Sunday, September 5, 2010

What Is A Nomen Oblitum? Not What You Probably Think

Above: Illustration of Manospondylus gigas by Matt Martyniuk, copyright.

In a previous post, I brought up the taboo subject of Manospondylus gigas, the large Lancian theropod named by E.D. Cope in 1886 and a potential senior synonym of Tyrannosaurus rex. Google "manospondylus" and the first hit is an old Q&A post by Mike Taylor called "So why hasn't Tyrannosaurus been renamed Manospondylus?"

Good question!

Aside from cultural inertia, the answer Taylor gave is this: "As of 1st January 2000, a new ICZN ruling has come into effect, saying that a name that's been considered valid for fifty years can't now be replaced by one that's been considered invalid during that time." This is also the answer Mickey Mortimer gave in some (but not all) relevant entries on the current Theropod Database. Brian Switek, in an old Laelaps post, gave the same answer: Manospondylus hasn't been considered valid in 50 years, so it's a nomen oblitum ("forgotten name"). He also suggested that this means T. rex has "protected status" which would have to be overturned by the ICZN in order for M. gigas to become valid.

The problem is that none of that has any bearing on what "nomen oblitum" actually means according to the current ICZN code. The ICZN states that in order for a name to be declared a nomen oblitum, all of the following things need to be true:
1. the senior synonym or homonym has not been used as a valid name after 1899
2. the junior synonym or homonym has been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years
3. a paper must be published citing evidence for #2, and citing both names together, declare that the junior synonym or homonym is being made a nomen protectum ("protected name") in accordance with ICZN article 23.9.

The confusion seems to come from #2. It's not a matter of the senior name not having been used in the past 50 years, but the junior name must have been used frequently enough in recent history in order to be eligible for conservation. Clearly, T. rex meets the second criteria. But what about the first and third?

For number one, the answer is I'm not sure, but I think so. It depends on what your definition if "is" is. Has Manospondylus been used since 1899? Definitely, yes, and in several papers, as Mickey Mortimer pointed out in the comments on my previous post on this topic. But was it used as valid? Most authors, even in the early 20th century, recognized that two vertebrae were pretty poor material to be basing a species on. Many of them considered it to be what we'd now call a nomen dubium ("dubious name"). For example, here's what Matthew & Brown (1922) had to say on the subject: "Osborn has already (1917) called attention to another fragmentary type, Manospondylus gigas, as possibly identical with Tyrannosaurus but based upon an inadequate type." They don't explicitly say it's valid or invalid (I'd like to know what Osborn 1917 actually aid on the matter but don't have that paper. Anyone?).

As for number three, it appears that the situation has never been adequately addressed in the literature, so the criterion is not satisfied. The issue came up in 2000, when Peter Larson claimed to have rediscovered the original Manospondylus locality, and more of the type specimen, confirming it is the same as T. rex. As far as I know, this has never seen print beyond an AP article (Anonymous, 2000. "Discovery could Endanger T.Rex Name." The Associated Press.)

In short, could M. gigas be a nomen oblitum? Maybe, depending on the meaning of "valid" and if somebody gets up the nerve to actually publish the case. Is Manospondylus a nomen oblitum as of right now? Definitely not, and it remains the valid senior synonym of Tyrannosaurus until and unless someone acts as revisor to the contrary.

Addendum: Just for fun, I looked up "valid" in the ICZN's glossary. Who better to determine what the ICZN means by valid than the ICZN? Here's the entry:
valid, a. (validity, n.) Of an available name or a nomenclatural act: one that is acceptable under the provisions of the Code and, in the case of a name, which is the correct name of a taxon in an author's taxonomic judgment.

Since the Code does not formally recognize nomina dubia as invalid names (or at all, really), this seems to indicate that M. gigas was considered valid by all those authors in the 20th century, at least under the ICZN's definition. Matthew and Brown, for example, did not consider M. gigas an invalid name (a junior homonym, improperly coined, etc.), just non-diagnostic. Which as far as the rules are concerned, is A-OK. Sorry kids, barring an act of ICZN, M. gigas looks like it's on solid footing as a currently valid name.

13 comments:

  1. Yikes! When did you whip that Tyran... I mean Manospondylus drawing up?

    Either way, this will probably stir some things up. Let the flame wars begin!

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  2. I'd like to know what Osborn 1917 actually aid on the matter but don't have that paper. Anyone?

    http://digitallibrary.amnh.org/dspace/handle/2246/1334

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  3. Again, and now we make a petition, the ICZN pretty much goes "really?", and then Tyrannosaurus is the valid name because authorities say so. Taxonomy is man-made and not a real thing per se, it is easy to change it.

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  4. "Definitely not, and it remains the valid senior synonym of Tyrannosaurus until and unless someone acts as revisor to the contrary."

    It could be a senior subjective synonym. Subjective synonymy (unlike objective synonymy) is in the eye of the beholder. Until Larson or somebody publishes on the further material, there's no reason to consider it diagnostic. (And even after that there are no rules about how to formulate species, just on what to name them once they are formulated.)

    As for whether it's valid, don't forget this part (emphasis added): "...the correct name of a taxon in an author's taxonomic judgment". If an author's taxonomy doesn't place the M. gigas holotype in the same species as the T. rex holotype (e.g., by resigning it to the bin of "non-diagnostic" or "incertae sedis"), then the author has judged M. gigas not to be the correct name. So I think #1 holds, unless you can find an explicit exception.

    And, yes, somebody should go ahead and perform step #3.

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  5. @dinogami: D'oh! Of course, thanks for that :) For the record, Osborn regards the genus and species M. gigas as "indeterminate." Which probably satisfies Keesey's reading of the ICZN. I can't imagine any of the later sources would have disagreed with him.

    @ Keesey: Regarding diagnosticity, clearly the specimens are not diagnostic at the species level. But given their presence in a time and place where only one other large theropod is present, and the total lack of indication that there is more than one species there, there is essentially no chance it is anything other than T. rex, as several publications have concluded. Unless you accept Nanotyrannus as valid, of course :)

    IMO questions like this are important for understanding prehistoric ecosystems, and here's a spot where taxonomy and nomenclature can actively get in the way of science. What's the use having several dubious genera/species floating around that are almost 100% likely to represent the same biological species, as far as we can reasonably discern? The only thing keeping this proliferation of obvious junk names is the reluctance on the part of scientists/taxonomists to bite the bullet and synonymize them unless and until evidence arise that they should be split again. I'm talking bio/ecological species here, not lumping between genera or something more arbitrary. We have no good reason to suspect there is more than one species of tyrannosaur in the various Lancian formations, so the nomenclature and things like M. gigas should be tidied up to reflect this. I don't care if M. gigas or T. rex ends up as the final valid name (though I'd definitely prefer T. rex!), just put all those odd bones into the same taxonomic pile already.

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  6. @ Matt: Does it really matter that the evidence points to only one large theropod is present?

    To me this is evidence that only one large predator inhabited parts of Lancian North America. Not that M. Gigas is diagnostic and thus has priority over T. Rex.

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  7. @Eric: But that's the thing. If there's only one large predator in Lancian western North America, then any indeterminate scrap IS diagnostic because of its provenance. For example, if I found a non-diagnostic hominid bone in La Brea pits, and we know there was only one hominid present, we can be certain it is referable to Homo sapiens based on provenance alone, and that any name attached to it would therefore compete for priority.

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  8. @Matt: But why should we use M. Gigas instead of T. Rex?

    True M. Gigas was named first but if it is actually non-diagnostic, then why should we use in instead of the later named but diagnostic T.Rex?

    I am not convinced that provenance alone makes M. Gigas a valid genus.

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  9. @ Eric: I would contend that it *is* diagnostic for the reasons I gave above.

    As I've written before, people are too liberal with their designations of momina dubia. We need to look at these as hypotheses.

    My hypothesis: M. gigas is the same species as T. rex.
    Null hypothesis: M. gigas is not the same species as T. rex.
    In support of the hypothesis, we have the fact that no more than one species of large tyrannosaur has ever been supported in the Lancian formations of North America. It's a bit weak sure, but to support the null, you'd need to presume that M. gigas is a valid species in its own right, one known only from a set of vertebrae, and that other bones, including shed teeth, have never been found in these formations despite over 150 years of extensive sampling.

    Clearly, the hypothesis that T. rex and M. gigas are conspecific is the most parsimonious, unless and until a definitive second species of Lancian tyrannoaur is found. Only then can M. gigas be considered a nomen dubium, because it will be presumably be impossible to tell if the vertebrae come from Tyrannosaurus or Hypotheticalsaurus. This is why Deinodon is a nomen dubium. It might be Gorgosaurus, it might be Daspletosaurus. It's almost certainly one of those two, but we don't and probably can't know which. In the case of M. gigas, there's no ambiguity. It can't be anything other than T. rex, as far as we know.

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  10. Very interesting regarding the exact necessities of nomina oblita. However, since stratigraphy is generally not allowed in diagnoses (or else we'd have tons of scraps from different formations deserving their own taxa) and Tarbosaurus was of similar size to Tyrannosaurus and is not known to differ in axial anatomy, I'd say that Manospondylus is a nomen dubium as far as we know. Now if you can compare the cervicodorsals of Tarbosaurus and Tyrannosaurus and find differences which the latter shares with Manospondylus, then we might need to reconsider things.

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  11. Christopher A. Brochu in 2003 did write that Manospondylus hadn't been used in 50 years and T. rex was in common use; but this doesn't seem to fulfill the criteria of ICZN Article 23.9.2, which require that one must "state explicitly that the younger name is valid, and that the action is taken in accordance with this Article; at the same time the author must give evidence that the conditions of Article 23.9.1.2 are met". Brochu doesn't actually do the last, simply stating that it's obvious that Tyrannosaurus is in use (which, granted, it is); nor does he mention Article 23.9.2 (though he does cite the ICZN generally), simply stating the rule as 'fifty years' of non-use (which is inaccurate at least as the code stands now; perhaps it's changed in the last 7 years).

    So yeah, I think this still technically hasn't been resolved.


    source: Christopher A. Brochu, Osteology of Tyrannosaurus rex: Insights from a Nearly Complete Skeleton and High-Resolution Computed Tomographic Analysis of the Skull (Society of Vertebrate Paleontology Memoir Vol. 7, (Jan. 14, 2003), pp. 1-138) http://www.jstor.org/stable/388933

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  12. well I guess now my favorite (large)theopod is m.gias

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  13. This is stupid, the names are "man-made" not "nature-made", there are to many rules just to put a damn name. "Tyrannosaurus rex" is "Tyrannosaurus rex", leave it as it is. That's why everybody hate the nerds and lawyers!!!

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