In 1868, paleontologist Joseph Leidy and artist Benjamin Waterhouse Hawkins collaborated on a freestanding mounted skeleton of Hadrosaurus. This was the first time dinosaur fossils had ever been displayed in this way, and the exhibit captured the public imagination like nothing before it. I’ve already written lots about the Hadrosaurus mount (see First Full-Sized Dinosaurs and A Visit to the Academy of Natural Sciences), but it seems there is still more to say.
Hadrosaurus mount under construction in Hawkins’ studio. Image from Carpenter et al. 1994.
Today, I’m interested in the Hadrosaurus head, or rather, the sculpted replica that stood in for its head. As I’ve covered before, the Hadrosaurus fossils recovered near Haddonfield, New Jersey accounted for less than a third of the animal’s skeleton. With two nearly complete limbs, 28 vertebrae, a partial pelvis and scattered teeth, Hadrosaurus was the most complete dinosaur known at the time, but a great deal of it was still unknown. Specifically, Hawkins had to create a skull from scratch, and conventional wisdom (e.g. these articles) has always been that he based his reconstruction on the skull of an iguana. That makes a certain amount of sense, since Leidy interpreted the Haddonfield teeth as having belonged to an herbivore, and an iguana is a contemporary herbivorous reptile.
Hadrosaurus teeth and dentary (plus some Astrodon teeth on the lower left). From Leidy 1865.
Let’s explore that claim a little more, though. The plate above presumably represents the entirety of the Hadrosaurus cranial material Leidy and Hawkins had to work with. In addition to an assortment of isolated teeth, they had two sections of a dental battery – that is, the grinding surface made up of interlocking teeth that we now know is typical of large ornithopods. One of the battery portions came from the lower jaw (Figs. 24 and 25) and one came from the upper (Fig. 26). The sculpted Hadrosaurus skull, which Academy of Nautral Sciences Associate Curator Ted Daeschler confirms is the only surviving part of the historic mount, is pictured below. Note that Hawkins plainly incorporated the dental batteries into his reconstruction, rather than straight rows of iguana-style teeth.
Hadrosaurus replica skull at Academy of Natural Sciences. Source
So in at least one detail, the Hadrosaurus model skull is not just a scaled-up version of an iguana. The thing is, though, now that I’m really looking at it, the model doesn’t look much like an iguana skull at all beyond the basic silhouette. Look at that broadly flared jugal, the strongly curved postorbital and especially the way the premaxilla and maxilla curve downward in a beakish fashion. None of these characteristics are present on your run-of-the-mill iguana skull, but they are so extreme and precisely modeled that I would be very surprised if expert anatomists like Leidy and Hawkins simply invented them.
Labeled Iguana iguana skull by Udo Savalli.
What does this mean? There are a few options.
- Hawkins and Leidy didn’t closely reference anything when creating the Hadrosaurus skull, and just made something up.
- Hawkins and Leidy based the Hadrosaurus skull on some contemporary reptile other than a green iguana.
- Hawkins and Leidy had more Hadrosaurus cranial fossils than we know about.
Option three is, of course, the interesting one, and is where I would appreciate if any actual hadrosaurid experts in the house would let me know if I’m talking nonsense. But don’t those peculiar non-iguana-like characters on the sculpted Hadrosaurus skull look just a bit like the actual hadrosaurid skulls that would be found in the 20th century?
Kritosaurus skull at AMNH. Photo by WikiMedia user Ryan Somma.
That downward-tilting rostrum in particular looks suspiciously similar. Is it possible that there was a more complete Hadrosaurus skull at the Haddonfield site, but it was lost or destroyed before Leidy’s publication? Maybe it was considered too fragmentary to collect and was left in the field, or maybe it fell apart in transit (J.B. Hatcher hadn’t invented field jacketing yet). Hawkins might have attempted to interpret sketches or hazy descriptions of lost material, and ended up with the model skull that survives today. I realize that this isn’t much to go on, and that it’s impossible to prove without some thorough archival research. But it is cool to think that maybe, just maybe, there was a bit more to the first American dinosaur than we known about.
References
Carpenter, K., Madsen, J.H. and Lewis, L. (1994). “Mounting of Fossil Vertebrate Skeletons.” In Vertebrate Paleontological Techniques, Vol. 1. Cambridge, UK: Cambridge University Press.
Leidy, J. (1865). “Cretaceous Reptiles of the United States.” Smithsonian Contributions to Knowledge Vol. 14, Article VI.
EXTINCT MONSTERS 
Very informative article.