My comment in support of the Diplodocus carnegii ICZN petition

September 8, 2016

If you keep an eye on the wacky world of zoological nomenclature, you’ll know that earlier this year Emanuel Tschopp and Octávio Mateus published a petition to the International Commission on Zoological Nomemclature, asking them to establish Diplodocus carnegii, represented by the ubiquitous and nearly complete skeleton CM 84, as the type species of Diplodocus.

That is because Marsh’s (1878) type species, YPM 1920, is a pair of non-diagnostic mid-caudals which no-one has paid any attention to since 1901:

Tschopp and Mateus (2016: fig. 1). More anterior of the only two reasonably complete caudal vertebrae of the type specimen of Diplodocus longus (YPM 1920) in dorsal (A), anterior (B), left (C), posterior (D), right (E), and ventral (F) views. The neural spine is lost. The estimated position within the caudal column is caudal vertebra 17â24. Note the transverse ridge between the prezygapophyses shared with AMNH 223 (1).

Tschopp and Mateus (2016: fig. 1). More anterior of the only two reasonably complete caudal vertebrae of the type specimen of Diplodocus longus (YPM 1920) in dorsal (A), anterior (B), left (C), posterior (D), right (E), and ventral (F) views. The neural spine is lost. The estimated position within the caudal column is caudal vertebra 17â24. Note the transverse ridge between the prezygapophyses shared with AMNH 223 (1).

I have now submitted a formal comment to the ICZN in support of the petition, in which I argue:

In its use as the definitive exemplar of the genus Diplodocus, as the foundation for numerous palaeobiological studies of the genus, and as the specifier for numerous important clades, the species D. carnegii is already effectively functioning as the type species of Diplodocus. Therefore the petition of Tschopp and Mateus (2016) requests only that the commission recognises de jure what is already the case de facto.

Anyone else who has strong feelings either in favour of or against the establishment of D. carnegii as a replacement type species for Diplodocus is welcome to submit their own comment to the ICZN. (I know of at least one person who has submitted a comment opposing the petition.)

The procedure is straightforward: just write your comment and email it to the Commision at (But it’s best also to copy your email to, as that seems to be where the ICZN is operating out of now: it took the NHM address four days to reply to my initial inquiry, but the Singaporean address responds quickly.)



23 Responses to “My comment in support of the Diplodocus carnegii ICZN petition”

  1. […] (Link) Back to School Thoughts (Link) More on an ICZN petition to preserve Diplodocus carnegii (Link) A Tiny Pterosaur (Link) / Un Pequeño Pterosaurio (Link) That Field Assistant (Link) The Road to […]

  2. Mickey Mortimer Says:

    “I know of at least one person who has submitted a comment opposing the petition.”

    That’s me.

    There are actually seven caudals plus a chevron which are still preserved and were redescribed by McIntosh and Carpenter (1998), who concluded the species was diagnostic and whose arguments Tschopp and Mateus never engage with. So no, not “a pair of non-diagnostic mid-caudals which no-one has paid any attention to since 1901.”

    I feel I adequately countered Tschopp and Mateus’ arguments and am happy to contribute to the literature in this case instead of endlessly sparring with Tim Williams on the DML over what parts of the ICZN should be ignored when we want a more complete type species/specimen.

  3. Are there any other Diplodocus caudal series of much value aside from the seven specimens included by Tschopp et al.? They could be useful in establishing the range of individual and serial variation we’re talking about here.
    The type specimen of Diplodocus longus has a combination of characters seen in no other specimen, and, in particular, it is clearly distinguishable from D. hallorum, as it lacks the anteriorly-placed neural arch and vertical neural spines that do not overhang the postzygapophyses of that species. As such, the only question about the validity of D. longus is its status relative to D. carnegii–it’s hardly a taxonomic problem which threatens taxonomic stability in any way.

  4. As far as your comment on D. longus potentially falling outside of traditional Diplodocus, its placement in Diplodocus is supported unambiguously among diplodocines by a ventral longitudinal hollow at least 10 mm deep in mid-caudal vertebrae and trapezoidal mid-caudal articular faces, as well as distoplatyan mid caudals unlike all diplodocines but Tornieria. So the placement of Diplodocus longus in Diplodocus is secure.

  5. Mike Taylor Says:

    No placement supported by a single character is ever secure.

  6. Supported by three characters, actually, as well as two or three characters which argue against its synonymy with D. hallorum. It also has two characters which differ from the type series of D. carnegii, though either could prove to be individual variation.

    To tell the truth, I would prefer it if Diplodocus was based on more informative material myself. However, the poor state of the Diplodocus longus type specimen doesn’t threaten taxonomic stability, so the decision to make D. carnegii the type specimen strikes me as more cosmetic than necessary (that said, I only recently graduated from college, so I acknowledge that my inexperience means I might be underestimating the inconvenience).

  7. Vahe Demirjian Says:


    I wrote a comment to the ICZN earlier this year in support of Case 3700, arguing that D. carnegii is based on complete material, even if D. longus could still be a valid Diplodocus species. Although an indeterminate diplodocine specimen from the Kirkwood Formation of South Africa (AM 6000) has a transverse ridge posteriorly interconnecting the prezygapophyses on the caudal vertebrae as in YPM 1920, the transverse ridge of AM 6000 is not as well-developed as that of the caudals of YPM 1920 (McPhee et al. 2016), suggesting that D. hallorum, D. longus, and AM 6000 might differ from one another in the degree of development of the transverse ridge posteriorly interconnecting the prezygapophyses on the caudal vertebrae. After reading an SVP 2016 abstract by Tschopp and colleagues whereby those authors retreat from their treatment of Diplodocus longus as dubious by suggesting that D. longus could be ancestral to D. carnegii and D. hallorum, I decided to write another comment to the ICZN whereby I’ve dropped my support for Case 3700 because a future paper based on the abstract by Tidwell et al. (2005) might confirm the “Morosaurus” agilis holotype as being from the same individual as YPM 1920.

    Blair W. McPhee, Philip D. Mannion, William J. de Klerk & Jonah N. Choiniere, 2016. High diversity in the sauropod dinosaur fauna of the Lower Cretaceous Kirkwood Formation of South Africa: Implications for the Jurassic–Cretaceous transition. Cretaceous Research 59: 228–248.

    Tidwell, V., K. Carpenter, and C. Miles. 2005. A reexamination of Morosaurus agilis (Sauropoda) from Garden Park, Colorado: Journal of Vertebrate Paleontology 25(supplement to 3):122A.

  8. Mickey Mortimer Says:

    Glad to see so much agreement here. The dinosaur community has recently lost sight of the fact that the type concept was never meant to indicate the most well preserved or described specimen/species. If it were, we’d have massive instability since many fossil taxa are based on incomplete specimens with more complete referred specimens that are then used “as the definitive exemplar of the genus …, as the foundation for numerous palaeobiological studies of the genus…” Think of the Sereno and Novas Herrerasaurus specimens with skull and forelimb vs. the partial holotype, the IGM Velociraptor specimens vs. the holotype skull, AMNH 5027 then Sue vs. the partial type Tyrannosaurus, Alioramus altai vs. type species A. remotus, AMNH 5339, UCMZ 1980.1 and RTMP 90.26.1 specimens of Struthiomimus compared to the fragmentary type, any of the complete Anchiornis, Sapeornis or Confuciusornis compared to the partial types, the Gansus skeletons compared to the type foot, etc, etc.. In the near future, expect this to apply to the three preliminarily described more complete Saurornitholestes specimens (MOR 660, UALVP 55700 and RTMP 88.121.39) compared to the fragmentary holotype, the Deinocheirus with the skull vs. the holotype arms, and for a non-dinosaurian example, Azendohsaurus madagaskarensis vs. type species A. laaroussii.

    As for D. carnegii being “the specifier for numerous important clades”, that’s due to authors not following Phylocode draft rules. Which are of course not even in effect. Using D. longus as the specifier as per Phylocode rules doesn’t cause any instability though, as everyone agrees it falls under the same concept of Diplodocus as D. carnegii.

  9. While I agree with Mickey that using *D.longus* as the type causes no phylogenetic issues, I must also admit that I’d rather we follow in the footsteps of *Archaeopteryx*, and use the most complete specimen as the type species for the genus; which is *D.carnegi*.

    Neither being the type affects *Diplodocus* in a significant way, and *D.carnegii* is more complete then *D.longus*, so I would prefer that *D.carnegii* become the type species for that reason, as it anchors the genus much more completely.

    But this is my amateur opinion only, of course!

  10. Mickey Mortimer Says:

    The most complete specimen of Archaeopteryx wasn’t chosen as the type species though. The holotype of the type species, A. lithographica (the London specimen), is jumbled anteriorly and missing most of the skull and hands. The equivalent to Tschopp and Mateus’ proposal in Archaeopteryx’s case would be to make the complete holotype of A. siemensii (the Berlin specimen) the type species. The Berlin specimen is the iconic Archaeopteryx after all.

  11. […] been interesting seeing the response to my comment on the ICZN petition to establish Diplodocus carnegii as the replacement type species of the genus […]

  12. Arjan Kop Says:

    I’ve read the proposaI and correct me if I’m wrong, but I didn’t see any particular need to assign a new type. In fact: “which no-one has paid any attention to since 1901” seems to indicate that the status of Diplodocus is actually quite clear. Why bother? Assigning neotypes is fine if the original types are lost and there is a need to redescribe a species, if the type series contains material of two species or something similar. In this case, it seems to be just a lot of discussion over nothing, which doesn’t do anything to help ensure stability. Assigning neotypes everytime a type loses a leg would keep millions of entomologists busy…

  13. Mike Taylor Says:

    Arjan (and others): see my folllowup post. In short, the idea that YPM 1920 is meaningfully the type of Diplodocus is a misleading legal fiction.

  14. Arjan Kop Says:

    But that’s the whole point. The current holotype is not posing any problems, or more precise, no-one seems argued that the holotype of the type species is not exemplary for the genus. Just ‘not being the best representative’ is no ground to make such a change.
    Many extant species are without types, and many more have types that are about as bad as they can get. I found one in a cardboard box, all in pieces kept together by a piece of paper, with many more individuals individually kept in pieces of that same paper surrounding it. Sad, but there was no discussion at that time about the description of that particular species, so there was no need to assign another type.

  15. Dean Mulyk Says:

    Just a question from a person who irregularity follows your blog. I am not a taxonomist, so please forgive my ignorance. Nor am I fully aware of the status of the various specimens in question.

    If people are certain that the other specimen should be the holotype why not just elevate it and or others to a paratype instead? Or, is the answer it is already?

  16. Mike Taylor Says:

    I don’t think you can make a specimen a paratype of a species if it’s not part of that species — an CM 84 is not part of D. longus. (Although some have suggested that longus and carnegii are the same species.)

  17. Mickey Mortimer Says:

    To answer Dean, a paratype by definition has to be part of the material originally referred to the species by the author. It’s not something that can be designated later. Since Marsh (1878) only mentions the holotype, Diplodocus longus will never have a paratype.

  18. […] at the start of September, I noted that Tschopp and Mateus (2016) had published a petition to the ICZN, asking them to establish Diplodocus carnegii as the type specimen of the genus Diplodocus — […]

  19. bricksmashtv Says:

    Speaking of McIntosh & Carpenter (1998), does anyone know where I can find this paper online (or if you have a PDF could you send it to me)?

  20. […] solution was to compare the vertebrae of A. louisae with those of Diplodocus carnegii, the default reference diplodocid, and see how they stacked up. With the cotyles scaled to the same vertical diameters, this is what […]

  21. […] Taylor 2017 is just a short comment on someone else’s ICZN petition. (In fact that one is so feeble I should just remove it from my CV.) […]

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