Ceratopsia

Skeletal mounts of Psittacosaurus mongoliensis, copyright Ninjatacoshell.

Belongs within: Genasauria.
Contains: Ceratopsidae.

The Ceratopsia are a group of herbivorous dinosaurs known from the Late Jurassic to Cretaceous of Asia and North America (with some less definite records from other parts of the world). Members of this group are characterised by a novel bone, the rostral bone, at the front of the upper jaw (which forms a narrow beak), and a tendency to the develop of a frill on the rear margin of the skull (You & Dodson 2004).

Big horned lizards
Published 23 June 2008
The ceratopsid Einiosaurus, from here.

Before anyone weighs in to complain about the title to this post, I know that dinosaurs aren’t lizards, the title was chosen in a spirit of tongue-poking and ribbing.

The Ceratopsia are a very well-supported clade of dinosaurs. Not least of the characters uniting its members is the presence of the rostral bone—a small toothless bone at the tip of the upper jaw that is unknown from any other dinosaur and demonstrates the presence of a beak in the ceratopsians. Some sources have pointed out that the name Ceratopsia is actually mis-derived and argued for the name Ceratopia instead, as well as Ceratopidae and Protoceratopidae instead of the more commonly used Ceratopsidae and Protoceratopsidae, but in this case a long history of usage has won out over strict linguistic accuracy*. Most authors accept that ceratopsians form a clade called Marginocephalia with the Pachycephalosauria, but it is worth pointing out that while it is the best-supported hypothesis to date, the support for Marginocephalia is not overwhelming and the question is worth former investigation. While Sereno (1986) placed the Marginocephalia outside the ornithopods, a recent analysis by Butler et al. (2008) produced a phylogeny that nested Marginocephalia within a number of taxa that had been regarded in the past as ornithopods, suggesting that marginocephalians are derived from within the “hypsilophodontid” grade of dinosaurs. Interestingly enough, this is actually more congruent with older pre-cladistic theories of dinosaur relationships that had implicitly derived both ceratopsians and pachycephalosaurs from ornithopod ancestors. It also reduces the significant ghost lineage that Sereno’s topology suggested for marginocephalians.

*Names ending in “-ops” have actually got a long history of being pains in the neck for zoological nomenclature. The ending “-ops” can be derived from the Greek word for “face”, which is masculine, or for “appearance”, which is feminine. Because many an author has ended a genus name in “-ops” without indicating which ending was intended, it is unclear for many such names whether they were meant to be masculine or feminine, a significant issue because it affects the form of any associated species names. It is because of this confusion that the ICZN has declared that all names ending in “-ops” are to be treated as masculine, regardless of derivation.

Reconstruction of Psittacosaurus by Pavel Riha.

The earliest known Ceratopsia date from the Late Jurassic. Ceratopsians can be divided into three distinct grades that have been classified as separate families in the past, but of which two are paraphyletic. These grades are the psittacosaurs, protoceratopoids and Ceratopsidae. The Ceratopsidae are the most familiar of the ceratopsians, and include the large horned quadrupedal forms. This group includes some of the first dinosaurs described from North America, albeit many from fragmentary remains which tragically means that such fantastic names as Agathaumus, Dysganus and (my personal favourite) Polyonax mortuarius, the “dead master of many”, have been resigned to the oblivion of nomen dubium status. I’m going to leave the Ceratopsidae for some other time and introduce the more basal ceratopsians.

Psittacosaurs are the basalmost group of ceratopsians—small and at least facultatively bipedal, they look not too different from a basal ornithopod and were classified as such when first described (Osborn 1924), though a connection between psittacosaurs and ceratopsians was also recognised quite early on (though again, in those pre-Hennigian days the separation of psittacosaurs from ceratopsians as part of a paraphyletic Ornithopoda was not really seen as a problem). The majority of psittacosaurs have been included in the genus Psittacosaurus—in fact, with over ten described species (though not all of these may be valid), Psittacosaurus provides a welcome exception to the tendency of dinosaur systematists to keep their genera as small as possible (while sixteen species have been referred to Triceratops, almost all of these are invalid—Ostrom & Wellnhofer 1990). In recent years, a few other “psittacosaur-grade” genera have been described, such as Chaoyangsaurus and Yinlong. The frill formed by the extension of the bones of the back of the skull that is so characteristic of other ceratopsians is absent from psittacosaurs, though a slight rearward curve of the squamosal (as well as the short snout) does help give the skull of Psittacosaurus a distinctly boxy appearance. Psittacosaurus is actually one of the best-known of all dinosaurs, with literally hundreds of known specimens of all different ages. One specimen is known that preserves a row of long tubular bristles running down the tail of unknown function, probably display*.

*With the admission that “display” is all too often something of a cop-out explanation for unusual structures.

Mounted skeleton of Archaeoceratops oshimai, one of the basalmost protoceratopoids, from here.

I’m using the name “protoceratopoids” (a term plucked more or less out of thin air) to refer to the taxa previously included in the Protoceratopsidae, a taxon now well established to be paraphyletic with regards to the Ceratopsidae (the two groups together forming the Neoceratopsia). Taxonomic concepts in this grade are currently a little unstable – there may be a more restricted Protoceratopsidae formed from taxa forming a monophyletic group with Protoceratops, while other protoceratopoids are parcelled off into families such as Leptoceratopsidae. In protoceratopoids we see the development of the frill characteristic of Neoceratopsia, albeit still fairly small in many species. Most protoceratopoids lack the horns of ceratopsids, and were also much smaller than the ceratopsids. Some protoceratopoids such as Leptoceratops (which if the run of available reconstructions is to be believed existed for no other purpose than to provide food for larger, meaner-looking reptiles) probably remained bipedal, but other lines became larger, heavier and eventually quadrupedal. Analyses differ as to how many times quadrupedality evolved in ceratopsians (You & Dodson 2004). One very basal protoceratopoid, Archaeoceratops oshimai, was a very gracile impish-looking little form that actually looks better adapted as a runner than does Psittacosaurus. Though often dismissed as basal forms, the bipedal ceratopsians were to survive for just as long as the quadrupedal forms, and Leptoceratops was actually a contemporary of Triceratops, one of the latest Ceratopsidae.

Mention should also be made of the role of Protoceratops as an accessory to one of the biggest frame-jobs in the history of palaeontology. The first known specimen of the theropod Oviraptor was discovered overlying a nest of eggs that were identified as belonging to Protoceratops. It was this that gave Oviraptor its name (“egg thief”), and for many years Oviraptor was reconstructed mercilessly plundering protoceratopsid nests. It wasn’t until fairly recently that it was discovered that the “Protoceratops” eggs didn’t belong to that taxon at all, but were in fact Oviraptor eggs, and far from stealing them, the much-maligned Oviraptor had probably been a diligent mother incubating them! I did attempt to speak to Protoceratops about its role in this shameful affair, but it refused to comment on grounds of being extinct.

The majority of known basal ceratopsians—all psittacosaurs and most protoceratopoids—come from Asia, particularly northern Asia, and this is universally accepted to be the place of origin of this clade. The Ceratopsidae, in contrast, is only known from North America, as is the sister taxon to Ceratopsidae, Zuniceratops. It appears likely that their ancestors dispersed to North America from Asia before giving rise to the Ceratopsidae. Again, how many times this dispersal occurred is uncertain – members of the Leptoceratopsidae were also found in North America. The analysis of Xu et al. (2002) placed Leptoceratopsidae in a very basal position distant from Ceratopsidae, while that of You & Dodson (2004) found them as sister taxa (though I should point out that the latter analysis included significantly fewer taxa than the former). Two records of Ceratopsia from outside Laurasia are rather problematic. The South American Notoceratops, based on a single jawbone, was originally described as a ceratopsian but is suspected to have been a hadrosaur—unfortunately, this question will probably never be fully resolved because the type specimen has gone AWOL. The Australian Serendipaceratops is supposed to be very similar to Leptoceratops, but is known only from a single ulna.

Ceratopsids: a Cretaceous flash in the pan
Published 25 June 2008
Leptoceratops, one of the latest-surviving ceratopsians, from here.

After I wrote the above section, Zach Miller asked if I could follow up my basal-ceratopsian-focused post with one on the more famous ceratopsids, which for various reasons, most significantly time, I had rather neglected.

Sorry, Zach—this is not that post.

But what I thought I would elaborate on was something I referred to offhand in that post about the significance of the basal ceratopsians compared to the ceratopsids proper. I mentioned that the small bipedal ceratopsians, despite their relative obscurity, actually persisted in North America for just as long as the giant ceratopsids, and were with them ’til the end. I would like to add to this that as surprising as it may sound to any readers who are only familiar with popular presentations of evolution and their tragic tendency to fall into the “March of Evolution” trap, this actually wasn’t much of an achievement. For even though ceratopsids are one of the iconic dinosaur groups, instantly recognisable by 95% of the developed world’s population, they weren’t actually around for very long.

Most of you will have probably heard of the Triassic, Jurassic and Cretaceous periods that together make up the Mesozoic era of earth’s history. While these periods are quite sufficient for broad generalisations about the history of life, palaeontologists generally find that they need finer-scale divisions to refer to more specific time periods. I recommend going to Palaeos.com if you want to see the subdivisions for the Jurassic and Cretaceous, because I’m going to have to refer to a few of them in the course of this post. I know I’ll be checking back there regularly as I write this post, because personally I can never keep track of them all.

Yinlong downsi, the earliest known ceratopsian, by Andrey Atuchin.

I mentioned in the previous post that the earliest ceratopsians are known from the Late Jurassic. Specifically, Yinlong downsi comes from the Oxfordian, which started about 161 mya (million years ago—taxon ages for this post have been taken from Justin Tweet’s Thescelosaurus! website). In the rough grade system I used in the previous post, Yinlong would be a psittacosaur-grade ceratopsian*, but phylogenetically speaking it is the sister taxon to later ceratopsians. The earliest and most basal known protoceratopoid-grade ceratopsian, Liaoceratops yanzigouensis, comes from early in the Cretaceous, some time between the Valanginian (starting about 140 mya) and the early Barremian (130 mya). The earliest known Ceratopsidae, in contrast, didn’t crash the party until the mid-Campanian (perhaps about 78 mya). Ceratopsians had been around for about 80 million years already by the time the ceratopsids appeared. Or to put it another way, less time separates us from the latest ceratopsids than separates the ceratopsids from the earliest ceratopsians! With their extinction at the end of the Cretaceous, about 65 million years ago, the Ceratopsidae are only known to have been around for about 15 million years—an impressively long time by human standards, but really not so very impressive when compared to the nearly 100 million years of ceratopsian history, or the more than 180 million years the Mesozoic lasted for in total.

*You may be wondering how the psittacosaur-grade ceratopsians fared in terms of longevity. Psittacosaurus is the latest well-established psittacosaur, and seems to have survived until about the end of the Early Cretaceous, about 100 mya. However, the analysis of Butler et al. (2008) suggests, albeit with rather low support, that the poorly-known (yet ambitiously-named) Micropachycephalosaurus hongtuyanensis might be a very basal ceratopsian. Despite this basal position, Micropachycephalosaurus actually dates from the Maastrichtian, the very last part of the Cretaceous. If Micropachycephalosaurus is indeed a ceratopsian (a proposition that should be taken very cautiously), then psittacosaur-grade ceratopsians survived at least relictually for almost the entirety of ceratopsian history.

True, the ceratopsids did attempt to cover up for lost time through rapid speciation, so that more ceratopsid taxa have been described from that last fifteen million years than all the non-ceratopsid ceratopsians over 100 million years, but this is like the rapid propagation of any fad—the flashy new designs may temporarily overshadow the old classics in the public eye but the classics are still very much there.

Systematics of Ceratopsia

Synapomorphies (from You & Dodson 2004): External naris high, separated from ventral border of premaxilla by flat area; rostral bone present; premaxilla enlarged; jugal with well-developed lateral flaring; wide dorsoventral length of infraorbital ramus of jugal; palatal extensions of maxillae contacting rostral to choana.

<==Ceratopsia
    |  i. s.: Micropachycephalosaurus Dong 1978ZY09, MCW04
    |           `--M. hongtuyanensis Dong 1978MCW04
    |         Xuanhuaceratops nieiP10
    |         Hongshanosaurus houiP10
    |--Psittacosaurus Osborn 1923 [incl. Protiguanodon Osborn 1923; Psittacosauridae]YD04
    |    |--P. gobiensisP10
    |    |--P. guyangensis Cheng 1983YD04
    |    |--P. lujiatuensisP10
    |    |--P. majorP10
    |    |--P. mazongshanensis Xu 1997YD04
    |    |--P. meileyingensis Sereno, Chao et al. 1988YD04
    |    |--P. mongoliensis Osborn 1923 [incl. Protiguanodon mongoliensis Osborn 1923, Ps. protiguanodonensis Young 1958]YD04
    |    |--P. neimongoliensis Russell & Zhao 1996YD04
    |    |--P. ordosensis Russell & Zhao 1996YD04
    |    |--P. osborni Young 1931 [incl. P. tingi Young 1931]YD04
    |    |--P. sattayaraki Buffetaut & Suteethorn 1992 (n. d.)YD04
    |    |--P. sibiricusP10
    |    |--P. sinensis Young 1958YD04
    |    |--P. xinjiangensis Sereno & Chao 1988YD04
    |    `--P. youngi Chao 1962YD04
    `--Neoceratopsia [Protoceratopidae, Protoceratopoidea]YD04
         |  i. s.: MicroceratopsYD04
         |           |--M. gobiensis Bohlin 1953 (n. d.)YD04
         |           `--M. sulcidens Bohlin 1953 (n. d.)YD04
         |         Kulceratops kulensis Nessov 1995 (n. d.)YD04
         |         Yamaceratops dorngobiensisBN08
         |         Bainoceratops efremoviT08
         |         Craspedodon Dollo 1883OBW10, N04
         |           `--C. lonzeensis Dollo 1883N04
         |         Cerasinops kodgkissiP10
         |         Helioceratops brachygnathosP10
         |         Auroraceratops rugosusP10
         |         Prenoceratops pieganensisP10
         |--Yinlong downsiBSN07
         `--+--Chaoyangsaurus Zhao, Cheng & Xu 1999YD04
            |    `--C. youngi Zhao, Cheng & Xu 1999YD04
            `--+--Liaoceratops Xu, Makovicky et al. 2002XM02
               |    `--*L. yanzigouensis Xu, Makovicky et al. 2002XM02
               `--+--Archaeoceratops Dong & Azuma 1997 [Archaeoceratopidae]YD04
                  |    `--A. oshimai Dong & Azuma 1997YD04
                  `--CoronosauriaYD04
                       |  i. s.: Ajkaceratops Ősi, Butler & Weishampel 2010OBW10
                       |           `--*A. kozmai Ősi, Butler & Weishampel 2010OBW10
                       |--CeratopsoideaYD04
                       |    |--+--CeratopsidaeYD04
                       |    |  `--Zuniceratops Wolfe & Kirkland 1998YD04
                       |    |       `--Z. christopheri Wolfe & Kirkland 1998YD04
                       |    `--+--Asiaceratops salsopaludalis Nessov, Kaznyshkina & Cherepanov 1989 (n. d.)XM02, YD04
                       |       `--LeptoceratopsidaeYD04
                       |            |--Montanoceratops Sternberg 1951YD04
                       |            |    `--M. cerorhynchus (Brown & Schlaikjer 1942) [=Leptoceratops cerorhynchus]YD04
                       |            `--+--Leptoceratops Brown 1914YD04
                       |               |    `--L. gracilis Brown 1914YD04
                       |               `--Udanoceratops Kurzanov 1992XM02, YD04
                       |                    `--U. tschizhovi Kurzanov 1992YD04
                       `--ProtoceratopsidaeYD04
                            |--Graciliceratops Sereno 2000YD04
                            |    `--G. mongoliensis Sereno 2000YD04
                            |--Protoceratops Granger & Gregory 1923YD04
                            |    |--P. andrewsi Granger & Gregory 1923YD04
                            |    `--P. hellenikorhinus Lambert, Godefroit et al. 2001YD04
                            `--BagaceratopidaeA03
                                 |--Magnirostris dodsoniOBW10
                                 |--Bagaceratops Maryańska & Osmólska 1975 [incl. Breviceratops Kurzanov 1990]YD04
                                 |    `--B. rozhdestvenskyi Maryańska & Osmólska 1975YD04 (see below for synonymy)
                                 |--Lamaceratops Alifanov 2003A03
                                 |    `--*L. tereschenkoi Alifanov 2003A03
                                 `--Platyceratops Alifanov 2003A03
                                      `--*P. tatarinovi Alifanov 2003A03

Bagaceratops rozhdestvenskyi Maryańska & Osmólska 1975YD04 [incl. Protoceratops kozlowskii Maryańska & Osmólska 1975YD04, Breviceratops kozlowskiiYD04, Gobiceratops minutusP10]

*Type species of generic name indicated

References

[A03] Alifanov, V. R. 2003. Two new dinosaurs of the infraorder Neoceratopsia (Ornithischia) from the Upper Cretaceous of the Nemegt Depression, Mongolian People’s Republic. Paleontologicheskii Zhurnal 2003 (5): 77–88 (transl. Paleontological Journal 37 (5): 524–534).

[BN08] Balanoff, A. M., M. A. Norell, G. Grellet-Tinner & M. R. Lewin. 2008. Digital preparation of a probable neoceratopsian preserved within an egg, with comments on microstructural anatomy of ornithischian eggshells. Naturwissenschaften 95: 493–500.

[BSN07] Butler, R. J., R. M. H. Smith & D. B. Norman. 2007. A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia. Proceedings of the Royal Society of London Series B—Biological Sciences 274 (1621): 2041–2046.

Butler, R. J., P. Upchurch & D. B. Norman. 2008. The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6 (1): 1–40.

[MCW04] Maryańska, T., R. E. Chapman & D. B. Weishampel. 2004. Pachycephalosauria. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 464–477. University of California Press: Berkeley.

[N04] Norman, D. B. 2004. Basal Iguanodontia. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 413–437. University of California Press: Berkeley.

Osborn, H. F. 1924. Psittacosaurus and Protiguanodon: two Lower Cretaceous iguanodonts from Mongolia. American Museum Novitates 127: 1–16.

[OBW10] Ősi, A., R. J. Butler & D. B. Weishampel. 2010. A Late Cretaceous ceratopsian dinosaur from Europe with Asian affinities. Nature 465: 466–468.

Ostrom, J. H., & P. Wellnhofer. 1990. Triceratops: an example of flawed systematics. In: Carpenter, K., & P. J. Currie (eds.) Dinosaur Systematics: Approaches and Perspectives pp. 245–254. Cambridge University Press.

[P10] Paul, G. S. 2010. Dinosaurs: A Field Guide. A & C Black.

Sereno, P. C. 1986. Phylogeny of the bird-hipped dinosaurs (Order Ornithischia). National Geographic Research 2: 234–256.

[T08] Tereschenko, V. S. 2008. Adaptive features of protoceratopoids (Ornithischia: Neoceratopsia). Paleontologicheskii Zhurnal 2008 (3): 50–64.

[XM02] Xu, X., P. J. Makovicky, X.-L. Wang, M. A. Norell & H.-L. You. 2002. A ceratopsian dinosaur from China and the early evolution of Ceratopsia. Nature 416: 314–317.

[YD04] You H. & P. Dodson. 2004. Basal Ceratopsia. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 478–493. University of California Press: Berkeley.

[ZY09] Zheng, X.-T., H.-L. You, X. Xu & Z.-M. Dong. 2009. An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature 458: 333–336.

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