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Author Topic: Were dinosaurs really "wiped out"?  (Read 4949 times)

Offline thedoc

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Were dinosaurs really "wiped out"?
« on: 09/04/2013 04:30:01 »
Jason  asked the Naked Scientists:
   
I was most surprised to hear, on Radio 5 Live 11th February, 2 highly qualified scientists say that "dinosaurs were wiped out" and that they were "cold blooded".

Dinosaurs evolved into birds which means they WERE NOT "wiped out" at all - most of the large ones were, but some smaller ones survived and eventually evolved into birds, meaning they are still all around us - many if us regularly eat them and/or their eggs!

Most palaeontologists also agree that they were also, like birds, endothermic.

Jason, Bournemouth

What do you think?
« Last Edit: 09/04/2013 04:30:01 by _system »


 

Offline CliffordK

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Re: Were dinosaurs really
« Reply #1 on: 09/04/2013 10:24:54 »
If one thinks of a single common ancestor theory.

Crocodiles & Alligators would have a single common ancestor.
And, all birds would also have a single common ancestor.

If you look at the avian family tree, a true branch point should indicate a single species.
http://static.flickr.com/44/167813713_3adadb52dd_o.jpg
With discussion here:
http://scientopia.org/blogs/thisscientificlife/2006/06/15/the-rise-of-the-feathered-dragons/

Anyway, it appears as if there were major branch points in the avian family tree about 93 million years ago, and again at about 65 to 75 million years ago. 

So, it wasn't "some" dinosaurs evolved into birds.  But, rather ONE dinosaur evolved into modern birds. 

65 million years ago, at the demise of the dinosaurs, perhaps less than a half a dozen avian species, already differentiated as birds, had progeny that survived until today. 

Add the crocodilians, and perhaps a few other species, and the number of dinosaur descendants is low.
 

Offline chris

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Re: Were dinosaurs really
« Reply #2 on: 09/04/2013 20:04:58 »
I've never really understood why it is that crocs, despite being evolutionarily older than dinosaurs, have survived for the last 300 million years but their land-living and marine dinosaur counterparts have all died out.

Why?
 

Offline Don_1

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Re: Were dinosaurs really
« Reply #3 on: 10/04/2013 10:44:50 »
I don't think there is a confirmed answer to the reason why the crocs survived. Many species of crocs did die out, but the modern croc has survived in roughly its present form for around 60 million years.

The terrestrial crocs which, like their aquatic cousins, evolved from archosaurs, around 250 million years ago, had all but died out by the Jurassic period. So by the time of the dinosaur extinction due to the KT event, crocs were only to be found in their semi-aquatic forms.

Dinosaurs seem to have benefitted from a fast growth spurt, which may have been to counter the chance of predation in their early life, but this may have become a disadvantage with the arrival of the KT event. Crocs, by contrast, have a slower more uniform growth rate and for the most part were smaller than many dinosaurs.

The amphibious tendancy of the crocs may also have been a great advantage. Split between a terrestrial and fresh water aquatic life, they may have been able to avoid the dissadvantages of both and reap the advantages of both. Being a cold blooded reptile, they could survive on a single meal for a considerable time and were not averse to taking carrion as well as their own kills. I think the crocs diversity was its saviour.
 

Offline chris

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Re: Were dinosaurs really
« Reply #4 on: 10/04/2013 12:38:32 »
Thanks, Don, for these interesting points. I am nonetheless surprised that the marine-dwelling dinosaurs - like ichthyosaurs and plesiosaurs etc - also disappeared, but sharks are still around yet are ancient too aren't they?
 

Offline CliffordK

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Re: Were dinosaurs really
« Reply #5 on: 11/04/2013 00:09:14 »
I think you're right.  The sharks began somewhere around 200 to 300 million years ago.

Certainly some species have died out, or evolved.

Megalodon was somewhat later, living between 1.5 million years ago, and 28 million years ago, long after the KT event.
 

Offline Don_1

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Re: Were dinosaurs really
« Reply #6 on: 23/04/2013 10:48:49 »
Thanks, Don, for these interesting points. I am nonetheless surprised that the marine-dwelling dinosaurs - like ichthyosaurs and plesiosaurs etc - also disappeared, but sharks are still around yet are ancient too aren't they?

I must confess, I too find it hard to understand how the KT event seems to have been so discrimanatory. However, in the case of marine dinosaurs Vs sharks I think there is an answer or two.

Plesiosaurs, like the other marine dinosaurs, were aquatic reptiles. This meant they would have to surface to breath, thus restricting them to a life near the surface or in shallow waters. Sharks were able to stay at deep levels. Also plesiosaurs, ichthyosaurs and others were predators, whereas sharks are not averse to carrion as well as being predatory. This means that the shark could even have benefitted from the KT event, in that more carrion became available as the surface dwelling dinosaurs died and their bodies sank to the levels inhabited by sharks.

Just as the ammonites (shallow water dwellers) became extinct where the nautilus (deep water dwellers) survived, it could be that the depth of dwelling was a major factor in survival or demise.

Some marine dinosaurs became extinct long before the KT event and some had become more omnivorous than their earlier ancestors. This could well be a pointer to another factor in the demise of the marine dinosaurs. Unable to reach great depth or to stay submerged for extended periods, their prey, true fish, may well have learned that escape from these predators was a simple case of going and staying deep until the threat was gone. Far from the simple mind we associate with the much maligned goldfish, fish may have begun to develop the avoidance techiques we see in schooling fish today. That coupled with their increasing speed may have left many marine dinosaurs outmanoeuvre and outclassed. 200 million years ago, sharks had already evolved into sleek, fast and highly manoeuvrable predators, capable of descending to great depth. There was an escape route for fish from the dinosaurs, but it only served to put the fish within the range of the sharks.
« Last Edit: 23/04/2013 13:32:33 by Don_1 »
 

Offline JimBob

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Re: Were dinosaurs really
« Reply #7 on: 23/04/2013 20:46:01 »
"One can never prove that an asteroid impact "killed the dinosaurs." Many species of dinosaurs  had in fact died out over the millions of years preceding the K-T events." - NASA

There was a significant event but let's not assume all the reptilian fauna 'croaked' into extinction.  It was ONLY? 70%!

 

Offline damocles

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Re: Were dinosaurs really
« Reply #8 on: 24/04/2013 02:58:59 »
Yes, there is certainly good evidence for an alternative theory or two. For an example see http://filebox.vt.edu/artsci/geology/mclean/Dinosaur_Volcano_Extinction/
This reads to me like good science, and I would suggest that Alvarez has won the political battle, but it is far from clear that he has won the scientific battle.
 

Offline OokieWonderslug

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Re: Were dinosaurs really
« Reply #9 on: 29/04/2013 15:04:33 »
The thing that has always bothered me about the K/T event is that if it was what killed the dinosaurs then why don't you find actual fossils IN the K/T layer? Logically there would be more fossils of dinosaurs in the layer if that is what killed them. Bodies would have covered the landscape ensuring bone bed formation at at least one site. But I have not been informed of even one. There should be a clear cut off at the boundary.

Anyone know why it is like that?
 

Offline JimBob

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Re: Were dinosaurs really
« Reply #10 on: 29/04/2013 15:28:30 »
I believe - but am not certain - that the die-off occurred before the iridium layer
 

Offline Peter the painter

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Re: Were dinosaurs really \
« Reply #11 on: 14/05/2013 14:07:29 »
They evolved. Big dinosaurs eating smaller could account for lack of fossils; as die off commenced [too little food for huge herbivores?] the meat eaters would have cleared up, but when all the food had gone they would have eaten each other. Don't see it as a one-off, sudden overnight event, maybe a million years looks instant from our perspective?

 

Offline katesisco

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Re: Were dinosaurs really
« Reply #12 on: 29/07/2013 00:12:32 »
I have this mnemonic to remember the oldest:  they are all cs:  colecanths, crocs, creepy crawlies (velvet worms) and crabs (horseshoe).  I have read the crocs are amazingly resistant to infection being as they live in bottom muck and shallow polluted water and yet stay healthy. 
It seems to me when I read Ward's/Brownlee's Rare Earth that there is a strong connection between the 65 my extinction and the follow-up punch of the carbon surge 56 my--9 my later. 
Do you think that these extinction events are actually a one-two punch?  Seems to me that the big punch is getting lesser and the space between getting shorter so what it could be is a Sol/Jupiter effect?
 

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Re: Were dinosaurs really
« Reply #12 on: 29/07/2013 00:12:32 »

 

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