Hello, I have a question about evolution regarding humans, dinosaurs, and birds.

First of all please excuse my ignorance, I thought id come to a forum to get a more interactive answer to this.

I fully believe in evolution and am an atheist, but something I cant get my head around is tracing life back to dinosaurs.

For example, evolutionary biologists figured out that all birds trace back to dinosaurs, and are in fact dinosaurs.

But arent we related to birds and all other species? And therefore should also be related to dinosaurs?

But also I remember hearing for a long time that dinosaurs became extinct. Many believing it was an asteroid that wiped out life on earth..

So are humans and all other life descendents of dinosaurs?

Im confused

Placentalia existed at the same time as dinosaurs. They're mammals.

Apparently the fossil evidence is a bit thin, but if you start with primates (or humans) and work your way back, placentalia are our closest ancestors that were alive 100 million years ago.

Apparently the connection between mammals and dinosaurs dates back to amniotes, about 300 million years ago.

 

Edited January 2, 20232 yr by Lorentz Jr

28 minutes ago, Lorentz Jr said:

Placentalia existed at the same time as dinosaurs. They're mammals.

Apparently the fossil evidence is a bit thin, but if you start with primates (or humans) and work your way back, placentalia are our closest ancestors that were alive 100 million years ago.

Apparently the connection between mammals and dinosaurs dates back to amniotes, about 300 million years ago.

 

Hi, thanks for your response, that clears up most of it for me. But then what about the idea that a catastrophic event wiped out the dinosaurs? Doesnt the fact that we have lineage tracing back suggest that there wasnt a catastrophic event?

No, there was an extinction event.

I think most mammals were relatively small back then. Lots of them, so I guess a few must have survived.

Edited January 2, 20232 yr by Lorentz Jr

47 minutes ago, Lorentz Jr said:

No, there was an extinction event.

I think most mammals were relatively small back then. Lots of them, so I guess a few must have survived.

Ok, thanks for clearing that up, appreciate your time

1 hour ago, Lorentz Jr said:

I think most mammals were relatively small back then.

Except for sabre-toothed tigers, mastodons, and/or probably other species. 🙄

Maybe it would be more accurate to say that some mammal species were small and at least some of the small ones survived.

Also, the asteroid supposedly hit in Mexico, and our ancestors came from Africa, which is on the other side of the planet. So maybe there weren't quite as many extinctions on that continent.

Edited January 2, 20232 yr by Lorentz Jr

17 minutes ago, Lorentz Jr said:

Except for sabre-toothed tigers, mastodons, and/or probably other species. 🙄

Maybe it would be more accurate to say some mammal species were small and at least some of the small ones survived.

Er, well, mastodons, sabre-toothed tigers, etc. appeared about 40m or more years later, from the Miocene onwards.  The mammals that existed at the end of the Cretaceous were indeed small and shrew-like.   

Edited January 2, 20232 yr by exchemist

4 minutes ago, exchemist said:

Your timing is out. Mastodons, sabre-toothed tigers, etc. came about 40m or more years later, from the Miocene onwards.  The mammals that existed at the end of the Cretaceous were indeed small and shrew-like.   

Hah! So I was right in the first place. I guess that makes sense, given how closely they resemble modern mammals. Thanks.

Edited January 2, 20232 yr by Lorentz Jr

25 minutes ago, Lorentz Jr said:

which is on the other side of the planet

When the asteroid hit, today's Mexico and East Africa were not where they are now. They were much closer to each other, separated by only about 80 degrees of longitude.

Anyway, the extinction event was global, affecting the entire planet, but differentially affecting different life lineages.

31 minutes ago, Genady said:

When the asteroid hit, today's Mexico and East Africa were ... separated by only about 80 degrees of longitude.

Anyway, the extinction event was global, affecting the entire planet, but differentially affecting different life lineages.

Another thing I forgot about. Maybe someone can discuss what affected survival rates.

3 hours ago, Adamchiv said:

So are humans and all other life descendents of dinosaurs?

Im confused

Just to clarify this last bit.

We're not descended from dinosaurs.

About 320 million years ago the ancestors of both humans and dinosaurs were to be found among a group of related small lizard-like creatures. One of these had made a few readjustments to its skull to improve the efficiency of its bite. It may have been a creature called Archaeothyris found in Nova Scotia, or a species very closely akin to this, and we (along with all other mammals) are their descendents.

Dinosaurs and all other modern reptiles are descended from one of the species that had not developed this advanced bite.     

Edited January 2, 20232 yr by sethoflagos
typo

12 hours ago, sethoflagos said:

Just to clarify this last bit.

We're not descended from dinosaurs.

About 320 million years ago the ancestors of both humans and dinosaurs were to be found among a group of related small lizard-like creatures. One of these had made a few readjustments to its skull to improve the efficiency of its bite. It may have been a creature called Archaeothyris found in Nova Scotia, or a species very closely akin to this, and we (along with all other mammals) are their descendents.

Dinosaurs and all other modern reptiles are descended from one of the species that had not developed this advanced bite.     

Thanks thats very interesting to learn

The mammals that we evolved from were small in the age of the dinosaurs. Most of the mammal species at the time probably DID go extinct along with the dinosaurs, it only needs a few to survive to start off a new era. There would be many vacant niches caused by the mass extinctions, so the mammals had the oportunity to evolve to fill those empty niches.

Nobody knows how some mammals survived, but it's likely that they lived underground. Snakes and crocodilians also survived, which might be directly related to their habit of burying their eggs. Some bird-like dinosoars might have buried their eggs too, just enough to give rise to the birds. (There are birds that bury their eggs today) Ants and dragonflies survived, maybe in tiny numbers, but would soon re-populate the Earth. Generally, it was big animals that died out, both on land and at sea. Maybe being small and numerous multiplied your chances of being tucked away somewhere safe when the disaster happened. Or maybe it wasn't the immdiate effect of the asteroid impact that caused all of the extinctions, but the massive climate change that followed and lingered for years, long enough to finish off big animals with high food demands.

We are related  to  dinos  and  every other thing.....

 

But  if  you want to  map  our  relation  to  dinos   you  must  go  back in  time   to the  time   mammals &  reptiles split their evolutionary  lines.......and then   make a U turn  and  again  go  forward in time  to  the  time......Dinos   have  evolved........

57 minutes ago, Saber said:

We are related  to  dinos  and  every other thing.....

 

But  if  you want to  map  our  relation  to  dinos   you  must  go  back in  time   to the  time   mammals &  reptiles split their evolutionary  lines.......and then   make a U turn  and  again  go  forward in time  to  the  time......Dinos   have  evolved........

Except that 'Present Reptiles' are not descended from dinosaurs. The lineages that were to become lizards & snakes, turtles & tortoises, the tuatara and the crocodilians had all split off from the sauria/archosaur line before dinosaurs were a thing..

18 minutes ago, sethoflagos said:

Except that 'Present Reptiles' are not descended from dinosaurs. The lineages that were to become lizards & snakes, turtles & tortoises, the tuatara and the crocodilians had all split off from the sauria/archosaur line before dinosaurs were a thing..

Thanx     so  it  should  be  this  way  right ?

Edited January 16, 20232 yr by Saber

1 minute ago, Saber said:

Thanx     so  it  should  be  this  way  right ?

No. Delete the lower 'Birds' and replace with 'Dinos'. Delete the extraneous 'Dinos' line.

Best would be to replace 'Reptiles' with 'Sauria' but I guess that's more for the purist than the common folk.

45 minutes ago, sethoflagos said:

No. Delete the lower 'Birds' and replace with 'Dinos'. Delete the extraneous 'Dinos' line.

Best would be to replace 'Reptiles' with 'Sauria' but I guess that's more for the purist than the common folk.

 

7 hours ago, Saber said:

 

Yes, that's the general idea.

I would advise anyone wanting to look more deeply into the extinction/evolutionary aspects of this to read Benton's excellent book.

Benton is professor of paleogeology at Bristol University, and heavily involved in the reasearch.

So the book is written for the semi knowledgeable layman but is rock solid in content and references .

It treats all 5 known major extinction events as well as some background material.