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Dryosaurids 101

The views expressed are those of the author and are not necessarily those of Scientific American.


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Dryosaurus, here pursued by the theropod Ceratosaurus. From wikipedia.

For no particular reason, I decided today to tweak text that originally appeared in the 2001 book Dinosaurs of the Isle of Wight (Naish & Martill 2001). Which dinosaurs did I choose to publish on? The most exciting of them all: the dryosaurids. I was kidding about the exciting part. The following text is really basic, and only intended for people who’ve never heard of these dinosaurs before. NB – don’t confuse Dryosauridae with Dyrosauridae. The latter is a clade of fossil longirostrine crocodilians, known from the Cretaceous, Paleocene and Eocene.

Pedal skeletons of Dysalotosaurus, from Galton (1981). The two images on the left show the same foot as seen from its dorsal (l) and ventral (r) side. These are surprisingly long, slender, narrow feet for an ornithopod. Digit I was absent in these animals. The foot at far right only has the third and fourth digits preserved. Scale bars = 50 mm.

Dryosaurids were medium-sized (c. 3-4 m total length) long-legged ornithopod dinosaurs with small forelimbs and proportionally small, short-snouted skulls. Because they’re superficially similar to ornithopods like Hypsilophodon, dryosaurids were once thought to be ‘hypsilophodonts’, and hence regarded as somehow ancestral or antecedent to the group that includes Iguanodon and the hadrosaurs. We now think that dryosaurids are members of Iguanodontia (though outside Ankylopollexia: the camptosaurid + Iguanodon + hadrosaur clade), and hence not close to Hypsilophodon. Undoubted dryosaurid records are from the Upper Jurassic and Lower Cretaceous (though read on). Dryosaurids were first reported in the 1870s from North America, were discovered in Africa early on in the 20th century, and were recognised in the European fossil record during the 1970s (the fossils concerned had been found much earlier, but misidentified as those of other kinds of ornithischian).

The type species for the group is Dryosaurus altus (Marsh, 1878) from the Morrison Formation of the USA’s Western Interior. A similar Tanzanian species (known from thousands of remains) was originally named Dysalotosaurus lettowvorbecki Virchow, 1919: some authors regard it as congeneric with Dryosaurus while others argue that obvious differences better support genus-level distinction (Hübner & Rauhut 2010). A lot of ink has been spilt over the similarity evident between the American and Tanzanian species and what this might mean for Jurassic biogeography (e.g., Galton 1977), but it now seems that the dinosaurs of these two regions aren’t as similar as once thought.

Reconstructed skeleton of Dysalotosaurus, as displayed at the Museum für Naturkunde, Berlin. Wow - was the tail skeleton really that long? Image by Masur, from wikipedia.

Lower Cretaceous English dryosaurid remains represent the species Valdosaurus canaliculatus (Galton, 1975). A Nigerian dryosaurid was originally named Valdosaurus nigeriensis Galton & Taquet, 1982 but has more recently been renamed Elrhazosaurus Galton, 2009. Kangnasaurus coetzeei Haughton, 1915 from the Lower Cretaceous of South Africa also seems to be a dryosaurid (McDonald et al. 2010). Callovosaurus leedsi (Lydekker, 1889), known only from a femur from the Middle Jurassic Oxford Clay Formation of England, has been identified as a dryosaurid (Ruiz-Omeñaca et al. 2007), in which case it’s the oldest iguanodontian. Because this identification pulls the origin of Iguanodontia down into the Callovian of the Middle Jurassic, the ghost lineages of many ornithopod taxa (including Hypsilophodon, Rhabdodontidae and Tenontosaurus) must be even longer than previously proposed (Weishampel et al. 2003, Naish & Martill 2008).

[PS - just to be clear on the citations and what I do, and do not, provide full references for... sometimes, when I mention an animal’s scientific name, I also list the name’s authorship. In order to distinguish this from a citation that I provide in the references, I include a comma. So, the full name for our species is Homo sapiens Linnaeus, 1758: when I mention ‘Linnaeus, 1758’ there, I don’t feel the need to add the full reference for that publication to the article’s bibliography. When binomial names become changed over time, we denote this by putting the taxon’s authorship in brackets. Example: Felis leo Linnaeus, 1758 is now Panthera leo (Linnaeus, 1758). This is a standard I’ve applied throughout Tet Zoo (I maintain it, where possible, across technical publications too), but I thought I should take time here to explain it.]

Given that dryosaurids appear both in the northern, Laurasian continents and the southern, Gondwanan ones, and originated prior to the fragmentation of these landmasses, it seems likely that they will eventually prove extremely widespread. Indeed, various fragmentary remains from the Upper Cretaceous of New Zealand, Antarctica and Argentina have all been suggested to belong to dryosaurids (see Ruiz-Omeñaca et al. 2007).

Skull of Dryosaurus altus, from Galton (1983).

Dryosaurids were bipedal with cursorial hindlimb proportions. Three long toes are present on each foot and a first toe, aka hallux, is absent (the toes thus represent digits II, III and IV). The dryosaurid skull is short and tall with large orbits shaded above by elongate, rod-like palpebral bones. In life, the palpebrals would have supported soft-tissue ‘shelves’ jutting out above the animal’s eyes, giving them a frowning demeanour much like than seen in living birds of prey. A peculiar feature of the dryosaurid skull is that the nostrils are open dorsally: there is no bar from the rostralmost portion of the premaxilla that joins the nasal over the top of the nostril.

Unlike Hypsilophodon and more primitive ornithopods, dryosaurids lacked premaxillary teeth, meaning that all cropping of food was performed solely by the beak – something common to nearly all iguanodontian ornithopods (there are annoying exceptions, like Tenontosaurus dossi). Dryosaurid maxillae and dentaries house serrated, leaf-shaped teeth which possess prominent ridges on the vertical midline. These teeth indicate that dryosaurids were leaf-eating herbivores.

While preparing this article I was surprised to find how few good life restorations there are of these dinosaurs. There are Greg Paul’s (but they’re not really available online)… and that’s about it. The other stuff is mostly terrible.

Anyway, for previous Tet Zoo articles on iguanodontian ornithopods, please see…

And for the Scientific American series on the ‘explosion of Iguanodon’, see…

Refs – -

Galton, P. M. 1977. The ornithopod dinosaur Dryosaurus and a Laurasia-Gondwanaland connection in the Upper Jurassic. Nature 268, 230-232.

- . 1981. Dryosaurus, a hypsilophodontid dinosaur from the Upper Jurassic of North America and Africa. Postcranial skeleton. Paläontologische Zeitschrift 55, 271-312.

- . 1983. The cranial anatomy of Dryosaurus, a hypsilophodontid dinosaur from the Upper Jurassic of North America and East Africa, with a review of hypsilophodontids from the Upper Jurassic of North America. Geologica et Palaeontologica 17, 207-243.

Hübner, T. R & Rauhut, O. W. M. 2010. A juvenile skull of Dysalotosaurus lettowvorbecki (Ornithischia: Iguanodontia), and implications for cranial ontogeny, phylogeny, and taxonomy in ornithopod dinosaurs. Zoological Journal of the Linnean Society 160, 366–396.

McDonald, A. T., Kirkland, J. I., DeBlieux, D. D., Madsen, S. K., Cavin, J., Milner, A. R. C. & Panzarin, K. 2010. New basal iguanodonts from the Cedar Mountain Formation of Utah and the evolution of thumb-spiked dinosaurs. PLoS ONE 5(11): e14075. doi:10.1371/journal.pone.0014075

Naish, D. & Martill, D. M. 2001. Ornithopod dinosaurs. In Martill, D. M. & Naish, D. (eds) Dinosaurs of the Isle of Wight. The Palaeontological Association (London), pp. 60-132.

- . & Martill, D. M. 2008. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: Ornithischia. Journal of the Geological Society, London 165, 613-623.

Ruiz-Omeñaca, J. I., Pereda-Suberbiola, X. & Galton, P. M. 2007. Callovosaurus leedsi, the earliest dryosaurid dinosaur (Ornithischia: Euornithopoda) from the Middle Jurassic of England. In Carpenter, K. (ed) Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs. Indiana University Press (Bloomington & Indianapolis), pp. 3-16.

Weishampel, D. B., Jianu, C.-M., Csiki, Z. & Norman, D. B. 2003. Osteology and phylogeny of Zalmoxes (n. g.), an unusual euornithopod dinosaur from the latest Cretaceous of Romania. Journal of Systematic Palaeontology 1, 65-123.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com! Follow on Twitter @TetZoo.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Heinrich Mallison 10:32 am 07/27/2011

    let me check Janensch 1961 for you – I bet he explains why he reconstructed the tail of Dysalotosaurus at that length :)

    Link to this
  2. 2. Heinrich Mallison 10:39 am 07/27/2011

    Janensch (1961) writes:

    “Der Schwanz ist beim Skelett von Dysalotosaurus um einige Wirbel länger ergänzt, als das bei den zwei von C. W. GILMORE konstruierten Skeletten von Camptosaurus, C. browni und C. nanus, geschehen ist. Die sehr gestreckte dünne Form der hintersten Schwanzwirbelkörper bei Dysalotosaurus kann wohl für einen recht langen Schwanz sprechen.”

    The tail has been replenished in the skeleton of Dysalotosaurus a few vertebrae longer than in the two skeletons of Camptosaurus, C. browni and C. nanus, constructed by C. W. GILMORE. The very elongated thin shape of the most posterior caudals in Dysalotosaurus does likely indicate a rather long tail

    The tail is a composite, with only the first 5 caudals belong together, and the final 12 are modelled by hand. Janensch chose to have 48 vertebrae all in all, and fitted different caudals by shape, trying to match sizes.

    Link to this
  3. 3. Heinrich Mallison 10:42 am 07/27/2011

    oh, the reference:

    Janensch, W. 1961. Skelettrekonstruktion von Dysalotosaurus lettow-vorbecki. Palaeontographica Suppl. VII Erste Reihe 237-240

    Link to this
  4. 4. naishd 10:45 am 07/27/2011

    That’s great, thanks a lot. It might be perspective, but the tail in that photo looks not only long, but also massive: almost tenontosaur-like in proportion to the rest of the body. Based on other iguanodontians and non-iguanodontian ornithopods, you’d certainly expect over 45 or even over 50 caudal vertebrae.

    Link to this
  5. 5. Paul Barrett 3:39 am 07/28/2011

    You might be interested to know that a redescription of Valdosaurus, including lots of previously undescribed material, is currently in press, due out in October. No life-reconstruction though…

    Link to this
  6. 6. Michał 4:42 am 07/28/2011

    Regarding Dysalotosaurus: wasn’t it formally described by Josef Pompeckj in 1920, with Virchow mentioning the name but not formally describing the taxon? I ask because I don’t have the original papers and there are contradictory statements about the authorship of the name in the literature.

    For what it’s worth, Nomenclator Zoologicus states that Pompeckj is the author:

    http://www.ubio.org/NZ/detail.php?uid=63671&d=1

    Link to this
  7. 7. naishd 5:20 am 07/28/2011

    Paul: that’s good news; at the moment the literature on Valdosaurus is scattered and messy. And some of the material (including that figured in Dinosaurs of the Isle of Wight) is great.

    Michal: it’s correct that Pompeckj diagnosed and described the taxon, but credit for coming up with the name (originally Dysalotosaurus lettow-vorbecki: yes, with hyphen) goes to Virchow (1919). Nomenclator Zoologicus is incorrect.

    Darren

    Link to this
  8. 8. BrianL 5:54 am 07/31/2011

    I’ve finally decided to register. I guess I’d hate to see the Tet Zoo commenters community die or at least get decimated over something so trivial.

    Anyhow, dryosaurids and (small) ornithischians in general often go overlooked. I think this is especially true for rhabdodontids. The information on those guys is very scattered and limited. What I basically wonder is what I should imagine rhabdodontids to have been like, in terms of external appearance and ecology. Is it also correct to imagine them as being odd, European island fauna?
    I also wonder if my impression of iguanodontians evolving several independent large-bodied clades in the lower Cretaceous is correct. Thanks already.

    Link to this
  9. 9. naishd 6:58 am 08/2/2011

    Thanks, Brian. I’ve done everything I can behind the scenes to get registration and logging-in removed, but I don’t think SciAm are going to go for it. I’m not happy about it, but not much I can do beyond leaving for elsewhere.

    I agree that the less showy ornithischians don’t get much popular coverage, and I aim to do my best to balance this in time. I’ll definitely be writing about rhabdodontids: recall that I recently did fieldwork in the Hateg Basin. So far as we know at the moment, yes, rhabdodontids were endemic to Cretaceous Europe, but they have a ghost lineage that extends back to the Jurassic and we know nothing of their early history. Large size in Iguanodontia probably evolved at least twice: in tenontosaurs and ankylopollexians. And maybe three times, depending on where you think the muttaburrasaurs go. I’ll have to blog about all of this at some stage.

    Darren

    Link to this
  10. 10. Mike from Ottawa 8:32 pm 08/7/2011

    Darren,

    When you say there are thousands of specimens of Dysalotosaurus how many individuals do these represent?

    BTW, on the registration guff, I’ve registered, logged in a week or more ago and have remained logged in since then. For folk considering the bother of registering and having to log in regularly, it may not be necessary to do it more than once, at least from one machine. If it is possible to just remain logged in essentially forever, it isn’t too much of a PITA and folk should be able to live with that.

    And Darren, if you do up stakes and shift TetZoo, we’ll follow you. None of the blog networks are of any significance, only the blogs.

    Link to this

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