Sunday, November 6, 2016


Out of the blue, my supervisor recently asked me if I knew anything about a piece of art depicting a shall-we-say stylized and retro dinosaur labeled "Claosaurus" at the Berlin Aquarium. This was one of those odd coincidences that we are taught to avoid in fiction: I'd been thinking about writing a post on Claosaurus, and now I was being commanded by the gods of serendipity. I've had a soft spot for this modestly publicized duckbill since before I was ten, when I read about it in a magazine and it became my first "hipster" dinosaur. (My second was Epanterias, because this was the late '80s/early '90s, when iconoclasts like Bob Bakker and Greg Paul had just raised the siren song for the splitting of Allosaurus fragilis and the community was not yet hardened by cynicism about mysterious giant theropods not known from enough material to draw a dirty look in the express checkout.)

Anyway, Claosaurus is one of Marsh's babies, via a typically circuitous route. The type species, C. agilis, is based on one of the rare dinosaur skeletons (Yale Peabody Museum [YPM] 1190) known from the Western Interior Seaway, like several of our friendly nodosaurs. It was recovered during the Yale expedition of 1871 from near Russell Springs in Kansas. By spring 1872, Marsh had a preliminary description ready, by which I mean a paragraph slotted into the miscellaneous items. In it he provides some measurements for the feet and vertebrae, dubs it Hadrosaurus agilis, and calls it a day after promising to provide a more substantial description "at an early date". The species does not appear to have greatly troubled his sleep, because "an early date" turns out to be early 1890. By this time, he has obtained more of the original specimen. It does not receive a great deal more treatment, buried as it is as one of the last items in a paper mostly devoted to his beloved Triceratops, although it does get a new generic name (Claosaurus) and one of the bones is figured. He also puts it in a new family, the Claosauridae, in recognition of "Only a single row of teeth in use [not sure how he determined this, as no other authors have cited it]. Cervical vertebrae opisthocoelian. Limb bones solid. Fore limbs small, and feet ungulate." In case you were wondering, Claosauridae never caught on, and has been basically dead since the turn of the 20th Century (Hatcher 1902).

The ilium (upper hip bone) of Claosaurus agilis in Marsh (1890), in which Claosaurus gracefully accepts its consolation prize of a new genus and family in lieu of a thorough description.

Claosaurus agilis managed to escape a detailed description for about 70 years, although it could not escape display. The skeleton was put into a panel mount, which unfortunately isn't great for accessibility. YPM 1190 has a more significant handicap, though: although most of the skeleton is there, something like 95% of the skull is composed of hope and plaster. Unless you are a titanosaur, paleontologists tend to forget about you if you don't have at least one decent skull bone. It was left to Lull and Wright to give it its first real description in their classic 1942 monograph. The reader quickly encounters another significant handicap: although most of the bones are indeed there, they are also almost invariably crushed and flattened. With the poor preservation, Lull and Wright can do little more than provide measurements and general characteristics. They define the genus by its still having Metatarsal I (the metatarsal that for us supports the big toe) and potentially by its "peculiar, broad, leaflike" teeth. The metatarsal would go on to be Claosaurus's one trump card for memorability. Unfortunately, Carpenter et al. (1995) devote a decent amount of space to exploding this claim: they find it more likely that the one actual bone in question (incidentally mounted as if it were the fifth metatarsal, which would be even more unusual) is actually the missing left fifth metacarpal, a hand bone (the one supporting the little finger in humans). Claosaurus agilis has remained difficult to work with, with Carpenter et al. (1995), Prieto-Márquez (2011), and Prieto-Márquez et al. (2016) each taking some time to gnaw on the poorly preserved bones but ultimately being unable to come up with a large number of distinguishing characteristics. It's agreed that C. agilis represents something near the base of Hadrosauridae, whether just within or just without, and it comes from a time and place that are not well-represented by dinosaurs (late Coniacian beds of the Smoky Hill Chalk Member, Niobrara Chalk Formation, Kansas per Prieto-Márquez 2011), but there's just not enough information left in YPM 1190 to build a particularly warm and detailed portrait of what could otherwise be an important species.

A selection of C. agilis's greatest hits, from Prieto-Márquez et al. (2016) via a Wikimedia Commons intermediary.

But that's not all! There are two other species that have been named to Claosaurus over the years. One of them we can deal with in a few lines. This is C. (?) affinis, "named" (more accurately mentioned with the unfulfilled promise of a later description) by George Wieland in 1903 for three large toe bones that are mostly of interest for showing the presence of hadrosaurs in the Pierre Shale of South Dakota. For unknown reasons the original type material was mislaid, and Lull and Wright (1942) mistakenly described a misplaced bone from YPM 1190 as C. (?) affinis, as later recounted by Gregory (1948), who found the actual intended type. So much for C. (?) affinis, doomed to linger forever as a taxonomic ghost.

The other species, though, was a keeper. The other species is C. annectens. Not immediately familiar? How about Edmontosaurus, or Anatosaurus? Marsh again gets the credit for C. annectens, although he must also get the credit for the idiosyncratic idea to include it in Claosaurus. Maybe he hadn't looked at C. agilis recently. At any rate, Marsh must have found this species much more interesting than C. agilis, because he both named (1892a) and published a skeletal reconstruction (1892b) in a single year. You may have seen a version of his reconstruction before, but here it is again.

From Marsh 1892b. I have no idea how the hip or the tail are supposed to work with the ischia running into the chevrons.

Hadrosaur nomenclature has often been a land of "every author for himself or herself", but it was particularly chaotic in the pre-Lull and Wright days, when Claosaurus, Diclonius, Hadrosaurus, Thespesius, and Trachodon duked it out for supremacy to represent large crestless duckbills. Creisler (2007) and the Wikipedia article on Edmontosaurus annectens give useful summaries of the situation. From Marsh's time up through Lull and Wright, C. annectens traveled under all of these genera. Lull and Wright temporarily stabilized the situation by making it the type species of new genus Anatosaurus, which later found its way to Edmontosaurus where it remains to this day, albeit sometimes uneasily.

And, finally, about the Berlin Aquarium? I have no documentary evidence, but I'm extremely confident that the animal depicted is actually C. annectens (aka Edmontosaurus), not C. agilis. C. annectens, after all, is the species that Marsh reconstructed, making it the obvious candidate for an artist. Incidentally, the "Claosaurus" piece is one of a group at the aquarium; its companions can be seen over at dinosaurpalaeo. The artwork dates to 1913, when the Aquarium was added to the Berlin Zoo (another bit of evidence which tallies with annectens, "Claosaurus" still being commonly used for its genus then). The artist was Heinrich Harder. These particular pieces do not show off his talents to their best advantage. I have to think that some of the odd aspects of the "Claosaurus", particularly its posture and proportions, are due to the constraints of the space, because he certainly could paint a duckbill that looked reasonably like a duckbill for the early 20th century, and he was capable when dealing with mammals.

Harder's mastodon, from here. I just like this mastodon, okay? For additional bonus mastodons, the pdf for Marsh 1892b below also includes Marsh's skeletal reconstruction.


Carpenter, K., D. Dilkes, and D. B. Weishampel. 1995. The dinosaurs of the Niobrara Chalk Formation (upper Cretaceous, Kansas). Journal of Vertebrate Paleontology 15(2):275-297.

Creisler, B. S. 2007. Deciphering duckbills: a history in nomenclature. Pages 185–210 in Carpenter, K. (editor). Horns and beaks: ceratopsian and ornithopod dinosaurs. Indiana University Press, Bloomington and Indianapolis, Indiana.

Gregory, J. T. 1948. The type of Claosaurus (?) affinis Wieland [not the whole thing, but almost all of it]. American Journal of Science 246(1):29–30.

Hatcher, J. B. 1902. The genus and species of the Trachodontidae (Hadrosauridae, Claosauridae) Marsh. Annals of the Carnegie Museum 1:377–386.

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

Marsh, O. C. 1872. Notice on a new species of Hadrosaurus. American Journal of Science (3rd series) 3(16):301.

Marsh, O. C. 1890. Additional characters of the Ceratopsidae, with notice of new Cretaceous dinosaurs. American Journal of Science (3rd series) 39(233):418–426.

Marsh, O. C. 1892a. Notice of new reptiles from the Laramie Formation. American Journal of Science (3rd series) 43(257):449–453.

Marsh, O. C. 1892b. Restorations of Claosaurus and Ceratosaurus. American Journal of Science (3rd series) 44(262):343–340.

Prieto-Márquez, A. 2011. Revised diagnoses of Hadrosaurus foulkii Leidy, 1858 (the type genus and species of Hadrosauridae Cope, 1869) and Claosaurus agilis Marsh, 1872 (Dinosauria: Ornithopoda) from the Late Cretaceous of North America. Zootaxa 2765:61–68.

Prieto-Márquez, A., G. M. Erickson, and J. A. Ebersole. 2016. Anatomy and osteohistology of the basal hadrosaurid dinosaur Eotrachodon from the uppermost Santonian (Cretaceous) of southern Appalachia. PeerJ 4:e1872.

Wieland, G. R. 1903. Notes on the marine turtle Archelon. I. On the structure of the carapace. II. Associated fossils. American Journal of Science (4th series) 15(87):211–216.

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