Sunday, August 27, 2017

75 years of "Hadrosaurian Dinosaurs of North America"

This Thursday will mark the 75th anniversary of the publication of "Hadrosaurian Dinosaurs of North America", published August 31, 1942. Written by Richard Swann Lull and Nelda E. Wright, "Hadrosaurian Dinosaurs of North America" is one of the classics of dinosaur science, and even today is one of the basic building blocks of any serious work on duckbills. As a GSA Special Paper, it is available for download, so if you have institutional access and pretty much any level of scholarly interest in hadrosaurs, you should pick up a copy.

Seventy-five years is a long time in dinosaur paleontology, and you may be dubious about the value of the book after all this time. To be honest, some parts are outdated, and some parts have aged better than others. The taxonomy and paleobiology sections are the most dated parts, while the anatomical discussion, measurements, and historical information are still more or less applicable. The scope of the book is ambitious, including basically everything worth knowing about North American hadrosaurs in 1942, from lists of specimens by location, to a discussion of the paleobotany of hadrosaur-producing formations, to a detailed anatomical section encompassing not only bones but the musculature and sense organs, to features of skin impressions, to tables of measurements, to a section of photographs, and of course the inevitable taxonomy and paleobiology, illustrated throughout by dozens of line drawings. You could easily make a case that hadrosaurs were the most completely known group of non-avian dinosaurs by 1942, thanks to abundant skeletons from Alberta, Montana, South Dakota, and Wyoming, and they probably remain such today. Tyrannosaurs are catching up, but they have a ways to go yet, and there aren't as many species nor as many skeletons. The sad thing is that there were even more ambitious plans for this volume: the original plan, as described in the introduction, was to cover *all* ornithopods (then including pachycephalosaurs, as "tröodonts"), worldwide. The reduction in scope was probably for the best; I certainly can't complain about the unity of focus. However, given how Lull and Wright handle "Anatosaurus", it would have been interesting to see how they would have handled Iguanodon. Maybe it would have disintegrated a little more gracefully.

I don't wish to cop images from the publication, so enjoy some AMNH duckbills instead. Here's Kritosaurus (in its Gryposaurus make-up).

Lull and Wright '42 opens with a short historical overview, which feels a little thin but is made up for by the historical information included in the taxonomic section. The historical overview also skips around a bit by geography, instead of being entirely chronological, so after going through the Alberta digs of the 1910s it detours to older work in New Mexico and Wyoming. This is followed by geologic and geographic distributions, with fold-out tables (liable to tear if you look at them funny when dealing with a physical copy, but then this is true of many 75-year-olds). Radiometric dating was barely a thing in 1942, so you will not find dates appended to the formations, although the introduction does put the time span from the Late Triassic to the end of the Cretaceous as 160 million years, which is pretty good if you include most of the Late Triassic with the Jurassic and Cretaceous. The inclusion of all of North America means that the finds east of the Great Plains are not neglected; Lull and Wright don't have a lot to say about most of the reports, because the material is generally very scrappy, but you at least get to read about the handful of finds in places like Alabama, Mississippi, and North Carolina. The geographic section is based around lists of specimens with catalog numbers, included material, and collectors, with all of the major institutions accounted for.

A discussion of paleoecology follows. This is one of the areas that has suffered, mostly because the authors interpret hadrosaurs as having "an aquatic or at least an amphibious mode of life" (p. 29). Their reasoning for this stems from their interpretation of the hands and tail as adapted for swimming, and the articulations of the limbs as not as well-finished as those of dinosaurs they regard as fully terrestrial. Interestingly, the jaws and teeth are not included in these aquatic adaptations; Lull and Wright's duckbills may be swimmers, but they are not scum-gummers. The authors are quite impressed with hadrosaurian feeding adaptations, describing derived hadrosaurs as possessing "a most perfect and efficient denture, not only for immediate but for indefinitely continued use, since no individual has been found in which the teeth were failing because of senescence" (p. 31). In fact, the main problem for the authors is figuring out what such perfect dentition was used for, eventually settling on horsetails (Equisetum). (Lull and Wright seem to have missed the German discussion on the Senckenberg mummy gut contents, Abel 1922 and Kräusel 1922, although they do include the papers in the bibliography.) They offer comparisons to the marine iguana and the moose. Regrettably, it seems that no one else at the time paid attention to their dietary discussion and happily kept feeding hadrosaurs on a soft diet of watercress and lily pads and such. It took a long time for the "duck bill = duck habits and diet" idea to die, but die it eventually did. The anatomical arguments made by Lull and Wright were disassembled in a number of sources, including Ostrom (1964), Galton (1970), and Bakker (1986). The "webbed hand" is now identified as distorted padding, and hadrosaur hands themselves are quite un-paddle-like, with short squat fingers and small surface area compared the hadrosaurs that were supposed to be swimming or steering with them. In addition, the hand cannot be rotated so that the palm faces backward (Senter 2012), leaving the poor swimming duckbill only the ability to "karate-chop" the water. The tail, although it certainly has tall spines near the hip, does not have a swimmer's profile and its mobility is restricted by bony tendons. The articular surfaces are not all that poor compared to the surfaces of other dinosaur limb bones.

The "Trachodon mummy", reaching out for...

Outside of the parts that have to do with aquatic hadrosaurs, the paleoecological and paleobiological sections are not terribly out of date, except in terms of obsolete names used for genera or formations. There are taxonomic tables of the plants and vertebrates found in hadrosaur-bearing formations, the former being of particular interest because a lot of us who are interested in or work with dinosaurs don't really know a lot about plants. On the question of defense, Lull and Wright more or less shrug their shoulders and make some vague statements about hadrosaurs using their moderate speed and presence of mind to avoid theropods on land. Tyrannosaurus gets called out as clumsy based on the laws of physics, with a quotation from a 1915 publication by William Diller Matthew: " animal which exceeds an average elephant in bulk, no matter what its habits, is compelled by the laws of mechanics to the ponderous movements appropriate to its gigantic size." Take that, T. rex! Lull and Wright mention that "none of the carnivorous dinosaurs gives evidence of ability to stalk or creep up on its prey" (p. 44), which is a bit unfair given that stealth rarely fossilizes. The authors also are puzzled by the absence of young hadrosaurs, which gets into the "cheneosaur" ball of wax coming up later. The "evolutionary trends" section is only a couple of pages and a diagram, the diagram itself not too unlike what someone might come up with today (except for the cheneosaurs) and the discussion itself being very dry stuff.

The anatomy section is based around Edmontosaurus and Anatosaurus (so, really, just Edmontosaurus), and is one area where the reduction in scope from all ornithopods to North American hadrosaurs is helpful; it's easier to work with just one group of anatomically similar animals! Because numerous hadrosaur skeletons were known by 1942 and all of the bones were well-represented, the descriptive parts of this section are still more or less as accurate today as they were then. One interesting point made by Lull and Wright here and in a section on posture and locomotion is that the anatomy of the hip is such that if the animal stands partially upright, the ball of the femur is braced against the weak joint of the ilium and pubis, instead of the strong ilium by itself. Therefore, hadrosaurs would not have habitually risen up in the human-like postures so frequently shown in old restorations and skeletal mounts. (Their point is somewhat undercut by the use of a reared hadrosaur for several diagrams.) They spend several pages on ossified tendons and note how they would have stiffened the tail, but never quite commit to the implications for using the tail for swimming. One of the more unusual features of the book is a detailed discussion of the muscles (including a healthy caudofemoralis, here identified as the coccygeo-femoralis). There is also a putative cheek muscle (their "buccinator"), included "to retain the food in the mouth"; Lull, as it turns out, was perhaps the leading pre-Dinosaur Renaissance booster of the cheeked dinosaur idea.

There is also a very useful summary of hadrosaur skin impressions. A few of their observations include:
  • Hadrosaur skin was notably thin
  • Hadrosaur beaks were up to several cm long and vertical. (The upside of this is that they would have all looked like they had thick solid mustaches.)
  • Impressions from the forearms of two different hadrosaur species (an edmontosaur and a corythosaur) show both had very large scales over the leading edge of the forearm
  • Integument on the thigh seems to have gone directly over the limb without folding around it; in other words, the thigh was "within the body" like a modern bird, and motion would have been mostly at the knee instead of the hip.
  • Hadrosaurs may all have had frills along the midline of the back, and some (but not all) had exaggerating features atop the frill (triangular objects in "Kritosaurus incurvimanus")
  • Different hadrosaurs had different scalation (see also Bell [2012, 2014] for further developments on this theme)
The anatomy section wraps up with a discussion of brain casts and the senses, including placement of the external ear. The authors infer that the sense of hearing was well-developed, which they regard as implying that hadrosaurs could make sounds.

A shot of the cutout exposing part of the skin impressions on the off-side of the Corythosaurus "mummy".

The last section of text is the taxonomic section, in which Lull and Wright discuss every North American fossil species that had been identified as a hadrosaur up to their writing. Although there is a great deal of useful information, this is also a section that has gone out of date in some notable ways. It's not so much the species that aren't there; if you check, the only significantly different group that wasn't known yet is the brachylophosaurs, most of the rest of the post-1942 species being additional species of genera already known. It's the species that *are* there, most notably a subfamily called Cheneosaurinae. Aside from amphibious hadrosaurs, the thing that most reminds the reader that this was written 75 years ago is that Lull and Wright accept what we now know as juvenile and subadult crested hadrosaurs as small adults of their own lineages. Thus, there are Cheneosaurus and Procheneosaurus (must resist urge to get in another dig at Lull for Procheneosaurus) and a bunch of species of Corythosaurus and Lambeosaurus that are no longer recognized. Edmontosaurus is also affected by this, with six species of Edmontosaurus and Anatosaurus we recognize today as growth stages of two species. (It might surprise you, but the Anatosaurus solution presented here is a great improvement on the chaotic treatment of the "North American flat-headed duckbill" that reigned for decades.) As mentioned, every North American species that had been considered a hadrosaur at one time gets an entry, so we get a half-page for Pneumatoarthrus peloreus (which the authors recognize as non-hadrosaurian and is now known to be a sea turtle, albeit one that sounds more like a lung condition), a page for Hadrosaurus tripos (now known to be a whale, from a misidentified geologic unit), and a few inches each for a bunch of tooth taxa, many of which Lull and Wright recognize as non-hadrosaurian. One usage difference you may notice is that Lull and Wright use "nomen nudum" where modern authors would use "nomen dubium".

Anatosaurus copei to Lull and Wright, today the grown-up stage of Edmontosaurus annectens. These are impressively big animals, even if the one on the far side would be in a pain in its backside if it made a habit of standing like that. In the background are several skulls and two Corythosaurus panel mounts, including the public face of the Corythosaurus "mummy".

The volume ends with a series of tables of measurements, a bibliography, and plates. Aside from some of the species and genera names used, these sections are more or less "nonperishable". If you're looking to scale anything, for, say, drawing/restoration purposes, you could do a lot worse than the tables. I do think the publication would have benefited from larger illustrations in the plates, but presumably there were cost issues to consider as well.

This brings us to the end of the book. It wears its 75 years pretty well; at worst, the ideas presented are in step with the times, and it is innovative in several areas, including diet, posture, and various aspects of external appearance. As long as people are still interested in hadrosaurs, it should remain an important reference.


Abel, O. 1922. Diskussion zu den Vorträgen R. Kräusel and F. Versluys. Paläontologische Zeitschrift 4:87. [in German]

Bakker, R. T. 1986. The Dinosaur Heresies. Kensington Publishing Corp., New York, New York.

Bell, P. R. 2012. Standardized terminology and potential taxonomic utility for hadrosaurid skin impressions: a case study for Saurolophus from Canada and Mongolia. PLoS ONE 7(2):e31295.

Bell, P. R. 2014. A review of hadrosaurid skin impressions. Pages 572–590 in D. A. Eberth and D. C. Evans, editors. Hadrosaurs. Indiana University Press, Bloomington, Indiana.

Galton, P. M. 1970. The posture of hadrosaurian dinosaurs. Journal of Paleontology 44(3):464–473.

Kräusel, R. 1922. Die Nahrung von Trachodon. Paläontologische Zeitschrift 4:80. [in German]

Lull, R. S., and N. E. Wright. 1942. Hadrosaurian Dinosaurs of North America. Geological Society of America Special Paper 40.

Ostrom, J. H. 1964. A reconsideration of the paleoecology of the hadrosaurian dinosaurs. American Journal of Science 262(8):975–997.

Senter, P. 2012. Forearm orientation in Hadrosauridae (Dinosauria: Ornithopoda) and implications for museum mounts. Palaeontologia Electronica 15.3.30A.

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