Ankylosaur week, day 7: Animantarx

And so, here we are, at the end of it all. Ankylosaur week has come and gone, but oh what a week it was. As I said at the beginning, the whole aim was to save myself work and time by not producing anything new - and this worked, more or less. Did I clear the backlog? Did I hell, but at least I tried...

So which ankylosaur ends the series? Initially I had hoped to cover bizarre little Liaoningosaurus paradoxus but, I won't lie, my choice of taxa has, in part, been inspired by the presence of attractive images and, sad to say, for little Liaoningosaurus I've found squat other than the photo of the holotype. So instead we're going to look at Animantarx ramaljonesi, a nodosaurid from the Cedar Mountain Formation of Utah [the images above and below show a reconstructed commercially available skeleton of this species]. Specifically, Animantarx is from the (probably) Cenomanian Mussentuchit Member of the Cedar Mountain Formation: it was part of a diverse and biogeographically significant fauna that included the iguanodontian Eolambia as well as pachycephalosaurs, neoceratopsians, small titanosauriforms, tyrannosauroids, troodontids, birds and dromaeosaurids, as well as the little metatherian Kokopellia, early snakes and a host of other animals (Cifelli et al. 1997, 1999, Kirkland et al. 1998).

The discovery of Animantarx is particularly interesting: the holotype was discovered by retired University of Utah radiology technician Ramal Jones using a radioactivity-detecting scintillation counter (thanks to Don Esker for correction) in an area where no bone was exposed on the surface. This makes Animantarx the only dinosaur that's been discovered 'remotely', and by the use of technology rather than human observational skills alone. The partial skeleton that was recovered includes most regions of the body except the tail. Like that of a few other nodosaurids, the skull roof of Animantarx was strongly domed and a small postorbital horn was present [skull reconstruction shown below, from Carpenter et al. 1999]. The armour that decorated the side of its lower jaw only covered the posterior part of the jaw (mandibular armour was more extensive in later nodosaurids like Edmontonia and Panoplosaurus).

Back in 1999, Animantarx was announced in the same press release that also discussed a new, gigantic nodosaurid from the Cedar Mountain Formation. The giant was apparently similar in body size to a big adult African elephant, and hence perhaps 9-10 m long or so in total. This initially led to some confusion, with Animantarx being misidentified as gigantic by some. However, the giant taxon remains unnamed and isn't from the Mussentuchit Member anyway, but from the older Ruby Ranch Member (it would have been contemporaneous with the also very large Cedarpelta). Animantarx actually wasn't particularly big: perhaps 4.5 m long or so.

What sort of nodosaurid was Animantarx? Carpenter et al. (1999) suggested that it might be closely related to Texasetes as both have similar cervical vertebrae, but in a later study Carpenter (2001) showed Animantarx as being close to Edmontonia.

One final thing about Animantarx: its name is excellent. Meaning something like 'living fortress', it was inspired by Richard Swan Lull's comment of 1914 that a live ankylosaur must have been 'an animated citadel'. I congratulate the authors on this imaginative, euphonious name (well, actually, I congratulate Ben Creisler, as the authors thank him for creating the name). It's true that lots of palaeontologists are now being clever with the names they give their animals, and among dinosaurs it's particularly nice to see new 'roots' being used for particular groups of dinosaurs. Names ending in 'pelta' are increasingly being used for ankylosaurs, such that we now have Sauropelta, Dracopelta, Mymoorapelta, Cedarpelta, Glyptodontopelta, Aletopelta, Bissektipelta and Antarctopelta in addition to Stegopelta (named in 1905). Sad to say, there are still quite a few palaeontologists unable to do anything better than place-o-saurus, and among ankylosaurs we've recently been burdened with Zhongyuansaurus Xu et al. 2007 and Zhejiangosaurus Lü et al. 2007. Sigh.

Anyway - I hope you enjoyed the ankylosaurs. The mural picture below, depicting Animantarx, was kindly provided by Mike Skrepnick and is used with permission (© M. Skrepnick, all rights reserved). Farewell, spiky beach-wanderer, your presence will be missed...

Valentine's day: how come Tone always gets more cards than me?

Refs - -

Carpenter, K. 2001. Phylogenetic analysis of the Ankylosauria. In Carpenter, K. (ed) The Armored Dinosaurs. Indiana University Press (Bloomington and Indianapolis), pp. 455-483.

- ., Kirkland, J. I., Burge, D. & Bird, J. 1999. Ankylosaurs (Dinosauria: Ornithischia) of the Cedar Mountain Formation, Utah, and their stratigraphic distribution. In Gillette, D. D. (ed) Vertebrate Paleontology in Utah. Miscellaneous Publications, Utah Geological Survey (Salt Lake City), pp. 243-251.

Cifelli, R. L., Kirkland, J. I., Weil, A., Deinos, A. R. & Kowallis, B. J. 1997. High precision 40Ar/39Ar geochronology and the advent of North America's Late Cretaceous terrestrial fauna. Proceedings of the National Academy of Sciences 94, 11163-11167.

- ., Nydam, R. L., Gardner, J. D., Weil, A., Eaton, J. G., Kirkland, J. I. & Madsen, S. K. 1999. Medial Cretaceous vertebrates from the Cedar Mountain Formation, Emery County, Utah: the Mussentuchit local fauna. In Gillette, D. D. (ed) Vertebrate Paleontology in Utah. Miscellaneous Publications, Utah Geological Survey (Salt Lake City), pp. 219-242.

Kirkland, J. I., Lucas, S. G. & Estep, J. W. 1998. Cretaceous dinosaurs of the Colorado Plateau. New Mexico Museum of Natural History and Science Bulletin 14, 79-89.