Lambeosaurus crest reinterpretation

So, while looking through old JVPs I ran across this oddity. Perhaps it has already been discussed elsewhere. Any dino-guys out there, feel free to chirp in.

[I have to confess, I threw this one together rapidly and I made a mistake. Andrew Farke and Jaime Headden steered me in a better direction. Even so, there’s still something  to say here. After further examination, I learned something. And no, I did not misinterpret a tracing earlier. There was no tracing. I was working solely on the tracing by Evans and Reisz (2007.]

Evans and Reisz (2007) took a look at the skull of Lambeosaurus magnicristatus (Fig. 1) and identified the bones and plaster that make up the crest. They put the nasal above and behind the orbit in a narrow strip. That struck me as odd. Odd things make for interesting posts.

 From Evans and Reisz (2007)the skull of Lambeosaurus

Figure 1. From Evans and Reisz (2007) in which the skull of Lambeosaurus has really morphed beyond the primitive patterns such that the lateral and ascending processes of the premaxilla were greatly enlarged to form the anterior rim of a large crest. The gray areas represent plaster. That adds a problem in that the boundaries of the various bones that make up the crest become even more difficult to ascertain.

The pattern of the bones in the Lambeosaurus crest might be more like this:

Lambeosaurus skull bones colorized.

Figure 2. Lambeosaurus magnicristatus skull bones colorized. Darker areas are plaster. Orange is support metal. Note the larger extent of the nasal as part of the crest than figured by Evans and Reisz (2007). This pattern of a larger nasal is more like that of Corythosaurus than the other species of Lambeosaurus. This also replicates the triple strip premaxilla shared with Corythosaurus.

The strongest lines in the Lambeosaurus crest might define bone sutures. Or they might represent cracks. Or they might represent bone surface irregularities. I went with sutures. I might be wrong.

The image below of Corythosaurus, Hypacrosaurus and another species of Lambeosaurus (Fig. 3) helps set the possibilities of the extent of the premaxilla and nasal – along with the minor contribution by the prefrontal in the first two taxa.

Lambeosaur ontogeny

Figure 3. Lambeosaur ontogeny with bones colorized. Nasal in blue. Premaxilla in yellow. Image from Brink et al. 2011.

Overall the broad crest of L. magnicristatus (Figs. 1, 2) appears closer in morphology to that of Corythosaurus (Fig. 3). The premaxilla appears to have three ascending processes in both taxa. The crest is expanded to a larger extent than in the other two. There appears to be a contribution from the prefrontal that Lambeosaurus lambei (Fig. 3) crest does not have.

Here again, I’m stepping out of my comfort zone, but I’m avoiding the temptation of calling the nasal narrow just because L. lambei has a narrow nasal. They are all closely related taxa. I’m probably missing some of the fine points that differentiate them.

Again, sorry for the earlier mistake. It did lead to some interesting study.

We’ll take a look at bones that make up crests soon, as I see similarities here to the pterosaur Tupuxuara (by convergence, of course).

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References 
Brink KS, Zelenitsky DK, Evans DC, Therrien F and Horner JR 2011. A sub-adult skull of Hypacrosaurus stebingeri (Ornithischia: Lambeosaurinae): Anatomy and comparison. Historical Biology 23(1):63-72.
Evans DC and Reisz RR 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.

7 thoughts on “Lambeosaurus crest reinterpretation

  1. Unfortunately for you, they did not “give two premaxillary per side,” but that it is a consequent (as your own “shading” suggests) that they are a single, bilateral pair of premaxillae, converging around the external narial fossa. A simple homology trick also resolves the rest of your problems (and don’t think that researchers on lambeosaurines haven’t encountered the identification issue before, it’s just been resolved through examination of broken specimens). The frontal is consistently submerged beneath the posterior extension of the nasal, as it is in saurolophine and in lambeosaurine hadrosaurs, in which it forms a small vertical buttress that the nasal overlies and then extends lateral and caudal to it, hiding it from view (also acheived by expandion of the rim of the orbit (which is formed here by the frontal, of all things!

    I suggest working back through the cited literature and current research.

  2. Jaime is correct – the premaxillae are heavily modified in hadrosaurs, split into two limbs on each side, hence the appearance of being doubled. The original published interpretations are indeed the correct ones, based on direct examination of specimens, both for adults and ontogenetic series.

    • I will also note I have spent considerable time with the literature and original fossil specimens of hadrosaurs over the past year – in fact, there is one on my workbench right now – and have independently confirmed the “traditional” interpretation. Photos are great, but more than once I’ve been fooled by them, prior to seeing the original specimens (and sometimes even after). Cracks often look like sutures, and sutures like cracks, and sometimes sutures are along cracks! And more than once, I’ve *wanted* to see a suture because I expected it to be there, but careful consideration showed that I was just fooling myself.

  3. As a lover of Corythosaurus since I laid eyes on my first model Airfix Corythosaurus in 1979 I always felt that this Lambeosaurus was infact a giant Corythosaurus…and the crest follows the natural growth pattern shape. Im no scientist BUT it just seems obvious. Cheers.

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