Leaellynasaura and Caudal Length in Ornithischians


Recent attention as risen in regards to a brief abstract submitted at the 69th Annual Meeting of the Society of Vertebrate Paleontology, held in September of 2009 in Bristol, England. There, William Matthew Herne presented a preliminary report of material previously referred to one of the classical austral ornithischians, Leaellynasaura amicagraphica [1], which is available here. Therein, Herne describes this specimen has having a tail of over 70 caudal vertebrae (unheard of before save in hadrosaurs), and comprising around 75% of the total body length. A fantastically long tail.

Leaellynasaura amicagraphica is a small ornithischian taxon based on a few specimens, including  a juvenile with a nearly complete (although mostly undescribed skull), and several referred specimens including a partial skull with an exposed endocast of the braincase [2], as well as some femora [3]. Further referred specimens have included partial skeletal material (as Leaellynasaura sp.) including one particularly interesting specimen including a nearly complete tail [1,3]. The latter is referred to in Herne’s work describing the full osteology of these specimens [1], and has been known for over two decades. It finally sees the light soon!

One of two claims made recently about this taxon concerns the incredibly long tail, and the potential of austral dinosaurs, as non-avian archosaurs, to self-regulate their body temperature below the Antarctic Circle. Some have proposed, based on recent data on integumental structures in ornithischians [4,5] that they might have possessed filamentous integument, “dinofuzz,” providing insulation and they would have hibernated [3]. But secondary to this is that at larger sizes, adaptation to cold weather with increase in surface area becomes more difficult, and as such animals that can reduce their overall surface area are better suited to cold environments. What use then a very long tail in an antarctic, austral dinosaur like Leaellynasaura amicagraphica? Mysteries, mysteries.

I am going to focus on that tail, although other questions are certainly interesting and deserving of their own time. I would like to say that extreme tail length is not unique to this taxon, or even among ornithischians, but for this point I will stick to ornithischians. This in no way invalidates Herne’s work, of course; even based on below, the caudal length and count exceed what we know in non-hadrosaur ornithischians. Nonetheless, it bears some comment to remark of the ridiculously long tail in some ornithischians.

The holotype skeleton of Scutellosaurus lawleri, MNA PL 175. Other material, including a paratype and referred cranial material, are known but not included. Scale bar equals 20 cm.

First up is Scutellosaurus lawleri [6], one of the most basal members of Thyreophora. Based primarily on the holotype, MNA PL 175, Scutellosaurus lawleri has a caudal series broken in two portions, and these I will discuss below.

The first section is composed of 36 elements and probably articulated with the intact sacral series, and measures 47.6 cm, and the last caudal preserved in the series is incomplete but represents over half of its vertebra’s length; the second section is composed of 21 vertebrae, the first of which is incomplete but also represents over half of a complete centrum and thus does not correspond to the last element of the first section, and measures 27.6 cm. Total, the caudal series represents a combined preserved length of 55.2 centimeters, and the last centrum is hardly terminal; projecting only that the two intermediate partial vertebrae are adjacent, and complete, one can arrive at a preserved caudal length of ~56 cm, which compares to the precaudal vertebral series of 34.6 cm, with estimated cranial extension to 40 cm.

It should then be noted that, because the distal end of the caudal series can include more vertebrae, it is not complete, and projecting a round 60 cm (likely short of the full length, but round numbers are nice and aesthetic) gives us a potential 100 cm body length, of which 60% (or more) is tail (projecting a less well-rounded number and a greater gap between the two sections of caudals only increases the percentage). With nearly 60 elements in the tail preserved, and likely more, places this within the range predicted for one of the specimens referred to Leaellynasaura amicagraphica [1]. As noted by Herne [1], hadrosaurs (by which I restrict myself to Hadrosauridae, as I assume does Herne) also have high caudal counts, but these numbers are mitigated by their shortness, where the brevity causes the caudal series to be shorter than the precaudal series in several hadrosaurs of note.

The holotype skeleton of Agilisaurus louderbacki, from ZDM 6011. Sacle bar equals 20 cm.

This also agrees well with Agilisaurus louderbacki [7], a very basal member of Ornithopoda. Based on ZDM 6011, where the preserved complete caudal series is 113 cm, combined with the precaudal series of 69 cm for a body length of 182 cm (tail is 62% of body length, and nearly twice precaudal length). And like Scutellosaurus lawleri above, the caudal series lacks the terminal vertebrae, and so was a bit longer.

Finally, it would be important to point out that under some projections (and the abstract of Herne [1]), Leaellynasaura amicagraphica is very mobile when it comes to ornithischian phylogeny, although inclusion of the total skeletal material in a matrix has never been done. If it were a basal ornithopod, a cerapodan of some sort, or a basal genasaurian, it would be very similar to the basal ornithopod Agilisaurus louderbacki and the basal thyreophoran (basal genasaurian) Scutellosaurus lawleri, which may indicate a basal trend in long-tailed ornithischians where each classic branch of Ornithischia (Thyreophora, Marginocephalia, and Ornithopoda) secondarily reversed the trend.

Other extremely long-tailed ornithischians also include Heterodontosaurus tucki, itself a systematically mobile taxon. Of course, none of these taxa seem to have tails that exceed ~65% of total body length, which Herne [1] proposes for Leaellynasaura amicagraphica, but they may have come pretty close.

Update (1): Andrea Cau reminds me (in comments) about Tenontosaurus tillettorum, which has been reconstructed by Paul (in various sources) to have a tail roughly 70% of the total vertebral length (slightly less when dealing with the skull). This is based on reconstructions which are collected from multiple specimens, so I may be more cautious about using this animal in support of such an argument, but it does suggest that extremely long tails are fairly pervasive in Ornithischia, even if they are not common.

[1] Herne, M. 2009. Postcranial osteology of Leaellynasaura amicagraphica (Dinosauria; Ornithischia) from the Early Cretaceous of southeastern Australia. Society of Vertebrate Paleontology, Abstracts. Journal of Vertebrate Paleontology 29(supp. to 3):113A.
[2] Rich, T. H. & Vickers-Rich, P. 1989. Polar dinosaurs and biotas of the Early Cretaceous of southeastern Australia. National Geographic Research 5:15-53.
[3] Rich, T. H. & Vickers-Rich, P. 1999. The Hypsilophodontidae from southeastern Australia. In Tomada, Rich & Vickers-Rich (eds) Proceedings of the Second Gondwana Dinosaur Symposium. National Science Museum Monographs 15:167-180.
[4] Mayr, G. Peters, D. S., Plodowski, G. & Vogel, O. 2002. Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus. Naturwissenschaften 89:361–365.
[5] Zheng X.-t., You H.-l., Xu X. & Dong Z.-m. 2009. An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature 458:333–336.
[6] Colbert, E. H. 1981. A primitive ornithischian dinosaur from the Kayenta Formation of Arizona. Museum of Northern Arizona Bulletin 53:1-61.
[7][n1] Peng G. 1990. [A new small ornithopod (Agilisaurus louderbacki gen. et sp. nov.) from Zigong, China]. [Newsletter of the Zigong Dinosaur Museum] 2:19-27.

[n1] It would be helpful to know the Romanized transcription for both the paper’s title and the journal in which it appears, if anyone can supply it!

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7 Responses to Leaellynasaura and Caudal Length in Ornithischians

  1. Andrea Cau says:

    I’m not an ornithischian expert, so, I can be wrong, but I remember that also _Tenontosaurus_ tail is claimed to be very long.

  2. Pingback: Tweets that mention Leaellynasaura and Caudal Length in Ornithischians « The Bite Stuff -- Topsy.com

  3. First up is Scutellosaurus lawleri [6], one of the most basal members of Thyreophora.

    Just out of curiosity, what do you think of Butler et al.’s (2007) recovery of Lesothosaurus as the basalmost thyreophoran? Not that it negates the position of Scutellosaurus as a basal thyreophoran, of course…

    This also agrees well with Agilisaurus louderbacki [7], a very basal member of Ornithopoda.

    Similarly, what do you think of Butler et al.’s (2007) recovery of Agilisaurus (and Hexinlusaurus and Othnielosaurus) outside of Ornithopoda? I ask largely because I’m working on retooling my ornithopod lecture for my Intro to Dinosaurs class and have been thinking about how to address this issue… Herne’s abstract also reported that Leaellynasaura itself may be outside Ornithopoda…

    It would be helpful to know the Romanized transcription for both the paper’s title and the journal in which it appears, if anyone can supply it!

    In Will Downs’ translation of Peng (1992), he lists it as “A new genus of small ornithischian from Zigong, Sichuan” in the journal Reports from the
    Zigong Dinosaur Museum
    , for what that’s worth. He was fluent in Chinese…

    Refs:

    Butler, R.J., Upchurch, P., and Norman, D.B. 2007. The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6(1):1-40. doi: 10.1017/S1477201907002271.

    Peng, G. 1992. Jurassic ornithopod Agilisaurus louderbacki (Ornithopoda: Fabrosauridae) from Zigong, Sichuan, China. Vertebrata PalAsiatica 30(1):39-51.

    • Jerry, I think Butler’s analyses, which tend to change paper to paper on finer details, are becoming increasingly better resolved with time. I would defer to him on matters relating to the explicit character features of many taxa, and their organization relative to phylogeny. My brief actual experience manipulating ornithischian matrices focused on pachycephalosaurs, heterodontosaurs, and basal Ornithopoda/pre-ornithopodan with others. One of my interests has been to attempt to resolve the massive issue regarding Heterodontossaurus, the most position-flexible taxon in Ornithischia, and in this, very few analyses recover the same relationship of taxa (even when they recover Hets in one spot consistently, other taxa move relative to them).

      Because of this, I am cautious about some taxa. I am aware that Agilisaurus louderbacki is a particularly basal taxon, but where it falls seems uncertain; Hexinlusaurus multidens (my favorite ornithischian) seems very Hypsilophodon-like. That’s a totally phenetic comparison, there, and not based on much data. One of the more interesting tools used to discriminate ornithischians, their teeth, may be less useful in doing so phylogenentically than many assume, and removing dental characters MAY result in a fundamental shift in phylogeny. I’m really interested in this test.

      It seems that one of the more interesting things about some ornithischians is that many of them, dentally, are not what they seem; and many more, postcranial, are just as convergent on basal taxa due to shared habitual lifestyles (extremely cursorial adaptations in basal dryomorphans and the Gasparinisaura/Talenkauen group with Eocursor, etc.), reduction of the postpubic process of the pubis into a split, or a variety of other things.

      With Lesothosaurus as a basal thyreophoran, it seems interesting and plausible. Obviously, a basal thyreophoran will look a lot like a “fabrosaurid” in the conventional sense, and this was Colbert’s “gut” assignment for Scutellosaurus /em> in the first place. When I wrote about Agilisaurus being a very basal member of Ornithopoda, I was being very off the cuff, and should have been more careful. I was, generally, less careful with the phylogenetic analyses than possible, but was missing the refs; I went with my recent memory.

      So my general impression is that there is (now) less stability in the ornithischian matrices being produced than there has been, but this is a great thing: I think the constantly shifting fabric of the story of phylogenic recovery will allow us to learn more about the animals we study. It is also symptomatic of that most sceintific of biological study: anatomical description in its details. If I had a class, I’d try that approach, perhaps. It’s very theoretical, and I have few practical suggestions on how to do it.

  4. Jay Nair says:

    Who is William Herne?

    Did you mean Matt Herne?

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