Dinosaurs

[MolotovCocktail]

The Dinosaurs were the dominant species on the planet for over 160 million years, and were wiped out about 65 million years ago. The one thing I was wondering was how they were able to evolve into such an enormous size in the first place. Another thing I want to know is if they influenced the evolution of other species, such as mammals. Did they also have any significant impact on the environment of the Earth too (much like the microbes did way back when)? One more thing I was wondering was why dinosaurs, or dinosaur-like creatures, did not evolve again?

[CDarwin]

One more thing I was wondering was why dinosaurs, or dinosaur-like creatures, did not evolve again?

 

I just saw that I could jump on this before I went to bed.

 

The early Cenozoic actually saw a bird radiation that included many species similar to their dinosaur ancestors. The genus Gastornis provides a prominant example.

 

http://en.wikipedia.org/wiki/Gastornis

[Airmid]

The one thing I was wondering was how they were able to evolve into such an enormous size in the first place.

Reptiles (and dinosaurs) are different from mammals in that they don't have a fixed body size. The longer they live, the bigger they become. So it might have been easier for dinosaurs to become giants than it would be for mammals, as long as they managed to live long enough.

Reptiles can also grow very fast. They are cold-blooded and so they don't need to spend energy from food to keep their bodies warm. There's a discussion going on whether dinosaurs were cold-blooded animals, or whether they were more like warm-blooded birds. Perhaps they even used a kind of in-between strategy.

Anyway, the dinosaurs had a very good background to become giants. It seems that growing large has an evolutionary advantage, but the environment and the general body plan of the animal must allow for it. For example, food and oxygen must be plentiful. Larger animals sometimes become more sluggish, so predators must be absent or the animal must have other means of protection. The leg bones must be strong enough to support the mass of the creature.

It isn't just dinosaurs that managed to grow to gigantic size. Check out some of the other Megafauna. Islands, where predators are absent, have yielded some huge animals.

 

Another thing I want to know is if they influenced the evolution of other species, such as mammals. Did they also have any significant impact on the environment of the Earth too (much like the microbes did way back when)? One more thing I was wondering was why dinosaurs, or dinosaur-like creatures, did not evolve again?

Dinosaurs didn't influence the environment like the microbes did. After all, microbes have managed to "pollute" out atmosphere with loads of oxygen which made animal life possible. But they would have had some influence, like mammals have today.

I think they had a bigger influence on other species than on the environment. As predators, they would have "helped" their prey to evolve: by killing off the weaker individuals the whole of the prey species would become faster, or stronger, or better at hiding. But not all dinosaurs were predators. There were very many species of dinosaurs that ate all kinds of foods. And that would probably have been their greatest impact: there simply wasn't room (in terms of ecological niches) for other kinds of animals to find a way to make a living.

After the dinosaurs were gone, suddenly there were plenty of opportunities for mammals to find food and prosper, and mammals took over the role that dinosaurs had before. So, in this way, the mammals are the new dinosaurs, and I think another "new dinosaur" will only have a chance to evolve when the mammals are gone.

 

Airmid.

[bombus]

Dominant species? What does that mean? There were always far more insects and even more bacteria etc etc, and what about plants?

 

Anyway, that aside, it could be argued that dinosaurs didn't all die out. Birds are really a form of dinosaur. In fact its very difficult to determine exactly what separates the birds from the dinosaurs.

 

Maybe dinosaurs were partially warm blooded i.e., on their way to developing full warm bloodedness, and a cooling climate (or a bolide impact) helped lead to their demise as they got too cold. I.e., reptiles survived because they could go into torpor and don't need much energy to survive, birds could fly to food sources, were small and were totally warm blooded and insulated by feathers, but dinosaurs, stuck in a half-way house, died out.

 

Also, genetic experiments on bird embryos shows that they still have the genes for teeth, it's just that these genes are turned off, so when global warming hits home and temperatures rise to what they were in the Jurrasic Period, it might favour dinosaurs again and not mammals, and they may come back (from birds).

[CDarwin]

There was probably a fair amount of dumb luck in the number of placental mammals that survived the end of the Cretaceous to radiate out and 'dominate the planet'. In addition to the dinosaur extinction, two out of three families of marsupials were wipped out, where the placentals lost none. The placentals weren't any better adapted to cold temperatures or massive planet-killing comets than the marsupials, it was just random chance.

[geoguy]

I agree with some of the comments in the above postings.

 

As a paleontologist we look at complete ecosystems and not 'just the big guys'. Dinosaurs were no more dominant when they were around than many orders in other classes of other phyla. There were other orders of reptiles, amphibians, fish and so on that were quite successful before, during and after the Mesozoic.

 

Success from a biologic perspective is propogation of genes. Occupying the macro niche of 'big' isn't necessarily a sign of success. One could argue that it's a 'default' niche and that more is happening on a smaller scale. The most successful mammals to date are 'small ones'. Primates haven't evolved larger than the average rodent because it's an advantage but because rodents were more successful in filling their niche. 'Small' microbes, invertebrates of various phyla, fish and so on aren't 'relegated' to their niches because of some mammalian dominance in evolution. The dinosaurs were only a small part of the Earth's ecology while they were around.

[CDarwin]

Primates haven't evolved larger than the average rodent because it's an advantage but because rodents were more successful in filling their niche.

 

I don't understand this statement. Are you putting Primates up as a particulary successful lineage, because other than humans they really aren't in either biomass or diversity. Primates have evolved quite a bit larger than the average rodent, as well. Not only are there some particularly big primates (200 kg gorillas, for example), but the average primate is at least a few kilograms, and the average rodent is in the below 1 kg range.

 

I think you just said what you were trying to say incorrectly.

[Sisyphus]

CDarwin, I think you misread post #6 to be saying the opposite of what it was. You and geoguy are saying the same thing, and he did NOT say it incorrectly. I don't really understand the confusion, particularly concering the text you yourself quoted...?

[geoguy]

I'll clarify. it isn't a positive to occupy the macro niches of an ecology anymore than the micro niches. Small rodents and insectivores and so on haven't been out competed by primates, carnivores, ungulates. Being 'big' (large mammals, dinosaurs) isn't 'dominating' an ecology. There is much more biodiversity and longevity of orders, classes and phyla of organisms as one moves towards 'small'.

 

A small lingulid brachiopod is more successful in it's niche than dinosaurs ever were. 'Successful' meaning a measurement of passing on more of its genetic material over hundreds of millions of years.

[geoguy]

The Dinosaurs were the dominant species on the planet for over 160 million years, and were wiped out about 65 million years ago. The one thing I was wondering was how they were able to evolve into such an enormous size in the first place. Another thing I want to know is if they influenced the evolution of other species, such as mammals. Did they also have any significant impact on the environment of the Earth too (much like the microbes did way back when)? One more thing I was wondering was why dinosaurs, or dinosaur-like creatures, did not evolve again?

 

Just to clarify that there are and have been organisms bigger than dinosaurs (Whales among the animalia and a host of trees of various classes among the flora.)

 

The large size of dinosaurs as terrestrial verterbates has been debated for decades. One theory that has had some legs is that various organisms are able to evolve quickly (in geologic time) along a certain course. With the larger genera of dinosaurs this was in physical size to compete with eachother. Among placental mammals it has been more who can evolve to reproduce quickly with large numbers of offspring (thus the success of rodents). 'Big' dinosaurs evolved larger size before the immediate competition could evolve brain size or reproduction advantage. As a ceratopsian (such as Triceratops) or hadrosauran dinosaur got bigger, so did the theropods who hunted them (such as T Rex)...an escalation of size. 'If' T Rex had the ability to develop brain size quicker, then he might not have had to rely on size but 'smarts'. 'If' Triceratops had been able to evolve higher reproductive rates then that may have been the route for more genetic success than evolving into a 'bigger' organism and emphasis on a higher % of offspring needing to reproduce.

[CDarwin]

I guess I just can't read.

 

Perhaps relevant: http://www.newscientist.com/article.ns?id=mg19325975.100&feedId=online-news_rss20

[MolotovCocktail]

Very interesting stuff. And yes, its obvious that I don't really know much about evolution, which is why I posted this.

 

I'll clarify. it isn't a positive to occupy the macro niches of an ecology anymore than the micro niches. Small rodents and insectivores and so on haven't been out competed by primates, carnivores, ungulates. Being 'big' (large mammals, dinosaurs) isn't 'dominating' an ecology. There is much more biodiversity and longevity of orders, classes and phyla of organisms as one moves towards 'small'.

 

You know, I never quite understood that until now. I guess its because the schools focus a lot more on the controversy of it rather than what it actually is or means

 

But I do have more questions though. One thing I've been wondering was the diversity of dinosaur species that have been found across the planet. It seems to me that they were the same everywhere, no matter what continent you found them on. Did the various types of dinosaurs survive only on the geographical location where they had the best chance of survival? And also, did each individual kind only survive in one kind of environment but not another, much like the way that lions (a mammal) could only survive in the savannas of Africa.

[foodchain]

Here is a good link I think for understanding such. You do have to do some clicking in it though, but when you get to images of dinosaurs, you can get some data about them, such as where they lived.

 

http://www.prehistory.com/colorchr.htm

 

Yes the debate about evolution seems to be slowly eroding understanding of such in some regards, so what have you. Next will be the attack on bivalves, surely its going to happen at some point, or that the debate about evolution might simply escape the horrible reality that humans are in a zoology book somewhere like other living things.

[CDarwin]

Primates haven't evolved larger than the average rodent because it's an advantage but because rodents were more successful in filling their niche.

 

Baha! I understand that statement now. I'm not sure why I didn't in the first place. In fact, I can provide supporting evidence. The smallest primates are the mouse lemurs who specifically fill the rodent niche on Madagascar.

[lucaspa]

Baha! I understand that statement now. I'm not sure why I didn't in the first place. In fact, I can provide supporting evidence. The smallest primates are the mouse lemurs who specifically fill the rodent niche on Madagascar.

 

There you go! It's all about ecological niches. When the dinos went extinct, there already were species that were rodent sized -- all of them, in fact. Some stayed there because they filled that niche very well. But there were all those other empty ecological niches and ways to earn a living. Therefore you get the radiation of mammals (and birds) into those empty niches. And thus primates are bigger, because there are already rodents earning a living as rodents!

 

So, in the colonization of Madagascar, somehow rodents didn't make it there. Now you have an empty rodent niche and only primates. So you get a primate to fill that niche -- because there was no rodent competition in Madagascar.

[geoguy]

Very interesting stuff. And yes, its obvious that I don't really know much about evolution, which is why I posted this.

 

 

 

You know, I never quite understood that until now. I guess its because the schools focus a lot more on the controversy of it rather than what it actually is or means

 

But I do have more questions though. One thing I've been wondering was the diversity of dinosaur species that have been found across the planet. It seems to me that they were the same everywhere, no matter what continent you found them on. Did the various types of dinosaurs survive only on the geographical location where they had the best chance of survival? And also, did each individual kind only survive in one kind of environment but not another, much like the way that lions (a mammal) could only survive in the savannas of Africa.

 

Yes and no. We don't have fossil records of most (99.9%) ecologies from any period in the Mesozoic. We just don't know the ake up of most ecologies. The richest fossil records are from the Late Cretceous here in Alberta: good info from formations spanning 82mya to the K/T extinction 64 mya. In these formations there was very little variation among terrestrial vertebrates. Albertasaurus evolved into T Rex...Centrasaurus into Triceratops, etc. but these are just variations on a theme. The ecologies had a similar mix of large and small theropods, ceratopsians, hadrosaurs, ankylosaurs, etc. ...and similar non-dino vertebrates (crocs, turtles, chamsosaurs and so on). I've collected literally thousands of fossils from Late Cretaceouss site and even after a couple decades couldn't distinguish a hadrosaur vertebra or raptor tooth from 82mya from one 65mya without other info providing location, etc. Why the stability? The most likely reason is stable climate but no one knows for sure.

 

That's a 17million year span. In contrast, our present ecology here in Alberta is greatly different from that just ten thousand years ago. There were mammoths, cheetahs, etc. In 1/1000 of the span of time there has been more change than in the last several million years of dino ecology.

 

Re your lion example. Lions were in N. america until recently (as were cheetahs and a few other 'Savannah' animals). Here is an interesting fact. The fastest land animal in the world is the cheetah. The second fastest is the North American Pronghorn. Why did pronghorns evolve to run so fast if the only predators in their environmnet are relatively (to pronghorns) slow running wolves, coyotes, cougars and bears? The answer is because pronghorns evolved along with cheetahs in the Pleistocene in N. america. Cheetahs became extinct in N. america but pronghorns didn't. Pronghorns can outzip any predator today but have no real need to shift into high gear. It's a classic example of how we sometimes can't find the reason for a particular trait in the current ecology but the fossil record explains what seems at first glance to be a quirky evolutionary tangent.

[lucaspa]

You know, I never quite understood that until now. I guess its because the schools focus a lot more on the controversy of it rather than what it actually is or means

 

Really? I don't know of any high school that focusses on the "controversy". Most just teach evolution. What schools are you talking about?

 

One thing I've been wondering was the diversity of dinosaur species that have been found across the planet. It seems to me that they were the same everywhere, no matter what continent you found them on. Did the various types of dinosaurs survive only on the geographical location where they had the best chance of survival? And also, did each individual kind only survive in one kind of environment but not another, much like the way that lions (a mammal) could only survive in the savannas of Africa.

 

They are very definitely NOT the same species from continent to continent. For instance, geoguy pointed out that triceratops and Edmontosaurus and T. rex are known only from N. America. But the larger Families or Orders that they belonged to were widespread. Thus, you find ceratopseans, hadrosaurs, and tyrannosids in other locations, but they are different genera and species.

 

Similarly, lions are a specific species of the family Felidae (cats). So, you find lions only in Africa, but you find tigers in Asia, cougars in N. America, panthers in S. America, etc. Different genera and species in different locations.

 

Remember, "mammal" is Class composed of thousands of species grouped in genera, families, and orders. Dinos are technically an order, but correspond to a Class. There are suborders, families, and genera within dinos.

[geoguy]

lucaspa, good examples.

 

Here's another variable. Fossil remains are rare.

 

If we take the 10 million year span we live in today and fast forward 100 million years, there would be scant records of what has existed in our current 10 million year span. There might be no record of the unique faunas of the Arctic, the Galapagos, the Amazon raon forest, nothing of the Africa and little of continental N. America, etc. We might have two windows of viewing into the period... for arguments sake, a small area of Queensland, Australia and bits of Madagasgar.

 

What would be concluded? Most mammals found were Marsupials and any primates that existed at the time were lemurs. (as lucaspa mentions, those lemurs didn't mean that all primates were lemurs). There might be no record of elephants, humans, bears, deer, squirrels, rats, dogs, etc. Little if any record of thousands of bird species..perhaps a few reptile and a few amphibians.

 

The fossil record of terrestrial life is like travelling around the world and taking a couple snapshots every few million years.

[CDarwin]

Really? I don't know of any high school that focusses on the "controversy". Most just teach evolution. What schools are you talking about?

 

Mine for one. I think in about any school in the South, there are going to be enough Creationist kids so that just teaching evolution is going to be impossible without constant objections. My Biology II class glazed over it completely.

[lucaspa]

lucaspa, good examples.

 

Here's another variable. Fossil remains are rare.

 

... The fossil record of terrestrial life is like travelling around the world and taking a couple snapshots every few million years.

 

While we're on a roll, let's remember that we undercount species in the fossil record. In fossils, we have to use the morphological species concept -- differences in appearance, and that is the appearance of the bones. The biological species concept looks at whether the populations interbreed. You can have species with very similar or identical bones but are really different species because of mating songs, courtship habits, etc.

 

So what we see in the fossil record is mostly genera. Most genera are known only by a single species. Edmontosaurus, for example, is the name of the genus, not the species. There were probably several species in that genera in the general area at the time.

 

Yes, we get snapshots. Which is also why we usually (but not always) get "intermediate" fossils and not the ancestor-descendent sequence of species to species -- technically "transitional" fossils.

 

An example I find useful right now is penguins. There are 14 or so species of penguin existing today. They are obviously intermediate between living on land and living totally in water. Say we come back 10 million years from now and find several species of fully aquatic animals that obviously came from birds. Well, ONE of the species alive right now will be their ancestor. But which one? If we were then and looked back at the fossil record corresponding to now, we would find one or two species of penguin probably. But the odds say that was not the direct ancestor species. It was an evolutionary "great uncle", not "great-grandfather".

[lucaspa]

Mine for one. I think in about any school in the South, there are going to be enough Creationist kids so that just teaching evolution is going to be impossible without constant objections. My Biology II class glazed over it completely.

 

I lived in Macon, GA for 10 years and both kids attended school there. My oldest took high schoool biology and there was no "controversy". They simply taught evolution. So I'm hoping your experience is not as widespread as you think. You may have been unfortunate in encountering a teacher with creationist sympathies.

 

There is, of course, no scientific controversy.

[CDarwin]

I lived in Macon, GA for 10 years and both kids attended school there. My oldest took high schoool biology and there was no "controversy". They simply taught evolution. So I'm hoping your experience is not as widespread as you think. You may have been unfortunate in encountering a teacher with creationist sympathies.

 

There is, of course, no scientific controversy.

 

Oh no, all of my science teachers are evolutionist. Maybe its just because I don't go to the most advanced high school, and the 'controversy' is just easier than the actual population genetics and what-not. We also have block scheduling which limits the amount of curriculum you can cover.

 

Georgia has some pretty good schools, too. I'd be interested to hear from people in say Alabama or Arkansas. In fact I think I might start a thread about that.

[lucaspa]

Oh no, all of my science teachers are evolutionist. Maybe its just because I don't go to the most advanced high school, and the 'controversy' is just easier than the actual population genetics and what-not. We also have block scheduling which limits the amount of curriculum you can cover.

 

Georgia has some pretty good schools, too. I'd be interested to hear from people in say Alabama or Arkansas. In fact I think I might start a thread about that.

 

As it turns out, Macon's was not a "pretty good school". When we moved to New York in my daughter's junior year we found out just how far behind the Macon high school was.

 

I would think that population genetics would be easier than the "controversy", since creationists accept "microevolution" and that is what population genetics is about. However, that doesn't seem to be what happened to you. So much for my logic on the subject!

 

I'd be very interested in hearing you tell what exactly was taught about evolution in your school. Perhaps you could start a new thread entitled "what I was taught in high school about evolution"? Thanks.