Genus and species: Isaberrysaura mollensis; the generic name honors Isabelle Valdiva Berry, who reported the type specimen. The etymology of the specific name is not stated, but presumably refers to the locality Los Molles, or perhaps the Los Molles Formation.
Citation: Salgado, L., J. I. Canudo, A. C. Garrido, M. Moreno-Azanza, L. C. A. Martínez, R. A. Coria, and J. M. Gasca. 2017. A new primitive Neornithischian dinosaur from the Jurassic of Patagonia with gut contents. Scientific Reports 7, article number 42778. doi: 10.1038/srep42778.
Stratigraphy and geography: Los Molles Formation, Middle Jurassic (early Bajocian based on the presence of ammonite Sonninia altecostata), Neuquén, Argentina.
Holotype: MOZ-Pv 6549 (MOZ refers to the Prof. Dr. Juan Olsacher Museum of Zapala, Argentina), a partial skeleton with most of the skull and lower jaws, and unprepared postcrania including vertebrate (6 neck, 15 back, unstated number of hip, and 9 tail), a partial pelvis, a partial shoulder blade, ribs, and fragments.
The type and so far only known specimen of Isaberrysaura mollensis comes from the Neuquén Basin, which has certainly produced its share of dinosaurs over the years, but few as old as this. The Los Molles Formation is described as a large delta prograding into a marine setting. The presence of ammonites in the section indicates we're out to sea (ammonites were many things, but terrestrial was not one of them), so perhaps we're looking at a bloat-and-float to get our dinosaur into the marine rocks. Presumably we'll learn more about the taphonomy once the postcrania are prepared and described.
For a fairly early ornithischian, Isaberrysaura had attained a decent size. The skull is about a half-meter long (about 20 inches), and the whole thing is estimated as on the order of 5 to 6 m long (about 17 to 20 ft), which may be longer than any other ornithischian until we hit the Late Jurassic. Given the body is undescribed, all we have to go on at this time is the head, which is pretty unusual-looking. It's a bit like someone tried to assemble a Thescelosaurus skull using the bones from a Stegosaurus skull. It's got a narrow wedge shape, both in side view and top view. The infratemporal fenestra is large (the hole behind the eye on the lateral surface of the skull), larger than the opening for the eye itself, which apparently has two supraorbital bones (these are the bones that give most ornithischians stern "eyebrows"). The teeth in the tip of the upper jaw (the premaxillae bones) are somewhat bulbous and have pointed tips, while the cheek teeth (in the maxillae) have broader, flatter surfaces with some very prominent denticles (bits that stick out from the teeth, larger than serrations).
|Isaberrysaura, not yet having decided whether it would major in Applied Stegosaurics or Ornithopody. Figure 2 from Salgado et al. (2017), full caption available here. Note the difference between premaxilla teeth (e) and cheek teeth (f, g).|
With its unique mug, Isaberrysaura has kind of an ambiguous placement among ornithischians. Salgado et al. ran it through several data sets, two of which put it as a basal neornithischian (the group that includes ornithopods, horned dinosaurs, and boneheads), the other finding it to be a thescelosaurid (parksosaurid of their usage). The results also did not rule out the possibility that it was an armored dinosaur. This is where the postcrania could help. The whole procedure is hindered by the limited record of ornithischians up to the Late Jurassic. Before the Late Jurassic, we're mostly looking at heterodontosaurids (very weird in their own right), some small unspecialized bipeds like Lesothosaurus, a handful of early armored dinosaurs that haven't committed to being either ankylosaurs or stegosaurs, and a few straight-up stegosaurs. There's a lot of space for surprises like this one, which could be anything from an ornithopod with a Stegosaurus mask to an armored dinosaur resolutely doing its own thing.
But enough classification; let's get down to the guts of the matter. The type specimen of Isaberrysaura also came with a clutch of seeds. There appears to be two types of seeds, a smaller type of unknown origin about 1 cm (0.4 in) long (I'm eyeballing here), and a larger type about 2.5 cm (1 in) long, interpreted as coming from cycads based on their anatomy. Without a thorough discussion of the taphonomy, I can't offer more than generalities, but this case appears to be similar to the Kunbarrasaurus case, where a dinosaur specimen with possible gut contents was found in marine rocks. This helps the case, because it is comparatively unlikely that a batch of seeds (of two distinct size classes) and an unrelated dinosaur are going to meet at the bottom of the sea. If further analysis show that indeed the stuff is more or less all seeds, the specificity helps the case as well. There does not appear to be any anatomical argument against an identification as gut contents; the stuff is in a reasonable place in the body, and the skull appears capable of reasonably selective feeding. What does a seed-rich diet suggest? First off, seeds are popular with a lot of animals, not just strict herbivores, who take advantage of the resource when it is available. Another thing to note is that the cycad seeds are whole, suggesting the animal just gulped them down without any processing. This says nothing for arguments about ornithischian mastication and the presence or absence of cheeks, but does tie in with how some modern animals deal with cycad seeds. The edible outer part gets digested, and the harder inner part containing the actual cycad embryo gets deposited elsewhere. In addition, cycads today are toxic, including their seeds. Salgado et al. suggested that Isaberrysaura might have used microorganisms in its gut to deal with cycad toxins.
|A seedy beast, quite literally. Figure 3 from Salgado et al. (2017), full caption available here. Sub-figure b shows the two different seed types: the larger cycad seeds (c) and the smaller undetermined seeds (s).|
Salgado, L., J. I. Canudo, A. C. Garrido, M. Moreno-Azanza, L. C. A. Martínez, R. A. Coria, and J. M. Gasca. 2017. A new primitive Neornithischian dinosaur from the Jurassic of Patagonia with gut contents. Scientific Reports 7, article number 42778. doi: 10.1038/srep42778.
Very cool and nice write up. I have been hoping for new and early ornithischians for a while. Also on my wish list: a giant heterodontosaurid!!ReplyDelete
You're welcome! I could go for a giant heterodontosaurid, too, now that I think about it!Delete
This post sort of made me think, what exactly made the authors conclude this was a neornithischian? They note that their analysis doesn't rule out it being a thyreophoran, and almost every character it shares with random neornithischians, it shares with thyreophorans, and also has characters only shared with thyreophorans.ReplyDelete
I remain unconvinced it is a neornithischian rather than a thyreophoran.
I think part of the issue has to do with the data sets they chose to run it through, which as mentioned by a couple of people on Facebook are better for neornithschians than thyreophorans.Delete