Teach the Rev

[Rev Blair]

Being more or less self-educated in evolution, sometimes (maybe more than that) I find myself getting a little confused on some things sometimes.

 

I'm hoping some of you don't mind helping me become less befuddled.

 

Presently I'm confused about the whole mammal-like reptile thing.

 

My current understanding is this:

 

They were the dominant species, then what's now part of Russia blew up, there was runaway global warming and a mass extinction. Over several million years the mammal-like reptiles became proto-mammals hiding in the bush and dinosaurs became the dominant species.

 

Is this more or less accurate? Does it match the current thinking, or am I half-remembering something from grade four science that's changed in the 30+ years since?

[CDarwin]

The notion that mammals were ecologically insignificant little scurriers beneath the feet of the dinosaurs has received some shocks in recent years. It appears that the Mesozoic mammals had diversified into beaver-like forms (Castorocauda) and even species that ate dinosaurs (Repenomamus).

[Rev Blair]

Cool. I had this impression that mammals were pretty much snack food back then.

[lucaspa]

Presently I'm confused about the whole mammal-like reptile thing.

 

My current understanding is this:

 

They were the dominant species, then what's now part of Russia blew up, there was runaway global warming and a mass extinction. Over several million years the mammal-like reptiles became proto-mammals hiding in the bush and dinosaurs became the dominant species.

 

Is this more or less accurate? Does it match the current thinking, or am I half-remembering something from grade four science that's changed in the 30+ years since?

 

The information I have says that mammals and dinos evolved at roughly the same time:

"Mammals and dinosaurs evolved from different groups of comparable-sized reptiles during the Triassic, which ran from 248 to 206 million years ago." http://www.newscientist.com/article.ns?id=dn6874

 

Mammals evolved from the mammal-like reptiles. Because they were on 2 legs and were partially warm-blooded, dinos outcompeted the early mammals for the large predator and herbivore niches. Also because they were only partially warm blooded and did not have insulation like feathers or fur, dinos had to grow very large to conserve body heat.

 

The article on Repenomamus doesn't dispute that (despite the hype). A meter was still pretty small for a dino and Repenomamus would have made a good meal for a velociraptor or tyrannosaur. Also, this occurred in S. America. Digs in N. America and Europe shows that most mammals were indeed vole or shrew sized or a bit larger.

 

So the dinos occupied the large herbivore and predator niches until toward the end of the Cretaceous. Their populations and diversity was in decline for about 10 million years when the Chixulub meteor did them all in.

[CDarwin]

The article on Repenomamus doesn't dispute that (despite the hype). A meter was still pretty small for a dino and Repenomamus would have made a good meal for a velociraptor or tyrannosaur. Also, this occurred in S. America. Digs in N. America and Europe shows that most mammals were indeed vole or shrew sized or a bit larger.

 

But they still weren't all just little shrew-like insectivores as tends to be the stereotype.

[lucaspa]

But they still weren't all just little shrew-like insectivores as tends to be the stereotype.

 

Not all of them. We now have two exceptions to that specific claim -- "all". However, these seem to be the outliers. We've got enough sampling in N. America and Europe to see that, in those areas, mammals were confined to small, shrew-like species. The stereotype is still very accurate. All we have are 2 exceptions to it in one location.

 

In the dino world, a meter isn't very big. After all, velociraptors are bigger than that. Compsagnathus and some of the other species in that family are smaller, but those are in Europe or N. America. I'd like to see a survey of the dinos from S. America and see if there are any small dinos there. I do recall that S. America is where the largest sauropods and theropods have been found. So I hypothesize that S. America is a a place where the small predator niche was not filled (for reasons unknown) by a dino such as Compsagnathus but instead was filled by a mammal.