Some Relief to Anticipation


I’ve recently had an opportunity to digest in part the contents of a book I mentioned back here.

In this work, authors perform much new taxonomic work, but there’s some theoretical stuff there, too. Eventually, I’ll get around to reading this volume, and savor every page. I’ve had a look at some of it, and taken my sense of the new taxa presented therein, but that’s less than half of what is really there. There is a LOT to say of Ceratopsia, even if we restrict ourselves to Ceratopsidae.

In the book, there are five sections, the first of which is a brief (very brief!) memoir of Peter Dodson, in his own words. The following sections describe the dinosaurs themselves: Part Two is systematic, and includes seven new taxa, along with descriptions of material that may be new taxa down the road, and a broader treatment of psittacosaurs specifically. Part Three is going to be my favorite (I can tell) as it is largely func-morph and evo-devo based. Part Four is historical and review in structure, rather than nitty gritty and bones. And Part Five revolves around collection (and re-collection) which is given brief time, but interesting nonetheless.

IUP made the first three chapters (Dodson, Sereno, and You et al.) available through Google Books. Reading through these, the first that deals with the dinosaurs themselves (Sereno’s) sparks some interest because it seeks to deal with a group of particularly basal ceratopsians, Psittacosauridae. I will talk more specifically about these in other posts. Today, I will talk about all the taxonomic acts present in the book.

The third chapter, You et al. [2] describe a new species of Archaeoceratops, based on a partial skull and postcrania. This new material, in the light of several other taxa, may requires a second look. Two features (a labial shelf to the dentary dentition and a contiuously rounded ventral aspect to the ventral margin of the dentary) suggest the new taxon, Archaeoceratops yujingziensis, is a leptoceratopsid, to which it was not directly compared. Several features of the skull are interesting, such as apically denticulated (the authors use “striated”) premaxillary teeth, so look forward to more on this later. I will also be adding it to a growing mural of marginocephalian snouts.

It should be noted that apart from Ceratopsia, ceratopsid phylogeny is pretty stable. The taxa are and continue to be, relatively well arranged with some taxa where they’ve been in the last twenty years. Most of the shifting around occurs at the base (as it typically does in phylogenetics) and there is always the issue of concerning ourselves in taxa based on subadult or younger specimens (Eoceratops, Brachyceratops, Avaceratops, etc.) but these are limited in general (and in some cases may be supplemented by adult material bearing diagnostic features also shared in the younger specimens (as in Avaceratops lammersorum).

Ceratopsidae is typically split into two, with some array of taxa outside of it in serial formation; these have been termed the Chasmosaurinae and the Centrosaurinae, for some of their most prominent, and earliest described, members. These two “subfamilies” are also referred to as the short-frilled and the long-frilled ceratopsids, and its perhaps the easiest way to distinguish them: Chasmosaurinae is primarily defined by elongated supraorbital brow horns (but not always) and a very long, slender squamosal extending along most of the frills lateral margin; Centrosaurinae, in contrast, have short brow horns, and shorter squamosals. Some taxa have muddied this a bit, but none of them on in the book.

Massive Horns from Mexico

Loewen et al. [3] describe the large, derived chasmosaurine Coahuilaceratops magncuerna, which is noted for having exceptionally huge supraorbital horns and is seemingly similar or nested within the Triceratops-Torosaurus clade of chasmosaurs (and some might say they are synonymous, but this is due to your perspective on ceratopsian taxonomy, or the conflation of the types on an ontogenetic basis, as has been argued by some ([4,5] and which accompanied some rather hyperbolic press releases, such as [6]). Coahuilaceratops magnacuerna may require some re-analysis of various very-southern chasmosaurine ceratopsid material from North America, along with the taxon described by [10]. The name means “big-horned Coahuila horned face” (I presume).

The Devil is in Utah

Kirkland and DeBlieux [7] describe the latest taxon from Grand Staircase-Escalante National Monument, following what appears to largely be an endemic set of taxa from the Kaiparowitz Basin that are substantially different from other latest Cretaceous taxa [8]. Here, Diabloceratops eatoni (“Eaton’s Devil-horned face” for El Diablo — The Devil, in Spanish, a proper name) has two long caudal epoccipitals that resemble the horns of a billy goat, and are the namesake features. There is a popular trend to ascribe goat-like, devilish features to a particular character in literature, lore, myth, and religion, and in this case, the anatomical similarity (almost caprine) is outweighed by the mythic. It certainly is devilish, though. The taxon is presumed to be the most basal centrosaurine, despite fitting superficially into the Centrosaurus/Styracosaurus-Einiosaurus-Pachyrhinosaurus grade where the second epoccipital pair are transformed into elongated spikes, rotated out, elongated into a set of three pairs, reduced to two pairs, then one pair, then gradually reduced. Medusaceratops lokii (see below and [12]) only exaggerates both of these trends (mythic and morphologic).

More Round than the Roundiest

Styracosaurus ovatus has been sticking around for a while, described by Gilmore in 1930 [9] for a partial frill fragment (noted as being very ovate in aspect, hence the name) with two pairs of epoccipital spikes (Styracosaurus albertensis had three). New material has permitted analysis noting that this is not a developmental feature, and this study allowed McDonald and Horner [10], along with placement of this taxon next to Einiosaurus procurvicornis and not next to Styracosaurus albertensis, to be given a new name: Rubeosaurus, forming a new combination Rubeosaurus ovatus.

The name means “thornbush lizard,” in reference to the various spikes. Together, the monickers give us the “ovate thornbush lizard.”

¡O jo! Really?

Along with Coahuilaceratops magnacuerna [3], Ojoceratops fowleri (“[Denver] Fowler’s Ojo [Alamo Sandstone] horned face”) is a Triceratops-Torosaurus grade chasmosaur of very large size, as described by Lucas and Sullivan [11]. It demonstrates yet another specimen of Maastrichtian chasmosaurine from southern North America that overlaps with range of the Triceratops-Torosaurus group (which has had fossils found in various Mexican and American states).

When the Greeks and the Norse came to America

No, I’m not talking about immigration, although the latter group did arrive before any other European group to be the first discoverers of the New from the Old. Remember what I said above about mythology and morphology? Ryan et al. [12] describe a taxon that was first found mixed in with an earlier, and completely unrelated taxon, Albertaceratops nesmoi [13]; the Albertaceratops material indicated a Pachyrhinosaurus-like centrosaurine, (where the second epoccipitals are laterally splayed and curve close to the margin of the frill rather than away from it) while the new taxon recovered is clearly chasmosaurine. Medusaceratops lokii (“Loki’s Medusa-horned face” — yes, that Loki and that Medusa) pushes the line of mythos-based taxonomy by using both Norse and Greek mythology.

Small Ceratopsians Should be Cautious

The last taxonomic paper, by Ott and Larson [14] should derserve a little more attention. Not because the material is especially exceptional, although it does add to our data of Hell Creek ceratopsians, but because of what the authors do with it. First, let me say that I think this nomenclature was a case where the authors went too far with the -ceratops trend in ceratopsian names. According to the ICZN’s Nomenclator Zoologicus, no one has named a taxon “Tatanka,” which refers to the Plains bison in Lakota. Wouldn’t that have been a great name? “Tatanka sacrisonorum” … ah well. Tatankaceratops sacrisonorum, as it is correctly known, is based on several fossils of small, apparently adult chasmosaurine from the Hell Creek Formation. The type skull, BHI 6226, is estimated to be just over 1 meter long, although it is missing most of the frill, and is quite small compared to 2-3 meter skulls of Triceratops, known from the same formation. Unlike what we know of juvenile Triceratops, the nasal horn is quite developed, implying to the authors a new taxon due to the implied adult age of the material at an extremely smaller size (less than 1/3). I am hesitant, however, based on the preservation, to argue this isn’t a subadult of a known taxon, but as the authors did not perform histological analysis based on what is known of Triceratops ontogeny [15], things could have gone another way. The whole name means “[Steve and Stan] Sacrison’s bison-horned face.”

[1] Ryan, M. J., Chinnery-Allgeier, B. J. & Eberth, D. A. 2010. New Perspectives on Horned Dinosaurs: the Royal Tyrrell Museum Ceratopsian Symposium. (Indiana University Press, Bloomington.)
[2] You H.-l., Tanoue K. & Dodson, P. 2010. A new species of Archaeoceratops (Dinosauria: Neoceratopsia) from the Early Cretaceous of the Mazongshan area, northwestern China. p59-67 in Ryan, Chinnery-Allgeier & Eberth (eds.) New Perspectives on Horned Dinosaurs: the Royal Tyrrell Museum Ceratopsian Symposium. (Indiana University Press, Bloomington.)
[3] Loewen, M. A., Sampson, S. D., Lund, E. K., Farke, A. A., Aguillón-Martínez, M. C., de Leon, C. A., Rodríguez-de la Rosa, R. A., Getty, M. A. & Eberth, D. A. 2010. Horned dinosaurs (Ornithischia: Ceratopsidae) from the Upper Cretaceous (Campanian) Cerro del Pueblo Formation, Coahuila, Mexico. p99-118 in Ryan, Chinnery-Allgeier & Eberth (eds.) New Perspectives on Horned Dinosaurs: the Royal Tyrrell Museum Ceratopsian Symposium. (Indiana University Press, Bloomington.)
[4] Scannella, J. 2009. And then there was one: Synonymy consequences of Triceratops cranial ontogeny. Society of Vertebrate Paleontology, Abstracts. Journal of Vertebrate Paleontology 29(supp to 3):117A.
[5] Horner, J. R. & Goodwin, M. B. 2009. Extreme cranial ontogeny in the Upper Cretaceous dinosaur Pachycephalosaurus. PLoS ONE 4(10):e7626.
[6] Science Daily, 2009. New analysis of dinosaur growth may wipe out one-third of species. Available here.
[7] Kirkland, J. I. & DeBlieux, D. D. 2010. New basal centrosaurine ceratopsian skulls from the Wahweap Formation (Middle Campanian), Grand Staircase—Escalante National Monument, southern Utah. p117-141 in Ryan, Chinnery-Allgeier & Eberth (eds.) New Perspectives on Horned Dinosaurs: the Royal Tyrrell Museum Ceratopsian Symposium. (Indiana University Press, Bloomington.)
[8] (http://www.scottsampson.net/index.php?page=dinosaur-research)
[9] Gilmore, C. W. 1930. On dinosaurian reptiles from the Two Medicine Formation of Montana. Proceedings of the United States National Museum 77(16):1-39.
[10] McDonald, A. T. & Horner, J. R. 2010. New material of “Styracosaurus” ovatus from the Two Medicine Formation of Montana. p142-168 in Ryan, Chinnery-Allgeier & Eberth (eds.) New Perspectives on Horned Dinosaurs: the Royal Tyrrell Museum Ceratopsian Symposium. (Indiana University Press, Bloomington.)
[11] Sullivan, R. M. & Lucas, S. G. 2010. A new chasmosaurine (Ceratopsidae, Dinosauria) from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico. p169-180 in Ryan, Chinnery-Allgeier & Eberth (eds.) New Perspectives on Horned Dinosaurs: the Royal Tyrrell Museum Ceratopsian Symposium. (Indiana University Press, Bloomington.)
[12] Ryan, M. J., Russell, A. P. & Hartman, S. 2010. A new chasmosaurine ceratopsid from the Judith River Formation, Montana. p181-188 in Ryan, Chinnery-Allgeier & Eberth (eds.) New Perspectives on Horned Dinosaurs: the Royal Tyrrell Museum Ceratopsian Symposium. (Indiana University Press, Bloomington.)
[13] Ryan, M. J. 2007. A new basal centrosaurine ceratopsid from the Oldman Formation, southeastern Alberta. Journal of Paleontology 81(2):376-396.
[14] Ott, C. J. & Larson, P. L. 2010. A new, small ceratopsian dinosaur from the Latest Cretaceous Hell Creek Formation, northwest South Dakota, United States: A preliminary description. p203-219 in Ryan, Chinnery-Allgeier & Eberth (eds.) New Perspectives on Horned Dinosaurs: the Royal Tyrrell Museum Ceratopsian Symposium. (Indiana University Press, Bloomington.)
[15] Goodwin, M. B., Clemens, W. A., Horner, J. R. & Padian, K. 2006. The smallest known Triceratops skull: new observations on ceratopsid cranial anatomy and ontogeny. Journal of Vertebrate Paleontology 26(1):103-112.

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2 Responses to Some Relief to Anticipation

  1. Jay Nair says:

    “; the material indicated a Pachyrhinosaurus-like centrosaurine, (where the second epoccipitals are laterally splayed and curve close to the margin of the frill rather than away from it) while the new taxon described therein was clearly chasmosaurine. Medusaceratops lokii (“Loki’s Medusa-horned face” — yes, that Loki and that Medusa) pushes the line of mythos-based taxonomy by using both Norse and Greek mythology. A short nasal ridge instead of a horn, and HUGE second epoccipitals make the Pachyrhinosaurus-grade centrosaur pretty funky looking, bearing an elaborate frill and a not-so-elaborate facial skeleton.”

    I am confused by the way you have worded this passage. I’m sure you already know Medusaceratops was described as a chasmosaurine by Ryan et al, but I wasn’t sure if you were calling it a centrosaurine when i read the above.

    “……Psittacosauridae. I will talk more specifically about these in other posts. Today, I will talk about all the taxonomic acts present in the book.”

    Can’t wait! – the chapter by Sereno looks very impressive, and is certainly more detailed than most other chapters in the book.

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