Terminology time

Having written about paraphyletic groups and the use of the term ‘rhamphorhynchoid‘ when talking about pterosaurs I thought it wise to discuss the issue in a slightly broader context and highlight the problem of such names. As I mentioned, I think ‘rhamphorhyncoids’ is a perfectly acceptable term as long as it is made clear that this is a paraphyletic group. But assuming you don’t want to do that (which is an understandable position), what are the alternatives?

First off some researchers prefer to use the term long-tailed pterosaurs and short-tailed pterosaurs for the rhamphoprhynchoids and pterodactyloids respectively. There are immediate and obvious problems with this approach. Firstly it is longwinded, and while clarity is to be valued in science communication, so too is brevity. Secondly, by using what are effectively colloquial terms it does not make clear the monophyly of pterodactyloids, since the both are given non-technical names. Thirdly and most obviously are the problems of the anuroganthids and Pteranodon since the former have a short tail unlike the rest of the rhamphorhynchoids, and the latter a long one. Thus the anuroganthiuds are then short-tailed, long-tailed pterosaurs and Pteranodon becomes a long-tailed, short-tailed pterosaur. Thus the use of long- and short-tailed is neither clear nor concise. Other variations (I guess you could point to the 5th toe, or the neck length) run similar risks.

Next we can use a nice general term such as ‘basal’ and ‘derived’ to refer to them. However, as above this suffers from ambiguity, since Rhamphorhynchus for example is a very derived rhamphorhynchoid and thus is a derived basal pterosaur, and equally Pterodactylus could be called a basal derived pterosaur. You would have to be explicit every time you used the word basal or derived and again this gets confusing and requires you make exact statements about what context you are using the words in each time you want to refer to a taxon.

Next you have the use of replacement words or phrases such as non-pterodactyloid pterosaurs, or basal clades, or others. These I do not have a problem with, again as long as they are clear (as non-pterodactyloid pterosaur certainly is). However, again, I do not think these terms are especially nice to use (rhamphorhynchoid is so much more succinct, and its worse in other groups – compare ‘prosauropods’ to ‘non-sauropodan sauropodomorph’) and they are hardly ‘time saving’ in as much as in any paper where you refer to them you will still have to include a sentence along the lines of “the non-pterodactyloid pterosaurs are a paraphyletic collection of basal taxa” just as you would when defining the rhamphorhynchoids.

Overall I find the putsch against paraphyletic terms annoying. I can’t see the harm in using them when they are clear and succinct and are carefully defined (and that is the case here). I don’t see icthyologists putting the word ‘fish’ in quotes constantly or writing about ‘non-tetrapod vertebrates’ (or if they are, I have missed it). People will even still use ‘reptile’ in its polyphyletic sense (i.e. not including birds or mammals) when convenient to do so (admittedly rarely), without problems. The only time this approach is problematic is where one term is synonymous with two different things (like dinosaurs can mean, well ‘dinosaurs’ [i.e. non-avian dinosaurs] or all dinosaurs including birds) and here distinction is necessary. For pterosaurs though, this is not the case. ‘Rhamphorhynchoids’ are paraphyletic, everyone knows they are and accepts that they are, so why replace one term (rhamphorhynchoid) with another longer one (e.g. non-pterodacyloid pterosaur) that still represents the exact same paraphyletic assemblage and still requires the same clarification?

As I recently wrote in a technical note on this issue in a paper “I prefer therefore the systematic term ‘rhamphorhyncoid’ which, despite being paraphyletic, is succinct, accurate and unambiguous”. I find it hard to fault that statement (even if I wrote it).

10 Responses to “Terminology time”


  1. 1 Zach Miller 25/12/2008 at 2:53 am

    As long as the reader has an understanding that anurognathids are included within rhamphorhynchoidea, I’m fine with that term being used to refer to the lower half of the Pterosauria. I’d like to voice my dislike of the term “non-avian theropod,” as it seems long-winded, too, but I don’t think there’s a better way.

  2. 2 David Hone 25/12/2008 at 9:52 am

    That’s about the size of it.

  3. 3 Mike Taylor 31/12/2008 at 8:27 pm

    Well, FINALLY! It is a relief to see someone else out there who is not signed up to the silly superstition that formal names mustn’t denote paraphyletic groups — a prejudice just as groundless and pointless as the older one that names ending “-inae” must be contained within superset groups named “-idae”.

    FOr goshsakes, people! Terminology is there to serve us, not vice versa. The world needs a term that, plainly and unambiguously, means “non-pterodactyloid pterosaurian”, and “rhamphorhynchoid” is that term. Likewise, prosauropods.

    (BTW., traditional Reptilia is not polyphyletic: it’s doubly paraphyletic.)

  4. 4 David Hone 31/12/2008 at 8:30 pm

    And pray tell Mike, what is the difference between doubly paraphyletic and polyphyletic? Can something be dodecadly paraphyletic?

  5. 5 Andy 01/01/2009 at 12:19 am

    I second Mike and David. . .sometimes the pursuit of being technically correct does indeed result in ridiculously clumsy phrases like “non-avetheropod tetanuran.” (I’m still having nightmares about revising that particular MS)

    No matter how bad phylogenetic nomenclature purism is, I think that ICZN latinization purism is even worse (this disease seems to afflict the Dinosaur Mailing List with distressing regularity). Thank goodness that the ICZN effectively shut down emendations of this flavor. . .not that it isn’t preventing the current “ceratopsid” vs “ceratopid” battle on the DML.

  6. 6 Mike Taylor 02/01/2009 at 6:43 pm

    David,

    A doubly paraphyletic group is a clade from which two clades have been removed (e.g. Reptilia = Sauropsida – Mammalia – Aves) — as contrasted with a singly paraphyletic group (e.g. traditional Dinosauria = clade Dinosauria – Aves). And, yes, you can if you wish have a triply, quadrupally or dodecadly paraphyletic — its just that the utility of such groups falls away quickly once you remove more than one or two groups, in fact I can’t think of any widely used group that is more than doubly paraphyletic.

    A polyphyletic group is different again — it’s one that can only be made by _adding_ multiple clades, rather than by removing subclades from a superclade. A classic example is the group of all “warm-blooded” animals, consisting of Aves and Mammalia, but omitting all other descendants of their most recent common ancestor. You can’t practically construct that as a paraphyletic group.

  7. 7 David Hone 03/01/2009 at 9:10 am

    Sorry Mike, I jsut can’t see the difference between an ‘n-paraphyletic group’ and a polyphyletic one. After all you could jsut name Tetrapoda and then remove 900 clades until you were left with all the bipeds and still calim that it’s jsut vbery very paraphyletic. I’ll stick to anyhting with more than one group being removed as being polyphyletic thanks, otherwise that nasty ambiguity rears it’s ugly head again.

  8. 8 Mike Taylor 03/01/2009 at 7:29 pm

    “I’ll stick to anyhting with more than one group being removed as being polyphyletic thanks.”

    David,

    I am sorry, but you simply can’t do that. It’s just not what the word means. It’s equivalent to saying something like “I’ll stick to anything that went extinct in the Mesozoic being a dinosaur thanks”.

  9. 9 David Hone 03/01/2009 at 8:22 pm

    Hmmm, well yes and no. I’m being pedantic or clinging to my ideas, but the deifinitions of paraphyly and polyphyly (from a couple of sources) don’t quite match up such that you and right and / or I am wrong – there’s a significant gap between them sicne they rely on different things. I can’t see the difference between having a near infinte capacity to take out groups and still call what’s left paraphyletic, not polyphyletic. Where does the difference lie?


  1. 1 The missing tail of Pteranodon « Dave Hone’s Archosaur Musings Trackback on 06/04/2009 at 8:22 am

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