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Old 08-29-2002, 02:51 AM
Darwin's Finch Darwin's Finch is offline
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Once more, with content!

So I decided to take a trip to Cecil's "storehouse of knowledge", and re-discovered the article, Pterosaurs aren't considered true dinosaurs. Why not?

Reading through the article, it occurred to me that it could probably use an update. So, being a) bored and b) a geek, here we go:

DINOSAURIA: THE EARLY YEARS

When the term "dinosaur" was first coined by Sir Richard Owen in 1842, it was for a group of three(!) then-known genera of large reptiles: Megalosaurus, Iguanadon and Hylaeosaurus (Cetiosaurus and Streptospondylus where also known at the time, but were not considered by Owen to be related to these three. Two other genera, Plateosuarus and Poekilopleuron, where also known at the time, but since Owen had not examined them, he did not include them within the group). The primary character which Owen drew upon to determine that these animals were related was the fusion of their sacral vertebrae; all three genera had this character, while other reptiles did not. This indicated, to Owen, common descent from a reptilian ancestor (obviously, they shared many other features with reptiles in general).

Owen therefore classified his "Dinosauria" as reptiles, granting Dinosauria the Linnaean rank of Suborder within Class Reptilia (incidently, he also classified them within Lacertilia, as he considered them to be simply really big lizards; thus his coining of the word "dinosaur", or "terrible lizard" -- he meant that literally!).

As more dinosaurs were discovered (largely as a result of the 'bone wars' between Othniel C. Marsh and Edward D. Cope during the mid-1800s), other classification schemes were advanced; perhaps the most notable was Marsh's proposed scheme of four separate Orders within Reptilia: sauropods, theropods, stegosaurs and ornithopods. This scheme, like many of the others proposed, was based on such characters as foot and tooth structure. However, Harry G. Seeley, in a paper written in 1887 and published in 1888, noted that all of these reptiles could be separated into two rather distinct groups, on the basis of hip structure: those with a forward-pointing pubis (the sauropods and theropods), and those with a backward-pointing pubis (the stegosaurs and ornithopods). He proposed the name of Saurischia for the former group, as this was the typical "reptilian" hip structure, and Ornithischia for the latter group, as this hip structure was reminiscent of that of modern birds (note that other characters, such as braincase and vertebrae structure, also served to distinguish the two groups in Seeley's scheme; however, primacy was given to the character of hip structure). Both groups were given the rank of Order within Reptilia.

Seeley also felt that Saurischia and Ornithischia were distinct, unrelated groups within Reptilia; Dinosauria proper was thus dismantled, and the term "dinosaur" became an informal one within scientific literature.

As a side note, Cecil mentions in his article that "until the 1970s paleontologists believed, in their heart of hearts, that there weren't any true dinosaurs. 'Dinosaur' was an informal term used to describe two distinct groups of animals, the Saurischia and the Ornithischia." An updated revision of this statement, then, would read, "between 1888 and the 1970s paleontologists believed...", since between 1842 and 1888, "Dinosauria" was accepted as a formal term.

Which brings us to:

DINOSAURIA REBORN

Around the mid 1970s, the concept of "dinosaur" underwent a bit of an overhaul. First up were Bakker and Galton, in 1974, who argued that Dinosauria be reunited and elevated to its own Class, with Aves subsumed within. A suite of features associated with upright stance, bipedality and increased metabolism were used to justify this new version of Dinosauria. Unfortunately, the premise of a new vertebrate class was generally not accepted, nor was the reiteration that dinosaurs were indeed monophyletic. Seeds of dissent had been sown, however. Argentinian paleontologist J. F. Bonaparte met similar resistance in 1976 when he likewise proposed that dinosaurs were monophyletic.

In 1993, Kevin Padian and Julian(?) May formally defined the various groups using phylogenetic systematics (aka cladistics). Jacques Gauthier had given Archosauria (the group containing dinosaurs, pterosaurs, crocodilians, and, eventually, birds) a cladistic overhaul around 1986, and had confirmed, based on his analyses of numerous characters, that a) dinosaurs were, as suspected, monophyletic -- that is, they represented a true group of animals descended from a common ancestor -- and b) that under strict cladistic defintions, Aves belonged within Dinosauria, as they, too, were descended from the same common ancestor as all other non-avian dinosaurs. (As a result, one encounters informal mention of "non-avian dinosaurs" in some literature.)

Anyway, Padian's & May's formal definitions for the groups were as follows:
  • Dinosauria = all descendants of the most recent common ancestor of Passer (Swallows) and Triceratops.
  • Ornithischia = all dinosaurs closer to Triceratops than to Passer (that is, eveything sharing a more recent common ancestor with Triceratops than with Passer).
  • Saurischia = all dinosaurs closer to Passer than to Ornithischia (that is, eveything sharing a more recent common ancestor with Passer than with Triceratops).

It was later proposed that Megalosaurus and Iguanadon should have been used instead of Passer and Triceratops, respectively, to define the groups, as the group thus described would be exactly the same as that proposed by Padian and May. This would have served primarily as an homage to Owen's original definition; regrettably, it was too late to change the definitions because of nomenclature priority rules (the suggestion occurred after Padian and May had formally published their deifnitions). This latter definition has gained popularity as an informal one, however.

So, now we have a (phylogenetic) definition of 'dinosaur': The most recent common ancestor of Passer and Triceratops (or Megalosaurus and Iguanadon, if you prefer), and all its descendants.

"But Finch," you ask, "what is a dinosaur?" And that is indeed a good question (and the point of this post, after all!).

The phylogenetic definition tells us who belongs to the dinosaur club. What we want, in order to determine how one gains entry into this club in the first place, is a diagnosis, or a set of characters which are unique to the members of a group (in cladistics terminology, such characters are termed synapomorphies, or shared derived characters, indicating a suite of novel characters shared by all, or most, members of the group) - in this case, of course, dinosaurs.

Such characters are largely a matter of observation and interpretation. However, a representative (and, if one is not versed in bone/skeletal terminology, possibly incomprehensible) list of such characters might be as follows:

1. Enlongate vomers that reach caudally at least to the level of the antorbital fenestra
2. Three or more sacral vertebrae
3. Scapulocoracoidal glenoid facing fully backward
4. Low deltopectoral crest that runs one-third or one-half of the way down the shaft of the humerus
5. Three or fewer phalanges in the fourth digit of the hand
6. Largely to fully open acetabulum
7. Fully offset proximal head of femur with a distinct neck and ball
8. Greatly reduced fibula
9. Well-developed ascending process of astragalus

(Modified from The Dinosauria, ed. Weishampel, Dodson & Osmolska, 1990)

A further-refined (and extended) list of characters, from various authors (post The Dinosauria, mentioned above), might be as follows:

1. Ectopterygoid lateral to transverse flange of pterygoid
2. Postfrontal absent
3. Temporal muscles extend anteriorly onto skull roof
4. Quadrate head exposed laterally
5. S-shaped neck
6. At least 3 fully incorporated sacral vertebrae (with 3rd incorporated from dorsal vertebrae)
7. Forelimb < 50% length of rear (reversals in several groups)
8. Humerus with elongate deltopectoral crest
9. Manus 4 with < 4 phalanges
10. Claws on 1-3 only
11. Semi-perforate (usually fully perforated) acetabulum with buttress
12. Brevis shelf on ilium
13. Ischium with obturator process restricted to anterior 1/3rd
14. Femur with ball-like head
15. Shaft of femur straight or bowed anteriorly
16. Femur vertical
17. Femur has greater, lesser & 4th trochanters
18. Tibia with cnemial crest
19. Well-developed ascending process of astragalus on anterior face of tibia
20. Calcaneum with concave surface for articulation of fibula
21. Metatarsals elongate and function as part of pes

(Note that not all authors regard all of the above characters as being diagnostic of Dinosauria. And some, such as the 3 sacral vertebrae [#6] and partially/fully perforated acetabulum [#11], carry more weight than others.)

So, what all this means is that 1) you are a dinosaur if you are descended from the most recent common ancestor of Passer and Triceratops, and 2) we can tell if you are, in fact, part of that group based on whether you possess the above characteristics (or, at least, the bulk of them).

Which brings us to pterosaurs.

Things are a little less clear where pterosaurs are involved. The general consensus is that pterosaurs are archosaurs (like dinosaurs) and belong to the clade Ornithodira (also like dinosaurs). Other ornithodires are Lagosuchus and Lagerpeton, which are believed to be early dinosaurian relatives (with Lagosuchus being the more dino-like of the two).

Not unlike dinosaurs, there are two main groups of pterosaurs: the small, long-tailed Rhamphorhynchoidea and the larger, short-tailed Pterodactyloidea. Both groups sport an enormous (relative to body size) digit IV (the equivalent of our ring finger), which supports the famous wing membrane. Some of the few uniting characters that have been agreed upon by various authors include large eyes, big brains, hollow bones, the presence of a keeled sternum (much like birds), and a bird-like scapula. In addition to the whole "giant finger" thing, of course. The aforementioned Dr. Padian put forth a number of synapomorphies for Pterosauria in 1997; however, he also admits that many of these characters are shared by Dinosauromorphs (the group which includes Dinosauria, Lagerpeton and Lagosuchus) in general.

So, the real difficulty, then, is in defining what pterosaurs are, as opposed to what dinosaurs are. Clearly pterosaurs do sport novel features (e.g., the structure of the wing). They also lack some of the aforementioned (and important) dinosaurian features, most notably those which pertain to the hip structure (dinosaurs are unique among reptiles in holding their limbs directly beneath the body, as opposed to them splaying out to the side; pterosaurs are thought to be splay-footed, though Dr. Padian disagrees). Pterosaurs also lack the "perforated acetabulum" [a hole where the three hip bones -- the ilium, ischium and pubis -- meet] that all dinosaurs, including birds, possess.

Arriving at a proper definition is further complicated by the fact that pterosaurs are represented rather poorly within the fossil record -- particularly early pterosaurs which might better allow researchers to determine their proper relationships to other archosaurs & archosaur relatives.

So, as things stand now, pterosaurs are not dinosaurs by virtue of descent: they are not believed to have descended from the most recent common ancestor of Passer and Triceratops. This has been determined, to the best ability given currently-known fossils, by the lack of a number of truly dinosaurian features, primarily those with respect to the structure of the hip. Future finds could, of course, place pterosaurs within Dinosauria; however, the current thought is that the primeval pterosaur is more likely to be either an offshoot of the eosuchians (early reptiles from the Permian which later gave rise to the archosaurs) or the same (or similar) archosaurian ancestors which gave rise separately to dinosaurs and crocodiles.

******************
MODERATOR NOTE: please be aware that this thread is from 2002-03 until revived near end of 2nd page, in post #66, in April 2014. That's OK, I just don't want someone getting worked up about responding to a post that's over ten years old, and expecting anyone to remember what they said (if they're even still here) -- CKDH

Last edited by C K Dexter Haven; 04-17-2014 at 08:31 AM..
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  #2  
Old 08-29-2002, 03:28 AM
Irishman Irishman is online now
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Thanks. Very well done, if so technical I really didn't follow the details much except to understand there are sets of features that differ enough to suggest the points of common ancestry split at different times.

Because I walked out of Cecil's Column still not really understanding why Pterosaurs weren't considered dinosaurs from the beginning. Oh, it said they were defined not to be dinosaurs, but didn't really explain why. Your answer kinda does.
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Old 08-29-2002, 03:51 AM
Darwin's Finch Darwin's Finch is offline
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Thanks

Are there any particular concepts / definitions / whatever which might need some clarification? Since it was already rather long, I did leave out a lot of such explanations. I do plan to "simplify" the characters list a bit (to make it a bit more comprehensible), but that wll have to wait until morning.
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Old 08-30-2002, 09:44 AM
Irishman Irishman is online now
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Like I said, the technical terminology is thick for the uninitiated, but you did a good job conveying the gist.
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  #5  
Old 09-03-2002, 09:24 AM
Go alien Go alien is offline
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One slight correction. Passer is the genus to which house sparrows belong (Passer domesticus).

http://animaldiversity.ummz.umich.ed.../p._domesticus$narrative.html

Swallows are (usually) in the genus Hirundo as in the barn swallow ( the common European swallow).

http://animaldiversity.ummz.umich.ed...ndo/h._rustica$narrative.html
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Old 09-03-2002, 11:46 AM
Darwin's Finch Darwin's Finch is offline
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D'oh! You're correct. I really meant sparrow, honest!

Thanks for catching that.
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Old 01-03-2003, 12:47 PM
Satyagrahi Satyagrahi is offline
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Thank you, Darwin's Finch, for an excellent presentation of this commonly glossed over detail--the matter of definition--in a popular and vivid subject. Of course, the common public's definition of a dinosaur would be something like "any over-size reptile, now extinct" but that's hopelessly vague to any student starting a serious study.

But your definition--all descendents of the most recent common ancester etc.--seems to state one thing that raises my eyebrows: According to taxonomists, all avians are dinosaurs. Do you mean to say that, by the official definition, all birds are true, living, in-the-flesh dinosaurs? This must be news to millions of schoolchildren.

I'm picturing a trivia question: Which of the following is a true dinosaur?

1. Pteranosaurus
2. Plesiosaurus
3. Pseudosuchus
4. Kimodo Dragon
5. common sparrow

Now THAT'S misdirection.
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Old 01-03-2003, 01:44 PM
Bosda Di'Chi of Tricor Bosda Di'Chi of Tricor is offline
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Bravo, Darwin's Finch!
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  #9  
Old 01-05-2003, 04:19 AM
Irishman Irishman is online now
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Satyagrahi, birds are not dinosaurs any more than humans are shrews. Sure, they evolved from dinosaurs the way humans evolved from a shrew-like ancestor, but they no longer are dinosaurs.
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Old 01-05-2003, 09:42 AM
John W. Kennedy John W. Kennedy is offline
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Well, that depends on whether you go by traditional or cladistic terminology. In traditional use, one group can split off from another group (e.g., the mammals split off from the reptiles). But in cladistics, a group is forever a member of every ancestral group (e.g., mammals are still amniotes -- which is the closest term to "reptile" in cladistic use).

What I am [i]not/i] sure of is the current state of affairs in this overall debate. Is all traditional Linnaean classification above the level of genus or so being replaced by a cladistic system, or are the two going to coexist forever?
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Old 01-06-2003, 10:32 PM
Freddy the Pig Freddy the Pig is offline
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Quote:
Originally posted by Irishman
Satyagrahi, birds are not dinosaurs any more than humans are shrews. Sure, they evolved from dinosaurs the way humans evolved from a shrew-like ancestor, but they no longer are dinosaurs.
No, the two cases are not analogous. Birds descend from dinosaurs, and therefore cladistically speaking they are dinosaurs. Humans and modern shrews share a common ancestor.

This whole cladistic classification thing keeps spawning a raft of related questions: Are humans apes? Are birds dinosaurs? Are birds reptiles? Are early tetrapods properly described as "amphibians"? Are early amniotes properly described as "reptiles"? The whole thing is worthy of a GD thread, but I'm afraid to start one--all they talk about over there are religion and politics.
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Old 01-07-2003, 01:51 AM
Breathe Exhaust Breathe Exhaust is offline
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Taming of the Shrew

My ex was a shrew, but that's another story.

Laypeople like me have trouble understanding how and why the greatest creatures on Earth became tiny sparrows. I understand basic evolution, and that drastic changes can take place when tens of millions of years are given. However, the the dinosaur to bird process is still puzzling. Of course, up until about ten thousand years ago we had flightless birds on the order of twelve feet tall, which is a link a little easier for us non-scientists to grasp. However, it's all so much more complicated!

If the Komodo Dragon is the largest living lizard, what is the largest crocodilian?
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Old 01-07-2003, 07:06 AM
Satyagrahi Satyagrahi is offline
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Ahhh, I think I discern the root of my confusion here. I learned the traditional, Linnaean system in school back several decades ago and I was unaware that 'cladistics' was a competing system of classification rather than a methodology within the Linnaean system.

OK. Since Darwin's Finch seems to be on vacation, I'll go google "cladistics" and become enlightened.

Thanks, everyone!
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Old 01-07-2003, 04:48 PM
Freddy the Pig Freddy the Pig is offline
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Quote:
Originally posted by Breathe Exhaust
Laypeople like me have trouble understanding how and why the greatest creatures on Earth became tiny sparrows.
Why? Why would you assume that bigger is always better? There are gazillions of examples of small critters evolving from large ones. I imagine, for example, that guppies have done quite a bit of downsizing over the millennia. And think of the size difference between tigers and pussycats, which are a lot more closely related than sparrows and tyrannosaurs.
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Old 01-08-2003, 10:18 AM
Irishman Irishman is online now
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jklann, you misunderstand me. I was not saying that humans are descended from modern shrews. I was saying humans are descended from a shrew-like ancestor. That ancestor would also be a shrew, of sorts. I abbreviated, because it is tedious typing "shrew-like ancestor" all the time.

Or to put it on a more similar note, sense I feel other objections coming. The shrew-like ancestor was a mammal, just as humans are mammals. The shrew-like ancestor was a rodent. Humans are not rodents. A bird is not a dinosaur, even though it descended from dinosaurs.

But apparently I'm not up on cladistics.

Breathe Exhaust, kill off all dinosaurs bigger than a chicken. Now is it easier to see how they became sparrows?
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Old 01-08-2003, 04:32 PM
Freddy the Pig Freddy the Pig is offline
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Quote:
Originally posted by Irishman
The shrew-like ancestor was a rodent. Humans are not rodents.
No, see, that's the key point. Actually, even modern shrews aren't rodents--they're insectivores, more closely related to moles than hamsters. But the important thing is that there's no special relationship between the "shrew-like ancestor" and modern shrews. The resemblance is superficial; we describe the extinct ancestor as "shrew-like" just because we need some living animal to compare it to so that we can picture what it looked like. The "shrew-like ancestor" is neither rodent nor insectivore; it can't belong to any order of mammals because it lived before the mammal clade divided into orders. It is the progenitor of every order.

Whereas with birds, they don't descend from "dinosaur-like ancestors"; they actually descend from dinosaurs.
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Old 01-09-2003, 01:40 PM
Breathe Exhaust Breathe Exhaust is offline
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Breathe Exhaust, kill off all dinosaurs bigger than a chicken. Now is it easier to see how they became sparrows? [/B][/QUOTE]


Oh, I assumed it was the end of the line for the "non-avian" dinosaurs when the asteroid slammed into the planet 65 million years ago. How then could triceretops (sp?) "evolve" into sparrow if its entire order was extinct?

I never assumed "bigger is better," it's just hard to fathom the amzaing process of evolution whereby enormous creatures become tiny ones. Speaking of pussy cats, I've heard house-cat size cats preceded lion-size cats in evolution, whereas the saber-tooth cats split off into another line and became extinct.
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Old 01-09-2003, 02:24 PM
John W. Kennedy John W. Kennedy is offline
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A) Not all dinosaurs were large -- ever. The immediate ancestors of birds were about chicken-sized.

B) But in any case, evolution produces smaller creatures in a situation where small creatures survive and reproduce a lot. (They don't even have to be "better adapted" than the large ones; they just have to be successful on their own terms.)
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Old 01-09-2003, 09:39 PM
mightyaphrodite mightyaphrodite is offline
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Quote:
Originally posted by Satyagrahi
Thank you, Darwin's Finch, for an excellent presentation of this commonly glossed over detail--the matter of definition--in a popular and vivid subject. Of course, the common public's definition of a dinosaur would be something like "any over-size reptile, now extinct" but that's hopelessly vague to any student starting a serious study.

But your definition--all descendents of the most recent common ancester etc.--seems to state one thing that raises my eyebrows: According to taxonomists, all avians are dinosaurs. Do you mean to say that, by the official definition, all birds are true, living, in-the-flesh dinosaurs? This must be news to millions of schoolchildren.

I'm picturing a trivia question: Which of the following is a true dinosaur?

1. Pteranosaurus
2. Plesiosaurus
3. Pseudosuchus
4. Kimodo Dragon
5. common sparrow

Now THAT'S misdirection.

I can tell you one thing.. they're all related.
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Old 01-09-2003, 09:55 PM
mightyaphrodite mightyaphrodite is offline
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Quote:
Originally posted by John W. Kennedy
Well, that depends on whether you go by traditional or cladistic terminology. In traditional use, one group can split off from another group (e.g., the mammals split off from the reptiles). But in cladistics, a group is forever a member of every ancestral group (e.g., mammals are still amniotes -- which is the closest term to "reptile" in cladistic use).

What I am [i]not/i] sure of is the current state of affairs in this overall debate. Is all traditional Linnaean classification above the level of genus or so being replaced by a cladistic system, or are the two going to coexist forever?
I'm just going to throw a bunch of comments into one post since this site is loading a bit slowly for me for some reason:

1. The fact that birds come from the same ancestors as dinosaurs shouldn't be a surprise to any of us. This is why the discovery of the archaopteryx was so important -- it showed us the "missing link" between birds and reptiles.

2. There was a comment made that dinosaurs were unique to other reptiles by having legs underneath them for support, rather than to the side. This is correct, but one must not forget that many dinosaurs also had legs at the side for support. I just don't want people to mistakenly believe that ALL dinos had their legs beneath them, as do modern mammals.

3. Cladistics is the older way of showing links between animals, and is not generally being done anymore. The new way of showing ancestry in science is phylogeny.

cladogram - a branching diagram showing the pattern of sharing of evolutionarily derived characteristics amoing species and higher taxa.

phylogeny - the origin and diversification of any taxon, or the evolutionary history of its origin and diversification, usually presented in the form of a dendrogram.

(definitions from:
Hickman, Roberts and Larson. 1998. Biology of Animals. New York: McGraw-Hill.)

4. As far as my 2nd year university text is concerned (the same book referenced just above), pterosaurs are decended from archosaurs, but are not listed as being grouped directly with the other dinosaurs: ornithischians, sauropods and theropods. The Archaeopteryx is also listed on its own, apart from other dinosaurs, but descended from archosaurs. Birds are shown as being directly descended from the archaeopteryx. It should be noted that archosauria also includes the crocodilians. Thus, crocs, dinos and birds are all intimitely related to one another.
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Old 01-10-2003, 01:57 AM
MuscaDomestica MuscaDomestica is offline
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Quote:
2. There was a comment made that dinosaurs were unique to other reptiles by having legs underneath them for support, rather than to the side. This is correct, but one must not forget that many dinosaurs also had legs at the side for support. I just don't want people to mistakenly believe that ALL dinos had their legs beneath them, as do modern mammals.
Which dinosaurs did not? I swore that the Archasaur ankle was a major diagnostic feature, but Crocs also had them (modern ones returned to the classic sprawling pose which is much better for the water.)
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  #22  
Old 01-10-2003, 07:50 AM
John W. Kennedy John W. Kennedy is offline
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Please note that in calling cladistics "old", you are speaking relatively. Most people's high-school biology, though it included evolution (except in certain backward and barbarous locales), nevertheless used pre-evolutionary taxonomy, in which a phylogenic line can run sideways between taxonomic siblings.
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  #23  
Old 01-10-2003, 01:29 PM
jimbobboy jimbobboy is offline
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Re: Taming of the Shrew

Quote:
Originally posted by Breathe Exhaust
...the Komodo Dragon is the largest living lizard ...
Where do they come from?
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  #24  
Old 01-10-2003, 04:24 PM
Breathe Exhaust Breathe Exhaust is offline
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Komodos

Komodo Dragons are a species of monitor lizard named for the island of Komodo in Indonesia. They used to be far more wide spread, but are now limited to Komodo and one or two other Indonesian islands. They're endangered but now pretty well protected.

Unlike crocodilians, they're primarily land animals, thus they expend much more energy. Hence, the must feed more often than crocs, and are more aggressive. The males can grow up to nine feet long. They prey on deer, wild boar, and whatever else they can find. They'll eat you too, given the chance.
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Old 01-10-2003, 04:56 PM
Irishman Irishman is online now
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Okay, my terminology is messed up. Let me boil down my point.

Humans are not shrew-sized four-legged fuzzy critters. They evolved from shrew-sized four-legged fuzzy critters, but are no longer so.

Birds evolved from dinosaurs, but are not dinosaurs.

Add a little more info on the Komodo Dragon bit. Where do monitor lizards fit into the overall picture? You've taken it one step and assumed the rest of us know how it fits from there. You assume too much.
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Old 01-10-2003, 05:49 PM
mok mok is offline
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Quote:
Originally posted by Irishman
Okay, my terminology is messed up. Let me boil down my point.

Humans are not shrew-sized four-legged fuzzy critters. They evolved from shrew-sized four-legged fuzzy critters, but are no longer so.
The only difference is that we are no longer shrew-sized. We certainly are four-legged fuzzy critters.

Quote:
Birds evolved from dinosaurs, but are not dinosaurs.

Irishman, the whole point is that there are two definitions of the word "dinosaur". The popular definition of "dinosaur" is "one of the many extinct giant reptiles" and does not include birds. This definition also includes things like plesiosaurs and pterosaurs, which popularly are dinosaurs but biologically are not. The cladistic scientific definition of dinosaur does include birds. So your statement Birds evolved from dinosaurs, but are not dinosaurs. is true by the popular definition, and false by the cladistic definition.

Let me ask you this, though: based on what you have read above, do you believe that birds are Archosaurs or not?

-mok
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  #27  
Old 01-10-2003, 06:49 PM
Freddy the Pig Freddy the Pig is offline
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It's certainly true, Irishman, that we can make statements like the following:

(1) Whales descend from land mammals, but they are not land mammals.
(2) Humans descend from small, furry mammals, but we are no longer small (as adults, anyway) or particularly furry (except for some of the hairier ones among us).
(3) All mammals, birds, and reptiles descend from a common ancestor that looked like a lizard--but very few look much like lizards today.

All of the above statements are true, and they convey useful information. But in every case the identifier on the right side is an informal, impressionistic description--nobody would pretend that "land mammal", "small, furry animal", or "a thing that looks like a lizard" is a valid zoological taxon.

Now the problem with birds and dinosaurs is that "dinosaur" does have a valid zoological meaning--a member of the clade Dinosauria, as explained by Finch above. And most biologists agree that birds are members are Dinosauria. But because dinosaurs are so well known, the word is also used impressionistically, and it creates a mental picture of a (usually) large, scaly, and long-extinct creature that doesn't accommodate birds.

One possible compromise is to say that birds are Dinosaurians but not dinosaurs, relegating "dinosaur" to an informal status like "early primate" or "egg-laying animal". But my personal preference, if the descent from early dinosaurs can be established beyond a reasonable doubt, is to expand our concept of dinosaurs to include birds.

There is a precedent. At one time people had trouble accepting that a whale could be a mammal. It doesn't fit the impressionistic image of a furry, four-legged land creature. As Melville wrote in Moby-Dick:

Quote:
The uncertain, unsettled condition of this science of Cetology is . . . attested by the fact that, in some quarters it still remains a moot point whether a whale be a fish . . .

The grounds upon which Linnaeus would fain have banished the whales from the waters, he states as follows: 'On account of their warm binocular heart, their lungs, their movable eyelids, their hollow ears, (lactation) . . . I submitted all this to my friends Simeon Macey and Charley Coffin, of Nantucket, both messmates of mine in a certain voyage, and they united in the opinion that the reasons set forth were altogether insufficient. Charley profanely hissed they were humbug.

Be it known that, waiving all argument, I take the good old fashioned ground that the whale is a fish . . .
Today, who would doubt for two minutes that a whale is a mammal? We learn in school that whales are marine mammals, and we take it for granted. Someday, it may be the same with birds and dinosaurs!
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  #28  
Old 01-10-2003, 07:29 PM
DrDeth DrDeth is offline
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Note that it is not universally accepted that Birds descended from Dinosaurs- as opposed to simply having a common ancestor. We used the "archosauria" term also, which does include crocs, birds & the classic dino.

The problem with using a term like "dinosauria" to include the class Aves (even thought they may be related, or even perhaps the same superclass, or even the same class) is that is confuses the layman & makes old books obsolete. Even though a number of biologists want to CALL birds=Dinos, a new name , which better shows the relationship and does not lead to such confusion is better. Certainly, when Owen coined the name, it was not intended to include "birds". So- even if birds & dinos are so closely related we need to lump them together- calling the class "dinosauria" is a bad idea- with "political" overtones.

Bakker- who really pushes hard the 'hot blooded dino" theory (which may well be correct) also pushes the "birds= Dinos" concept to strengthen his theory.

Jklann- in the old "birds, beast & fish" classification- a whale fits within "fish" better than "beast". If you define an animal by outward characteristics & niche (which is a perfectly fine way of doing so, note)- then a whale is more a "fish" than a "beast". Of course- if you define them cladisticly or phlyogenically- then it is clear a whale is a mammal.
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  #29  
Old 01-10-2003, 07:57 PM
mightyaphrodite mightyaphrodite is offline
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Quote:
Originally posted by MuscaDomestica
Which dinosaurs did not? I swore that the Archasaur ankle was a major diagnostic feature, but Crocs also had them (modern ones returned to the classic sprawling pose which is much better for the water.)
Sorry, I stand corrected. I checked my own references and it turns out that I was just remembering that information incorrectly. Yes, all dinosaurs did stand upright. Crocs, by the way, were always sprawled to the side,and are intermediates between traditional lizards and dinosaurs. The Croc hip-joint is actually referred to as "pre-dino" in my book, since Crocs are more upright than lizards, but their legs are still out to the side, unlike dinosaurs.
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  #30  
Old 01-10-2003, 08:01 PM
mightyaphrodite mightyaphrodite is offline
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Quote:
Originally posted by John W. Kennedy
Please note that in calling cladistics "old", you are speaking relatively. Most people's high-school biology, though it included evolution (except in certain backward and barbarous locales), nevertheless used pre-evolutionary taxonomy, in which a phylogenic line can run sideways between taxonomic siblings.
I'm not referring to high school biology, I'm talking about what I've been learning in my university studies. Cladograms were the old way of showing evolutionary trends, but that is changing over to phylogenies, because phylogenies are now being accepted as "more correct" though cladograms are often still used as supplements. Most modern biological texts show phylogenies, not cladistics.
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  #31  
Old 01-10-2003, 08:03 PM
mightyaphrodite mightyaphrodite is offline
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Quote:
Originally posted by mok
The cladistic scientific definition of dinosaur does include birds. So your statement Birds evolved from dinosaurs, but are not dinosaurs. is true by the popular definition, and false by the cladistic definition.
[/B]
Actually, that statement is false either way, because birds are NOT descended from dinosaurs, they're descended from archaeopteryx. Archaeopteryx was NOT a dinosaur, but is related to them to the degree that all are considered part of archosauria.
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  #32  
Old 01-10-2003, 08:43 PM
Geobabe Geobabe is offline
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Do they eat other animals, these Komodo dragons?
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  #33  
Old 01-11-2003, 01:11 AM
Freddy the Pig Freddy the Pig is offline
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Quote:
Originally posted by mightyaphrodite
Actually, that statement is false either way, because birds are NOT descended from dinosaurs . . .
That's your opinion. Many evolutionary biologists hold a different opinion. See, for example, http://www.ucmp.berkeley.edu/diapsids/avians.html. Or, for that matter, see the OP.
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  #34  
Old 01-11-2003, 08:14 AM
John W. Kennedy John W. Kennedy is offline
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Quote:
I'm not referring to high school biology, I'm talking about what I've been learning in my university studies.
Yes, and you're talking, in large part, to a bunch of confused laymen who are lucky if they remember more of their high-school biology than they do of their fourth-grade "general science". This is "The Straight Dope", not "The Journal of Evolutionary Biology".

What I originally said still goes; the essential problem here is a failure to "get" the new classificatory principle, as first made popular by cladistics, that evolutionary descendants ought not to be regarded as taxonomic siblings.

(Actually, I find myself rather confused by your account of phylogeny-not-cladistics. It sounds as though this new system replaces deductions based on concrete fossil evidence with mere guesswork.)
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  #35  
Old 01-11-2003, 03:36 PM
Freddy the Pig Freddy the Pig is offline
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Quote:
Originally posted by John W. Kennedy
(Actually, I find myself rather confused by your account of phylogeny-not-cladistics. It sounds as though this new system replaces deductions based on concrete fossil evidence with mere guesswork.)
Yeah, I was wondering about that too. My understanding was the cladistics was the primary methodology by which we determine phylogenetic relationships, especially within the fossil record where DNA comparison isn't an option.
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  #36  
Old 01-11-2003, 08:27 PM
mightyaphrodite mightyaphrodite is offline
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Quote:
Originally posted by John W. Kennedy
Yes, and you're talking, in large part, to a bunch of confused laymen who are lucky if they remember more of their high-school biology than they do of their fourth-grade "general science". This is "The Straight Dope", not "The Journal of Evolutionary Biology".

What I originally said still goes; the essential problem here is a failure to "get" the new classificatory principle, as first made popular by cladistics, that evolutionary descendants ought not to be regarded as taxonomic siblings.

(Actually, I find myself rather confused by your account of phylogeny-not-cladistics. It sounds as though this new system replaces deductions based on concrete fossil evidence with mere guesswork.)
Actually, phylogeny is more based on DNA, rather than strictly physical characteristics. A lot of taxonomy has changed since DNA was found to be the source of genetic material in the 50's.
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  #37  
Old 01-11-2003, 08:53 PM
mightyaphrodite mightyaphrodite is offline
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Quote:
Originally posted by jklann
That's your opinion. Many evolutionary biologists hold a different opinion. See, for example, http://www.ucmp.berkeley.edu/diapsids/avians.html. Or, for that matter, see the OP.
It's not my opinion. It's what I've seen in several different Herpetological texts.

(note: herpetology is the study of reptiles and amphibians)
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  #38  
Old 01-11-2003, 10:25 PM
Darwin's Finch Darwin's Finch is offline
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Golly! I did, actually, go on vacation for a week, and only now got back. I didn't expect to see this thread resurface!

Most of the points that have been raised in my absence have been addressed, but there are a couple issues that I'd like to clarify:

Quote:
Originally posted by John W. Kennedy
(Actually, I find myself rather confused by your account of phylogeny-not-cladistics. It sounds as though this new system replaces deductions based on concrete fossil evidence with mere guesswork.)
Essentially, the whole point of phylogenetic systematics (the methods of systematics which uses cladistics to produce phylogenetic trees) is to reconstruct evolutionary lineages. Linnaean classification fails to do this, as it implies no necessary relationships between, say, birds (Class Aves), and reptiles (Class Reptilia), and essentially only groups "like with like".

Cladistics (which is, again, a method; the resulting cladogram is not a phylogenetic tree, but rather one hypothesis for an evolutionary relationship between organisms) relies on nested groupings of unique features to arrive at proposed relationships. The hypotheses thus created can then be tested against other organisms/groups to further refine the relationships. For example, if I wish to claim that birds are directly descended from dinosaurs, then I should be able to point to specific features which both dinosaurs (as popularly understood) and birds possess. Further, I should be able to produce features which are unique to birds (or that I can establish as being analogous rather than homologous, if a similar character is found elsewhere). And so on. The same applies for establishing relationships between pterosaurs and dinosaurs. Thus far, the weight of the evidence is that a) birds are descended from dinosaurs (though there are still a few detractors, e.g., ornithologist Alan Feduccia), and b) pterosaurs aren't.

As far as terminology of clades, personally, I don't have a problem with birds being dinosaurs, as opposed to simply stating they are descended from dinosaurs. Ultimately, both mean the same thing: birds are birds, and dinosaurs are ancestral to birds, just as earlier archosaurian reptiles were ancestral to dinosaurs, and so on.
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  #39  
Old 01-12-2003, 12:56 AM
Freddy the Pig Freddy the Pig is offline
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I'm still kinda confused. Is it true that cladistics is "not generally being done any more"? What other methods besides cladistics are used to create phylogenetic trees? (DNA analysis?) And where do "dendrograms" (referenced by mightyaprhrodite enter the picture?
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  #40  
Old 01-12-2003, 02:04 AM
Darwin's Finch Darwin's Finch is offline
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It most certainly is not true that cladistics is a thing of the past -- all things considered, it's relatively new; as you can see from the OP, dinosaurs didn't start getting a cladistic workover until the '70s. Cladistic methodology itself was developed by Willi Hennig in 1950. Cladistics is, in fact, the current dominant paradigm in systematics.

A dendrogram is simply an alternate form of branching diagram. An example (for dinosaurs) can be seen here. Compare this to the cladogram version here.
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  #41  
Old 01-12-2003, 02:16 AM
Darwin's Finch Darwin's Finch is offline
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By the way, the University of Kansas's Natural History Museum Publications website has a good primer on cladistic methodologies.
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  #42  
Old 01-12-2003, 08:38 PM
Breathe Exhaust Breathe Exhaust is offline
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____________________________________________________
Irishman:

Add a little more info on the Komodo Dragon bit. Where do monitor lizards fit into the overall picture? You've taken it one step and assumed the rest of us know how it fits from there. You assume too much.
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How do I assume to much? I'm far less qualified to say where monitor lizards fit into the overall picture than some others on the list. I managed to emerge form 16 years of education without ever taking a biology or zoology course, so this thread is not so much debate as education for me. I learned what I know about the Komodo Dragon from television documentaries. I wouldn't pretend to have a scientist's grasp on the subject.
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  #43  
Old 01-12-2003, 09:20 PM
Darwin's Finch Darwin's Finch is offline
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I missed the Komodo Dragon bit quoted above. Komodo Dragons (Varanus komodoensis) are in a completely separate reptile lineage from archosaurs. Within Reptilia, there is a branch known as Sauria. This branch splits into Archosauromorpha on the one hand (which, in turn, contains Archosauria, and therefore dinosaurs, pterosaurs, crocodilians and birds), and Lepidosauromorpha (which contains, among numerous other critters, the varanid lizards [aka "monitor lizards", which include Komodo Dragons], as well as the various extinct aquatic reptiles: mosasaurs, plesiosaurs, ichthyosaurs, and nothosaurs -- creatures often mistaken for "aquatic dinosaurs").

So, the short answer is that Komodos are only distantly related to dinos and pterosaurs.
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  #44  
Old 01-13-2003, 10:02 AM
jimbobboy jimbobboy is offline
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Would a Komodo dragon, then, be considered a member of the lizard family?
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  #45  
Old 01-13-2003, 12:59 PM
DrDeth DrDeth is offline
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Quote:
Originally posted by Geobabe
Do they eat other animals, these Komodo dragons?
Yes- they are more or less big lizards, and are carnivourous. They like goat. They would eat you, given the chance, although they do not "hunt" humans for food normally.
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  #46  
Old 01-13-2003, 08:38 PM
Irishman Irishman is online now
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jklann said:
Quote:
All of the above statements are true, and they convey useful information. But in every case the identifier on the right side is an informal, impressionistic description --nobody would pretend that "land mammal", "small, furry animal", or "a thing that looks like a lizard" is a valid zoological taxon.
I was getting an inkling of this when I posted. Thank you for phrasing it in a way that got it through my thick skull.

Quote:
Now the problem with birds and dinosaurs is that "dinosaur" does have a valid zoological meaning--a member of the clade Dinosauria, as explained by Finch above. And most biologists agree that birds are members are Dinosauria. But because dinosaurs are so well known, the word is also used impressionistically, and it creates a mental picture of a (usually) large, scaly, and long-extinct creature that doesn't accommodate birds.
And this is a serious problem for biologists to address.

John W. Kennedy said:
Quote:
What I originally said still goes; the essential problem here is a failure to "get" the new classificatory principle, as first made popular by cladistics, that evolutionary descendants ought not to be regarded as taxonomic siblings.
Um, what? I think what you're saying is that just because two different groups are subdivisions of a previous ancestor, that does not make them necessarily at the same layer or status in the taxonomic scheme. Correct? The whole Kingdom Phylum Class Order Family Genus Species thing.

Breathe Exhaust said:
Quote:
How do I assume to much? I'm far less qualified to say where monitor lizards fit into the overall picture than some others on the list.
Oops, it appears I'm the one doing the assuming. You spoke so authoritatively I thought you knew more about the subject than I. Guess I was wrong.

Darwin's Finch said:
Quote:
I missed the Komodo Dragon bit quoted above. Komodo Dragons (Varanus komodoensis) are in a completely separate reptile lineage from archosaurs. Within Reptilia, there is a branch known as Sauria. [Lengthy list of technical terms deleted.]

So, the short answer is that Komodos are only distantly related to dinos and pterosaurs.
Um, right. So I ask a question, then don't understand the answer. All those dang terms are confusing and hard to keep straight. Which is the whatsit after the thingabob?

Within Reptiles, there is a branch that then has two branches - one leading to dinosaurs, pterosaurs, crocodiles, and birds; the other leading to monitor lizards (komodos, iguanas, etc) and various other extinct forms.

More info on Komodo Dragons was found with a quick google search.

Quick overview: http://www.scz.org/animals/d/komodo.html
Quote:
Diet
Wild: anything they can catch, favorites include deer, goat, wild boar and even smaller komodos, will eat carrion
At SCZ: rats and mice
informative story form article (lengthy):
http://www.sciam.com/article.cfm?art...A8809EC588EEDF

jimbobboy, it is a monitor lizard (iguanas are monitor lizards), so I think so.
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  #47  
Old 01-13-2003, 08:54 PM
Geobabe Geobabe is offline
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Quote:
Originally posted by DrDeth
Yes- they are more or less big lizards, and are carnivourous. They like goat. They would eat you, given the chance, although they do not "hunt" humans for food normally.
Totally off topic, but...I believe I read somewhere that a foreign potentate gave America some Komodo dragons. Is that true?
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  #48  
Old 01-13-2003, 09:10 PM
Darwin's Finch Darwin's Finch is offline
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Quote:
Originally posted by Irishman
Um, right. So I ask a question, then don't understand the answer. All those dang terms are confusing and hard to keep straight. Which is the whatsit after the thingabob?

Within Reptiles, there is a branch that then has two branches - one leading to dinosaurs, pterosaurs, crocodiles, and birds; the other leading to monitor lizards (komodos, iguanas, etc) and various other extinct forms.
Well, that is rather what I said; I just gave the names of the branches as well

Although, to ammend your clarification: within Reptiles, there is a branch which then has two branches - one branch leads to dinosaurs, pterosaurs, crocodiles and birds; the other leads to another group which in turn contains monitor lizards, etc. That is, Komodos are several branches deep within this other branch.
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  #49  
Old 01-13-2003, 11:27 PM
Zappo Zappo is offline
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Quote:
Originally posted by Geobabe
Totally off topic, but...I believe I read somewhere that a foreign potentate gave America some Komodo dragons. Is that true?

<hijack>

Yes. The former premier of Indonesia, Sukarno, gifted this country with two Komodo dragons some years back. They're now residing at the National Zoo in Washington.

</hijack>
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  #50  
Old 01-14-2003, 08:39 AM
Rue DeDay Rue DeDay is offline
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<continued hijack>

If you were in the vicinity of Cincinnati.....you would take the kiddos to the Cincinnati Zoo, and there you would see two Komodo dragons....the world's largest living lizard. (Even if they don't look like Oriental robes or breathe fire.)

</continued hijack>
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