To B.b. or not to B.b — or — So what is a “genus” anyway?

September 12, 2009

Introduction

Back when the Xenoposeidon paper came out, we suggested that Xeno could be the first repesentative of a new sauropod “family”, and then discussed at some length: what is a “family” anyway? Now that the Brachiosaurus paper is out, and I’ve argued that the species “Brachiosaurusbrancai is generically distinct from Brachiosaurus altithorax, it’s time to talk about what a genus is (and so what “generically distinct” means).

In an unnecessarily snarky aside at the end of the last entry, I implied that Randy Irmis would be the one to say that, because my phylogeny recovered “Brachiosaurusbrancai as the sister taxon to Brachiosaurus altithorax, it could and should remain in the genus Brachiosaurus, irrespective of the morphological differences between the genera.  He didn’t quite do that — although Daniel Madzia very nearly did — but Jaime Headden certainly did over on the Dinosaur Mailing List, and even ended up asking: “So my question is this: Why do we need Giraffatitan, and cannot have a Brachiosaurus proteles etc.?”

There are plenty of possible responses to this, but before we plough into that, here is a pretty picture:

Ligament rugosities on the neural spines of Brachiosaurus dorsals

Brachiosaurus altithorax holotype FMNH P25107, presacral vertebrae 5-7, neural spines in right posterolateral view

Brachiosaurus altithorax holotype FMNH P25107, presacral vertebrae 5-7, neural spines in right posterolateral view

The more retentive among you SV-POW! veterans might remember way back in the very first month of this blog when I showed you what I said were the last four presacral vertebrae of the Brachiosaurus altithorax holotype FMNH P25107.  Actually, I don’t know what I was thinking — they were presacrals 4-7, not 1-4, but that’s not the point.  The point is that Mike From Ottawa (whatever happened to him?) asked about the very rugose anterior surfaces of the neural spines, and I replied:

What the photo doesn’t show (but if you stay tuned long enough you’ll probably see one that does) is that the posterior faces of the neural spines have very similar rugosities. In life, these would have been the anchor points for epaxial muscles and ligaments. In Brachiosaurus altithorax (but not B. brancai) these have a distinctive inverted-triangle shape. In the most posterior pair of B. brancai dorsals, which are co-ossified, the ligament joining their neural spines is itself ossified. Picture to follow some time, I guess :-)

I am finally following up on the first half of that promise: the picture above shows the three most anterior of those same four presacral vertebrae from the Brachiosaurus altithorax holotype, but this time in right posterolateral view, so you can see the posterior faces of the neural spines.  And you’ll notice that on the back of each spine, as well as on the front, there’s a large and extremely rough inverted triangle.  I’ve yet to see anything at all like that in any other sauropod — Giraffatitan and the Archbishop included.  Very distinctive.

Right then — back to genera!

Rampant genera on the loose!

Here’s a practical reason to reject the idea that if two taxa are sisters, then they should be regarded as congeneric: Jaime wants to retain the species brancai within Brachiosaurus because it is (in the current analysis) the sister to the type species Brachiosaurus altithorax.  He then wants to put the species proteles into Brachiosaurus because the species we all know as Sauroposeidon proteles is (presumably) the sister to the Brachiosaurusaltithorax-and-brancai clade.  But by induction, if we accept Jaime’s policy, whatever is sister to that clade must also be subsumed into Brachiosaurus, so that we end up losing Titanosauria, Camarasauridae, Diplodocoidea, etc. — Diplodocus carnegii becomes a species of Brachiosaurus.  The good side of this scheme is that eventually, we’ll work our way up to the base of Amniota, at which point I become a member of the species Brachiosaurus sapiens.  That, I could get on board with.  But in other respects, this classification would not be so hot.

I’m assuming that no-one really wants this, and so that advocates of the Sister-Taxa-Are-Congeneric school (hereafter STAC) recognise that you have to draw a line somewhere.  But where?  And how do you choose where?  [Only time will tell whether I just coined an AHATWNUABPANTA.]

How to choose between specific and generic separation

At this point, I am reminded of when I used to be on a mailing list for wannabe writers. Lots of dogma on that list — people saying “don’t overdo adverbs” and “make sure you have enough incidental detail” and so.  People trying to nail down an algorithm for good writing.  But the best advice I saw on that list was from Jane MacDonald: “My personal advice is don’t overdo, or underdo, anything in your writing.  Do it exactly right.”(*)  That’s my attitude to drawing genus boundaries.  It is, frankly, an art; and there are no substitutes for taste, experience, judgement, familiarity with the group in question and all those other touchy-feely qualities that uber-cladists would love to find a way to abolish if they could.  But they can’t.  There is no algorithm for this.  I also think of an observation by computer scientist Bjarne Stroustrup, the inventor of the C++ programming language: “Design and programming are human activities; forget that and all is lost.”  The same is true of palaeontology.  (And of, well, everything.)

Here’s the thing, folks: a genus, just like any other taxon, is there to be useful.  Its purpose is not to conform to a dogma, but to inform and enlighten.  In the new paper, I wrote that “generic separation is warranted since the two species are more different from each other than, for example, Diplodocus and Barosaurus Marsh, 1890″ (Taylor 2009:798).  I stand by that as a great way to figure out when the morphological differences  between two species merit generic separation: it’s all about conveying degrees of difference.  And, yes, of course I know that the morphological extent of a genus in sauropods is completely different from its extent in, say, botany, where the genus Quercus (oaks) has 700 species or something stupid.  Yes, I fully accept that there is no rigorous and absolute standard by which we can determine The Right Place to drop a genus boundary.  Sure.  But that doesn’t let us out from the responsibility of making the best judgements that we can, based on relevant prior art, recognised conventions, congruence with similar decisions and — there it is again — good taste.

(*) Actually, that is only the second best advice I saw on the wannabe writers’ mailing list.  The best advice of all came second-hand, and was passed on by Greg Gunther: “I was on an [email] list with Tom Clancy once.  Mr. Clancy’s contribution to the list was, ‘Write the damn book’.”  Top advice.

Nomenclatural stability

And so finally I come to Randy’s comment.  In response to his question, I guessed that when I put them all in a matrix together, the Archbishop will form a clade with Brachiosaurus, and Sauroposeidon with Giraffatitan.  Like this: ((Brachiosaurus altithorax, “The Archbishop”), (Giraffatitan brancai, Sauroposeidon proteles)).

,–Brachiosaurus altithorax
,<
/  `–“The Archbishop”
<
\  ,–Giraffatitan brancai
`<
`–Sauroposeidon proteles

And Randy said:

For the sake of discussion, if the topology is as you say, then I do support the generic separation of altithorax and brancai. Now, of course, as you might surmise, if the two sub-clades are well-supported, I would also advocate putting altithorax and the NHM Tendaguru taxon in the same genus, and brancai and Sauroposeidon in the same genus.

Now I yield to no man in my respect for Randy, whose work exceeds my own humble output by a truly humiliating factor, and who makes it even worse by being such a nice guy.  But I hope he will not take it the wrong way if I say that here, he is talking the purest arsegravy.  Suppose the topology came out the way I guessed, and we adopted his suggested nomenclature.  Then five minutes later Paul Upchurch comes along with a new analysis that finds the Archbishop closer to Giraffatitan after all: and suddenly Brachiosaurus archbishopus becomes Giraffatitan archbishopus.  Five more minutes pass and Jeff Wilson publishes his new phylogeny, in which “Sauroposeidonproteles is sister to Brachiosaurus altithorax, and so what was briefly Giraffatitan proteles becomes Brachiosaurus proteles.  Later that afternoon Jerry Harris shows that Cedarosaurus is more closely related to Brachiosaurus altithorax than the species proteles is: at this point, presumably, either Cedarosaurus gets sunk into Brachiosaurus, as B. weiskopfae, or My Big Fat Brachiosaurus Genus gets smashed up and suddenly, woah, proteles needs its own genus after all and Sauroposeidon is back!

Hands up who wants to deal with tracking all that nomenclatural shifting back and forth?  Hmm, thought not.  Folks, when we name a new species of an existing genus we are betting the nomenclature on the phylogenetic hypothesis.  This is just a dumb thing to do in this day and age — especially if you work on dinosaurs which (A) are big and usually very incomplete and so their positions can’t  be known with certainty; (B) are trendy enough to be subject to a stream of new phylogenetic analyses; and (C) are in a field where pretty much everyone seems to be hot for mandatory monophyly of genera.

So I end with a plea: unless you know for certain that your new taxon is super-closely related to the type species of an existing genus, and unless you are sure that this isn’t going to change with subsequent discoveries, please put your new species in its own monospecific genus.  That way, nomenclature is independent from phylogeny, which is surely how we all want it.  A new monospecific genus is essentially a uninomial that happens to be spelled with a space in the middle.  And uninomials are nice: they rescue us from Linnaeus’s dumb mistake in lumbering nomenclature with binomials.

This has been an Unwelcome Education Product.

Acknowledgements

Many thanks to Jim Farlow for suggesting the title of this post, which I have cheerfully stolen.  I have no idea whether he agrees with the arguments presented in this article.

References

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61 Responses to “To B.b. or not to B.b — or — So what is a “genus” anyway?”

  1. salva Says:

    I disagree with several points of your discussion (I guess, I´m on the STAC :P)

    Rampant genera. The rule of priority make that situation impossible. Of course it is possible to put on synonymy all genera except the ones named by Linneaus. I agree with you: the line must be somewhere, but the “rampant genera” argument is not a valid one.

    I do not think that nomenclatural stability is a good argument for monospecific genera. Monospecific genera not carry any information about the grouping of the species (which is the reason for binomials!). Biodiversity is so huge that usually we need more than the binomial to recognize the group (for instance, the family, etc.). Following your arguments, if there are no reason for a binomen, then there is no reason to families, or to name any clade (they are subject of suddenly change), so why to classify? A no classification schema would be perfectly stable.

    As a member of the STAC, for me, nomenclature and phylogeny are deeply attached. Nomenclature is a consequence of the phylogeny. The power of the periodic table, is that it produces a natural classification, we can know some about the fluor because is an halogen, even if we do not know any other thing. Biology is most difficult, but a nomenclature without accounting phylogeny is just random naming.

    As you cite Bjarne, and he always stress about code-reusability and generality (through inheritance of classes) in C++, I speculate that if in someway he can give a nomenclatorial advice, it would be keep the more general genera!

    Forgive for being so long :P, and by the way you run a wonderful blog :)

  2. Nathan Myers Says:

    Even better… Stop conflating genus name with phylogenetic position. Just give it a binomial, and leave it the hell alone. If it uniquely identifies something, it’s doing its job. If something that started out assigned a different genus name turns out to be closer, fine. Let it.

    Our brains are wired to remember names. Continually changing those names damages the apparatus we think with. It makes us unnecessarily even more stupid than we are already inclined to. The botanists who shoehorned hundreds of species into Q. aren’t stupid. Your approach works too. Thesis, antithesis, synthesis: just let be.

  3. Mike Keesey Says:

    “…at which point I become a member of the species Brachiosaurus sapiens…”

    I’m sure you know this, but the rules of priority would actually have FMNH P25107 as a member of Homo altithorax.

  4. Mike Taylor Says:

    Ah, poop. Mike Keesey is right, of course — what a downer. In that case, the last shred of a reason to support STAC is gone.

  5. Jaime A. Headden Says:

    Mike,

    ” Suppose the topology came out the way I guessed, and we adopted his suggested nomenclature. Then five minutes later Paul Upchurch comes along with a new analysis that finds the Archbishop closer to Giraffatitan after all: and suddenly Brachiosaurus archbishopus becomes Giraffatitan archbishopus. Five more minutes pass and Jeff Wilson publishes his new phylogeny, in which “Sauroposeidon” proteles is sister to Brachiosaurus altithorax, and so what was briefly Giraffatitan proteles becomes Brachiosaurus proteles. Later that afternoon Jerry Harris shows that Cedarosaurus is more closely related to Brachiosaurus altithorax than the species proteles is: at this point, presumably, either Cedarosaurus gets sunk into Brachiosaurus, as B. weiskopfae, or My Big Fat Brachiosaurus Genus gets smashed up and suddenly, woah, proteles needs its own genus after all and Sauroposeidon is back!”

    Your solution is simple, elegant, and requires no new taxonomy except defining the individuals and determining how the species relate:

    Brachiosaurus altithorax, B. brancai, B. proteles and your fictional B. “archbishopus”. This requires no messy moving species around i9nside concordant containers with any other species. It also reinforces the problem with erecting the “genus” and assuming it exists separate from the species (the problem exists in all mandated RANKS, and I am surprised you didn’t mention the word in your entire post, when that is the only use the term GENUS has received in relation to this nomenclature. Your issue, when affirming use of genus, is to support the meaning of genus (you dance around this here, in the paper, etc., and this is understandable given how difficult it should be to support use of genus without supporting ranks, and the concordant problems).

  6. andy Says:

    While Quercus does have an impressive number of species, I’ve always been impressed by how every single type of monitor lizard, from the pygmy goanna to the Komodo dragon, is lumped into the genus Varanus.

  7. Mike Taylor Says:

    Jaime:

    let me be clear on what I’m trying to achieve here — what I really want is uninomials, so that I don’t have to go messing with the name whenever the phylogeny changes. There are two ways to do that:

    — one is to treat the genus+species combination as a uninomial, by making genera monospecific;

    — the other is to pour all the species into a single genus and the ignore the genus name completely and treat the species name as a uninomial. I assume that’s what oak specialists do over in the botany class.

    The latter solution is fine so long as all the species remain within the big clade that the genus defines. The problem comes when one of the Quercus species turns out to be more closely related to Lithocarpus, or a Fagus species turns out to be more closely related to Quercus. At that point (if you want to insist on monophyletic genera, as it seems most people do), you have to move the species in question, and that means its binomial changes — which is just what I’m trying to avoid.

    If instead we treat the genus name (rather than the species name) as the uninomial, that problem doesn’t arise: Giraffatitan could turn out to be highly derived clam that is merely convergent on true brachiosaurs, and its name would remain Giraffatitan. That is a very desirable property: a name is a label, and we shouldn’t switch labels.

    Salva:

    “I do not think that nomenclatural stability is a good argument for monospecific genera. Monospecific genera not carry any information about the grouping of the species (which is the reason for binomials!).”

    You are conflating naming (which should remain constant forever) with phylogeny (which cannot and should not remain static). There is a huge difference between “It turns out that Giraffatitan is a somphospondylian closely related to Euhelopus” and “It turns out that Brachiosaurus brancai is a somphospondylian closely related to Euhelopus zdanskyi, and so it must be renamed Euhelopus brancai“. Change your phylogenetic hypothesis all you want — it’s all good. Just leave the names alone, so I can understand what your new phylogenetic hypothesis actually is.

    No, indeed: as you say, monospecific genera do not carry any information about the grouping of the species. And that is as it should be. Neither do they carry information about the estimated mass of the animal, and that is also how it should be. I don’t want Giraffatitan to change its name from Giraffatitan 30 tonnes to Giraffatitan 25 tonnes when its mass is recalculated to take pneumaticity into account — so why would I want it to change to Euhelopus brancai when its position in the phylogeny is recalculated? Names are for naming.

  8. Andreas Johansson Says:

    I do not think that nomenclatural stability is a good argument for monospecific genera. Monospecific genera not carry any information about the grouping of the species (which is the reason for binomials!).

    And that’s why binominals are bad – they force us to make claims about things we might prefer not to.

    Would it help anyone if everytime anyone refered to Gorilla they had to specify whether it belongs to Pongidae or Hominidae?

  9. Andreas Johansson Says:

    xpost with Mike.

  10. Mark Wildman Says:

    Great post again Mike. This has come just right for Bristol, so much so that I think I’ll follow you around and watch from a safe distance. It’s gonna be fun…..

  11. Tor Bertin Says:

    This’s sorta an extension on a comment I made on a similar topic at the Archosaur Musings, but I always couldn’t help but wonder just how we would classify Candids were we to have no extant analogues and only fragmentary bits of bone to work with. Their size range is astounding (doubly so when you include the domesticated dog); yet they’re all part of the same genus.

    Not that I’m suggesting that your paper on B.b. is wrong by any extent (you did a great job with it), but I can’t help but feel that sometimes the rush to name a new genus is a bit extreme and unwarranted; specifically when the characters used are 95% size-based (for a comical example, what would happen if we found a poodle skull and a great dane skull in a single formation, without knowing the identity of the domesticated dog? We know now that they’re part of the same species, yet by the looks of them surely they are recently split sister taxa!).

    Though of course that’s complicated through the fossil record, where remains are almost always fragmentary. Compare the number of fossils found to the number of organisms that probably existed, and I’m amazed (and honestly pretty thrilled) that we can create some kind of order within it at all.


  12. Tor Bertin Says:

    (though… I suppose on a certain level the poodle and great dane are sister taxa!)

    Does the sister taxa definition extend within a species level, given that the domesticated dog in all forms stems from roughly a single group?


  13. “I implied that Randy Irmis would be the one to say that, because my phylogeny recovered “Brachiosaurus” brancai as the sister taxon to Brachiosaurus altithorax, it could and should remain in the genus Brachiosaurus, irrespective of the morphological differences between the genera. He didn’t quite do that — although Daniel Madzia very nearly did […]”

    Nope:o) My comment was actually very far from “nearly”, Mike;o) In your previous post you wrote that “[“Brachiosaurus” brancai] must be placed in its own genus,” which I disagree with, but not because these two taxa (G. brancai [note that I use this combination] and B. altithorax) were found to be sister taxa in your phylogenetic analysis. The reason why it’s not necessary is that genus is – generally – a box of unlimited size (and doesn’t need to be monophyletic). It didn’t and doesn’t mean that I don’t buy your conclusions. I do because (1) your paper (not your analysis; I sill think it was unnecessary in this case) persuaded me that these two taxa differ from each other more than other taxa that sit within their own genera do (though any statement à la “G. brancai and B. altithorax differ from each other more than Barosaurus does from Diplodocus” is still just a taxonomic marketing:o)), and also (2) because of another reason that I don’t want to discuss here further (at least for now):o)

  14. Jaime A. Headden Says:

    Just to make sure, Mike didn’t actually name <Giraffatitan, he’s just supporting it on what I think are superficial and excessive grounds. As Tor Bertin above say, one could easily argue that a Great Dane and a poodle are more distinct from one another than a “species” of bird might entail. If any such difference means we should make any taxonomic level a uninomial (as Mike wishes) we need to know where to start this, otherwise subspecies, varieties, etc in nature all become fair game. This “metric” (as Tom Holtz likes to use it, a genericometer) has so far been a relative yardstick for the researcher’s ego — this time supporting the argument above that researchers are prone to knew names for the sake of exposure, not because a species needs a uninomial.

    And let us not get into the issue that Mike actually named these as bionomial compoundsa of a species and genus, as he specifically used the phrases dealing with specific and generic differences in the relevant taxa. If the utility of Brachiosaurus brancai and Giraffatitan brancai are the exact same, but the name “Giraffatitan” is not in general use because of a variety of reasons, elevation of it to some perceived rank of viability becomes excessive, and the paper does not reason why generic distinction is somehow better for a name than specific.

  15. Tor Bertin Says:

    To clarify, I wasn’t singling out Mike specifically; just commentating on a broad issue that seems to be somewhat related to the discussion at large.

  16. Tor Bertin Says:

    Mike, just read the last portion of your post–I find myself very much agreeing. The gap between modern species and generic relativity and what qualifies as a distinct genus in modern paleontology is somewhat frustrating, but for the sake of a good means of comparison (which really is what all of this discussion is about–clade, genera, species are all concrete ways to think about an abstract concept) renders such a high degree of generic separation probably necessary unless you want to redo the system from scratch.

  17. Zach Miller Says:

    Dealing with fossil animals is an additional hassle because you don’t have soft-tissue structures to differentiate them. Different species of modern birds can be diagnosed based on plumage or minor differences in beak shape (which might not be reflected in underlying osteology). Paleontologists don’t have that luxury.

    My own rule of thumb, as a paleo-artist, is that if the skeletal differences between two closely-related taxa warrant a change in outward appearance, it’s a different genus (that includes proportional differences, so Brachiosaurus and Girrafititan are “valid” under this scheme). However, if the skeletons don’t differ enough to reflect a differing outward appearance, but they are regionally disparate, that’s a species separation.

    Not very useful in a strict sense, but it helps me sleep at night. :-)

  18. Matt Says:

    The Brachiosaurus altithorax/”Brachiosaurus” branci is one of the most interesting debates going on dinosaur phylogenetics. Correct me if I’am wrong, I thought sauropod species were classified according to species by their dorsal vertebrae. If this is the case B. altithorax and B./G branci seem to have some differences in their vertebrae to warrant the African species a sub species of brachiosaurs(Paul 1988).
    Could the differences between B.altithorax and “B” branci be similar to the problem seen in telling Tyrannosaurus rex apart from Tarbosaurus bataar? Carpenter considered the species so similar that he thought Tarbosaurus should be called Tyrannosaurus bataar. However as I’m sure you all know Jurum has a paper which shows the two species are different enough to warrant Tarbosaurus as it’s own valid genus.
    Either way the new paper on Brachiosaurus altithorax will hopefully open a new line of research on brachiosaurus and the brachiosaurids in general.

  19. Mike Taylor Says:

    Matt,

    There is nothing in a sense “special” about dorsal vertebrae such that species and genus determinations should be made upon them alone — but it is a fact that dorsal vertebrae are particularly diagnostic in pretty much all sauropods, and that those of Brachiosaurus and Giraffatitan vary more obviously than do, say, the femora of those two taxa. In general, these two differ from each other much more than do Tyrannosaurus and Tarbosaurus.

  20. M. O. Erickson Says:

    “Linnaeus’s dumb mistake in lumbering nomenclature with binomials.”

    I still use grades for my clades. I wholeheartedly agree with the fallowing, taken from Predatory Dinosaurs of the World:

    “At the other extreme, a few workers, such as Jacques Gauthier in his 1986 study of theropod-bird relationships (these days, we can replace the previous 15 words with “just about all workers”) hold forth that a taxonomic system should be based solely on phylogeny. In this system grade is avoided, so there are no classes, families, or the like; each name merely designates a major phylogenetic splitting point. Supposedly this is less arbitrary than the Linnaean system. But this is really only true if every two species are given [their own genus] name, something [that] is not workable. If instead reasonable judgments are made as to what splitting points will be named, then the system is really as arbitrary as any other. Even then, phylogeny-only classification systems are hard to understand because they lack equivalent rankings to guide one by. More importantly, as we traditional… workers like to say, ‘grade is as important as clade.’ So grade should and can be formally recognized in classification, as outlined above.”

    What can I say, I’m an evil Linnaean traditionalist.

  21. Jaime A. Headden Says:

    Mike Taylor wrote:

    “In general, these two differ from each other much more than do Tyrannosaurus and Tarbosaurus.”

    This is a frame of reference that deserves qualification. How much do these differ in, say, 1) gross anatomy, 2) general aspect, or 3) morphological characters? Note that 1 and 3 are not identical, as they differ in how a character/taxon is proscribed relative to other taxa and exclude autapomorphies, while the former permits autamorphies and mass/proportional differences that are or can be excluded from a matrix.

  22. M. O. Erickson Says:

    Hey, wait a second. My avatar with the little yellow creature- that’s my baby picture! Where’d you find it?

    *joke*

  23. M. O. Erickson Says:

    On a serious note, this is how I determine what is a genus and what is just a species:

    Step 1) Pick up a well-established extant genus (like Canis, Varanus, or Felis, the latter being the one I will use here).

    Step 2) Pick up your two extinct taxa (this example will use Brachiosaurus altithorax and Giraffatitan brancai, obviously).

    Step 3) Lay out all members of the extant genus in a nice little row (be it a mental or literal one).

    Step 4) Compare to your extinct taxa.

    Do the extinct taxa fall within the range of variation shown by the extant genus (Felis)? If so, you can conclude that your taxa represent species. Or do they fall outside the range of variation in the extant genus? If so, you can conclude that your taxa represent genera.

    Using this scheme, B. altithorax and G. brancai are indeed distinct. Tyrannosaurus rex and Tarbosaurus bataar, however, would probably come out cogeneric – especially if you happen to use a more variable extant genus, like Varanus. So would Ornithomimus velox and Struthiomimus altus. Thus we would end up with:

    Brachiosaurus altithorax

    Giraffatitan brancai

    Tyrannosaurus rex

    Tyrannosaurus bataar

    Ornithomimus velox

    Ornithomimus altus

    Now, I’m the first to admit this method is not flawless, but I think it serves the purpose well.

  24. Matt Says:

    Mr. Erickson,
    I think your idea your presented sounds very good. This topic is indeed getting more and interesting. Another thought that crossed my mind today on determing a genus and species, are the two species of African Elephant. The two were once considerd one species, however DNA test showed Loxodonta are now are a plains and a sub species forest elephant.
    Which raises more questions when this method is applied to dinosaurs. True, we can’t DNA test the animals, however it does complicate the fossil record even more. I would venture say there are more cogeneric species within dinosaur groups.

  25. M. O. Erickson Says:

    “Mr. Erickson,
    I think your idea your presented sounds very good.”

    Hey, thanks dude. :-)

  26. Tor Bertin Says:

    Unrelated, but I think basically anyone who visits here would appreciate this–

  27. Mike Taylor Says:

    M. O. Erickson,

    (Can’t we call you by your first name? Or is it just “M.”?)

    You method for determining whether to consider two species is congeneric is pretty good, but it does suffer from an important flaw: the degree of morphological closeness that is taken to indicate congenericity varies a great deal across the animal kingdom (and even more once you move into plants, as we saw above in the case of oaks), so what’s good for dogs might not be good for sauropods. (Can we even meaningfully evaluate whether two species of, say, slugs are “more different” from each other than two species of cat are?) So rather than comparing brachiosaur disparity with dog disparity, you really need to compare with disparity elsewhere in the sauropod tree. (Admittedly that’s tricky when they’re all extinct).

    In short, we can’t hope for correctness in any very rigorous sense. The best we can hope for is consistency: which of course is why I compared Brachiosaurus/Giraffatitan disparity with Diplodocus/Barosaurus.

    Regarding your other post and the quote from Greg Paul on the utility of ranks: as you’ll know if you’re a long-time SV-POW! reader, I have no objection to tentatively labelling particular clades as “family”, or whatever other rank you please — just so long as we all recognise that we do not mean anything objective by this, and we’re adding the label only as a helpful guide for those who use our work. A family — of extant animals but even more so with extinct ones — can never by anything more than a roughly outlined bucket containing a certain amount of disparity.

  28. Nathan Myers Says:

    Given the set of already assigned species names, would it introduce any ambiguity to take the Quercus approach, and call them all Sauropodus this and Sauropodus that? You could give each specimen a unique specific name and still be far better off than your typical entomologist. Anyway, have two sauropod specimens ever been found at one site, in one stratum? I’m doubting that any two found specimens could have interbred, even in principle.

    Enforcing congenericity and eliminating conspicificity would eliminate so many potential fights as maybe to force you all to pay attention to, you know, actual science.

  29. Mike Taylor Says:

    In principle, there is something to be said for the Quercus approach, in that it would give us uninomials. However, there are at least three problems:

    1. Lack of continuity with established names — good luck getting all the kids’-book authors to start writing about carnegii, excelsus and altithorax instead of Diplodocus, Apatosaurus and Brachiosaurus.

    2. Synonyms: in general it’s fine for multiple genera to have synonymous species, but once you synonymise all the genera, you’d have to rename conflicting species within the new megagenus. (I can’t think of examples offhand, though.)

    3. Boundary of Sauropodus. We can all be confident that the species altithorax and carnegii are soundly nested within Sauropodus, but what about the animals near the origin of the clade? If Yunnanosaurus turned out to be a sauropod after all (i.e. more closely related to Sauropodus loricatus than to Melanorosaurus readi), we’d have to rename it Sauropodus huangi); and if Sauropodus ingenipes turned out not to be a sauropod, it would have to go back to being Antetonitrus.

    For all these reason and more, if we were to formally convert our current nomenclature to a uninomial system (which by the way we all know is never going to happen), genera would be the only practical way to go. Better still, informally, that is the way things are going anyway!

  30. Michael. O. Erickson Says:

    “(Can’t we call you by your first name? Or is it just “M.”?)”

    Didn’t know full first name was required. Fixed.

    (Is there a “commenting rules” page anywhere? That would be helpful.)

    “You method for determining whether to consider two species is congeneric is pretty good, but it does suffer from an important flaw: the degree of morphological closeness that is taken to indicate congenericity varies a great deal across the animal kingdom (and even more once you move into plants, as we saw above in the case of oaks), so what’s good for dogs might not be good for sauropods. (Can we even meaningfully evaluate whether two species of, say, slugs are “more different” from each other than two species of cat are?) So rather than comparing brachiosaur disparity with dog disparity, you really need to compare with disparity elsewhere in the sauropod tree. (Admittedly that’s tricky when they’re all extinct).

    In short, we can’t hope for correctness in any very rigorous sense. The best we can hope for is consistency: which of course is why I compared Brachiosaurus/Giraffatitan disparity with Diplodocus/Barosaurus.”

    True, true. The main point of my proposed method is simply to use modern genera as guidlines for extinct genera, not necessarially that sauropods and dogs (or cats) would make a really good comparison.

    “Regarding your other post and the quote from Greg Paul on the utility of ranks: as you’ll know if you’re a long-time SV-POW! reader, I have no objection to tentatively labelling particular clades as “family”, or whatever other rank you please — just so long as we all recognise that we do not mean anything objective by this, and we’re adding the label only as a helpful guide for those who use our work. A family — of extant animals but even more so with extinct ones — can never by anything more than a roughly outlined bucket containing a certain amount of disparity.”

    It sounds like we are more like-minded than I thought. Basically, I feel that Linnaean ranks – while being wholly artifical – are helpful rather than harmful in taxonomy because, for example, they allow one to quickly and painlessly identify which clades are more inclusive and which ones are more exclusive (“Oh, that clade represents a ‘Kingdom’, therefore it’s more inclusive than the other clade, which is a mere ‘Family'”).

    One other thing – is your (very, very good) skeletal the first one ever made of Brachiosaurus altithorax? Having searched for a skeletal of it forever, it would certainly seem so.

    Okay, two more things – In the paper, you explain that B. altithorax probably had “somewhat sprawling” forelimbs. So what’s up with the parassagital forelimbs in the skeletal?

  31. Michael. O. Erickson Says:

    Sorry ’bout the long comment.

  32. Mike Taylor Says:

    Hi, Michael. No, first names are not required — it’s just that if I’m going to be directly addressing you, I prefer to use one than calling you M. O. Or guessing “Mr. Erickson” when you might really be Dr. Erickson and take offence :-)

    No, there’s no “commenting guidelines” page for SV-POW! — we’ve not needed one up to this point, the posts have not been attracting abusive comments. Hopefully it’ll stay that way!

    It sounds like we are more like-minded than I thought. Basically, I feel that Linnaean ranks – while being wholly artifical – are helpful rather than harmful in taxonomy.

    I do wish people who describe a thing as “wholly artificial” would not immediately conclude that the thing is therefore useless. My computer is pretty artificial, yet I’ve found it useful on one or two occasions! I think the use of ranks can be harmful, because they can mislead people into thinking we know more than we really do; but so long as we’re careful about that — so long as the ranks are our servants and not our masters — I agree that they can have a role.

    One other thing – is your (very, very good) skeletal the first one ever made of Brachiosaurus altithorax? Having searched for a skeletal of it forever, it would certainly seem so.

    As far as I can tell, yes, it’s the first and only Brachiosaurus altithorax reconstruction; if anyone knows differently, please tell. In fact, to the best of my knowledge, there has only ever been one life restoration of this species — it has been understandably overshadowed by the African species.

    Okay, two more things – In the paper, you explain that B. altithorax probably had “somewhat sprawling” forelimbs. So what’s up with the parassagital forelimbs in the skeletal?

    What makes you say the forelimbs in that reconstruction are parasagittal?

    … and, of course, your long comment is NOT a problem. Here, we welcome thoughtful discussion. Some things just can’t be said in soundbites.

  33. Michael. O. Erickson Says:

    “Hi, Michael. No, first names are not required — it’s just that if I’m going to be directly addressing you, I prefer to use one than calling you M. O. Or guessing “Mr. Erickson” when you might really be Dr. Erickson and take offence :-)”

    Ah, I see. He he.

    “No, there’s no “commenting guidelines” page for SV-POW! — we’ve not needed one up to this point, the posts have not been attracting abusive comments. Hopefully it’ll stay that way!”

    Yes-sir-ee.

    “What makes you say the forelimbs in that reconstruction are parasagittal?”

    Because the elbows are facing backwards. I take “somewhat sprawling” to mean that the elbows face outwards, like a crocodilyan’s – or like Janensch’s reconstruction of G. brancai.

  34. Mike Taylor Says:

    “What makes you say the forelimbs in that reconstruction are parasagittal?”

    Because the elbows are facing backwards. I take “somewhat sprawling” to mean that the elbows face outwards, like a crocodilyan’s – or like Janensch’s reconstruction of G. brancai.

    Well, “somewhat sprawling” doesn’t mean like a lizard — just a little out of the parasagittal plane. I think that’s quite compatible with allowing flexion of the elbow to move the forearm anteriorly.

    By the way, let me be clear that I am by no means convinced of this sprawling — as it happens, I didn’t modify the skeletal reconstruction to reflect this possibility, because it is only a possibility, and not one that I find particularly likely as it makes so little mechanical sense. But I really am perplexed by that laterally deflected glenoid articular surface of the coracoid — if anyone out there has ideas about it, I am ready to hear!

  35. Vertebrat Says:

    Maybe it’s too obvious to mention, but binomials save on memory – it’s easier to remember Quercus than 700 quercily-named monotypic genera. The tiny genera so common in dinosaurs are rather annoying to non-specialists who can’t remember where Futalognkosaurus goes.

    Going rankless neatly avoids this whole issue, since any containing clade is a legitimate “genus”. With rankless binomials, you can legitimately use whatever size of genus you please, or several at once for maximum helpfulness:
    Sauropoda/Brachiosauridae/Brachiosaurus/Giraffatitan brancai. (By the way, how do rankless binomials handle agreement with plural names? Primatis sapiens? Primates sapientes? Primates sapiens and watch the Latin speakers wince?)

    Given the set of already assigned species names, would it introduce any ambiguity to take the Quercus approach, and call them all Sauropodus this and Sauropodus that?

    I think the etymologically correct form is Sauropus. (It’s preoccupied by a plant, but who cares?) However that clade already bears the noble name of Sauropoda.

  36. Michael. O. Erickson Says:

    “By the way, let me be clear that I am by no means convinced of this sprawling — as it happens, I didn’t modify the skeletal reconstruction to reflect this possibility, because it is only a possibility, and not one that I find particularly likely as it makes so little mechanical sense. But I really am perplexed by that laterally deflected glenoid articular surface of the coracoid — if anyone out there has ideas about it, I am ready to hear!”

    Well, the only plausible explanation I can think of for the laterally deflected glenoid surface would be if the humerus were slanted a bit out of parasagittal plane (“semi-sprawling”). Not like a lizard, as you said, but sort of a very slight “half-pushup” posture. (I am thinking of a somewhat toned-down version of Janensch’s G. brancai, but if that’s a bad thought just let me know.) However, it is true that it makes little mechanical sense – but then again, Nature rarely conforms to our understandings and conceptions.

  37. Nathan Myers Says:

    The redoubtable David M. asserted that the notion of a slightly sprawling brancai, which I had suggested might provide better support against toppling sideways, was absurd on bone linkage grounds. Evidently it’s time for another cage match.

  38. Michael. O. Erickson Says:

    But about stress load on a sprawled humerus – just to make sure, are you remembering to take into account the musculature? The humerus would not be bearing the stresses all by itself.

  39. Michael. O. Erickson Says:

    “The redoubtable David M. asserted that the notion of a slightly sprawling brancai, which I had suggested might provide better support against toppling sideways, was absurd on bone linkage grounds.”

    Um – brancai, yes, but we’re talking about altithorax, which has a glenoid surface that is suggestive of a slightly sprawled posture.

  40. Michael. O. Erickson Says:

    In reference to the first of the two preceding comments – Not that I seriously think that you would forget to do that.

  41. Mike Taylor Says:

    Yes, consideration of musculature makes the mechanics of sprawled humeri more complex; but not necessarily less stressful. When the humerus sprawls, both the bone and its muscles are under more stress than when it’s vertical.

  42. Michael Says:

    “As far as I can tell, yes, it’s the first and only Brachiosaurus altithorax reconstruction; if anyone knows differently, please tell. In fact, to the best of my knowledge, there has only ever been one life restoration of this species — it has been understandably overshadowed by the African species.”

    There are pictures of a skeletal mount and a restoration on Wikipedia: http://en.wikipedia.org/wiki/Brachiosaurus

  43. Michael. O. Erickson Says:

    “Yes, consideration of musculature makes the mechanics of sprawled humeri more complex; but not necessarily less stressful. When the humerus sprawls, both the bone and its muscles are under more stress than when it’s vertical. ”

    Considering that this is very true, I am as perplexed as you are as to why this sprawling would be present (assuming for a moment it even was present).

  44. Mike Taylor Says:

    Yes, Michael (not Erickson) — you’re right that there is a life restoration on the Wikipedia page. I meant that there was only one published restoration (which I will blog about some time).

    As for the Field Museum’s skeletal mount: I discussed its chimaeric nature on Tetrapod Zoology a while back. It has Brachiosaurus elements in it, but you’d be pushing it to call it a B. altithorax skeletal mount. It’s more a sort of an idealised version of the complete renaissance brachiosaurid.


  45. Wow, I go away for four stinkin’ days and now in addition to my email backlog there’s all this to read!

    Congrats on getting the paper out Mike :D

  46. Matt Wedel Says:

    But I really am perplexed by that laterally deflected glenoid articular surface of the coracoid — if anyone out there has ideas about it, I am ready to hear!

    Okay, here’s my relatively uninformed wiffling, which you are free to shoot down. It seems to me that the direction of the glenoid deflection really depends on the orientation of the coracoid. Let’s say, hypothetically and merely for the sake of argument, that in B. altithorax the glenoid was more ventrally and medially located than in G. brancai. That would make the coracoid lean out more, and what looks like a lateral deflection on a vertically-oriented bone might have been a ventral deflection on a dorso-laterally oriented bone.

    Either that, or the standard cop-out on sauropod limb weirdness: gobs and gobs of cartilage, of unparalleled thickness and little-known properties.

  47. Mike Taylor Says:

    Nice idea about moving the coracoid itself around, so that the humerus is oriented vertically while still articulating neatly with the glenoid — but it won’t work, I’m afraid, the coracoid flange is too extreme. Some time soon, I’ll show you what I mean with a rare SV-POW! appendicular post.

    Gobs of cartilage are unavoidable anyway, of course — in the shoulders and hips of ALL sauropods. But the more I look at that FMNH 25107 coracoid, the more I suspect it’s pathological.

  48. Michael. O. Erickson Says:

    “But the more I look at that FMNH 25107 coracoid, the more I suspect it’s pathological.”

    Dang, I wish we had another coracoid to compare it to…

  49. Michael. O. Erickson Says:

    Another B. altithorax coracoid, of course :D

  50. Matt Wedel Says:

    But the more I look at that FMNH 25107 coracoid, the more I suspect it’s pathological.

    Why, just because it doesn’t fit expectations? The “it’s probably pathological” thing is a handy fallback when confronted with weird morphology because (I strongly suspect) very few of us are qualified to diagnose it in equivocal cases, and it’s almost impossible to falsify. Recognizable skeletal pathology in the fossil record usually means healed fractures, gross invasive resorption, or florid proliferative bone growth–as opposed to, say, an articular surface that isn’t pointed in quite the expected direction, or equally subtle morphological changes in the absence of evidence of disease or trauma. If the bone was broken and healed, we’d see the scar (but we don’t). If the joint had been screwed up by arthritis to the point that the humerus ground out a new articular surface, we’d see the deep grooving of bone-on-bone contact and proliferation of bone around the edges of the joint (but we don’t). So you’re postulating some pathological condition that reoriented the glenoid a LOT but left the bone itself looking perfectly healthy.

    There’s also the Copernican or statistical argument against pathology here, which is that the chances of our only B. altithorax coracoid being pathological are vanishingly small. Unless you’ve got some compelling evidence that I don’t know about, pathology seems far less likely than us just not understanding how brachiosaurid shoulders worked.

  51. Michael. O. Erickson Says:

    Dang you, Matt! I was planning on saying all that, and you beat me to it! And worst of all, you said way better than I would have!

    :D

  52. Mike Taylor Says:

    But the more I look at that FMNH 25107 coracoid, the more I suspect it’s pathological.

    Why, just because it doesn’t fit expectations? The “it’s probably pathological” thing is a handy fallback when confronted with weird morphology because (I strongly suspect) very few of us are qualified to diagnose it in equivocal cases, and it’s almost impossible to falsify.

    You’re right that “it’s pathological” can be a feeble escape-hatch when the shape or structure of a particular bone is too weird — just as “sexual selection” has become the feeble escape-hatch when the overall shape of an animal is too weird. I do try not to play that card too often :-) Still, this IS a weird bone. Maybe we should come back to it after I’ve posted the pictures. (Have you seen them?)

    On the difficulty of recognising or falsifying pathology, my thought as I was writing the initial comment was that it would be cool if we could get a chunk of the laterally directed flange to Sarah or someone else who can histo it and recognise what’s going on with the bone structure.

    Recognizable skeletal pathology in the fossil record usually means healed fractures, gross invasive resorption, or florid proliferative bone growth–as opposed to, say, an articular surface that isn’t pointed in quite the expected direction, or equally subtle morphological changes in the absence of evidence of disease or trauma.

    Point taken, but I think the coracoid could be proliferative bone-growth. (It certainly isn’t broken and re-healed). The effect is not subtle.

    There’s also the Copernican or statistical argument against pathology here, which is that the chances of our only B. altithorax coracoid being pathological are vanishingly small.

    Yep.

    Unless you’ve got some compelling evidence that I don’t know about, pathology seems far less likely than us just not understanding how brachiosaurid shoulders worked.

    … except that this requires us to believe that the Brachiosaurus shoulder — not brachiosaurid, but just that one particular genus — worked differently from every other sauropod shoulder.

    Well, I hope you’re right (especially as I used it as an autapomorphy in the paper!) But I am beginning to have my doubts.

    By the way, I think this may be the first SV-POW! article to get past the 50-comments landmark (even if quote a lot of them are my own).

  53. David Marjanović Says:

    The people who really work on huge genera use subgenera and/or superspecies, and (in botany) additionally sections and subsections – these are forbidden in zoology (yes, really).

    Step 1) Pick up a well-established extant genus (like Canis, Varanus, or Felis, the latter being the one I will use here).

    Sounds entirely reasonable, but doesn’t even remotely work. Maybe 10 years ago or less, Felis was cut to thin slices. OK, even the one slice that still bears the name Felis contains a lot of species, but it’s much, much, much smaller than Felis of old. And that, in turn, is much, much smaller than 19th-century Felis which included Panthera and probably the entire rest of extant Felidae.

    Three years ago, Bufo was blown to smithereens (mostly equivalent to the previous superspecies), and the many subgenera of Rana were elevated to genus rank (with some complications). Rana is a genus that has been shrinking throughout the last 250 years.

    Varanus, with its about 70 species, will probably be carved up in the next 5 or maybe 10 years.

    Anolis has four hundred species. Is that comparable to Felis?

    Extant genera are not comparable to each other (by any measure). Your method tries to make extinct genera comparable to extant ones – and assumes that the extant ones are comparable to each other. That assumption is incorrect. Drastically incorrect. Cripplingly incorrect.

    Basically, I feel that Linnaean ranks – while being wholly artifical – are helpful rather than harmful in taxonomy because, for example, they allow one to quickly and painlessly identify which clades are more inclusive and which ones are more exclusive (”Oh, that clade represents a ‘Kingdom’, therefore it’s more inclusive than the other clade, which is a mere ‘Family’”).

    But even that’s not the case.

    Absolutely nothing stops a family from containing more species or more disparity (however measured) than a kingdom, except for the one kingdom that includes that family.

    And under some of the more recent eukaryote classifications, this has probably already happened. If not, go to class and family to find loads of examples.

    Ranks distort the minds of everyone involved.

  54. Mike Taylor Says:

    David, you have to stop repressing your true feelings like this. Let it all out — tell us what you really think. You’ll feel better afterwards.

    :-)

  55. Michael. O. Erickson Says:

    Okay David, you think I’m wrong, and maybe I am. There are nicer ways of saying it :)

  56. Michael. O. Erickson Says:

    In my opinion, ranks distort the minds of everyone involved.”

    Fixed it for you :)

  57. David Marjanović Says:

    No, it’s a demonstrable fact. :-|

    Have I mentioned the Phylogenetic Biodiversity Index already?

  58. Nathan Myers Says:

    M.O.: Here’s a hint: if somebody else says it, it’s their opinion. We don’t need to see every sentence preceded by “In my opinion, …” If you are inclined to disagree on something, go ahead; you don’t even need to tell us. If you have some objective reason why we should disagree, too, and you tell us that reason, we might learn something; or you might.

  59. Fabrizio Says:

    Very interesting post, seriously
    Besides the phylogenetic placement keeping changing, which i fully agree with…

    Mr. Taylor, so do you support the “ANY SPECIES NEEDS ITS OWN GENUS” (=ABSOLUTE MONOSPECIFITY) rule? Ive been advocating it for more than a year in forums

    If this rule was applied, we could DELETE SPECIES and leave genera alone and treat them as we treat species today
    4 example, we could call Giraffatitan brancai JUST “brancai”

    Also, this rule would help a lot and give any species the attenction it deserves. 4 example, when someone says AMPHICOLIAS, ALMOST EVERYONE thinks about fragillimus. But what the old AND REAL TYPE species, ALTUS (which has even been included
    And this even they ignore non-type species: for example, in the family ceratosauridae and Hyaenodon genus there are a lot of species, but the problem is that ALL of them are lumped in the genera Hyaenodon and Ceratosaurus

    I red many times in paper labels saying something like “Apatosaurus skull”. But WHICH SPECIES does the label refer to? I cant really know. Im referring to the recent description of Apatosaurus brain by Balanoff et al (2010)
    Also, i think this post by Martyniuk is very useful
    http://dinogoss.blogspot.com/2011/01/scientific-anachronism-and-why.html

    I would also resurrect the many old and forgotten genera being once attriubuited to non-type species like Phobosuchus, Megalania, Seismosaurus, Harpagornis, Dinosuchus (the caimanine), Aenocyon and above all Brontosaurus
    And id call ALL non-type species (of ALL taxa) not having received their own genera yet by putting “”: id call Diplodocus carnegii just “D”. carnegii. And it would be even better if someone then would give carnegii its own genus, so the SPECIFIC NAME carnegii could be abandoned, and the diagnosis of carnegii be transferred to this new genus
    T. rex would become just Tyrannosaurus

    Little non-sauropod offtopic: i think that synonymizing GENERA
    4 example, saying Anatotitan copei is just a species of Edmontosaurus is saying nothing. SPECIES are the REAL taxonomic objects, genera as nothing more than a linnean relict being ball and chains
    Also, Sander showed that S. sikanniens is closer to Shastasaurus, so renamed it Shastasaurus sikkaniensns. If any species would have had its own genus, what Sander did would have been unnecessary

    PS
    Sorry for the lenght of my post and my non-perfect english :)

  60. Mike Taylor Says:

    Fabrizio, I do agree that for Mesozoic dinosaurs, trying to place species in genera is a bit of a fool’s game. I think that, while there’s no official policty, the community of dinosaur workers is gradually coming to a consensus that monospecific genera are nearly always the best approach to take, and I am certainly in agreement. I find it hard to imagine a situation where I would name a sauropod as a new species of an existing genus: I think it would nearly always either seem similar enough to be a member of an existing species, or different enough to warrant a genus. Because that’s the lumpiness of sauropod taxonomy.

    But I’d hesitate to say that should be the approach taken in all of taxonomy. Dinosaurs are unusual because (A) there are not many of them; and (B) most are known from incomplete remains so that we can’t state certain phylogenetic positions. If I were an extant-beetle worker, I would not relish having to come up with 400,000 unique uninomials.


  61. […] *Just to complicate things further, Russell’s decision to lump Gorgosaurus into Albertosaurus is no longer supported by most of today’s specialists. Gorgosaurus and Albertosaurus are different taxa, but they are still more closely related to one another than to any other known species. Keep in mind as well that many taxonomical discussions concerning dinosaurs come down to personal preference, rather than actual reflections of biodiversity. […]


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