Are group common ancestors normally small and generalised?

[delboy]

Hello everybody.

 

There seems to be a trend that new groups start from a small and fairly generalised form. The synapsid reptiles had diversified into some very large and varied forms yet the mammals evolved from a very small general type. And I think the first reptile was quite small and lizard like.

 

Is it a trend that new groups normally stem from a small species (in invertebrates too?). If so is it known why?

 

 

[Ringer]

Not necessarily. It depends on the niche that's being occupied.

[EdEarl]

I agree with Ringer. Additionally, at one time life on Earth was only single cells; thus, all large organisms began from smaller organisms at some time in their ancestry.

[delboy]

Thanks for the replies.