"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."
In other words, Birds are closely related to Dinos. Birds may be descended from Dinos. But the real reason why “birds= dinos” is because Padian’s & May *defined * them as such, just recently. Padian’s & May decided to bring back a scientifically disused term and redefine it.
It’s a bit like if we found a new subspecies of horse and named it “Eohippus”, or name a new species of monitor lizard “Brontosaur”.
So, yes, “birds= dinosaur” but “dinosaur” no longer means what it once meant. They just redefined the word. I don’t know why, perhaps to push a scientific theory (such as Bakker’s insistance that Dinos were all warm-blooded). But in any case, it was stupid to do so. “Dinosaur” already had a strong meaning to most non-scientist dudes, and that meaning did not include birds. Dinosaur had no real scientific meaning for around a hundred years. There was no need to resurrect and redefine a term that already had meaning to the common man. Sure, perhaps they wanted a term for a grouping that included Aves, Saurischia and the Ornithischia, but there was no reason to make that term “Dinosauria”.
Emphasis added. I’m not sure if you’re saying this or not, but it sounds like you’re trying to define a paraphyletic clade. Isn’t that a contradition? I clade, by definition, is monophyletic.
DrD: That gets a “yahbut” from me, and I’m typing from memory without cites here, so I’ll look forward to someone confirming or correcting my comments:
The overwhelming majority of paleoornithologists concur that the bird ancestor is to be found among the dinosaurs, or in the immediately allied archosaurs (what used to be called “thecodonts”) that were ancestral to both groups. There are dissenting views that place the bird ancestor among the primitive crocodilians and the prolacertiforms, and one bizarre hypothesis based in morphological adaptations that is founded neither in paleontological nor biomolecular evidence that suggests they are the sister group to the mammals – but these are “fringey” views compared to the “dinosaur or his uncle” group, which seems to have something close to consensus support.
Accordingly, taxonomically they fall into the same clade.
In traditional Linnaean taxonomy, a definition is not required to describe a group. Groups are diagnosed by certain characters, but little, if any, thought is given to what else should belong in a given taxon based on relationships. To the extent that it does so today, it has borrowed from cladistics.
Cladistics uses both definitions and diagnoses, as I explained in the linked thread. Definitions are largely made so that people know what organisms ought to be included in a group, whether or not all members are actually known. By defining “Dinosaur” in a cladistic sense, it has scientific meaning, rather than just saying, “any large, terrestrial reptilian from the Mesozoic”.
The definition of “Dinosaur = most recent common ancestor of Passer and Triceratops, and all its descendants” is not arbitrary. It was already shown that Ornithischia + Saurischia constituted a monophyletic clade, and that clade was called Dinosauria, much as it had always been (the disagreements between the 1880s and 1970s were basically whether Dinosauria was, in fact, monophyletic, but the definition of Dinosaur = Ornithischia + Saurischia was still accepted, even if it was considered informal during that period). The key redefinition came with the inclusion of birds in that group, as it had only more recently begun to be established that birds were descendants of theropods. And, since theropods were in turn members of Saurischia, birds ought to be placed therein as well. The one benefit Padian & May’s definition has over the proposed Iguanadon and Megalosaurus reference points is that birds become explicit members of the clade, rather than implicit ones.
See, the thing is, Dinosauria today means essentially the same thing it has meant all along, both in scientific terms and “enlightened layman” terms (I exclude those laymen who insist on lumping everything vaguely reptilian in the group, for example the aforementioned Dimetrodon). It just now has a more exact, and scientifically valid, meaning.
And I really don’t see why that’s a bad thing. Other workers are free to re-examine the group at any time and come to the conclusion that the group is really polyphyletic (which would be the case if birds did not, in fact, descend from theropods), or paraphyletic (if it were to be shown that, for example, the origins of Pterosauria lay within the clade), or that it really is monophyletic as is currently claimed. So long as the evidence is there, scientists will eventually come around.
No, I’m saying that in taxonomy which pays attention to cladistics (which in my opinion it should), there may be appropriate uses for paraphyletic groups – recognizing that they are not full clades. My “fish” and “dinosaur” examples are good ones – “Vertebrates that are not tetrapods” and “Ornithischians and saurischians that are not birds, and which became extinct in or before the K-T event” are useful definitions of something quite practical to discuss. An angler or a tropical fish fancier is perfectly well aware that his shark, gar, lungfish, or lamprey is not quite a standard teleost – but it’s a “fish” by a reasonable definition that omits jellyfish, squids, polychaete worms, lancelets, etc. The 11-year-old who has developed a “thing” for paleontology knows the difference between a dinosaur and a Dimetrodon, a mammoth, a baluchitherium, a plesiosaur, or other extinct big beasties that are not dinosaurs – but he’s not actively interested in including an English sparrow or a woodpecker in his dino statue collection.
To talk intelligently about those parts of a clade that exclude a more highly developed and specialized, widely radiated crown group, is not an improper thing to do. There are a number of useful statements that can be made about, e.g., non-ruminant artiodactyls, non-myomorph rodents, “Ornithopods” (bipedal ornithischians), or chondrosteans and holosteans (the earlier two radiations of actinopterygian osteichthyes). The key point is to note that you are intentionally excluding crown groups from the various clades.
That was essentially my point. I respect cladistic analysis (with minor reservations already mentioned); my problem with it lies solely in the fact that it makes identifying degree of relationship more difficult. But not every useful natural group is ipso facto a clade – some are products of an earlier radiation successfully adapted for a given set of niches, one unit of which went through another explosive radiation to fill an entirely different set of niches. Aquatic gill-breathing fin-bearing endoskeletal vertebrates constitute a useful group – even though not a clade, because they in turn gave rise to the tetrapods. Pigs, peccaries, hippos, and oreodonts do constitute a group with common characters – even though they in turn gave rise to tylopods and ruminants.
Dinosauria hardly “means essentially the same thing it has meant all along”. Until just a decade ago, it did *not * include birds. And, dinosauria was rather inexact when Owen came up with the name in 1842- only three dinos were known, and he apparently didn’t notice the significant difference between Saurischia and the Ornithischia, which isn’t suprising as he had so little to look at. So, really “dinosauria” had no real definition (not enough specimens) until there was no more “dinosauria” as of 1888. It’s quite possible Owen would have thown the pelycosaur Dimetrodon and the winged pterosaurs into “dinosauria”, had he known of them- or more likely he would have excluded Megalosaurus. Then from 1888 to 1993, dinosauria had no real scientific meaning. So 'all along" would be for some 13 years. And, between that time, the term “dinosauria” meant to most dudes= “The term dinosaur is sometimes used informally to describe other prehistoric reptiles, such as the pelycosaur Dimetrodon, the winged pterosaurs and the aquatic ichthyosaurs, plesiosaurs and mosasaurs, although technically none of these were dinosaurs.” (Wiki)
And, why is it a “bad thing?”
Here’s a quote from Wiki: "*Using the strict cladistical definition that all descendants of a single common ancestor are related, modern birds are dinosaurs and dinosaurs are, therefore, not extinct. Modern birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs.
However, referring to birds as ‘avian dinosaurs’ and to all other dinosaurs as ‘non-avian dinosaurs’ is cumbersome. Birds are still referred to as birds, at least in popular usage and among ornithologists. It is also technically correct to refer to birds as a distinct group under the older Linnaean classification system, which accepts paraphyletic taxa that exclude some descendants of a single common ancestor. Paleontologists mostly use cladistics, which classifies birds as dinosaurs, but some biologists of the older generation do not.
For clarity, this article will use ‘dinosaur’ as a synonym for ‘non-avian dinosaur’, and ‘bird’ as a synonym for ‘avian dinosaur’ (meaning any animal that evolved from the common ancestor of Archaeopteryx and modern birds). The term ‘non-avian dinosaur’ will be used for emphasis as needed. It should be noted that this article’s definition of ‘bird’ differs from the definition common in everyday language; to most non-scientists, a ‘bird’ is simply a two-legged animal with wings and feathers."*
Those three cumbersome paragraphs are why “it’s a bad thing”. When we ask the question “Why did the dinosaurs go extinct?” (and excellent question even today), having to add the ridiculous term “non-avian” before the word “dinosaur” is why it’s a bad thing. Having some pedantic asshole correct you when you talk about the “extincion of the dinosaurs” by saying “Birds are not extinct thus you are wrong in your very premise that dinosaurs are extinct” is why it’s a bad thing. Having laymen think that scientists are a bunch of loonies when scientists say “birds are dinosaurs” is why it’s a bad thing.
And, there’s no plus side. Well, sure, it does point out the close relationship of Aves, Saurischia and the Ornithischia, but so would a new term for the Superorder. ( “Ornsauraves” )Thus, there are NO good reasons for the “new/old name” and at least four strikes against it.
Not to mention- It’s stupid, it’s silly and it’s pedantic.*
*So was the renaming of Eohippus IMHO, as the animal is far closer to a “dawn horse” than a “Hyrax-like beast” Hyracotherium. Richard Owen who found the first bones 1841, actually suspected that *it was a primate due to its teeth, * instead of the “very first horse”. Not to mention, Eohippus is a lovely name, while Hyracotherium is harsh. Owen may have found the first bones, but he had no idea what it was he found. If we are going to go by “first described” then it’s still “Felis Leo”. One way or the other.
OK. I didn’t think so, but it wasn’t clear from that post.
I’m still struggling to understand what relationships you think are being obscured. I guess it depends on which relationships you consider to be important. The fact that X and Y look alike are not, to me, important.
But that’s not correct. It’s not “gill-breathing fin-bearing endoskeletal vertebrates” that specifically gave rise to tetrapods, but a certain type of “gill-breathing fin-bearing endoskeletal vertebrates” that did. To the extent that the whole group gave rise to the tetrapods, that will be recognized by the larger clade that includes all those “gill-breathing fin-bearing endoskeletal vertebrates” + the tetrapods.
It did however, include Ornithischia + Saurischia, which was my point. And birds have been recognized since the discovery of Archaeoptyerx fossils in 1861 to share an affinity with what was then considered to be “dinosaurs”. So whether they were actually considered dinosaurs at that point is largely irrelevant. There were creatures known by most as “dinosaurs”, and there were creatures known by everyone as “birds”, and Archaeopteryx fossils showed the two were very similar – possibly even related.
Inexact or no, Owen did come up with the name Dinosauria to describe the three then-known representatives. Other fossil reptiles were subsequently found which were placed in that group. In 1888, the known dinosaurs were divided, by Seeley, into Ornithischia and Saurischia. While he may have advocated disbanding Dinosauria as a clade, it was too late to abandon the term altogether. Since then, of course, even more specimens have been found, and those specimens have verified that both Saurischia and Ornithischia are monophyletic, and that the two groups are closely related, and, having been derived frmo a common ancestor, constitute a monophyletic clade. Thus, Owen was right all along on this point, and Seeley was wrong.
Doubtful, as the genus Dimetrodon was named by Cope in 1878, and was not classified as a dinosaur by anyone at the time (and if anyone would have done so, it would have been Cope! Rather, he classified it as a sphenacodontid). The first pterosaur fossil was discovered in 1784, so they were known (if poorly understood) when Owen coined the name Dinosauria. He did not place them within it.
Not surprising, as “Dinosauria” had been effectively dismantled by Seeley. Once the name lost footing in the scientific community, it became a dumping ground. However, the key point is that Seeley was wrong. Once the group was re-examined and found to be monophyletic, and therefore, a valid clade, the name Dinosauria was restored (as was proper, given rules of nomeclature priority), and all those hangers-on were evicted. The continued informal usage is a holdover from the fact that it tends to take time for the general public to catch up to scientific discoveries.
Those paragraphs are cumbersome because the person who wrote them used cumbersome language. As Polycarp has remarked, there are times when it is occassionally useful to refer to paraphyletic groupings. “Non-avian dinosaur” is an example of such. Non-avian dinosaur = All of Ornithischia + (Saurischia - Aves). It can be useful to refer to that group as it specifically excludes a group of animals that constitutes a single clade in itself, with its own set of synapomorphies (shared, derived characters). “Non-avian dinosaur”, then, is any dinosaur that does not share those characters. Birds are generally just called birds (or avians)…I have rarely, if ever, seen “avian dinosaur” in the literature.
As for the question, “Why did the dinosaurs go extinct?”, I think it’s perfectly valid to be pedantic in such a case, as it sheds new light on the issue: non-avian dinosaurs did go extinct. ALL of them. BUT, the avian ones did not. Why? IF birds are truly dinosaur descendants, then it cannot be said there was anything inherent in dinosaur-ness that resulted in the extinction, as there were survivors. And that is every bit as important to point out as the fact that none of the traditional dinosaurs survived. Advancing the field, and all that. New data ought to be incorporated, and the fact that some remnants of the dinosaur clade survived is damned interesting.
I suspect you then feel it is also “stupid, […] silly and […] pedantic” to consider humans “apes”. The bottom line is this: priority rules apply: Owen coined Dinosauria. Modern research has verified the monophyletic nature of Owen’s clade. Modern research has shown that Aves lies within that clade. No need to come up with a new name, as one already existed. Aves still exists as its own clade. The only thing that has changed is the composition of Dinosauria, and that was only to bring everything in line with what had been suspected for over a century: that birds and dinosaurs (of the non-avian variety, of course ) were related.
I agree that Eohippus is a more elegant name for the critter, but Owen knew the rules, and he should have researched a bit more fully before assigning a name to a critter which already had one. Nevertheless, it happens. Laelaps was a nice name, too; unfortunately, it already belonged to a beetle so priority fell to Dryptosaurus.
Er…this needs to be corrected. I’m not sure what the hell I was thinking here…
Owen found the first fossils, and named the critter Hyracotherium in 1840-1841. O. C. Marsh later (~1876) found a complete specimen, and named it Eohippus. Marsh’s name stuck until it became clear that what Marsh found was the same critter that Owen had found two and a half decades earlier, at which point priority rules dictated that Owen’s original name be used. Wortman in 1896, Trouessart in 1898, and Matthew is 1899, to name a few, published data supporting the synonmous nature of the two genera. That Eohippus persisted into the 20th century is but another example of the delay between scientific findings and their acceptance in popular literature (though there were, admittedly, papers published which also attempted to re-validate the name Eohippus, even as late as 1999).
)Thus, there are NO good reasons for the “new/old name” and at least four strikes against it.
) were related.