I’ve wondered about this, too. Not only the Dinosaurs, but creatures people often think of as dinosaurs (but which aren’t) went extinct at the same time – sea reptiles like Ichthyosaur and Mosasaur and Kronosaur. and flying reptiles like Pterosaurm Pterodactyl, Rhamphorynchus, and a gazillion others. Small dinos died off, yet the crocodiles and monitor lizards and tortoises and tuatara lived on.
Furtrhermore, the Ammonites all died off in the world’s oceans, yet plenty of pother cephalopods survived ( Ammonoidea - Wikipedia ) Why?
Generally, smaller and more adaptable species survived. For several million years, likely the biggest thing on land was the Croc.
Of course for the “Birds is Dinos” crowd, that poses the question “If birds are dinos, why did not any of the smaller (and even possibly warm-blooded and feathered) “true” dinos survive?”
That question has absolutely nothing to do with whether or not birds are classified as dinosaurs. You might as well ask why ornithischian dinosaurs are classified as dinosaurs when none of them survived, even though some saurischian avian dinosaurs survived.
Some groups survive major extinction events simply because of the luck of the draw. However, in the K-T event there are some ecological commonalities among the groups that survived in comparison to the ones that didn’t.
In general, large animals didn’t survive because they need lots of food and need to forage over wide areas. This is especially true of carnivorous and homeothermic forms. Small animals, especially insectivores and seedeaters, were more easily able to find food even ifthey were homeotherms, like birds and mammals.
The avian dinosaurs that survived (many, probably most avian lineages exant at the time, went extinct) may have been able to do so because they fed on insects and seeds; also, since they were able to fly they were able to cover more ground in search of food. Of course, the same considerations could have applied to the smaller pterosaurs. The reason they became extinct may have just been chance; or if they were less diverse than Cretaceous birds, then a large scale extinction event would have been more likely to kill off all of them, rather than just most of them as in the case of the avian dinosaurs.
Non-homeothermic freshwater groups, such as amphibians, turtles, and crocs, survived fairly well. The reasons for this are not entirely clear, but it may be due to the fact that many of these can survive poor conditions by hibernation or estivation.
Well, some of it can be laid to just bad luck. I can easily imagine a scenario where the last breeding pair of some mammal lineage happened upon some decaying carcass and at it five minutes before the last breeding pair of some coelurosaur happened along. Then we’d be wondering why all dinosaurs except birds and coelurosaurs went extinct, or more likely Linnaeus would have classified those extant coelurosaurs as toothed flightless birds, and it wouldn’t seem strange to us, any more than classifying whales as mammals doesn’t seem nonsensical to us.
Remember that lots of early mammal lineages from the Cretaceous went extinct, as well as early bird lineages like the Enantiornithes. So it’s misleading to think “Mammals survived” or “Birds survived”. A very few mammal types survived, and that reduced subset of lineages radiated into all modern mammals, a very few bird types survived, and those survivors radiated into all modern birds.
I think the flying reptiles would have been affected in a similar manner to the larger dinosaurs. This does not explain why a compsognathus, about the size of a chicken, would die out while a croc that is many times larger would not.
I believe the ichthyosaurs died out long before the mass extinction but I’m not positive. Still if sharks could survive as well as large fish, why couldn’t the plesiosaurs?
Is it possible (I am not a paleontologist or geologist or basically any other kind of –ist) that the iridium from the meteor impacts combined with volcanism going on and the resultant climate change triggered an inherent weakness in the species’ respiratory systems? I know I’m really talking out of my ass but my theory could be as feasible as anything else.
Compsognathus went extinct long before the K-T extinction – it was a Jurassic critter.
Ichthyosaurs died out about 25 million years before the K-T event. Mosasaurs and plesiosaurs died out along with the non-avian dinos, though. As for why they died and not sharks, it could very well be related to differences in diet. If, for example, plesiousaurs ate assorted molluscs (like the aforementioned ammonites), then when their food source died out, they wouldn’t be far behind. However, there simply isn’t enough resolution in the fossil record to identify exactly when a given group died out, and thus to be able to determine a proximate cause for extinction.
I doubt that irridium could be the culprit: There’s very, very little irridium in an asteroid. It’s just that there’s even less of it in the Earth’s crust.
DrDeth, some of the smaller, warm-blooded and feathered “true” dinosaurs did survive. They’re the ones we call “birds”. What do you mean by “true” dinos if not them?
Aves spilt off in the late Jurasic, maybe a little earlier.
No “dinosaurs” survived as there never were any “dinosaurs” in the first place. It was an error made by Richard Owen, in 1842. What is mostly thought as “dinosaurs” is TWO distinct Orders- the Ornithischia (bird-hipped) and Saurischia (lizard-hipped). Thus, there are Ornithischia, and there are Saurischia , but there is no Order “Dinosauria” as Owen thought.
For decades other giant extinct reptiles- pelycosaur Dimetrodon, the winged pterosaurs, and the aquatic ichthyosaurs, plesiosaurs and mosasaurs- were also called “dinosaurs” and this has stuck in the popular mind- to a laymen these are all “Dinosaurs”. But they are not Ornithischia, or Saurischia, the “classic dinosaurs” aka the “true dinosaurs”.(But see how we are already having problems with the word and it’s meaning).
Now, as of now, it appears that Aves spilt off from theropod dinosaurs- a type of Saurischia.* Thus, under some systems, they could be considered a member of the order Saurischia, but are instead generally considered to be members of the Class Aves. In fact, Aves has many Orders within it. This gets confusing.
However, if one must lump together Ornithischia, and Saurischia into one “Super Order” and if one must (for no particular good reason) name that Super-Order “Dinosauria” then if Aves are descended from the Saurischia they are thus a member of the “Super-Order Dinosauria”. But really, there is no need to create a Super-Order nor any need to give it the rather confusing name “Dinosauria” which laymen will always equate with all extinct giant reptiles.
But still- for now, that is the generally accepted way- there is such a Super-Order and they did decide to use the term “Dinosauria” for it. Thus, assuming they are all correct, birds *are *members of the Super-Order Dinosauria. But like it or not, they are not “dinosaurs”, since the word “dinosaur” has a different meaning than “Members of the Super-order Dinosauria”- since like it or not, dictionaries aren’t written by the newest theories in Science. Words have meanings outside of what some scientists would like them to mean. Thus, the *word * “dinosaur” means “any of a number of giant extinct reptiles” thus not “birds”. But I concede if you said “Aves are generally now considered to be a member of the Super-OrderDinosauria” you would be correct.
Also of course, calling birds "dinosaurs’ means you have to use the silly-assed construction “non-avian dinosaurs” to refer to the classic “dinosaurs”.
But still, in any case- it appears there were small members of the Orders Ornithischia, and Saurischia extent at the end of the CT, and they may well have been warm-blooded and feathered. But still, none of them survived, just members of the Aves, which had split off some 100 millions years previously. Why did none of those small feathered and warmblooded creatures survive? Why just those who had split off from the “main” Theropod line some 100 MY prior? Odd. Perhaps they weren’t so close to Aves, niche-wise.
Still and all, the Orders that did survive were mostly smaller and more adaptable.
*(This is disputed mind you- An alternate theory to the dinosaurian origin of birds, espoused by a few scientists, states that birds evolved from early archosaurs like Longisquama, thus they are not descended from the Saurischia. This is hotly disputed)
Except, DrDeth, that many modern taxonomists are now convinced that the Saurischia and the Ornithischia had a common ancestor among the Erythrosuchids, with almost nothing except what has traditionally been considered a dinosaur or a bird, and all of those groups, derived from that common ancestor. Hence, “Dinosauria” as a valid classification has been resurrected.
(I don’t insist this is the correct classification; I merely raise it as a point of disagreement to your more-or-less flat assertion that “Dinosauria” is polyphyletic and not a useful taxonomic group, which seems to be slowly in the process of being superseded.)
Also remember that the variety of classic Dinosauria, which was never great, was down to only about 50 species when the presumed comet hit. Less variety means fewer niches filled and less likelihood that some of the species would be in niches less affected by what killed everybody else.
As for birds, they are highly mobile, and crocs and mammals might have hibernated (yeah, I know what alligators do is not true hibernation but it’s close enough) through the “nuclear” winter. Perhaps it is because dinos couldn’t hibernate that there are none of them left.
If you’re talking about the category “dinosaur” as used in the lay consciousness, isn’t it part of the definition that they’re extinct? A “dinosaur” (as opposed to a member of Dinosauria) is a big, extinct, reptile-like creature. The reason all members of that category went extinct is simply that anything that didn’t go extinct would be defined out of the category.
Not so! As I mentioned in this thread, there were about 213 known genera still extant near the end of the Cretaceous. That translates to at the very least 213 species, possibly more, and again, that’s only those we actually have fossils for.
As for the status of Dinosauria, see my thread here. If anyone made a mistake with respect to the classification of dinosaurs, it was Seeley. Since Seeley, of course, many more fossils have been found which flesh out the early history of dinosaurs, and there is a good deal of evidence to support a common origin for both Ornithischia and Saurischia. That unified group is called Dinosauria. There are few, if any, paleontologists who disagree with this classification scheme today. By any reasonable standard, Dinosauria exists as a valid taxonomic group, whether you are a traditionalist (and assign it the in-my-opinion utterly meaningless rank of "Superorder "), or a cladist, or any other -ist.
There is, of course, some disagreement on where birds fall. IF birds evolved from theopod ancestors, then birds are necessarily dinosaurs for the same reason humans are apes. IF birds did not evolve from any dinosaur, but from separate archosaurian ancestors, then, well, birds aren’t dinosaurs. The bulk of the evidence favors the former hypothesis.
And, technically, Longisquama was not an archosaur, but an archosauromorph.
Indeed you make a good point. “Dinosaur”= “Giant extinct reptile” to most dudes.
But words are a tricky thing. I can tell you that Unicorns are not only not mythological, but many Americans have seen one alive, in the flesh. OTOH, Penquins are not only restricted to the Northern Hemisphere, but are extinct to boot. Of course, here I am not referring to the “Horse with a horn on it’s head” from Medieval mythology, but the Unicorn from the Bible- almost without doubt the Rhino. As to the “Penquin” the word came from a Welsh term for the Great Auk- which are now extinct- but when extant, 100% Northern.
Ah, but you say those are not “scientific” terms. Sure, but then I can state that Dragons are very much real- “Draco” is a genus of small gliding lizards from SE Asia. I have seen one. Thus, I have seen a real live dragon. :eek:
And Science has not fully accepted the whole “Birds are Dinos” thing yet. Aves is still generally regarded as a Class, but if birds are dinosaurs, then we have Super Order Dinosauria, Order Saurischia, Suborder Theropoda, with Aves being a grouping (likely an “Infraorder”) below a Suborder. But Aves contains a Subclass (NEORNITHES) and something like 2 dozen Orders within that Subclass. However an “Infraorder” cannot contain dozens of Orders in it- as an “Order” is a higher grouping than an Infraorder. Now, Modern Ornithologists seem to accept that Birds are closely related to Dinosaurs sure- but I have not read of any of them giving up every one of the couple dozen Orders that “used to exist”. It is impossible for an Infraorder to contain Orders within it. Explain that? AFAIK, Ornitholgists are simply ignoring the whole “Aves is now a Infraorder” thing. Passeriformes continues to be an Order to them, “Theropods” or no.
I have no doubt that Birds are closely related to Dinosaurs (and Cladisticly may be part of a whole) but to me, using terms like “non-avian dinosaurs” for those which did go extinct is a silly-ass idea.
In any case, Birds have been around as a separate grouping for some 200 million years, no matter their common ancestors.
Oh and if Protoavis really was a Bird, then things get very interesting!
While DrDeth’s post mistakes traditional taxonomic categories for the reality they are supposed to be describing, and will I’m sure be refuted by Darwin’s Finch, he does bring up a very valid point:
In popular discussions of cladistic classifications, there is no easy way to identify the relative degree of distinctness or closeness of two clades. Murids and Cricetids constitute a clade distinguishable from outlying groups; so do Tetrapods and Sarcopterygians. There’s nothing in my statements to suggest that I’m talking first about two related families of rodents and second of two superclasses of vertebrates.
Likewise, there is no convenient way to say “all the creatures that evolved these adaptations but which did not go on to evolve these other adaptations” – even when such part-clades excluding “crown groups” do constitute a clearcut group in the popular eye.
“Animals which spend their adult life on land or semi-aquatically, breathing air, but their larval stage as gill-breathing water dwellers” constitutes a valid group, traditionally Class Amphibia – frogs, toads, salamanders, and caecelians. But cladistics would simply say that they are basal tetrapods, no more closely related to each other than they are to the Amniotes – reptiles, birds, and mammals in the traditional grouping.
The obvious example of dinosaurs from our present discussion is yet another shortfall in cladistics. There’s obviously a clear grouping of carnosaurs, sauropods, ornithopods, ankylosaurs, ceratopsians, and other related groups that excludes feathered flying (or secondarily flightless) forms. And “dinosaur” is the useful term for them – and one that can reasonably be used to exclude dimetrodon, plesiosaurs, and all the other non-dinosaur extinct reptiles. But cladistically, since birds are a surviving crown group descended from dinosaur stock, they must be included within the dinosaurs.
Prosimians is yet aother such group. There are some clear relationships between lemurs, lorises, the aye-aye, bushbabies, etc., that distinguish them from monkeys of all sorts, apes, and man. Yet again cladistics insists that there is no valid term to describe them.
A new and better taxonomic system is needed, that takes the useful data uncovered by cladistic analysis, but structures it in a form that can be used by people interested in describing coherent groups of animals without inordinately long modifiers to distinguish out groups that evolved beyond where they stayed.
You’re going to have that same problem, no matter what taxonomic scheme you use, if that scheme is centered around the presumed evolutionary history of a group. There’s no getting around the fact that evolutionary lineages are a) branching and b) nested. If the nested groups are used as the basis of a taxonomic unit, then you will run into the exact same problem whether you use cladistics or Linnaeus’ scheme or any third option. My objection to Linnaeus’ scheme is that it was orginally conceived as a gradistic scheme (which, for those whose eyes glaze over when folks start talking systematics, basically means that organisms were grouped more by similarities in morphology than by evolutionary relationships). One result, of course, is that birds are given the same “rank”* as mammals, reptiles, amphbians, etc., which completely obscures any real, evolutionary relationships between those groups.
It is worth noting that cladistics also relies on morphological similarities & differences, but the starting assumption is that there is an evolutionary relationship between the groups being examined, and that we can therefore group any similiarites into being ancestral (meaning they are carried over from previous groups) or derived (meaning they are “new inventions” for the group in question). Thus, the task becomes one of separating out homologies from analogies, and identifying which characters are ancestral and which are derived (note that that’s a gross simplification of the process).
[It also worth noting that a cladogram is not a phylogenetic tree; it’s a hypothesis for evolutionary relationships. Several cladograms can be constructed for a given assemblage of species; it then becomes the task to determine which of those cladograms represents the “best fit” of the data, in terms of a presumed evolutionary descent (e.g., does it make more sense that character A evolved multiple times in many species, or that perhaps character A is the result of shared ancestry between those species who possess it?).]
Efforts have been made, of course, to make the Linnaeus scheme of nested groups with ranks more compatible with cladistics (i.e., to make the Linnaeus scheme more suitable to the evolutionary history of lineages). The result is a sort of taxonomic inflation, whereby instead of the original Kingdom, Phylum, Class, Order, etc., we now have Supra-this and Super-that, and Infra-so-and-so. In order to make birds fit within their presumed evolutionary space in such a scheme, you need countless more subdivisions, since you now have to take what used to be a Class, shoehorn it into what used to be another Class (Reptilia), and even within a previous Order (Saurischia), and so on. Thus, you now need Supras Infras and Supers in order to make everything fit. All of which is a bit of a waste, since you can just use a freakin’ cladogram to convey the same arrangement without creating unnecessary additional ranks.
At any rate, going back to my original point, if you use a nested taxonomic scheme, you will always have need to separate out those within a group from those not in that group. Modern Linnaen taxonomies suffer the same problem as cladistic ones (since they are modelled after cladistics, after all). Perhaps the simplest solution is to remove the stigma from paraphyletic groups (such as “non-avian dinosaurs”), and allow such to be given at least an informal name. The problem here is that certain names, like “dinosaur”, are muddled by a century of scientific neglect, and as a result it has become a layman’s dumping ground for all manner of creatures. The public just need to be re-educated on what is or is not a dinosaur (not a big deal, since our perception of dinosaurs themselves has changed from earlier depictions of them as sluggish, tail-dragging monsters who were simply waiting to die off so mammls could take over, to one of a varied, active, and above all, evolutionarily successful group of animals). Personally, I have no problem with “non-avian dinosaur” because it’s obvious to what one is referring (assuming one abides by the established scientific meaning of “dinosaur”). And the fact that there must therefore be “avian dinosaurs”, and that such a group includes those crows or jays outside or the cockatiel on my shoulder, or even my namesake, is just too darned cool.
To my mind, ranks are an unnecessary – obfuscatory, even – element to any classification. A given classification is only as useful as the information it provides. The names of groups - Mammalia, Reptilia, Dinosauria, Aves – provide information as to what characters the members of that group share. The nesting component tells the evolutionary history of the group (e.g., Reptilia > Dinosauria > Aves). But, ranks such as Family or Order tell us absolutely nothing. They tell us nothing about diversity, since an entire Phylum could house just a single species (not that this is necessarily the case now, but there are no provisions preventing such). There is no way to meaningfully compare equivalent ranks (e.g., Class Mammalia and Class Aves). All we can really tell is that a Class is subsumed within a Phylum (both Class Mammalia and Class Aves are within Phylum Vertebrata); but then we could tell relative positions of groups within groups from any nested taxonomic scheme. There is no new information that the rank provides over the name (which is essentially shorthand for the characters which unite a group) and the nested position in the taxonomic hierarchy (which tells us the presumed evolutionary relationship to other groups). This is, above all, the primary reason I reject Linnean taxonomies.
I seem to recall that this is the case for the ginkgo tree, is it not?
But I disagree with what you’re saying about the usefulness or lack thereof of ranks. If I tell you that two species are members of the same clade, that tells you nothing about how closely related they are, since there exists a clade which includes all terrestrial life. But if I tell you that they’re members of the same genus, you’ll know that they’re very closely related, as opposed to if I say they’re just members of the same kingdom, you’ll know that they’re not particularly related at all. By the same token, if I tell you that the Ginkgo is the only species in its phylum, then you’ll correctly deduce that it isn’t particularly related to anything else.
Genus and species are a bit different from higher ranks. For one thing, they are an established part of the binomial name for any species. Further, cladistics does not disregard either of those names. They are also regulated by the ICZN (for animals) or the ICBN (for plants), and there are a number of rules for determining validity, priority, etc., which the higher ranks do not have.
But, again, the rank really doesn’t tell you anything about relationships. If I tell you that Reptilia is a Class and Aves is a Class, what can you tell me about their relationships? If I tell you that Artiodactyla is an Order and that Cetacea is an Order, what can you tell me about their relationships? If I tell you that Tyrannosaurus is a member of Kingdom Animalia and Daspletosaurus is a member of Kingdom Animalia, what can you tell me about their relationships?
It’s the nesting of taxa, not their ranks, that describes actual (or presumed) relationships.
I could also tell that by looking at the nested groups for that taxon. The rank adds no new information that was not already available from the nested nature of the classification scheme.
Basically, what I am getting at is this: there is no fundamental difference in information between
Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata
Class Mammalia
Order Chiroptera
Family Pteropodidae
Subfamily Pteropodinae
Genus Eidolon
Species helvum
Family Phyllostomidae
Subfamily Desmodontinae
Genus Desmodus
Species rotundus
In both cases, you can see that E. helvum and D. rotundus are most closely related at the Chiroptera node, and that they are thus presumably more closely related to each other than to any mammal which falls outside of Chiroptera. Similarly, they would be more closely related to any other mammal than to any species which falls within Vertebrata but outside Mammalia. Whether Chiroptera is an Order, Family, Subfamily, Class, Superorder or whatever is completely irrelevant to making that determination.
Ginkgos are presently classified as the sole member of the Division Gingkophyta; Divisions are the equivalent of Phyla for plants.
According to this list, there are at least two animal Phyla, Placozoa and Micrognathozoa, with only a single known species, and two others, Xenoturbellida and Cycliophora, with 2 and 3 species respectively. Of course, the diversity of such obscure invertebrates is so poorly known that there could well be additional species in each group. But at any rate, Phyla range enormously in diversity, from 1 to probably millions for the Arthropoda.
Excellent posts by Darwin’s Finch, which explain well the misconceptions about taxonomy and cladisitics inherent in DrDeth’s posts, and save me the trouble of doing so.
Nothing at all silly about it. Such constructions are routine. Birds are a clade, possessing certain derived characters, nested within the clade of dinosaurs. There really is nothing wrong with referring to the rest of the clade as “non-avian” dinosaurs to distinguish those that have the derived characters of dinosaurs but lack those of birds.
The Passeriformes are the largest Order of birds, making up about half of all birds. For convenience ornithologists routinely refer to passerine and non-passerine birds, even though the latter is a paraphyletic group. Likewise in some contexts it may make sense to refer to non-hominid primates or non-placental mammals. “Non-avian dinosaur” is just as legitimate as any of these.
AFAIK, Ornitholgists are simply ignoring the whole “Aves is now a Infraorder” thing. Passeriformes continues to be an Order to them, “Theropods” or no.