Sunday, August 26, 2018

Dryosaurus elderae and the revenge of Nanosaurus agilis

It's been a busy few days over at The Compact Thescelosaurus, with new alvarezsaurs, nodosaurs, and dryosaurs. For this post, I'm going to focus on Carpenter and Galton (2018), which not only describes new species Dryosaurus elderae, but also is quite important for previous subject Nanosaurus agilis, and in general ticks off several of my boxes anyway ("hypsilophodonts", Morrison Formation, National Park Service areas, etc.).

Figure 2 from Carpenter and Galton (2018), showing the distribution of bipedal Morrison ornithischians. A keen-eyed observer who's familiar with the Morrison fauna might notice the absence of Drinker nisti and Othnielosaurus consors, and an abundance of Nanosaurus agilis...

Dryosaurus elderae

Dryosaurus elderae is actually pretty familiar for a new species, because it is based on a skeleton that has long been the public face of Dryosaurus.

Clipped from Carpenter and Galton's Figure 27; A is CM 3392, the holotype of Dryosaurus elderae, in panel mount form; B is the same specimen in a new freestanding mount.

Genus and species: Dryosaurus elderae; the generic name is a combination of the Ancient Greek "drys" referring to "oak" or "forest", apparently for the inferred environment of the animal, and "sauros" for "lizard", and the species name honors the late Ann Elder, a National Park Service paleontologist and geologist who worked at Dinosaur National Monument. This gives us "Ann Elder's forest lizard".
Citation: Carpenter, K., and P. M. Galton. 2018. A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA. Geology of the Intermountain West 5:167–207.
Stratigraphy and geography: The holotype and the four referred specimens all come from the Carnegie Quarry of Dinosaur National Monument in Uintah County of northeastern Utah. The quarry, in turn, is in the middle Brushy Basin Member of the Morrison Formation, and you probably don't need me to remind you that it's Late Jurassic in age.
Holotype: CM 3392 [Carnegie Museum of Natural History, Pittsburgh, Pennsylvania; occasionally the acronym is given in the literature as CMNH instead], a partial articulated skeleton including the skull and lower jaw, six cervicals, thirteen dorsals, the sacrum, rib pieces, the pelvis, the right shoulder girdle and humerus, pieces of the right femur and tibia, the articulated left foot, and three other complete or partial metatarsals. Most of the skeleton was discovered in March 1910, with the head and partial neck found later. The specimen was exhibited as a panel mount at the Carnegie from the 1940s to the early 2000s, when it was converted to a freestanding mount which went on display in 2006 (Carpenter and Galton 2018).

Four other specimens from the quarry have also been assigned to this species, the most significant being a partial juvenile (CM 11340), and a braincase (CM 87688) which had gotten into the holotype of Camptosaurus aphanoectes and made it seem strange enough to warrant a distinct genus for a while (Uteodon). D. elderae differs in various details from D. altus and Dysalatosaurus lettowvorbecki, such as a deeper maxillary ramus of the jugal below the orbit, relatively elongate cervicals, and a longer, lower ilium (Carpenter and Galton 2018). We spent some time with dryosaurids way back in 2014, and not a lot has changed since then, except I'd extend the Morrison species into the early Tithonian. Carpenter and Galton (2018) prefer including Dysalatosaurus lettowvorbecki in Dryosaurus, and also consider the generic-level distinctiveness of Eousdryosaurus nanohallucis to be questionable. They also note that CM 1949, a putative "Dryosaurus" specimen from Wyoming included in the Horner et al. (2009) growth rate paper, seems to be an undescribed form with a camptosaur-like ilium and a dryosaur-like leg, which would have something of an adverse effect on Horner et al.'s conclusions for Dryosaurus.

The revenge of Nanosaurus agilis

When we last checked in with Nanosaurus agilis, it was a historical curiosity known from a single specimen limited more or less to bone impressions. Carpenter and Galton (2018) come to a new conclusion that, if you accept it, instantly catapults N. agilis back into scientific relevance: that N. agilis is the same thing as the other attempts at describing small bipedal Morrison "hypsilophodont-grade"* ornithischians, namely Drinker nisti, Nanosaurus rex (aka Othnielia), and Othnielosaurus consors. Because N. agilis is the oldest name, it winds up the winner. You can think of N. agilis and Drinker as names given to the youngest individuals, and the Othnielosaurus/"Othnielia" specimens as older (but not necessarily fully grown).

*Yes, I'm well aware that "hypsilophodonts" are about as monophyletic as the clade of people named "Frank"; you can mentally replace "hypsilophodont" with "small bipedal ornithischian of nebulous classification" if you'd prefer, but my way's shorter.

Carpenter and Galton (2018) find that the various specimens assigned to Drinker nisti, Nanosaurus agilis, and Othnielosaurus consors share a set of characteristics that are unlike those found in the other bipedal Morrison ornithischians (Fruitadens haagarorum, Dryosaurus altus and elderae, and Camptosaurus dispar and aphanoectes). For example, in the dentary, there are:
  • Dentary tapering anteriorly
  • Gently convex ventral border of dentary
  • Anterior dentary teeth slightly procumbent (lean forward)
  • Widely spaced posterior dentary teeth
  • Tooth roots well exposed
  • Dentary tooth row continuing almost to the symphysis (the joint at the front)
  • Triangular crowns wider than the roots
  • Coronoid process (the part that sticks up) inline with tooth row rather than offset laterally

Figure 7 from Carpenter and Galton (2018), showing various jaws of the Morrison "hypsilophodont" (A through K) with Fruitadens (L), Dryosaurus (M), and Camptosaurus (N) for comparison.

In my opinion Carpenter and Galton have successfully demonstrated that there is basically one Morrison "hypsilophodont", although this doesn't necessarily exclude the possibility of anatomically similar species within the sample, as with the two Morrison species of Camptosaurus and Dryosaurus. The second part of their argument, that the Morrison "hypsilophodonts" should all be Nanosaurus agilis, may be harder to accept given the admittedly poor quality of the N. agilis holotype, and one could argue that it should be avoided. I'm not sure where that would leave the name of this taxon; it could be back to Othnielia rex, or maybe new combination Drinker consors if rex is also thought to not be up to snuff. However, the type of N. agilis does include a reasonably clear impression of a tooth-bearing dentary, which shows all of the features mentioned above. On that basis, it's hard to say that Nanosaurus agilis doesn't deserve serious consideration as the name of record.

Miscellaneous observations

The type material of Drinker nisti could not be located at two institutions where it was supposed to have been at one time or another. I suppose the other logical possibility would be in Bob Bakker's possession, as the original lead researcher.

In case you were wondering, no word on the other putative bipedal Morrison ornithischians Brachyrophus altarkansanus, Laosaurus celer, L. gracilis, Symphyrophus musculosus, Tichosteus aequifacies, or T. lucasanus, which is understandable considering that the sum total of fossils of those six species amounts to something like two to three dozen vertebral centra and some bits of limb bones. If someone else wants to take them on, they aren't going anywhere.


Carpenter, K., and P. M. Galton. 2018. A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA. Geology of the Intermountain West 5:167–207.

Horner, J. R., A. D. Ricqlès, 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(3):734–747.


  1. We now live in a world where Troodon has lost relevance at the hands of its long-time synonym Stenonychosaurus, but formerly dubious Nanosaurus has consumed the more well-known Othnielosaurus and Drinker.

    1. Hi,

      Drinker isn't exactly a well-known dinosaur, because despite being discussed and illustrated in technical and popular literature since 1990, no one had the chance to examine the material first-hand. Galton (2007) only focused on teeth of Morrison ornithischians and his erection of Othnielosaurus for L. consors have been rendered arbitrary by Carpenter and Galton (2018). However, comparing the current Troodon situation with the current Nanosaurus situation is inappropriate because almost no one thought that the Dinosaur Park material referred to Troodon might represent more than one species, even though the describers of Talos stressed the possibility of Troodon being dubious.

    2. Sorry, maybe I wasn't quite clear. I'm not complaining about these classic names falling out of usage. My comment also wasn't really a comparison of the two situations. I was simply stating how bizarre and neat it is that our understanding and nomenclature can shift so quickly, and how a popular name like Troodon or Othnielosaurus could fall out of usage at any moment, for whatever reason, whether through synonymy or by being shown to be dubious.

    3. Troodon has been on borrowed time for a long time. It should have been declared a nomen dubium long before recent publications declared the last rites. Objectively, there's no reason why Troodon should've been treated any different to Deinodon and Trachodon.
      As for Drinker, it's disgraceful that the material has apparently disappeared. IIRC, Bakker suggested that it was a tree-climber; but like a lot of his ideas, this should probably be taken with a barrow of salt. Still, it'd be good to examine the original material.

  2. I like Nanosaurus replacing Othnielia, Othnielosaurus and Drinker. It just feels neat and tidy, somehow. One thing that does bother me, though, is the lack of comparison to non-Morrison basal neornithischians and ornithopods such as Kulindadromeus, Hexinlusaurus, Agilisaurus, and Hypsilophodon. I'd like to know how many of the characters supporting their synonymy are actual synapomorphies.

    Given that there are two species of Dryosaurus and Camptosaurus in the Morrison, I expect that there will be two species of Nanosaurus as well. Could it be anagenesis in action?

    1. Concerning diagnostic characters: therein lies the rub. It's one thing to have a form in the Morrison that can be distinguished from other Morrison dinosaurs, and another thing to have it be diagnostic among other ornithischians.

      (And if there are multiple species of Nanosaurus, it may be the case that Nanosaurus agilis is undiagnostic within the genus Nanosaurus, although that also strays toward the whole conceptual can o' worms about what paleontological genera and species represent.)

    2. Hypsilophodon has been consistently recovered as a basal ornithopod by most cladistic studies except that for Burianosaurus by Madzia et al. (2017), who use Clypeodonta to include Hypsilophodon and Cerapoda. By contrast, Agilisaurus, Hexinlusaurus, and Kulindadromeus have been recovered outside Cerapoda, including by Boyd (2015). If Nanosaurus, Kulindadromeus, Agilisaurus, and Hexinlusaurus form a monophyletic clade in a future cladistic analysis, then Nanosauridae would be the only available name for that clade.

    3. That's not really what I was talking about. What I meant to say was that, because Carpenter and Galton didn't compare Nanosaurus agilis, Othnielia rex, Othnielosaurus consors, and Drinker nisti to other basal neornithischians, it is unclear whether the similarities they listed between the specimens of those four species are actual synapomorphies linking them together, or neornithischian symplesiomorphies. If all of the similarities that were highlighted are symplesiomorphic, then their overall similarity simply reflects their common nature as basal neornithischians and the lack of meaningful differences between the specimens is a result of their incompleteness preventing the recognition of diagnostic characters. If, however, those characters are synapomorphic, then those four species form a clade and the lack of meaningful differences between the specimens may be because they are conspecific.

  3. "The type material of Drinker nisti could not be located at two institutions where it was supposed to have been at one time or another."

    Even better- "The
    holotype catalog number, CPS 106, was said to belong
    to the Colorado Palaeontographical Society housed at
    the University of Colorado Museum, Boulder, Colorado.
    Such a society nor its collection was ever recognized
    by the museum (P. Robinson, University of Colorado,
    personal communication, 2017)..."

    Yet Bakker is credited with providing various illustrations, so they had access to him. So there must be more to the story of why this society was mentioned in the Drinker paper and where the type specimens are.

    As for the "undescribed form with a camptosaur-like ilium and a dryosaur-like leg", the only dryosaur-like character is said to be the tibia being longer than the femur. So I suspect this is just a case where a traditional "key character" dividing hypsilophodontids and iguanodontids in the 70s is being propped up.

    The Nanosaurus situation is similar. That whole portion reads like something from before autapomorphies or cladistics were used. General similarity plus they lived together- bam! Synonyms. I wouldn't doubt they all are synonyms, but you have to do your work and compare them to non-Morrison taxa.

    1. This is almost another post in itself, but I did a quick scan through basal-ornithischian-through-basal-iguanodont dentaries and came up with the following:

      Considering these characters:
      1. Dentary tapering anteriorly
      2. Gently convex ventral border of dentary
      3. Anterior dentary teeth slightly procumbent
      4. Widely spaced posterior dentary teeth
      5. Tooth roots well exposed
      6. Dentary tooth row continuing almost to the symphysis
      7. Triangular crowns wider than the roots
      8. Coronoid process inline of tooth row rather than offset laterally

      Agilisaurus – 1, 2, 6, 7 yes, 3, 4, 8 no, 5 partially
      Albalophosaurus – only partial dentary; 7 yes, 4, 8 no
      Anabisetia – partial dentaries; 1, 2 maybe no, 4, 5, 8 no
      Changchunsaurus – 1, 2, 3, 5, 8 no, 6 yes, 7 probably
      Eocursor – 1 not distinctly, 2, 4, 5 no, 7 yes; 8 is claimed no
      "Eugongbusaurus" – dentaries present but few details apparent; 1, 2 may be no, 5, 7 may be yes
      Gasparinisaura 1, 2 slightly, 3, 4, 5 no, 6 yes, 7 half (triangular N, crown wider than root Y)
      Haya – skooshed, but 1 maybe, 2, 6 yes, 3, 4, 5, 8 no, 7 probably
      Hypsilophodon – 1, 6, 8 yes; 2, 3?, 4, 5 no, 7 half (triangular N, crown wider than root Y)
      Jeholosaurus – 1, 4, 5, 8 no, 2 slightly, 7 yes
      Kulindadromeus – 1 slightly, 2, 4, 5 no, 6 probably
      Lesothosaurus – 1, 6, 7 yes, 2, 3, 4, 5 no
      Orodromeus – 1, 2, 3, 4, 5 no, 6 yes
      Oryctodromeus – 1, 2, 4, 5 no
      Parksosaurus – 1 yes, 2-6 no, 7-8 not clear
      Qantassaurus – 1, 2, 6, 7 yes, 3, 4, 5 no
      Ratchasimasaurus – 1 yes, 2-8 no; in general quite distinct qualitatively
      Scutellosaurus – 1, 6, 7 yes, 2 slightly, 3, 4, 5 no
      Talenkauen – 1 yes, 2 slightly, 3, 4, 6 no, 5 to an extent
      Tenontosaurus – 1, 2 slightly, 3, 4, 5 no, 6 yes, 7 half (triangular N, crown wider than root Y)
      Thescelosaurus – 1, 6, 7 yes, 2 in part, 3, 4, 5, 8 no

      I used "slightly" for 2 as generally meaning convex posteriorly but concave or straight anteriorly. Heterodontosaurids and rhabdodonts were omitted due to their substantial dental specializations.

      My interpretation is that 1, 2, 6, 7, and 8 are plesiomorphic (but useful in the field to distinguish one Morrison jaw from another), whereas 3, 4, and 5 require further evaluation for their suitability as diagnostic characteristics for Nanosaurus. I would be careful with 5 as potentially taphonomically influenced.

      Unfortunately, the dentary is either unknown or very poorly known in Hexinlusaurus and Yandusaurus.

    2. Thank you for the pdf!

      Hexinlusaurus – 1, 2, 6, 7, 8 yes, 3 yes with the provision that *all* of the teeth are depicted with a slight forward slant, 4 no, 5 yes in one dentary and no in another (taphonomy?)

      Hexinlusaurus is particularly similar, although it can be distinguished from the Morrison form by Hexi having more closely packed teeth with less triangular crowns, and the anteriormost teeth being conical.

    3. I commend Carpenter & Galton on trying to make sense of a taxonomic mess that is not of their making (thanks largely to Marsh). As you say, the N. agilis holotype is of very poor quality. The morphology of individual teeth cannot even be determined. At the moment, their approach (pooling several taxa into N. agilis) appears to be the least worst solution. As long as there is evidence of only one Nanosaurus species, it might stick. Otherwise, there's trouble.

      "it could be back to Othnielia rex, or maybe new combination Drinker consors if rex is also thought to not be up to snuff."

      O. rex has a femur as holotype, so it's toast. Drinker is lost (possibly forever). Also, Drinker's diagnostic characters might be juvenile traits, like the "multi-cuspid marginal denticles on the cheek teeth"/"cusplets".

      One potential solution could have been to make YPM 1882 (the partial skeleton originally named Laosaurus consors, later the type of Othnielosaurus) the neotype of Othnielia. After all, this skeleton is what was traditionally thought of as Othnielia. This would mean Drinker could be sunk into Othnielia, and Nanosaurus could be abandoned (again).

    4. One more note on Hexinlusaurus: for 5, I should have stated that the dentary with "yes" only had two teeth remaining, whereas the dentary with "no" had complete dentition, so "yes" is most probably loose teeth.

      On the femur of Othnielia rex: if only people could somehow use this "postcrania" to look for diagnostic characteristics, but then we all know that is impossible for bipedal ornithischians.

      (I kid, I kid, but it's a strange world when Thescelosaurus neglectus, based on a fine but headless skeleton, is almost entirely diagnosed from cranial characteristics.)

      On an Othnielia neotype: my experience is a little different: BYU 163 was Othnielia to me. I'm not sure I even knew about consors as anything other than a name in a list until 2006!

    5. "if only people could somehow use this "postcrania" to look for diagnostic characteristics, but then we all know that is impossible for bipedal ornithischians"

      Not just bipedal ornithischians. Ever try to tell a ceratopsid or hadrosaurid from another based on its "postcrania"? Why, they're identical, as far as the eye can see. I think modular evolution was first proposed for ceratopsids- the body remained boring (probably) and only the sexy frill and horns evolved. "Wow! A ceratopsid postcranium! Reptilia indet."

  4. The paper looks somewhat rushed. If I'm interpreting this statement correctly ("Owning to the difficulty to access the original publication describing “Drinker”..."), they didn't read Bakker &c's 1990 description of Drinker in Hunteria. (BTW, i have a copy if anyone's interested.)

    Plus there's this typo:
    "The material includes parts of five juveniles from an alleged 30 found together in an oval mass of mudstone 1 m across that was interrupted [sic] as a communal burrow (Bakker, 1996)."
    Shame this material can't be located... it's the first putative evidence of burrowing in ornithischians.

    Finally, how does one spell "Pierce" - as in the author of the 2006 publication of a dentary from Little Houston Mammal Quarry, referred to Othnielia. The original publication has the author as "Richard J. Peirce", but Carpenter & Galton have it as "Pierce" (as do other publications).

    1. I thought it was odd that they couldn't get the Hunteria article. Galton was the second author, after all.

      There were other typos and things I would have changed on wordsmithing grounds, but that seems to be common in many articles these days. I can confirm that the author should be "Peirce", per my copy of the volume and his obituary (he passed away in 2007).

    2. Bakker &c's description of Drinker is probably not essential; there's no plates, just hand drawings of a few teeth, vertebrae, hindlimb elements. Still, it's odd that neither Carpenter and Galton could get their hands on it.

      One thing that's useful in the original description is that Bakker &c note that teeth tentatively referred to Nanosaurus by Galton (1983) "are more probably referable to the new genus Drinker". So Carpenter & Galton (2018) were not the first to make this connection. However, Carpenter & Galton took the reverse approach, and referred Drinker to Nanosaurus.

      Thanks for info regarding Richard Peirce.

    3. I think it more likely the authors recognized the difficulty in accessing Hunteria, so included the figures. Galton includes previously published illustrations as a form of completeness in other papers, like those on Staurikosaurus, Pantydraco, Thecodontosaurus, Heterodontosaurus and many on Plateosaurus.

      Mind sending me a pdf of Drinker's description, Tim?

  5. Just sent it Mickey. Includes a bunch of other taxon descriptions too.