I realise that dinosaurs had scales, and laid eggs, and bear many skeletal similarities to today’s living reptiles. However, they are also said to be the ancestors of birds, which also have scales (on their legs, anyway) and lay eggs. Why do we “know” that dinosaurs were cold-blooded? Why do we know they weren’t the largest, non-flying ‘birds’ the world has ever seen? I realise the earth was warmer in those days, but some dinosaurs apparently lived at the poles where it was not warm, and this defies rational explanation - if they were cold-blooded.
It occurred to me recently that, though I have been taught all my life (and thus believed all my life) that dinosaurs were reptiles, what I’ve been learning about them recently doesn’t seem at all like reptile behavior, or even biology. It seems more like the behavior and biology of warm-blooded creatures.
You must be about my age. I was also taught in school (back in the 60s) that dinosaurs where cold-blooded reptiles. Today, however, many paleontologists — Jack Horner is probably the best known — think that dinosaurs were a precursor to birds and believe they were warm-blooded. (Dr. Horner has written a number of popular books. Take a look at your library.) To the best of my knowledge, no one knows what dinosaur skin looks like.
My kids are on a dinosaur kick right now. So we’ve watched many (recent) videos, read many books and they ALL say the dinosaurs were reptiles. The definition of reptile includes ‘cold-blooded’. Now, I’m aware that there are certain schools of thought that perhaps dinosaurs might have been warm-blooded - or that some of them, such as the pterasaurs, may have been warm-blooded, but I see no shift in general scientific thought that dinosaurs were, or even might have been, anything other than gigantic cold-blooded reptiles.
Of course, no, not all scientists believe any individual theory. I’m talking about the general line of thought.
As for the skin, actually, that’s not true: there have been discoveries of fetal dinosaurs in the shell, with fossilized skin fragments. Also, and this is utterly fascinating, the recent discovery of the ‘mummy’ of a hadrosaur in Montana. So we do know what the skin of some dinosaurs was like.
Because it is damn tough to find behaviours in a fossil skeleton. The remains showed reptilian type teeth and bones. Any extrapolation past that might not have been justified.
“Reptilia” is pretty much a grab-bag classification. If the vertebrate has fur and gives milk, it is a mammal. If the vertebrate has a beak and feathers, it is a bird. If it is scaleless and lays soft eggs in water, it is an amphibian. All other vertebrates are reptiles.
Fur, milk, feathers, and soft eggs do not fossilize well at all. Therefore, given that the hard parts of a dinosaur look more like a giant lizard of crocodilian than anything else wandering around nowadays, they were catagorized as reptiles.
Dinosaurs were first described scientifically around 1840. They had been recognized as a special type of reptile since that time. No one who actually studied the critters was very surprised when Dr. Ostrum at Yale published his work in the 1970s showing just how many features the smaller carnosaurs share with early birds like archeaopteryx.
The popular image of sluggish giant lizards has not been scientifically accepted since at least the 1920s, but no one told the writers of science vulgarisations or the producers of Hollywood films.
If you had been taught that they were sluggish, your teachers are to blame.
(Don’t get me started on what a fuzzy term “warm-bloodedness” is, as any workable definition has to include tunas and leatherback sea turtles, who are functionally but not metabolically homoiothermic.)
I don’t know which books and videos you’ve been looking at, of course, but it may be possible that they’re out of date, even if they’re recently published.
Order Dinosauria would not work, as the Saurischia and the Ornithischia are probably descended from different ancestrial groups. There are too many differences between the two for them to be monophyletic.
(Cool Stuff Item #157: Birds are cladistically saurischians, that is modern birds are lizard-hipped dinosaurs.)
Actually, there has been a substantial body of theory for over 20 years that birds, and not modern reptiles are the most direct descendants of the dinosaurian line, and may even have been somewhat warmblooded. Though this was a contentious hypothesis when presented by maverick paleontologiests in the 1970s, I think that the general professional consensus today is that this is either “probably true” or “extremely compelling.”
Note that this is subtly different than what you asked. The difference is important.
How do we know that dinosaurs weren’t birds? Because there were no birds when the dinosaurs arose. Archeopteryx, commonly called the first bird or true proto-bird, dates back to 150 mullion years ago. The “age of dinosaurs” is generally considered to have begun at the end of the Paleozoic era [570 million to 245 million years ago] but the true dinosaurs lived in the Mesozoic era [245 Myr to 65 Myr – “Myr” = “million years ago”].
I’m not trying to baffle you with strange names. The unfamiliar words I’m using make great search terms for learning more on your own.
[ul]
[li] The great swamp and fern forests thrived in the Carboniferous period (360 million years ago). [/li][li] In the early Permian period (286 Myr) we have clear fossil evidence of the sailback reptiles, like [http://www.prehistory.com/dimetrod.htm]dimetrodon, which are a strong part of the public conception of “dinosaurs” – but actually preceded the true dinosaurs by 40 Myr.[/li][li] The first small dinosaurs (and primitive mammal ancestors, and major reptile lines like turtles and crocodiles) arose in the Triassic period 245-210 Myr[/li][li] Birds, along with many of the larger dinosaurs [diplodocus, stegasaurus, brachiosaurus] evolved during the Jurassic period. [/li][li] The full bloom of the Dinosaur age, including many of the dinosaurs featured in the poorly named movie “Jurassic Park” was during the Cretaceous 145 Myr. This is also when the modern mammals began.[/li][li] The last true dinosaurs are considered to have died out by 65 Myr, AFAIK[/ul][/li]
I’d like to pause for a moment of silent meditation on the subject of “a million years”. In crude terms, humanity could have a nuclear war that wipes out all trace of civilization, and left the species as a single pocket of crippled, irradiated survivirs barely surviving to reproductive age, and still reinvent agriculture, language, and sicial structures, and migrate to cover the Earth in 50,000 years. Depending on whose estimates you follow, that’s roughly how long it too us to do it the first time (though we had waves of outward migrations prior to that, the genetic studies I’m aware of indicate that the last wave of migration to all the continents was on the rough order of 100,000 years ago)
In a single million years, mankind could have risen and fallen 10-20 times. Please have some respect when we start tossing around tens of millions.
Uh, this is now disputed – modern cladistics sees both saurischians and ornithischians as coming from the same ancestral clade. I’ll let some of the more skilled paleos. here discuss that further, but Dinosauria was resurrected as a valid classification a while ago, though not fully accepted by all paleos. with professional right to an opinion on it.
If you watch Jurassic Park, there is a scene where the Raptors are chasing the kids around the kitchen. One scene shows the raptor exhale on some window glass, causing it to fog up. This was someone’s vague attempt to show he believes they were warm blooded.
My OP in this this thread adresses many of the questions raised here. Note that on the subject of physiology, there is still ongoing debate as to whether dinosaurs in general were more typically reptilian or mammalian/avian in nature. Likely, there was significant variation in dinosaur physiology, ranging from mass endotherms to true endotherms, and possibly some tending more towards ectothermy.
The linked thread also addresses this point (specifically): pterosaurs weren’t dinosaurs. They were flying reptiles who were contemporaneous with dinosaurs, and were related, but they weren’t dinosaurs anymore than crocodiles were (or are).
As noted by Polycarp, no dinosaurian paleontologist (that I know of) currently disagrees with the notion that Ornithischia and Saurischia descended from a common ancestor, and that they are all rightfully members of Dinosauria. I prefer not to get into the whole Class vs. Order thing (since I don’t agree with the traditional Linnaean taxonomic requirement of ranking taxa), and will simply say that Clade Dinosauria is accepted to be composed of Clades Ornithischia and Saurischia (which, in turn, contains Clade Aves [birds]), and is contained within Clade Reptilia (there are further subgroupings between Reptilia and Dinosauria, but you get the idea).
Okay, I am not a paleontologist by any stretch of the imagination, but I am a Sue docent, so I do have some small access to paleontologists, and the pros at the Field Museum, anyway, think Jack Horner’s a looney toon. This is a question I get asked a lot, though. The answer we’re supposed to give is that while there is debate on the topic, the scientists at the museum do believe that dinosaurs were cold blooded.
Interestingly, that web page gives a different answer:
Huh. I’ll ask Dr. Makovicky, the big cheese paleontologist, what he thinks when next I see him. He likes to check in with us lowly docents from time to time to make sure we aren’t telling people that humans and dinosaurs lived together in harmony.
Horner may well be a looney toon, but I would be very surprised if any dinosaur paleontologists believed that as a rule dinos were “cold-blooded”. At worst, the evidence is ambiguous one way or the other. At best, we have significant evidence that at the very least, those dinos on the path to bird-dom were probably endothermic. With the most recent Chinese proto-bird finds, the fossils suggests that at least some dinos had a feathery covering, the purpose of which was most likely insulation.
Just a few weeks ago I went down to the San Diego Museum of natural history and they had a fascinating exhibit on feathers and flight and it seemed pretty clear that birds descended from dinosaurs. They have found fossils with feather impressions on China that they had on display there that were absolutely amazing.
I’m incredibly tired, so I won’t try to explain everything, but just give you links that provide why there is strong evidence that at least some dinosaurs should be considered more bird like than reptilian.
Then just google the dinos in question for more fun! You can even see horribly outdated pages like this. Which is based on the Oviraptor. The poor Oviraptor was named such because when it was discovered, scientists believed that it was trying to steal and eat eggs. Through later disoveries, they found out that the Oviraptor was actually trying to protect its babies! The picture of the Oviraptor they had in the museum had it covered in feathers and looking like a really, really ugly turkey.
And since I know very little about these topics, some questions of my own.
Are there any reptiles with feathers? Could there be?
Depends on your approach to taxonomy. If you are a traditional Linnaean taxonomist, then no (although the Liaoning dinos would throw a wrench into this, unless they were simply classified as birds). If you are a phylogenetic systematist, then, yes: Aves lies within Dinosauria, which in turn lies within Reptilia; thus birds are, by definition, feathered reptiles.
Currently, no. There is some debate as to whether early birds were ecto- or endo-thermic, however (based, for example, on the absence of respiratory turbinates in early forms. Others disagree that the lack of such structures is diagnostic of ectothermy).