other birds B13 are tiny dinosaurs? 10 is incomprehensible. And 11 is just weird. Do they mean ghosts?
There's two schools of thought on avian evolution:
1. Birds evolved from the Theropod dinosaurs group.
2. Both birds and dinosaurs both evolved independently, from the original, more ancient, Archosaur [sp?] reptile group.
There are arguments both for and against both theories.
But yes, birds are reptilian in origin - and so are mammals.
Cynodonts were among the pre-mammalian reptiles: they had pits in their faces where whiskers grew, and whiskers are highly specialised hair. Hair is one of the prerequisits for being classed as a mammal.
Our earbones (malleus, stapes and incus) were once three of the four bones that made up the reptile lower jaw - reptiles today still use their lower jaws to transmit sound to their eardrums.
So we mammals - and also birds - have links to our reptilian ancestors. Birds, dinosaurs and crocodilians evolved from the Diapsid group of reptilles, mammals from the Synapsid group. The other group, the Anapsids are the turtles and tortoise, etc.
The three groups are distinguished by the number and position of temporal fenestrae (holes) in their skulls - but let's not go there!!!
"But reptiles lay eggs! Mammals don't!", I hear you say.
Well... If you look at living monotremes (echidnas, platypus, etc) they are living mammals that still lay eggs and have quite a few primitive, reptilian features - and we placental mammals have eggs to, just always inside us. So do the marsupials.
So both birds and mammals are highly evolved reptiles - as bizarre as that sounds, we are: birds went one way, we went the other, reptiles trundled along up the centre.
Phew!! Cool, innit?
