Synonymy

I’ve covered a fair bit of taxonomy on here before, though there it lots more to come. However, I though it worth starting with synonymy since it’s pretty common in archosaur palaeontology and has led to a few misconceptions in the past. Synonymy is basically the practice of putting two or more names together as a single taxon because they are all the same thing but have multiple names.


This can happen occasionally when two parts of a single specimen have been named but of course it’s rare that two (or even one) people manage to split and animal in half and name different halves different things, though it does happen.

More common is that two different specimens have been described as two different genera or species but on closer examination they turn out to belong to the same taxon. This of course used to be pretty common since scientific communication was much slower and it could be years before you saw a paper by a colleague that showed that his new dinosaur was the same as yours (Cope and Marsh were especially good, or perhaps rather, bad, at this). Sometimes this is instantly obvious – both specimens are complete enough for an easy comparison and it’s obvious that there’s not enough evidence to consider them as separate species so they should be synonymised and brought together under a single name.

Now the more common situation is that two animals were named from two different but non-overlapping (or not overlapping enough) specimens. You might have a nice skull that’s diagnostically different to every other skull known so you reasonably think it’s a new species. In another formation a colleague has a new set of legs and a tail that look different to everything else known and names them too. Later on a third specimen turns up that’s nearly complete and it turns out that your skull sits on a skeleton that features a remarkably familiar tail and legs – you have both named the same animal and now it has two names. As an aside, this phenomenon is especially common in plant palaeontology where sometimes the leaves, twigs, trunk, bark, roots, flowers, seeds and fruit of a single taxon have all been named as different species at various times.

The resolution of this is, in theory, quite simple. Get a paper published that formally explains why the two specimens are both considered part of the same species and basically delete one of the names. The choice of which name goes if almost always down to the ‘principle of priority’, i.e. whichever name was published first is kept and the other one is demoted. This has been complicated in the modern age by the speed of publication and the appearance of advanced online publications and even online only publications which has required some changes to the rules as well as causing headaches (and the odd bit of acrimony) for taxonomists. It’s of course not always that simple as of course issues of ontogeny, variation and even age can play a role (if the two fossils are separated by 20 million years they’re unlikely to be from the same species even if they do look very similar).

There are exceptions to the principle of priority, but these are few and far between and easiest to skip for now though as a very brief example, ‘Brontosaurus’ was petitioned to be held over Apatosaurus on the basis that it was much more famous and would confuse or irritate the public. As you probably know by now, it lost out, though that hasn’t stopped the average reporter despite the fact that the formal synonymisation was formally put forward in 1903!

All of this causes confusion because it means that often names apparently vanish (like Brontosaurus, Aublysodon, and Laelaps) which can confuse people. Brontosaurus disappears from all the books, museum notices and TV shows (well, it *should* even today the damned thing still hangs around, but anyway) and people don’t realise where it went. Of course in a sense, it never went anywhere as in theory at least it’s a name that should not have existed in the first place. But since most of the public don’t realise how synonymy works (or even that it happens at all) they either don’t realise that the name is valid or assume that the old name / sign was a mistake rather than a formal change in the taxonomy (i.e. that the researchers screwed up and couldn’t tell their brontosaurs from their apatosaurs which of course is not exactly true and certainly not fair on the researchers. Oh alright, some researchers). That means that old names get re-used, annoying taxonomists and frustrating people who want to find out about say Antrodemus but can’t because books never seem to mention it anymore since it’s not valid.

Obviously the internet helps here a lot with sites often including old names so leaving a paper trail for people to follow but it is a problem and I once got trapped live on air on a radio show when asked about some taxon I’d never heard of and I didn’t know what it was. It turned out to be some obscure European sauropod whose name had lasted all of about 6 months before being synonymised but had clearly lived on somewhere long enough for a researcher to pull it up and the host ask me about it. Keeping up to date with the current taxonomy can be difficult (and of course there are disputed about names) but it’s very important to avoid confusion and the unwarranted multiplication of species.

19 Responses to “Synonymy”


  1. 1 Mike Taylor 05/10/2010 at 9:11 am

    Thanks, Dave, useful post. Just two points:

    “[Synonymy] used to be pretty common since scientific communication was much slower and it could be years before you saw a paper by a colleague that showed that his new dinosaur was the same as yours (Cope and Marsh were especially good, or perhaps rather, bad, at this).”

    Cope and Marsh had no excuses, mind you. Even if the general pace of scientific publishing was slower in those days than it is now, Cope and Marsh were exceptions, and churned out sequences of short descriptive papers in a torrent. Each would certainly have been aware of the others’ publications. The masses of synonymy between their taxa are consequences more of ego than of miscommunication.

    “‘Brontosaurus’ was petitioned to be held over Apatosaurus on the basis that it was much more famous and would confuse or irritate the public. As you probably know by now, it lost out.”

    Unless you know something I don’t, there was never an ICZN petition to conserve the name Brontosaurus — just a lot of moaning about the switch. Or do you have a reference for an actual petition?

    • 2 David Hone 05/10/2010 at 9:25 am

      Hi Mike, well I think Cope and marsh do at least have the excuse of the time they were living in when definitions were less rigorous and details in papers could be lacking, but yes, in their particular cases I’d agree that they could have been rather better.

      As for the petition, I had thought Bakker lodged a formal one, but perhaps not. i must confess i don’t know for sure.

  2. 3 Christopher Taylor 05/10/2010 at 9:35 am

    Nice post. I apologise in advance for tangentifying…

    As an aside, this phenomenon is especially common in plant palaeontology where sometimes the leaves, twigs, trunk, bark, roots, flowers, seeds and fruit of a single taxon have all been named as different species at various times.

    The situation’s a little complicated in this regard because most of those cases are morphotaxa (or form taxa or organ taxa or whatever your preferred terminology is) and you can’t really synonymise morphotaxa as such except with equivalent morphotaxa (so two wood morphotaxa could be synonymised but not a wood morphotaxon and a flower morphotaxon). This is because the two may not exactly correspond (so two extinct species of tree may have produced different flowers but have indistinguishable wood).

    well, it *should* even today the damned thing still hangs around

    Yeah, I don’t get the persistence of Brontosaurus either. It’s been over a century since it was synonymised. Just get over it already! (And I’d be surprised if there was an actual petition, seeing as the synonymy was effected over 50 years before the IC[ode]ZN was even published.

    Laelaps is another slightly different case, being a homonym and all. There is still an animal called Laelaps, just not the one you’re referring to😉.

    • 4 Mike Taylor 05/10/2010 at 9:38 am

      Come on, Christopher, you must get that the name Brontosaurus is just plan cool in a way that Apatosaurus isn’t. I’m not saying that’s a reason to conserve it; but I can certainly understand why people want it to be the right name.

      It almost makes you wish that there was a new sauropod in the works with a Brontosaurus-like name, doesn’t it? As a sort of tribute. Wouldn’t that be cool?

      • 5 William Miller 06/10/2010 at 9:10 am

        Since ‘genus’ has no objective definition, I suppose you *could* split ajax, excelsus and louisae as three different genera.

      • 6 David Hone 06/10/2010 at 9:13 am

        Genus does have no objective definition, but within groups the point is to try and make it consistent. If you split these into different genera then you’d probably have to split up a bunch of other sauropod, even other dinosaur species into new genera. It would be no more right or wrong as such, but would be profoundly awkward and a lot of work. Taxonomy is there to serve us and generating a tone of work like this is not a good idea and would help no-one so it simply won’t be done unless there’s really good reason to think these things are more distinct than previously thought (as Mike did with Giraffititan).

      • 7 Mark Robinson 06/10/2010 at 10:44 am

        Hmm Mike, it sounds like you’re alluding to something that might be getting published soon? And as you’re an all-round decent chap, may I also presume that, since it’s you that’s doing the name-dropping, you are one of the authors? *begs for additional morsel*

        Of course, there has been an actual Brontosaurus for some years now. I refer to none other than 9949 Brontosaurus, an asteroid. It has the second-coolest name, 3834 Zappafrank being the first.

      • 8 David Hone 06/10/2010 at 11:00 am

        Doesn’t it just? And I normally have a fair idea of what Mike is up to. I wonder what is in the pipeline…?

    • 9 David Hone 05/10/2010 at 9:51 am

      Nothing wrong with tangentifying my tangentification. Obviously I’m not as up on my fossil plant taxonomy as I had though (oddly enough). Thanks for the correction. Still, I do know a couple of palaeobotanists and I can always make them groan and roll their eyes by asking them if their species are still valid of if someone has now found some flower of X attached to branch Y and with leaf Z attached.

  3. 10 Jens Klump 05/10/2010 at 11:40 am

    A great summary of the reasons for the synonymous use of taxonomic names and perils of doing so. This is also an issue when trying to derive the stratigraphical age of a geological formation when taxonomic names of stratigraphic marker taxa change. To allow scientists to assess and explore synonymies Robert Huber (MARUM, Univ. Bremen) and I (GFZ Potsdam) developed TaxonConcept as a database for synonymies. http://taxonconcept.stratigraphy.net

    We described TaxonConcept in Huber, R., und J. Klump (2009), Charting taxonomic knowledge through ontologies and ranking algorithms, Computers & Geoscience, 35(4), 862-868, doi:10.1016/j.cageo.2008.02.016. also available at http://edoc.gfz-potsdam.de/gfz/get/13007/0/d8b09c133462792c99eb6a163a6c5601/13007.pdf

    TaxonConcept is online and you are welcome to explore it. http://taxonconcept.stratigraphy.net/search.php?taxonname=cretacea

  4. 11 jay 05/10/2010 at 7:18 pm

    “It almost makes you wish that there was a new sauropod in the works with a Brontosaurus-like name, doesn’t it? As a sort of tribute. Wouldn’t that be cool?”

    what, a Brontotitan?

  5. 12 Mike Taylor 05/10/2010 at 8:01 pm

    “Brontotitan”? I’d hope we could come up with something a bit better than that. Oh, did I say “we”? Sorry, no, I meant “whatever groups might be working on sauropods than they plan to give Brontosaurus-like names”.

  6. 14 Taylor Duane Reints 06/10/2010 at 12:38 am

    Believe it or not I consider Brontosaurus valid, because it seems more different from Apatosaurus ajax than A. louisae is. If you are an extreme lumper, like Greg Paul, then Brontosaurus would still be obsolete, but when you think about it, saying Brontosaurus excelsus is in the genus Apatosaurus is like saying Daspletosaurus torosus is in the Tyrannosaurus clan.
    I guess it just hasn’t caught on😉

  7. 15 Matt Martyniuk 06/10/2010 at 12:54 am

    Great post! about the petition…
    “As for the petition, I had thought Bakker lodged a formal one, but perhaps not.”

    This would be unnecessary, because the synonymy between _Apatosaurus_ and _Brontosaurus_ is at the genus, rather than species level. _Apatosaurus ajax_ is not synonymous with _Apatosaurus excelsus_ according to any papers I’ve seen. Therefore, lumping these together in the same genus is a subjective decision. _Brontosaurus_ is a valid genus name if you want it to be (but you’d need to coin a new one for _A. louisae_, otherwise _Apatosaurus_ becomes paraphyletic). There’s no rule saying a genus must have multiple species.

    Compare the situation with _Baryonyx_ and _Suchomimus_. Everyone agrees they’re distinct species (_B. walkeri_ and _S. tenerensis_). But some researchers have started to lump them both together as _B. walkeri_ and _B. tenerensis_. There’s no right answer, so saying “_Suchomimus_ doesn’t exist anymore” doesn’t really mean anything.

    In other words, contrary to popular belief, the use or disuse of _Brontosaurus_ are both semantic, rather than scientific, arguments. Both are equally valid opinions, because there’s no definition of genus. The synonymy is just as much a result of cultural inertia as the popular persistence of _Brontosaurus_!

  8. 16 Mike Taylor 06/10/2010 at 11:26 am

    Sorry, everyone, I realise I’ve turned into that guy I hate who hints at delicious new work in the pipeline and then refuses to elaborate. I really shouldn’t have said anything, and I really can’t say more — not least because I am not the sole author so that if I stole the thunder, it wouldn’t just be mine that I was stealing.

    (Hmm … Brontolestes … that would be a good name. But it’s not the one I have in mind.🙂 )

    Taylor and Matt: Upchurch et al. (2005) did a very useful specimen-level phylogenetic analysis of Apatosaurus, recovering a monophyletic five-specimen cluster of A. ajax, in a trichotomy with A. excelsus (limited to YPM 1980) and a small A. parvus clade. FMNH P25112 was the outgroup, then the two-specimen clade representing A. louisae, which is therefore the most basal Apatosaurus species according to this analysis. That’s all perfectly compatible with the currently dominant scheme of nomenclature for these animals. IIRC, though, Lovelace et al.’s SVP poster (NOT their paper) recovered the WDC Supersaurus closer to A. ajax than to the other Apatosaurus species. If that’s right, then either Supersaurus could be made a species of Apatosaurus, or Apato could be exploded into three (or more) genera. Or we could just accept that genera are sometimes paraphyletic.

  9. 18 Matt Martyniuk 07/10/2010 at 12:08 am

    Thanks Mike, I didn’t know Upchurch had done a specimen-level analysis. Cool stuff. Still, though, doesn’t this come down to lumping vs. splitting? Whether or not Supersaurus falls among Apatosaurus, since “genus” is a subjective concept, whether to explode or not explode Apatosaurus has nothing to do with the position of Supersaurus, just personal taste and/or historic inertia. It’s no more or less valid to classify each Apatosaurus species in its own genus than to lump all diplodocines into Diplodocus.

  10. 19 Mike Taylor 07/10/2010 at 12:41 am

    “Still, though, doesn’t this come down to lumping vs. splitting?”

    Yes. If you want, you can follow 1880s practice and refer all sauropods to Cetiosaurus.

    “Whether or not Supersaurus falls among Apatosaurus, since “genus” is a subjective concept, whether to explode or not explode Apatosaurus has nothing to do with the position of Supersaurus, just personal taste and/or historic inertia.”

    That is roughly true — though many people want to make all genera monophyletic, which constrains their options somewhat.

    But we mustn’t make the mistake of seeing that genera are not objective and concluding that they are therefore useless. Within a broad taxonomic group such as Sauropoda, it’s useful to maintain the historical approach of trying to keep roughly similar amounts of morphological variation within each genus. Yes, this is subjective: it requires taste, experience and judgement.


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