“Toroceratops” Matters, as an Open Discussion

So there’s this debate, which I may have discussedmore than once, twice, or thrice — before, in which it is argued that the taxa Triceratops and Torosaurus represent young adult and old adult representatives of the same species. I’ve argued caution, discussed this with several of the proponents of synonymy and with its detractors, and overall enjoyed the debate. Whether the type species of Torosaurus, latus, is a synonym of one of the species of Triceratops is as yet unknown — the proponents do not make this referral, which is mandatory to conclude their containing “genera” are synonyms (especially when they themselves argue that latus “doesn’t exist”); being a synonym or not, or the status of Nedoceratops hatcheri (nee Diceratops), doesn’t actually matter in the long run to me. I’m more interested in the process than the product.

In February of 2012, the Yale Peabody Museum hosted a debate between Dr. Jack Horner — who advocates the synonymy of the taxa — and Dr. Nick Longrich, who works at Yale and is an opponent to this argument. Dr. Longrich and colleague Dan Field, along with Raymond M. Alf Museum‘s Dr. Andy Farke, have argued that not only is Torosaurus latus distinct from any Triceratops, that Nedoceratops hatcheri is an intermediate form, but also that the basic arguments from Jack Horner (of the Museum of the Rockies and Montana State University, where he teaches) and his former student Dr. John Scannella need to be borne out to be used. Needless to say, this debate is very interesting, especially in the latter section, and this is embedded below the fold.

Let’s put aside the heated back-and-forth between Drs. Jack and Nick for a moment: both are passionate men and invested in the science of their positions. In the posts I link to at the top of this post are any indication, I’ve come down heavy against Horner and Scannella, oh whom the latter has argued back his case on this blog, but not because of any deep-seated need to keep these taxa separate. Let’s also put aside the argument of Longrich in which apparent phyletic diversity can somehow trump the needed in-depth analysis of the material and assessment for variation and ontogeny among and within taxa. Both sides have made great points in their defenses of their own work, and I admirably support the process by which the authors are extending the debate in careful, reasoned papers.

Where I have stressed difficulties accepting a case is on the presentation of its data, or rather the lack of said data purporting things argued for. Horner and Scannella have, for example, stressed preservational regimes through various sedimentary types for articulation or otherwise, stratigraphic arrangement of specimens within the Hell Creek Formation leading to phyletic diversity at their ends (which suggests utility for other taxa), and preponderance of morphological data distributed among various specimens that conform to both taxonomic and ontogenetic distinctions between specimens, but which form a continuous cline. The problem is, as Longrich points out towards the end of the video, and which receives an answering “We’ve done that, too” from Horner, is that the data isn’t out there. We do not have it. He has it. To discuss data, one must make that data available, open, accessible, and comprehensive. One needn’t have to perform the study themselves to then find this information, or crawl back through the MOR’s files. Presumably, this information can be made available, hosted or “published” on Figshare or a number of other data-collecting sites, and which permit workers to examine the material. It can be hosted by the publishers of their next paper, with a supplemental framework, so that the data which is argued for is available. This, rather than attempting to counter an argument with a playground “Yes I did!”

The form should be that if one is trying to counter a claim, one must present the information that counters that claim, not merely assert it. This was my problem with the original “Toroceratops” paper, and it’s still there: The explicit information that indicates that Torosaurus latus, its type specimen, is a member of a specific species of Triceratops, is what is required to sink Torosaurus. It is not even enough to say that Torosaurus latus falls within variation between Triceratops horridus and prorsus, for we may just recognize the latter by its own “genus”; indeed, we seem to be teeming in purported “triceratopsin” ceratopsids, from Eotriceratops xerinsularis, Ojoceratops fowleri, or even Tatankaceratops sacrisonorum. Part of the problem stems from the lack of quanlification of variation, something which Longrich mentions in his paper with Field, and in his response in the debate in the video. It is Horner and Scannella’s assertion that this variation is, almost always, ontogenetic, and one might think that’s something one has to back up with solid data; especially their arguments about metaplastic reformation of bone shapes. I’m also rather put off with the assertions that Horner might be convinced if we found a baby Torosaurus. My response is: How would you tell? Might some of your specimens BE juvenile Torosaurus? This is especially true if the ontogenetic trend Horner argues for is true, but is exclusive of Torosaurus. How does one extricate that from the “Toroceratops” synonymy angle?

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It is pretty simple:

If I were to make a conclusion based solely on the information presented in the papers discussed in these posts, I would likely conclude that the strict variation suggests “Torosaurus” is distinct from “Triceratops.” I would not so readily support Horner’s argument, because the assertions for ontogeny are, as they were with Pachycephalosaurus (first link above), admittedly shaky. We don’t have the data yet to make a more informed decision independently. Horner and Scannella mention many hundreds of specimens, and that is wonderful, but for all their histological sections, these features (as argued by Longrich) have to be put into context, and there’s little of that. We don’t know a lot about dinosaur ontogeny and its variation, especially its potential evolution in small clades. We also have no real basis for the rather dramatic and extreme dimorphism between “Triceratops” and “Torosaurus,” where the former “grows” into the latter in a mere year or two, right as they hit “full maturity,” and right before senescence or death — well, outside of insects. No bird or reptile we have so far shows such extreme morphological disparity in such a short time span, and we might want to consider this caveat and present our context first.

I do not disagree with Horner and Scannella, and I don’t necessarily agree with Longrich, Field, or Farke; rather, I feel that if the data itself cannot tell the tale, if the interpretive story crafted by the authors has to lead me there, then the data mustn’t be very strong. And if isn’t — yet — we shouldn’t be making such sweeping conclusions.

With all due respect to the principles involved, thank you for reading.

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15 Responses to “Toroceratops” Matters, as an Open Discussion

  1. I tend to agree with Nick, but as a field guy, I would approach it a bit differently. I would be looking closer at the evolution of Torosaurus and Triceratops out of the Early Maastrichtian. The North American fossil record is way better than most people give it credit for. We need more people doing field work in the gaps in the record. I liken a lot of this to a party fishing boat; someone catches a nice fish off the stern and every one runs to the stern of the boat. We need more in Utah’s North Horn Formation and Mesaverde Fm. and Wyoming’s Evanston Fm. and New Mexico’s Ojo Alamo Fm.
    I have been pushing for a Torosaurus utahensis project for years.

    • I have to admit that it seems like Horner and Scannella have the more compelling case; but that Longrich and Farke have presented important, and critical, wrenches to this theory, while at the same time working from a less ontogeny-driven model of anatomy. The reliance of ontogeny on the model, and the extended growth series presented by H&S, obscures some details I would love to have resolved, but I fear the general gross similarity among juvenile and possibly even subadult chasmosaurines would make this difficult, and that it is difficult to not think that the famous MOR baby “Trike” may, in fact, be a Toro.

    • Doug says:

      I here ya there, Master Kirkland. Fowler managed to pique my interest in the Ojo Alamo formation. So far that was the only one. But all this talk about Torosaurus has made me reconsider the North Horn fm. As far as i can tell, there’s only 3 dinosaurs known from it. I had always thought this was because the formation produced only a few fragmentary remains (the same with the Javalina formation in Texas). But maybe it’s because the hell Creek formation has been hogging all the attention.

      For whayever it may mean to you, i have added the North Horn fm. to my “hit list”. If i can ever get my plans of the ground, i’ll do my best to get out there.

  2. Anonymous says:

    I generally agree with your post, however only one minor point; genera can be synonymised without the type species being a synonym of another species. If one genus is shown to be paraphyletic to another (or polyphyletic as in your Triceratops/Torosaurus example) you can lump them all into a single genus and retain the two type species as valid, distinct individuals. This of course is a decision that the individual researcher makes, based on their own perception and philosophy (and we get to the age old question of whether you’re a lumper or a splitter).

    • Thanks for the comment. I tend to be a stickler for specificity: the species is a group of organisms based on a type specimen, being it a syntype series, genotype, or holo (or lecto) type; a genus is based on a species, and then on a specimen. If we take the trio of taxa generally mentioned (and rather, there are four, but for now we’ll stick to three), we get several possible arrangements of taxa:

      1. Horridus + Prorsus + Latus
      2. Horridus (incl. Latus) + Prorsus (incl. Latus)
      3. Horridus + Prorsus > Latus
      4. Horridus + Latus > Prorsus
      5. Horridus < Prorsus + Latus

      In the case where one argues for 1, Triceratops has priority so far as all taxa might seem to comprise a single clade BUT one can arrange the species in similar token by “genera,” with horridus the type of Triceratops, latus the type of Torosaurus, and prorsus the type of a new taxon. The arrangement remains the same, no synonymy occurs. Similarly, one might argue that 2 is what Horner and Scannella prefer, in which latus cannot be discriminated from either horridus or prorsus, but this is not what they’ve stated in press; the authors have merely argued that Torosaurus is a synonym of Triceratops, leaving it ambiguous their treatment of the species arrangement or synonymy, allowing us option 1, but we also have access to options 4 and 5, with 4 being the one argued for by Longrich and Field; Farke also has supported this, and systematic analysis follows Longrich and Field.

      If one suggests that Torosaurus can be subsumed into Triceratops with no disposition of the species, then it leaves another confused on the alternative: It is semantic that we argue that the grouping of these three species be called Triceratops but not any other name, or treating the grouping by a new name with Triceratops and Torosaurus as further specified names. To avoid this, latus must be subsumed into either horridus or prorsus to avoid ambiguity, and thus by which the case can be tested. Horner and Scannella suggest this, but do not do synonymy work, as I understand it is pending further and promised stratigraphic work. And it is thus why I argue that merely calling latus Triceratops (in their works, the use of species nomenclature is generally avoided, as the authors are arguing they represent anagenetic lineages) improper.

  3. Hikaru Amano says:

    Longrich and Field also raises a critical weakness in the use of histology: what if the rates and/or extent of bone remodeling is not always consistent within, between, and/or amongst the different skeletal elements within the same individual(with some bones having a juvenile microstructure while an immediately adjacent bone having a senescent microstructure)? In such cases, sectioning those bones even within the same individual may give very conflicting results about its maturity. How would they discriminate bone remodeling microstructure caused by old age from ones caused by differences in the distribution of stresses experienced by various regions of a bone? Oh by the way, the recent article about the detection of soft tissues inside a Triceratops horridus horncore is a rather exciting discovery…maybe viable soft tissue preservation inside dinosaur bones is considerably more common than scientists once believed. I wish somebody would subject those soft tissues to biomolecular examinations in order to reconstruct the biomolecular profiles of the species of Triceratops and Torosaurus.

    • It is for this reason that most histological sections are made of longbones or of ribs, but not much else. The diagnostic utility of using cranial histological sections is a younger, and more nascent thing as yet. This is one of the criticisms that Horner et al. will eventually have to overcome, though they have attempted to address it, as they have attempted to argue that brow-horn sections are useful and diagnostic for age. Being able to sample across multiple age classes with multiple types of these is the only real choice, but these specimens are rare. Postcrania are also not as collected as cranial bones in the field when it comes to ceratopsians; not only are cranial remains considered more diagnostic, they are more identifiable, more readily preserved, and more likely associated, unlike postcrania which can scatter, are not always clearly of ceratopsian origin, or associated with skulls. You need bonebeds, not surface scatter, to do the latter, and there are few of those for Triceratops and the Hell Creek in general.

  4. Hikaru Amano says:

    brow horn orientation are diagnostic of a particular age group (small, stubby in nestlings and pups; curves backwards in late juveniles and early subadults; straight in late subadults; curves forward and upward in young adults, and curves mostly forward in old adults). But Horner et al. themselves said that brow horns are made of metaplastic bone…basing on that statement, we may reason that it would be even more prone to more varying rates and/or extent of bone remodeling due to changes in force distribution at different parts of the element(i.e. suppose one brow horn came from a small, late subadult individual and another brow horn came from a much larger individual at the same phase of ontogeny. Since the larger individual’s brow horn experiences more stress (maybe due to weight) than that of the smaller guy, the larger animal’s brow horn would likely experience more bone remodeling than the other one, perhaps in order to better compensate for its weight. I would still support the interpretations based on a combination of biomolecular and morphological examinations than morphological+histological ones since in cases when what the biomolecular examinations indicate and the histological analyses are trying to point at, biomolecular examinations are more reliable(refer to journal articles I cited in my older posts dated on January last year). Naturally, I would even prefer if the biomolecular+morphological data would be placed in a strat context in order to see how does the biomolecular profile of Triceratops varies over time along with their morphological evolutionary development. Same goes for Torosaurus. Also, it seems that the North Horn Formation Torosaurus specimens have relative abundances comparable to those of the co-eval Hell Creek Formation but to “standard Triceratops”, something which is particularly strange if Torosaurus is the senescent phase of the latter.

    • The brow horn histology issue works slightly for Horner’s argument, though: they argue that “Trorosaurus” show a histological value that works when you extend the metaplastic reformation through ontogeny from previously established “Triceratops” specimens. That is, horn cores of “Torosaurus” are MORE metaplastically remodelled than those of “Triceratops” “adults.” This can be useful, though there is no METRIC by which deformation occurs, either the presence, absence of tissues, relative tissue abundances, or relative density/porosity which one can run by any given specimen. Much of this is “eyeballed.” I am prone to agree with the argument that “Torosaurus” specimens are generally adult, but it is the other conclusions (assignment to “Triceratops” of certified juveniles) that causes things to get murkier. It is those issues that need to be resolved, as well as tracking the expression of diagnostic characters of prorosus/horridus through ontogeny; currently, most juvenile specimens are generalized to “Triceratops,” but not one of the species. It is possible that they may NOT be assignable to species, or that they can represent juvenile “Torosaurus.”

      The tale is not done. There is more work to be done, and Horner’s team are indeed going back and working on that stuff.

      • Hikaru Amano says:

        And the lack of a standard is exactly what I’m trying to point out in the reliability of using cranial elements for histology since it has not yet been established how truly reliable they are. In the three possible types of standards of remodelling you have mentioned (presence/absence, proportions, and tissue integrity/density), which amongst them is/are truly reliable? And in assessing maturity based on cranial element microstructures, when do they occur at particular phases of ontogeny? Those three may come in any possible combinations (and some combinations have the potential to give very conflicting results).

        • I do not know. I am not sure others know quite how reliable they are. There has been work on it, but I am not so versed in it to pull it up immediately. I know that Horner, Farke, and others have cited it, and that leads to yet more. Histology in general is a weakness of knowledge on my part; I do not pretend to know it as well as those who’ve written on it in formal papers. Because of this, I approach the subject cautiously, generally, rather than specifically. This means I am more inclined to take their words for it … as far as I understand the subject. There is no full faith and credit given, and I wonder if I should hold this position even if I knew as much as them. The fact is, histology of some bones (humeri, femora, tibiae, ulna?) are better at predicting ontogeny than others (ribs, scapulae, ilia, skulls). Certainly, much of this is due to the process by which these bones form (endochondral versus dermal/membraneous) and the pressures that act upon them. In the end, the basic assumption to be taken from Horner’s data is that the histology of brow horns is that as the skeleton increwases in size, increasing levels of absorption/reformation occur, altering the original bone, and that this affects shape and length, and apparently curvature. I am actually MORE interested in the process of curvature and its effect on the overlying tissue than the structure of the underlying, save how it influences or is influenced by that overlying tissue. And that, I think, is something only being cursorially approached in this debate. What, pray tell, do the external tissues that surround the skull have to say about this debate?

  5. Hikaru Amano says:

    At any rate, I would still want to see Torosaurus and Triceratops being subjected to biomolecular profiling to see whether the biomolecular examinations would support ontogenetic synonymy implied by histological anlyses(and what kind of synonymy) or contradict it and support separation as distinct taxa (as indicated by morphology). It seems that nucleic acids could even be preserved for several millions of years (I just forgot the article, but it tells that the antibodies that exclusively attack avian DNA sequences reacted to the Brachylophosaurus sample. Since the samples were prepared under very strict, sterile protocols, the most likely explanation for such a result is that they are genuinely dinosaurian nucleic acids). I know that even if genuine dinosaurian nucleic acids survived up to the present day, those DNA sequences discovered are likely just represent portions of some genes or another. Coincidentally, bones which you cited as more reliable at gauging the ontogeny phase of an individual are also the most likely to harbor surviving good quality preserved soft tissues. I once asked Dr. Farke about his opinion about the prospect of subjecting Triceratops and Torosaurus samples to biomolecular profiling. He said that while it is possible with enough samples (provided biomolecule recovery works in suffient amounts of fossils), scientists would need to collect much more specimens than what we currently have in order to build comprehensive profiles. With that in mind, he said that if some scientists were to do it, maybe they should start first with collagen and/or keratin since they are the most likely survivors.

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