The Validity of Lambeosaurus - Anybody Know A Good Lawyer?

Reconstruction of Didanodon altidens specimen ROM 794 (aka Lambeosaurus lambei,
aka Procheneosaurus praeceps) by Matt Martyniuk, all rights reserved.

I've talked a lot on this blog about my personal justifications for using "old fashioned" names for many groups or species of stem-birds. In many cases, names which were in common use during the 19th and early 20th centuries were replaced later by one or two influential scientists for reasons which don't really hold up when you look at the codes that govern naming in biology. For example, Manospondylus gigas may currently be the correct name for the theropod we know and love as Tyrannosaurus rex, but this possibility has almost never been discussed because everybody assumes it's a nomen oblitum - a name out of use for so long that it becomes automatically invalid under the International Code of Zoological Nomenclature (ICZN). Note the word "assume"--as I've written before, most people, even working scientists, don't really know what criteria must be met to classify a name as obsolete.

The name of one very well-known dinosaur is in such a sorry state that it's like the Manosponylus / Tyrannosaurus debacle squared. The genus Lambeosaurus, a well-known hadrosaurid with a distinctive squared-off crest with a backward-pointed prong, was named twice prior getting its popular moniker, and neither of those names can be considered obsolete, since they were both coined during the 20th century.

The first name given to fossil material (in this case a jaw) now universally attributed to Lambeosaurus was Didanodon. In a 2006 review of hadrosaurs, Lund and Gates stated (without discussion) that the genus and its type species, Didanodon altidens, were nomina nuda, or "naked names" lacking the proper description necessary to establish them. But is this really the case?


The problem is that Didanodon was given its name in two parts, by different scientists in the same journal volume. Lawrence Lambe (the paleontologist who would later be honored in the name Lambeosaurus lambei) and Henry Fairfield Osborne co-edited a two-paper 1902 volume of the journal Contributions to Canadian Paleontology (part II), the entirety of which is public domain and can be downloaded as a pdf.

In his contribution, Lambe named and described a number of dinosaur species from what is now called the Dinosaur Park Formation of Alberta. One of these was a new species of hadrosaur which he classified in the genus Trachodon, as Trachodon altidens, based on a distinctive lower jaw. The description (on page 76 of the volume, see pdf) was fairly thorough, especially for the time, and nobody, not even nomenclatural sticklers, could possibly argue that T. altidens was not properly coined. In other words, there is no possible way to consider the name a nomen nudum as Lund and Gates did--it's too bad they did not provide any explanation for doing so.

Reconstructed Lambeosaurus
growth series by Nobu Tamura, licensed.

It's possible that Lund and Gates really intended to describe the genus Didanodon (not the species D. altidens) as a nomen nudum, but here's where things get sticky. Lambe, in his own paper, never considered T. altidens to be anything but a new species of Trachodon of the subgenus Pteropelyx. Osborne, on the other hand, suggested in his own section of the volume (page 19) that altidens could represent a new genus or subgenus, for which he proposed Didanodon. And that's the only mention I can find of the name Didanodon in the literature until 2006 (admittedly using a cursory Google Scholar search). It seems as though Osborne's name was either forgotten, completely overlooked, or dismissed as merely a non-binding suggestion.

Here's where the nomenclatural lawyering comes in. As typically interpreted, the ICZN mandates that a genus must be given a diagnosis and a type species to become "available" (official). However, for older papers, more leeway is given. Bear in mind that plenty of genus names that are accepted today went years without a clear type species (like Ornithocheirus, type species still a matter of dispute today!) or with no type species at all (like Pterodactylus). It is always possible to assign a type species to a genus at a later date without changing the status of the genus name as "available".

Furthermore, the ICZN provides that for any genus name coined before 1960, if only one species was included (i.e. the genus was monotypic when named), that species automatically becomes the type--a situation that would seem to apply to Didanodon altidens.

But can a genus named as basically an off-hand comment like that really be valid? This is controversial with other names, like Aviremigia, which was coined as a "suggestion" to be used if such a name is later deemed necessary. That name falls outside the purview of the ICZN, though, where anarchy will continue to rule until the establishment of the PhyloCode. Aviremigia is valid if you want it to be, and nobody can challenge you because there are no rules to do so by.

The ICZN, though, does have rules to govern the status of families, genera, or species named as "conditional proposals" (Article 15.1), and I think a statement which boils down to "this may be a new genus, in which case it is called Didanodon" is a clear case of a conditional proposal. It states that while any conditionally-proposed names coined after 1961 are invalid, those coined before 1960 may be valid if all the other conditions for naming a genus are met (i.e. it must be stated that the intent is to name a new genus, a type species is available, it's formed correctly when in Latin, etc.).

As far as I can tell, this is the case for Didanodon, which cannot, therefore, be considered a nomen nudum, contrary to Lund and Gates.

Ok, where does all this leave Lambeosaurus? There have generally been three widely-supported species assigned to Lambeosaurus: L. lambei, L. magnicristatus, and L. paucidens. L. paucidens is known from a paucity of material (see what I did there?), and is now generally considered either dubious or a synonym of L. lambei. Since it's from the same stratigraphic level and falls within the range of ontogenetic variation seen in L. lambei, there's really no reason not to consider it a synonym, at least provisionally. L. magnicristatus is generally considered distinct, but as pointed out by Evans and Reisz (2007), both known specimens come from a higher stratigraphic level than all other lambeosaurine species in the Dinosaur Park Formation, so it either completely replaced, or is a chronspecies of, the L. lambei. All of the potential older synonyms of Lambeosaurus, therefore, would become synonyms of Lambeosaurus lambei, specifically, and can't be considered nomina dubia.

Reconstruction of juvenile Didanodon altidens specimen
AMNH 5340 (previously Procheneosaurus praeceps)
by Matt Martyniuk, all rights reserved.

The other older synonym of Lambeosaurus lambei is Procheneosaurus praeceps, based on juvenile specimens that fit nicely into the known lambeosaurine growth series. Ontogeney is responsible for much of this taxonomic confusion, as juvenile lambeosaurines were originally thought to be adults of small-crested, small-bodied species known as "cheneosaurids" (Cheneosauridae is now a junior synonym of Hadrosauridae, and Cheneosaurinae of Lambeosaurinae).

It looks like Didanodon altidens is almost certainly the correct name for Lambeosaurus lambei. Can Lambeosaurus be saved? Only by petitioning the ICZN. This would certainly help tidy up the nomenclature and preserve a very widely used name. But here's where we all may have been retroactively lawyered by a previous ICZN decision from the early 20th century, also having to do with Procheneosaurus!
You see, as George Olshevsky has explained, Procheneosaurus was itself originally named, like Didanodon, without a type species in mind (in a photo caption, no less). The same juvenile lambeosaurine skeleton was later formally made the type specimen of Tetragonosaurus. This issue was brought before the IXZN to clarify, and they ruled that Procheneosaurus was valid, Tetragonosaurus was a junior objective synonym ,and as with all ICZN decisions, they added Procheneosaurus praeceps to the list of officially endorsed valid zoological names (ICZN Opinion 193). This may present a bigger problem than the dubious validity of Didanodon for poor old Lambeosaurus. It would be easy to have the ICZN officially suppress Didanodon altidens as a nomen rejectum (rejected name). But next in the line of priority is Procheneosaurus praeceps, which as we speak sits happily in the published lists of names with the ICZN stamp of approval.

Would the ICZN switch a name from a nomen conservandum (officially conserved name) to a nomen rejectum because a slightly newer name has since become very widely used? I don't know if there is precent for this or if there are any guidelines the ICZN would use to rule either way.

In other words, the only hope for the survival of our beloved Lambeosaurus is a good lawyer.

• Osborne, H.F. (1902). "Distinctive characters of the mid-Cretaceous fauna." Contributions to Canadian Paleontology, vol. III. Part II, On the Vertebrata of the mid-Cretaceous of the North West Territory.
• Lambe, L. (1902). "New genera and species from the Belly River Series (mid-Cretaceous)." Contributions to Canadian Paleontology, vol. III. Part II, On the Vertebrata of the mid-Cretaceous of the North West Territory.
• Lund, E.K. and Gates, T.A. (2006). "A historical and biogeographical examination of hadrosaurian dinosaurs." Pp. 263- in Lucas, S.G. and Sullivan, R.M. (eds.), Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35.
• Evans, D.C., and Reisz, R.R. (2007). "Anatomy and Relationships of Lambeosaurus magnicristatus, a crested hadrosaurid dinosaur (Ornithischia) from the Dinosaur Park Formation, Alberta." Journal of Vertebrate Paleontology, 27(2): 373-393.