The “Toroceratops” Debate is Entering a New Round!


SUNDAY SUNDAY SUNDAY!!! Torosaurus and Triceratops go head-to-head!!!! Pay-Per-View only, $29.99!!!!

To recap:

The uppermost Hell Creek and related beds on the Laramidian side of the regressing interior seaway of North America during the Maastrichtian has played host to a number of titanic ceratopsians. Given the names Triceratops, Torosaurus, Nedoceratops, debate has plagued these taxa as to whether they are synonyms. Outliers have been named, included apparently basal relatives such as Eotriceratops, Ojoceratops, and even Tatankaceratops.

Triceratops used to be very speciose, with 10 and more species encapsulated under the umbrella, all displaying reasonable variation that, in the early days of dinosaur paleontology, we can potentially excuse the describers to thinking reflected systematic variation. But advances mean changes. These species have been whittled down, and now only two remain: horridus (the type species) and prorsus. On the other hand, the taxon Torosaurus has only had three species named for it, latus (the type), gladius (subsumed into the former), and utahensis (which some suggest should be split off). Additional possible species have since been named, but phylogenetic analysis renders them as outliers, with the caveat that Torosaurus and Triceratops are generally considered distinct clades, which Nedoceratops hatcheri often finds itself in the middle of.

Speaking from the finding of samples of skulls across a broad swath of ontogenetic stages from across the Hell Creek of Montana, Johns Scannella and Horner have presented an argument that renders all Hell Creek ceratopsians (generally) into one taxon, Triceratops, although the question of which species fall where has been left open (and I would say problematically so, as this renders the debate of synonymy questionable). In response, however, Andrew Farke and Nicholas Longrich have produced a series of responses, to which in turn Scannella and Horner have responded, which have both either supported the validity of Torosaurus with respect to Triceratops (it is an outlier to the Triceratops clade comprising the two species), or Nedoceratops hatcheri (as a distinct taxon intermediate between the two). This has become known as “Toroceratops,” a spirited debate that spans the literature for the last few years and is allowing researchers to bring tool after tool into the arsenal of answering that most important of taxonomic questions:

“Is this taxon valid?”

Andrew (Andy) Farke has a new paper out in PLoS in which he and his colleagues (Maiorino, Farke, Kotsakis & Piras) use 2D lateral view geometric morphometrics to assess total and partial skull shape among a broad sampling of Triceratops, Torosaurus, and Nedoceratops skulls to answer whether the shapes of these skulls tend to cluster together regardless of or in conjunction with ontogeny. Principle to Scannella and Horner’s theory is the argument that the Torosaurus skull morphology reflects a full maturity of the cranial morphology that, despite size, no Triceratops skull has ever reached. This would suggest that Torosaurus is a peramorphic adult of the Triceratops skull, which retains a decidedly “adult” aspect for most of its life, but then drastically changes. Unfortunately, as Farke and his coautors note, the absence of coordinate postcranial long bone (femur, tibia, rib) histology associated with skulls and placed in stratigraphic sequence confounds work that has, effectivelly, focused on a highly variable set of bones, the skull. Morphometrics is a good way to sample this work, but it seems that it is merely one step out of many. Next would be to sample geometrically different views of the skull (dorsal, ventral) as well as to potentially use full 3D morphometrics to capture conclusively the full range of variation possible. This latter option preserves the ability to create landmark point clouds, but refines them in that it can do this regardless of perspective and with higher difelity: 3D point clouds are generated by meshes created from scanning in three dimensions the skull directly, rather than a map created from a side view that, barring some artsy skills, is plagued by the distortion of size relative to the camera.

But this is not to say that the study is bad; it is not. Farke et al. fiund that Torosaurus skulls do not group with Triceratops skulls, though some odd specimens that have been considered integral to the debate seem to be on the margin between then. This isn’t the final answer, and the “Toroceratops” debate is far from over.

Maiorino, L., Farke, A. A., Kotsakis, T. & Piras, P. 2013. Is Torosaurus Triceratops? Geometric morphometric evidence of Late Maastrictian ceratopsid dinosaurs. PLoS ONE 8 (11): e81608.

About these ads
This entry was posted in Biomechanics, Morphometrics, Paleontology, Science Reporting and tagged , , , , , . Bookmark the permalink.

11 Responses to The “Toroceratops” Debate is Entering a New Round!

  1. Andy Farke says:

    Thanks for featuring the article–just a few comments:

    1) It is very important to note that the work in the paper is largely Maiorino’s–as second author I am a distant second! I am a member of Leo’s dissertation committee, and have advised him on many issues ceratopsian, but in terms of the geometric morphometrics he is the boss. This is not just to deflect blame to Leo for any errors anyone discovers (<–I am being facetious), but also to ensure he is appropriately credited for his work!

    2) 3D geometric morphometrics would be desirable, but is a very tricky beast when it comes to skulls of this size. That said, you are absolutely correct to note that 2D is a simplification. A necessary one, but a simplification nonetheless.

    3) As a side note, John Scannella and I generally avoid the term "debate" these days….it implies a little more political rhetoric and rancor than what is actually going on. Of course, that doesn't mean everyone else avoids the term!

    • 1) My convention was to associate your name with your previous work on the subject, though I do note you are not primary author. I listed out the authorship later in the text, but it was an association for the sake of continuity.

      2) I think hand scanners might be the best way to go about the process. At least just surface scanning the skulls will help.

      3) I like the more conventional/technical form of the debate. I hate that the term is clouded by politics. I will find a more artful way to put it.

  2. Regarding the Torosaurus and Triceratops debate, What is the data on the dates of the fossils? What margin of years are we talking between the two Maastrichtian Ceratopsians finds? Take modern Deer for example, the variation in species that we see, and the geographical and geological distribution of deer species. Within just a 5 million year space of time, there could have been multiple separate speciations occur that adds to the already wide range of diversity of Cervids. Another example would be cichlid fish in the African rift lakes. What would their fossil record possibly look like and how would we determine their speciation based on fossil evidence where things such as color, soft tissue, and behavior are lacking?

  3. Alessio says:

    Interesting to hear about this new study; i’ve always been partial to the “Toro is NOT Trice” side of the discussion, something in this particular case of lumping has always sounded off to me (as other Horner’s theories these days)…

  4. Hikaru Amano says:

    So far, I have not seen someone who tried to address the issues raised by Longrich in the youtube video of his debate with Horner: have Scanella and Horner’s team (or anyone for that matter) accounted for the possible pitfalls that could make bone tissue structure remodeling not a good indicator of maturity? (actually, I have started writting about this issue half a year ago that ontogeny is not the only factor/process that significantly affects bone remodeling). Turns out that using bone tissue remodeling as an indicator of maturity has a lot of pitfalls. Results from a number of experimental studies concerning bone tissue remodeling that have been published in many journal articles starting from the early 1960s demonstrate that factors and/or processes such as differences and/or changes in the mechanical stress regimes of different bones in different regions of an animal’s body, developmental origin of bones, differences and/or changes in the metabolic regimes of an animal, health, and/or nutritional status all significantly (and at times even radically) affect the rates and/or extent of bone tissue structure remodeling. By themselves, each one of those factors and/or processes are considerable pitfalls on the reliability of bone tissue remodeling as an indicator of maturity. However, those phenomena (including ontogeny) also interact with some-and at times, even all-of the other above-mentioned factors and/or processes in much more complex ways (which are not yet discovered and/or understood) to affect the speed and/or degree of bone tissue remodeling even more significantly that each one of them on their own. Not only could the rates and/or degree of bone remodeling be very variable between and amongst different bones at different parts of an individual (and amongst members of its species), bone tissue remodeling could also be very variable at different portions within the very same skeletal element. As a matter of fact, the lamb bone shown by Longrich in his presentation have ILLUSORY OLD ADULT TISSUE STRUCTURE due to the intense remodeling caused by the heavier mechanical strain experienced by the bone. Hence, bone tissue remodeling needs to be tested much more rigorously to see if it truly works reliably as on indicator of maturity (and minimize-if not totally eliminate the significance of the phenomena that could become pitfalls in its utility as an estimate of maturity) in living animals before we could confidently use it on non-avian dinosaurs.

    References:

    Kini,U. and Nandeesh,B.N. (2012). Physiology of Bone Formation, Remodeling, and Metabolism. Radionuclide and Hybrid Bone Imaging, pp 29-57.

    McFarlin,S.C., Terranova,C.J., Zihlman,A.L., Enlow,D.H., and Bromage,T.G. (2008). Regional variability in secondary remodeling within long bone cortices of catarrhine primates: the influence of bone growth history. J. Anat., 2008 (213): pp308–324. doi: 10.1111/j.1469-7580.2008.00947.x.

    Oers,R.F.M.v., Ruimerman,R., Tanck,E., Hielbers,P.A.J., and Huiskes,R. (2007). A unified theory for osteonal and hemi-osteonal remodeling. Bone, 42 (2008): pp. 250–259.

    Pazzaglia,U.E., Andrini,L., and Nucci,A.D. (1997). The effects of mechanical forces on bones and joints:experimental study on the rat tail. J Bone Joint Surg [Br] 1997;79-B:1024-30.

    Ruimerman,R. (2005). Modeling and Remodeling in Bone Tissue. Netherlands: Technische Universiteit Eindhoven.

    Terrier,A., Miyagaki,J., Fujie,H., Hayashi,K., and Rakotomanana,L. (2005). Delay of intracortical bone remodelling following a stress change: A theoretical and experimental study. Clinical Biomechanics, 20 (2005): pp. 998–1006.

    (PS: this is the icing on the cake- in ankylosaurs, the extent of bone tissue structure remodeling in juveniles is already comparable to that of old adults of other taxa [i.e. ornithopods, sauropods, ceratopians]. So this indicates that the extent of bone tissue remodeling in not always a good indicator of maturity.

    Stein,M., Hayashi,S., and Sander,P.M. (2013) Long Bone Histology and Growth Patterns in Ankylosaurs: Implications for Life History and Evolution. PLoS ONE 8(7): e68590. doi:10.1371/journal.pone.0068590).

  5. Pingback: A Look Back at the Bite Stuff, 2013 Edition | The Bite Stuff

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s