No K-T extinction event: No Dinosaur Killer WI

[Smaug]

There is no necessary reason why mammals must be smarter than reptiles. That, or any other advantage, could easily be usurped by the dinosaurids.

That reminds me of this movie trailer thats out. I got a big head, and little tiny arms.... funny stuff.

 

[Ran Exilis]

One thing I'd like to say though; one of the things that bothers me about these debates about wether the dinosaurs were OR warmblooded OR coldblooded, is that people use the defenitions of warmblooded and coldblooded as they apply to modern terrestrial animal groups, and then try to apply them to ancient extinct animal groups that were nothing like any modern animal group.

I do agree that at least some branches of dinosaurs were developing or had developed some form of a warm-blooded metabolism, however, keep in mind that dinosaurs were still evolving and "experimenting" with different possebilities, including not just a warmblooded metabolism, but I'd say different kinds, stages or types of warmblooded metabolism, and I'd also say that at least a number of primitive species were effectively coldblooded as well.

I mean, surely we can assume that at least some of the earlier dinosaurs that were developing a warmblooded metabolism did not possess the kind of advanced and developed warmblooded metabolism we find in birds and mammals today, right?

For example; tuna's and certain species of shark have a 'mechanism' that allows them to keep their bodytemperature a few degrees higher than their surroundings, yet they do not fit the defenition of a warmblooded animal, even though this adaptation doesn't really make them cold-blooded either.

In other words: there's not really a distinct line between "warmblooded" and "coldblooded".

Having said that, I think that at least several branches of dinosaurs as well as synapsides at some point gradually began developing what would eventually be a fully developed warmblooded metabolism in their descendants, in which I would like to point out that, IMHO, this was most propably a gradual process, resulting in lots of species that were not really coldblooded or warmblooded by our modern definitions, or close to either one of them, but not yet it.

 

[strangeland]

Some sort of sentient species would eventually have developed, but not humans of course.

 

[Umbral]

I must respectfully disagree. The Dinosaurs blew the mammals out of every evolutionary niche above that of the mouse by being much better and then stuck around for around for almost 200 million years. More, as birds.

At no point have they shown any indication that they are developing intelligence.

When we look at how long vertebrate life hung around on earth, as well as how many improbable events and close calls we had, when doing it, it seems an exceptionally low-probablilty thing.

A different issue I have been wondering about is how much the K/T extinction had to do with the drop in the oxygen levels of the atmosphere? It seemed reasonable to me that the impact, fires (Worse with their oxygen levels) and extinctions could have reset the atmosphere composition.

And when the biosphere recovered, a new equilibrium got established?

This is just my own speculations of course. Anyone have any real info?

 

[zoomar]

Many people have obviously grasped this fact, but it still bears repeating: "dinosaurs" were not reptiles (at least not reptiles as we define them today). This is regardless of whether or not they were endothermic. Also, the vast majority of dinosaurs were small animals, including the birds. Dinosaurs did not "evolve into" birds. Birds are merely small flying dinosaurs which survived the K-T boundary. Birds were around since the Jurrasic and coexisted with numerous other species of feathered, high metabolism dinosaurs which did not survive. It is reasonably to speculate the birds survived because a flying animal is much better able to find and exploit livable habitats than a terrestrial one.

Regarding intelligence, I also like to believe that the evolution of sentience is virtually inevitable given the evolution of necessary precursers (free manipulatory organs, etc), but that is really a religious statement, not a "scientific" one. It is based on a sample of one (us), without considering the evidence against.

It needs to be remembered that for over 100 million years many species of dinosaurs possessed virtually all the apparent physical neccesities of intelligence based on the hominid model (free hands with flexible digits, upright posture, excellent eyes with binocular overlap, high metabolism, social flocks or packs) without ever producing anything more intelligent that an ostrich or pigeon (at least based on fossil evidence). Thus, I would consider the belief that dinosaurs would eventually produce an intelligent species if the K-T event never occured a faith statement, not a scientifically viable one. It happens to be one I believe, but not for any scientific reasons. Actually I find it almost easier to believe there actually were "intelligent dinosaurs" in the cretaceous, but that they left no fossil evidence, but that is another story.

 

[Mike Stearns]

The thing you have to realize about Dinosaur evolution is that Dinosaurs evolved at MUCH slower rate than humans. The idea of Dinosaurs becoming sentient is not a complete impossibilty IMO. After all, Palentonological evidence indicates that Velocoraptors had brains approximately the same size a modern chimpanzee and chimp are roughly as intelligent as a 5 year old human child. It would have taken at longer than the human evolutionary process, but I don't think its a complete impossibilty.

 

[Emperor Qianlong]

The thing you have to realize about Dinosaur evolution is that Dinosaurs evolved at MUCH slower rate than humans. The idea of Dinosaurs becoming sentient is not a complete impossibilty IMO. After all, Palentonological evidence indicates that Velocoraptors had brains approximately the same size a modern chimpanzee and chimp are roughly as intelligent as a 5 year old human child. It would have taken at longer than the human evolutionary process, but I don't think its a complete impossibilty.

The statement that Velociraptors had the sentience of a chimpanzee is from Jurassic Park III. No real world paleontologist ever stated that (at least, none that I'd know of). A statement closer to reality would probably be that the most brainiest dinosaurs that lived in the late Cretaceous were slightly less intelligent as modern birds.

 

[Tony Jones]

The thing you have to realize about Dinosaur evolution is that Dinosaurs evolved at MUCH slower rate than humans.

What do you base this statement on? As far as I know there's no reason to believe dinosaurs evolved any more slowly than any other living things.

 

[Emperor Qianlong]

What he meant may (perhaps) have been that there apparently wasn't any selective pressure for dinosaurs to evolve large brains.

 

[Ran Exilis]

A different issue I have been wondering about is how much the K/T extinction had to do with the drop in the oxygen levels of the atmosphere? It seemed reasonable to me that the impact, fires (Worse with their oxygen levels) and extinctions could have reset the atmosphere composition.

And when the biosphere recovered, a new equilibrium got established?

This is just my own speculations of course. Anyone have any real info?

Coincidentally, there's an article about this on the site of National Geographic.

http://news.nationalgeographic.com/news/2005/09/0930_050930_mammal_oxygen.html

Suprisingly, this article actually states that during the Eocene, after Earth's biosphere had recovered from the K-T mass extinction, oxygen levels actually spiked to 23%.

I'm still looking up more information about oxygen levels during the Cretaceous.

 

[zoomar]

What do you base this statement on? As far as I know there's no reason to believe dinosaurs evolved any more slowly than any other living things.

Exactly. There is no such thing as a "dinsoaurian" or "human" evolutionary rate. The rate of evolution is a product of mutation rates, breeding rates, and natural/sexual selective processes. Humans diverged quickly from the other homoniod apes because our ancestors were faced with a particular set of selective processes, probably in a very localized environment, which favored increased intelligence and upright posture, together with a few lucky mutations affecting language ability and cognition. Plus, we started with a much better monkey brain than any dinosaur/bird has.

 

[ninebucks]

I disagree. There is just no way that the dinosaurs could ever have developed a sense of hearing that is as acute and adaptable as that of mammals, but I have already explained why that is.

And another noteworthy detail: ever taken a good look at mammalian brains?

You see, if you compare the brains of placental mammals to those of birds, reptiles, or even non-placental mammals, you'll immediately see an obvious difference: the brains of placental mammals have this typical 'wrinkly' structure, which is unique to placental mammals (even though it is less developed in some species [rabbits, for example] than it is in others [felines, primates, cetaceans, etc.]).

Now then, the function of these 'wrinkles' is that they increase the surface of the cerebral cortex, and thus its capacity. This gives placental mammals an edge over non-mammals and non-placental mammals, although other types of brains can be very efficient as well, such as the brains of octopi, crows and parrots.

Having said that, most dinosaurs just didn't have the kind of brains that were as flexible and adaptable as those of the placental mammals that were around at the end of the Cretaceous.

Any explanation you gave is, with all due respect, wrong. Part of evolution is the process whereby beneficial mutations are passed from one generation to the next. To say that one set of mutations can occur in one genus but categorically can never occur in another shows a drastic misunderstanding in how evolution works.

 

[zoomar]

Any explanation you gave is, with all due respect, wrong. Part of evolution is the process whereby beneficial mutations are passed from one generation to the next. To say that one set of mutations can occur in one genus but categorically can never occur in another shows a drastic misunderstanding in how evolution works.

I'm not sure that is what Ran was saying. What he was saying is that it is certainly helpful if certain necessary pre-existing structures have already evolved. The rapid evolution of human intelligence was made possible by the fact that, over 30-odd million years selective pressures had already provided our ancestors with a brain structure suitable for further evolution toward higher cognition. Only minor incremental mutations would be required to get from a monkey brain to a human brain. As far as we know, no dinosaurian brain (birdish/reptile in structure) had bnecome preadapted for this relatively easy growth. You don't usually get a magic mutation which suddenly creates a big "wrinkly" brain out of a bird brain.

 

[Ran Exilis]

Any explanation you gave is, with all due respect, wrong. Part of evolution is the process whereby beneficial mutations are passed from one generation to the next. To say that one set of mutations can occur in one genus but categorically can never occur in another shows a drastic misunderstanding in how evolution works.

Let's see, where shall I start?

Ah, there: by that logic, one could even say that it would also be perfectly plausible to say that snakes and lizards could develop functional gills, sharks or coelacanths (those who actually know a thing or two about the unusual anatomy of the coelacanth know what I'm talking about) could develop functional lungs, insects developing an internal skeleton and perhaps even a fully developed bloodstream.

However, the evolution of species is limited by the anatomy and physiology of the species on the matter, and a development that is only a few mutations away for species A could very well be next to impossible for species B, just because species B has a different anatomy that may even make these mutations and adaptations impossible because the anatomical structures that are improved and adapted in species A could be so different in species B that evolving and adapting them in the same way as species A did, would simply be impossible.

And before you're going to ask; yes, I am very familiar with the concept of converging evolution, i.e. unrelated species (or more correctly: lineages) that develop similar adaptations (and often a somewhat similar appearance) because they adapt to the same circumstances.

However, I would also like to point out that, out of all things, converging evolution in species often shows how the basic anatomical and overall genetic characteristics still limit the extent to which these animals can adapt, and even then, the basic design of the two converging species already has to be quite similar if they are ever going to evolve into two clearly similar species.

And if the two converging species are not quite similar to begin with, then some degree of converging evolution may still be possible, but it would only be more likely that the evolving species on the matter evolves adaptations that still fulfill roughly the same purpose as the adaptations of the species it is "mimicking", but these adaptations would propably still be very different solutions to the same problem and would propably be unique to the species on the matter.

And after all that comes the issue of propability: it may not be impossible for a species or lineage to develop certain features or adaptations, but that doesn't mean that many of the more unlikely evolutionairy possebilities are statistically likely to happen, because the greater and more fundamental an adaptation is, the more factors must support or stimulate the development of such an adaptation, and don't forget that huge changes also require the development of several intermediary stages, and it is not uncommon that animals evolve into such "intermediary stages" for entirely different reasons.

For example, lungs developed from primitive swim bladders that were originally hydrostatic organs, and the fact that some types of swim bladders could actually double as an organ that could extract oxygen from the air was in fact little more then an unforeseen side-effect.

And the more radical a change, the more supporting or stimulating factors are needed to make a species or lineage evolve so much, and the more unlikely it becomes that the species on the matter actually makes this radical change.

So in the end, it is more likely that different species or lineages develop their own *usually* unique solutions to the same problems, rather than mimicking the exact same solutions that work for other, completely different species and lineages.

To extrapolate this to the claims that some dinosaurs could develop brains that are similar to those of mammals at some point: I'm not even excluding that dinosaurs could develop complex brains, and I admit that seeing the great degree of intelligence that certain cephalopods, crows and parrots have displayed surely forced me to re-evaluate my previous opinion about the "unmatched" qualities of the brain design of placental mammals.

However, I stick with my point that, even though some branches of dinosaurs would have been quite capable of developing complex and relatively advanced brains, these brains would most propably not resemble those of mammals in their basic design, i.e. the 'wrinkly' structure. Furthermore, the brains of the most intelligent dinosaurs were developing more like the brains of birds than the brains of mammals; the capacity of the brain was increased because dinosaurs and birds were developing a thicker cerebral cortex, instead of a 'wrinkly' structure that enlarges the surface of the cerebral cortex.

Had the most intelligent dinosaurs developed in even more intelligent creatures, then they would most propably develop a cerebral cortex that only becomes thicker and larger, instead of becoming wrinkled like the brain of a placental mammal.

 

[Emperor Qianlong]

Actually, perhaps a dinosaur with an arboreal lifestyle might have evolved into sentience (perhaps, in analogy to primates). Just an idea. However, I remember that arboreal dinosaurs were very few.

 

[Mark]

Exactly. There is no such thing as a "dinsoaurian" or "human" evolutionary rate. The rate of evolution is a product of mutation rates, breeding rates, and natural/sexual selective processes.

Yes and no. While there is no single rate of evolution in a lineage, there are lineages that generally evolve more quickly. These lineages are often used for biostratigraphy. North American Land Mammal ages are frequently used in North America (hence the name) because mammals evolve quickly. Also because mammal teeth are distinctive and preserve well.

One thing to remember about analyzing dinosaur evolution is that we really don't have that many specimens with enough morphologic and stratigraphic detail to analyze their evolution in detail.

Anyway, it took synapsids ~300 million years to produce enough intelligence to make the Web. Diapsids still haven't.

 

[zoomar]

Anyway, it took synapsids ~300 million years to produce enough intelligence to make the Web. Diapsids still haven't.

And let's make sure they never do!

 

[Analytical Engine]

And let's make sure they never do!

What's that supposed to mean?