Sunday, September 14, 2014


No doubt you are sick of hearing about giant sauropods, and another post about Spinosaurus would cause headaches, nausea, and vomiting (if not, there's The Bite Stuff, Skeletal Drawing [one and two], The Theropod Database Blog, and Theropoda [one and two], as well as a bevy of news media accounts). What you need is an ornithopod, and fortunately we have one, a dryosaurid known as Eousdryosaurus nanohallucis by way of the Late Jurassic of Portugal. For those of you not fortunate enough to be an initiate (yet), dryosaurids were modestly-sized bipedal herbivores, mostly legs and tail, on the order of 3 or 4 meters long. Like all modestly-sized bipedal herbivores of an ornithischian persuasion that did not include any unusual skeletal features like frills or domeheads, they were once considered hypsilophodonts. Detailed study and the discovery of more "hypsilophodonts" showed that what we now call dryosaurids were more derived ("advanced", for you time-travelers from the past) ornithopods than most of the "hypsilophodonts", and formed a small knot of Middle Jurassic to Early Cretaceous dinosaurs known mostly from leg and pelvic remains. Dryosaurids as a whole are among the most obscure dinosaurs, being small herbivores with no unusual features. If you run across one in popular media, it's probably there to serve as background filler or carnivore chow. They are not to be confused with the considerably more threatening dyrosaurids, extinct crocodilians that lived from the Late Cretaceous to the Eocene. As if in warning of this, the Paleobiology Database currently has "Dryosaurus phosphaticus" (which ought to be Dyrosaurus) as a species of Dryosaurus. Dryosaurus is the flagship dryosaurid, and if you'd like to spend some time in contemplation of it, you can check the Carnegie Museum of Natural History's page on how they remounted their specimen (previously in a panel mount featuring the classic "bipedal dinosaur standing partially upright like a dope"), or Dinosaur National Monument's page.

A more naturalistic stance. NPS photo of the Carnegie's new mount.

On to the guest of honor, Eousdryosaurus:
  • Genus and species: Eousdryosaurus nanohallucis, the genus name meaning "eastern Dryosaurus" in reference to this dinosaur being a Dryosaurus-like animal on the east side of what was then a young Atlantic ocean, and the species name referring to the reduced hallux, or big toe
  • Citation: Escaso, F., F. Ortega, P. Dantas, E. Malafaia, B. Silva, J. M. Gasulla, P. Mocho, I. Narváez, and J. L. Sanz (2014). A new dryosaurid ornithopod (Dinosauria, Ornithischia) from the Late Jurassic of Portugal. Journal of Vertebrate Paleontology 34(5):1102–1112.
  • Stratigraphy and geography: Praia da Amoreira-Porto Novo Member of the Alcobaça Formation, upper Kimmeridgian Stage (Upper Jurassic), Porto das Barcas, Lourinhã, west-central Portugal
  • Holotype: SHN(JJS)-170 (Sociedade de História Natural, Torres Vedras, Portugal), a partially articulated specimen including the last sacral (hip) vertebra, the first eight tail vertebrae and their chevrons, the left ilium (the main bone of a dinosaur hip, usually being substantially longer than tall and forming roughly the upper half of the hip socket), the left hind leg, and the right thigh bone (femur).
You may be familiar with the Lourinhã Formation, and truth be told the Praia da Amoreira and Porto Novo names are usually associated with that formation. Leaving aside the subtleties of stratigraphic nomenclature, fully as complex and persnickety as biological nomenclature, the Alcobaça and Lourinhã formations are present in the same general area (the region of the broad projection into the Atlantic Ocean interrupting what would otherwise be a fairly linear coastline), and were deposited at about the same time, although the Alcobaça Formation is reported to skew older and more marine. The Portuguese rocks form a sort of triumvirate of Upper Jurassic dinosaur localities with the firmly terrestrial Morrison Formation of western North America (where we get Allosaurus, Apatosaurus, Camarosaurus, Diplodocus, Stegosaurus, and pals), and the Tendaguru Beds of Tanzania (Dicraeosaurus, Elaphrosaurus, Giraffatitan, Kentrosaurus, etc.), which like the Portuguese rocks exhibits marine and brackish-water influence. These three formations are noted for having comparable animal life, showing that the provincialism of dispersing continents wasn't yet in full effect: the same groups were present, more or less, in the three areas, although the genera and species differed. Mateus (2006), linked above, has a chart that details the faunas; there's been some things added or tweaked since then, but you get the idea. With the description of Eousdryosaurus, we see the same thing for dryosaurids: similar albeit distinct animals in all three, with Dryosaurus altus in the Morrison and Dysalotosaurus lettowvorbecki in Tendaguru.

So, how does Eousdryosaurus fit in with the other dryosaurids? Conveniently, it is known from leg and pelvic remains, which means it is comparable with practically all other dryosaurids. The type individual seems to be a bit on the small side, estimated around 1.6 m long, appropriate for an immature Dryosaurus or Dysalotosaurus (curiously, dryosaurids seem to have had different growth patterns than other dinosaurs, and experienced indeterminate growth; we don't have evidence for skeletally "adult" examples of Dryosaurus or Dysalotosaurus [Horner et al. 2009; Hübner 2012]). Eousdryosaurus differed from other dryosaurids in a number of skeletal details. The feature that inspired its species name is the greatly reduced "big toe"; there's only a metatarsal and a single lonely phalanx bone. Most ornithopods either had two phalanges or eliminated this toe altogether.

Below is a sort of "flash card" for known dryosaurids, providing a quick reference to the time and place (you'll have to click to expand). I've been toying with doing something like this for a while; the continents are easy, but geologic ages tend to vary between publications over decades: formation ages become better refined, they occasionally move up or down a stage, and the dating of the stages has changed over time. No, Kangnasaurus did not exist over 45 million years; there's just poor age constraint on the rocks it was found in.

Click to embiggen; it expands like one of those spongesaurs.


Escaso, F., F. Ortega, P. Dantas, E. Malafaia, B. Silva, J. M. Gasulla, P. Mocho, I. Narváez, and J. L. Sanz (2014). A new dryosaurid ornithopod (Dinosauria, Ornithischia) from the Late Jurassic of Portugal. Journal of Vertebrate Paleontology 34(5):1102–1112.

Horner, J. R., A. de Ricql es, K. Padian, and R. D. Scheetz. 2009. Comparative long bone histology and growth of the ‘hypsilophodontid’ dinosaurs Orodromeus makelai, Dryosaurus altus, and Tenontosaurus tillettii (Ornithischia: Euornithopoda). Journal of Vertebrate Paleontology 29:734–747.

Hübner, T. R. 2012. Bone histology in Dysalotosaurus lettowvorbecki (Ornithischia: Iguanodontia)—variation, growth, and implications. PLoS ONE 7:e29958. doi: 10.1371/journal.pone.0029958.

Mateus, O. 2006. Late Jurassic dinosaurs from the Morrison Formation, the Lourinhã and Alcobaça Formations (Portugal), and the Tendaguru Beds (Tanzania): a comparison. New Mexico Museum of Natural History and Science Bulletin 36:223–231.

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