Nodosaurus: more than a corduroy armadillo

Ankylosaurians, be they clubbed or club-less, labor in relative anonymity among dinosaurs, bundles of roughage trundling along, only briefly intersecting the limelight of flashier dinosaurs. A few get a bit more press, enough to put them in a respectable second tier of popularity (Ankylosaurus and Gastonia, particularly). Despite being the traditional namesake for the club-less ankylosaurs*, Nodosaurus is not one of them. Instead, it fills a role not unlike a venerable distant relative who occasionally shows up at family functions to hover on the sidelines. We know he or she is there and we show due deference, but there's no particularly warm connection of familiarity. The closest it's gotten to a star turn since it was named in 1889 was as a John Sibbick illustration in the "Normanpedia", where it is depicted as a sort of vaguely armadillo-like creature suspiciously eyeing the reader and bearing a precise gridwork of button-like armor pieces, without a hint of spikes or plates. Oddly, the skeletal restoration on the next page shows a distinctly different pattern of armor, featuring alternating bands of large scutes between the ribs and smaller pieces over the ribs, which unintentionally give it a sort of corduroy texture. As we shall see, there does indeed appear to a corduroy pattern over part of the animal, but there was also a lot more going on.

*This great tradition goes back all the way to the 1970s (Coombs 1978). Prior to this, ankylosaurs were just kind of there as one sort of mash. After this, ankylosaurs were still just kind of there, but now there were two flavors.

It's actually pretty easy to acquire a bibliography on Nodosaurus; all you need are three papers, Marsh (1889), Lull (1921), and Carpenter and Kirkland (1998), and everything else is commentary. They can all be found online for free, as well. As mentioned, Nodosaurus was named in 1889, by Marsh. He evidentially did not rate it among his highest achievements, although he did give it a perfunctory family (Marsh 1890) and thus saved us from Acanthopholididae potentially having priority. (His description of Nodosauridae, in its entirety, is "Heavy dermal armor. Bones solid. Fore limbs large. Feet ungulate." There's a haiku in there somewhere.)

Marsh (1889) is much better known for providing the name of Triceratops for his "Ceratops" horridus as well as two more species, T. galeus and T. flabellatus, which became one of his best jokes when he renamed it Sterrolophus. (Either that, or he had a genus quota he needed to fill that day.) New genus and species Nodosaurus texilis warranted most of a page and the only figure in the article, an illustration of some bony armor. Having never seen a large ankylosaur, he not unreasonably compared it to his old favorite Stegosaurus. The armor inspired both the genus name and species name ("textilis" after the coarse-fabric-like texture). Marsh reported that it was supported by the ribs and arranged in a series of rows. He also commented on the powerful forelimbs, the hands, the ribs with their T-shaped cross-sections, and the tail vertebrae. Finally, he estimated its length at a now-inexplicable 30 feet (9 meters), and provided the provenance, limited to the "middle Cretaceous of Wyoming." Lull (1921) and Carpenter and Kirkland (1998) come to the rescue regarding the provenance. The type specimen, Yale Peabody Museum (YPM) 1815, was found in 1881 by William H. Reed about 1.5 miles (2.4 km) southeast of Como Bluff's Quarry 13 in Wyoming. Although there has been some controversy about the formation, it probably came from a zone of septarian nodules in the Belle Fourche Member of the Frontier Formation, deposited in the early Late Cretaceous (Cenomanian) (Carpenter and Kirkland 1998).

The armor of Nodosaurus: the osteoderms that launched a few dozen species.

Marsh, of course, was of the "publish-and-forget" school, and never got around to doing more with Nodosaurus. It was left to Richard Swann Lull to provide a proper description, in 1921. By that point, YPM 1815 consisted of the pelvis, sacrum, fragments of the scapulae (shoulder blades), most of the left hind limb and part of the right, partial forelimbs, 13 complete caudal vertebrae and fragments of others, a mass bearing three dorsal vertebrae and their ribs and armor, another mass with ribs and armor, and various isolated armor pieces. Curiously, the caudals do not form one series but are from throughout the tail, which suggests to me that there was more of the skeleton at one point. The obvious suggestion in hindsight is that this was a bloat-and-float.

The armor of Nodosaurus is usually depicted either as Lull's bony corduroy or Sibbick's grid. As illustrated in an interpretive figure in Lull (1921) with a transparent overlay, there actually is a segment of in situ armor preserved as Lull described it, with large pieces forming a band between ribs, from somewhere along the torso. This is not all, though. Although Nodosaurus in either Lullian or Sibbickian form is always depicted with only knobs of armor, Lull devoted a fair chunk of the article to the *other* scutes, spines, and plates, which were not included in his influential restoration. Lull was impressed with the diversity of armor, finding it to class with notably spiky and plated Hoplitosaurus, which he thought might be a synonym at the genus level. A couple of salient points for anyone wishing to illustrate Nodosaurus:

• Unlike various other ankylosaurs, such as Polacanthus and Stegopelta, there was no armor tightly attached to the ilia, so apparently no sacral shield as we are now used to seeing. Lull found two rows of scutes flanking the spines of the sacral vertebrae but did not think that armor actually extended over the broad ilia themselves, based on the distribution of blood vessel impressions. In addition, instead of the corduroy extending over the hips, these scutes were flat (not nodular) and hexagonal (not squarish or rectangular).
• Nodosaurus had a healthy selection of keeled, pointed, and spiny osteoderms, including: a keeled plate, possibly from the base of the tail; a pointed plate found near the 17th tail vertebra, interpreted as part of a row on the upper surface of the tail; and a spine-like plate larger than those known for Hoplitosaurus, at least in fore-and-aft diameter, and perhaps as much as 25 cm (10 in) tall. Lull did not illustrate most of these, for which you will have to turn to Carpenter and Kirkland (1998).

Lull (1921)'s restoration, which highlights the known bones and includes some useful information about the size, but omits the spikes and plates.

Generally, most obscure dinosaurs are obscure because they're known from marginal material, or they aren't the right kind of dinosaur (generally the bitey kind, but relative dinosaur popularity fluctuates over time). Nodosaurus gets a bit from both Column A and Column B, but it's certainly deserving of more attention, and could stand a thorough modern redescription (as well as a re-think in the illustration department). It's almost a century since Lull (1921), after all.

Incidentally, in some lists, you may see that Nodosaurus textilis includes as many as four specimens. These other specimens are the type specimens of Hierosaurus coleii (now Niobrarasaurus), Hierosaurus sternbergii, and Stegopelta landerensis, so essentially all of the poorly known Western Interior Seaway ankylosaurs. This was following the synonymies in Coombs (1978), which were frustratingly presented without discussion. Nodosaurus, true Nodosaurus, is known from nothing but the holotype YPM 1815.

References:

Carpenter, K., and J. I. Kirkland. 1998. Review of Lower and middle Cretaceous ankylosaurs from North America. New Mexico Museum of Natural History and Science Bulletin 14:249–270.

Coombs, W. P. 1978. The families of the ornithischian dinosaur order Ankylosauria. Palaeontology 21(1):143–170.

Lull, R. S. 1921. The Cretaceous armored dinosaur, Nodosaurus textilis Marsh. American Journal of Science (5th series) 1(2):97–126.

Marsh, O. C. 1889. Notice of gigantic horned Dinosauria from the Cretaceous. American Journal of Science 38:173–175.

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