Centrosaurinae

   The centrosaurines, as previously described, are usually recognized by their prominent nasal horns, subordinate brow horns, short squamosals in a short frill, a tall, deep face relative to the chasmosaurines, and a projection into the rear of the nasal fenestra. They experienced their greatest diversity in the Judithian age of the LK, tailing off during the Edmontonian before apparently disappearing altogether in the Lancian. They also have more prominent cranial ornamentation, including a wide variety of spikes and nodules on the frill. It has been suggested that they wrestled with their nose horns by pushing against an opponent's horn.
       There are two general types of centrosaurines, centrosaurinids and pachyrhinosaurinids. Derived centrosaurinids have hook-like projections on the rear of the frill and unreduced nasal horns; derived pachyrhinosaurinids have rough, thick pads where nose and brow horns would be. It is quite probable that they could have engaged in pushing and shoving matches with them.
       Bonebeds of centrosaurines are known, particularly for Styracosaurus, Centrosaurus, Pachyrhinosaurus, and Einiosaurus. It is believed that these formed when a herd attempted to ford a river, and a number of them were drowned, like what happens today in Africa when wildebeest attempt a crossing. From studies of this bonebed material, researchers have discovered that as centrosaurines aged, their diagnostic facial features changed greatly. Centrosaurine juveniles as a rule looked alike, no matter the taxon. Their nasal horns were transversely compressed structures, formed from the paired nasal bones; this split horn rapidly fused from the tip down as the individual neared adulthood, and was later subject to further modifications. Their brow horns were subdued structures that in some cases were lost for uncertain reasons by the adult individuals. Juvenile centrosaurine frills were thin, fragile objects, often without the large fenestrae so characteristic of the adults; the margin was simple and scalloped, and the midline was ridged. By contrast, the frills of subadults were sometimes as large as those of adults, with fenestrae, but with varying degrees of full-fledged adult ornamentation. It appears clear that the major features that separate adult centrosaurines, like horn and frill configurations, appeared "late" in life (reproductive maturity and cranial ornaments may have kicked in at 3 years old); young centrosaurines, no matter the genus, all looked pretty much like Brachyceratops. This is an idea that would put the kibosh to some formerly accepted genera like Brachyceratops and Monoclonius.

<--Centrosaurinae
     |--Diabloceratops
     `--+--+--Avaceratops
          |    `--Nasutoceratops
          `--+--Albertaceratops
               `--+--"Centrosaurini"
                    |      |--+--Rubeosaurus
                    |      |    `--Styracosaurus
                    |      `--+--Spinops
                    |           `--+--Centrosaurus
                    |                `--Coronosaurus
    
               `--Pachyrhinosaurini
                         |--+--Sinoceratops
                         |    `--Xenoceratops
     
                   `--+--Einiosaurus
                              `--+--Achelousaurus
                                    `--Pachyrhinosaurus

Centrosaurinae:

Taxon or Taxa: Time/Place: Comments:
Diabloceratops eatoni Kirkland and Deblieux, 2010 middle Campanian (LK) of Utah Diabloceratops is another in the group of basal centrosaurines that had long brow horns and short nasal horns. In fact, the type specimen practically has no nasal horn, just a couple of blunt knobs. For variety, it also has a pair of freaky long parietal spines, hence the name. For those of you keeping score at home, it is based on the Last Chance skull. The Nipple Butte skull is assigned to Diabloceratops sp. They are from the Wahweap Formation of Grand Staircase-Escalante National Monument, and should not be confused with the (no fewer than three at this point, including Kosmoceratops and Utahceratops) ceratopsids from the overlying Kaiparowits Formation.
Avaceratops lammersi Dodson, 1986 (?Ceratops) middle-late Campanian (LK) of Montana Avaceratops is known from a partial subadult skeleton, with a skull of an older subadult possibly belonging to it. In defense of Avaceratops as a valid taxon, it appears to have a solid frill and pronounced brow horns, and certain features suggesting it is a basal ceratopsid, like more pointed unguals. It occasionally been proposed as Ceratops, or allied to Triceratops. Where it belongs is not certain; it could be basal to the chasmosaurine-centrosaurine split.
Nasutoceratops titusi Sampson, Lund, Loewen, Farke, and Clayton, 2013 early late Campanian (LK) of Utah After having spent several years in the wilderness as "Nasutuceratops", this distinctive form has been described under a slightly different name. It is known from fossils belonging to three individuals, including a mostly complete skull with partial neck, arms, and shoulders. The snout is very tall but has more of ridge than a distinct pointed horn core. The brow horns more than make up for the lack of snout: they are long, and curve first away from the skull, then forward, and then twist slightly away. Combined with the prominent "forehead", the impression is that of certain cattle. The frill is rimmed by small rounded epoccipitals, not the larger processes of other centrosaurines.
Albertaceratops nesmoi Ryan, 2007 middle Campanian  (LK) of Alberta This genus was the first described well-supported centrosaurine with long brow horns (well, maybe Avaceratops, but it might be too basal). Now, of course, it's all the rage. It is known from a complete skull from the Oldman Formation of Alberta, and possibly skull fragments from the Judith River Formation of Montana. The skull looks something like an Achelousaurus with long brow horns and a ridge for a nasal pad.

Centrosaurinae i.s.:

Taxon or Taxa: Time/Place: Comments:
Brachyceratops montanensis (N.D.) Gilmore, 1914 middle late Campanian (LK) of Montana This animal is known from the remains of five juveniles. With the new understanding of centrosaurine growth, it is clear that the diagnostic value of the juvenile remains is dubious at best; the remains could belong to either an established adult taxon or its own valid species, with unknown adults. A sixth specimen, first thought to be a potential adult, appears to be a partially-grown Rubeosaurus.
Monoclonius crassus (?N.D.) Cope, 1876 middle-late Campanian (LK) of Montana and Alberta Although it has a good deal of historical significance, Monoclonius has been at the center of a good deal of historical muddling as well. For example, the name, which means "single shoot" (not "one horn"!) refers to the root of a tooth included in the original type material that is actually hadrosaurid. It also has been long confused with Centrosaurus. "True" Monoclonius material, as shown by the partial frill now used as the type, has a simple frill border and is rather thin, unlike other centrosaurines. This is a common pattern for juvenile and subadult individuals of centrosaurines in general, leading to the conclusion that Monoclonius likely is founded on the remains of subadults. Of course, subadults of which one is the million dollar question; the type is from the Judith River Formation, which is not well-known in terms of horned dinosaurs, so conceivably that original partial frill, the type of Monoclonius, represents an animal which is otherwise unknown to science and could, with the future discovery of better material, be called Monoclonius. Although it is often illustrated, it is poorly known; many such illustrations are actually of Centrosaurus.
M. lowei is the species that gets kicked around the most, because it's represented by most of a skull that's not quite like any other skulls. This skull has an unfused nasal horn and simple parietal ornamentation, but it also has little juvenile bone texture and it's among the largest known centrosaurine skulls. It could be from a species that looked juvenile when adult (paedomorphic), or a subadult of an unusually large Judithian centrosaurine, or just a late bloomer of a known centrosaurine.
"Monoclonius" sphenocerus (N.D.) Cope, 1889 middle-late Campanian (LK) of Montana "M." sphenocerus is the only species of Monoclonius named by Cope that really lives up to the folk etymology for the genus: it is based on a partial snout with a big, straight nasal horn. Although it has been compared to Styracosaurus albertensis or Centrosaurus nasicornus, geo-stratigraphically a more apt comparison is probably to Rubeosaurus, which also features a large (but curved) nasal horn.

"Centrosaurini": You know, that "tribe" thing we mid-late 1990s dinosaur website authors were so fond of... it took about fifteen years for them to start working their way in, and I'm not sure that it's the best idea, at least not necessarily tied to ranks.

Taxon or Taxa: Time/Place: Comments:
Rubeosaurus ovatus McDonald and Horner, 2010 (originally Styracosaurus ovatus Gilmore, 1930) early late Campanian (LK) of Montana Rubeosaurus began taxonomic life as a species of Styracosaurus, and stayed there for a long time in obscurity, known only from a partial parietal. Restudy and some additional material have given us a better picture, and it turns out to have been something like a cross between Styracosaurus and Einiosaurus. It had one of the heftier nasal horns among centrosaurines, with a long base. The frill ornamentation consisted primarily of four spikes arranged in two Vs (VV), sometimes with a short third spike flanking it. If your memory serves you well, you'll recall that the proposed Two Medicine Formation Einiosaurus-Achelosaurus lineage had a third unnamed centrosaurine at the base. Guess what the additional material for Rubeosaurus is.
As you may know, especially if you've been reading this page scrolling down, Brachyceratops was long thought to include five partial juvenile specimens found together and one larger partial specimen found years later, which was first thought to be a possible adult. It is not complete, and several lines of evidence indicate it is not full grown; first, the nasal horn is only known from a half, suggesting that it was not completely fused and thus not adult; second, the frill is very large, particularly when compared with the rest of the skull (in particular an unusually short tooth row), suggesting that it belongs to a subadult; third, the frill is thin, as is common with immature centrosaurines; fourth, the frill lacks parietal fenestrae, another character of immature individuals; fifth, the frill has juvenile bone texture;  and sixth, skeletal remains found with the skull are very small for an adult. I am satisfied that this skull and partial skeleton belong to a subadult individual. Interestingly, it also shows prominent but incomplete nodes on the frill's margin; the position and number of these nodes correspond fairly well to the pattern seen in adult individuals of Einiosaurus. This evidence hints that the large specimen of Brachyceratops may actually be a subadult of it or its relative Rubeosaurus. Revision of the material indicates that it is the latter; it's nice to get one of these once in a while.
Styracosaurus albertensis Lambe, 1913 (?Centrosaurus) early late Campanian (LK) of Alberta This animal is instantly familiar to anyone interested in classic dinosaurs, due to its bizarre frill. S. albertensis is defined by the presence of two large frill spikes on either side of the midline, with the inner pair longer than the outer pair, but after that you get quite a bit of variation. Some have a third pair of spikes, like the type skull, and one or two further spikelets; some have just rounded nubbins. Some have little tabs where Centrosaurus has its midline-pointing hooks, others have true hooks. There are two knobs of varying development where Centrosaurus has its big, forward-pointing tongue-like processes arching over the parietal fenestrae. Subadults have pyramidal brow horns, which are reabsorbed in adults. There may be sexual dimorphism, but it's hard to tell at this point.
The type of this animal is a spectacular skull, missing the lower jaw (recovered at a later date), the right side of the frill, and part of the nasal horn. It has an apparent pathology on the left side of the frill; the next time you see a restoration, note how the smallest of the three spikes is partially overlapped by the next spike. It appears that the frill was fractured between the two spikes and telescoped together, so that the frill should actually be a few cm longer. Additionally, the nasal horn, which is incomplete, has traditionally been assumed to come to a point and be about twice as long as preserved, but remains from other individuals suggests that the tip is blunt, and that not that much is missing.  
Spinops sternbergorum Farke, Ryan, Barrett, Tanke, Braman, Loewen, and Graham, 2011 late middle Campanian (LK) of Alberta Spinops just goes to show you never can tell. It is based on remains collected nearly a century ago for the Natural History Museum in London (formerly the BMNH), but not displayed or described because of their fragmentary nature. Skip forward over ninety years of ceratopsid research, and it turns out that C. H. Sternberg, part of the collection party, was right when he thought the bones were distinctive. Spinops combines the great flavor of Styracosaurus with the classical elegance of Centrosaurus: it includes both at least one pair of long spikes like the former genus with the forward-facing frill hooks of the latter. It is known from bonebed remains from a currently-lost bonebed site, which was the first scientifically-excavated dinosaur bonebed in Alberta.
Centrosaurus apertus Lambe, 1904 (?Styracosaurus and/or Coronosaurus) late middle-early late Campanian (LK) of Alberta Centrosaurus has as its most distinctive features a long, variably curved nasal horn, a thick frill, two short hooks at the rear of the frill pointing toward each other, and two long hooks overhanging the holes of the frill.  It was long confused with Monoclonius, and for a time in the late 1980s and early 1990s was known as Eucentrosaurus (Chure and McIntosh, 1989) because it was thought its name was preoccupied by that of a lizard's. Eventually, it turned out that the lizard's name had never been published, so Centrosaurus the dinosaur continues along. Occasionally some trouble comes up with Kentrosaurus as well, but the differing pronunciations keep the two separate. It is known from over fifteen skulls, some with skeletons, and some bonebed material as well. It was a common Judithian dinosaur. Dimorphism has been seen in the known specimens; one form has features like a longer frill, a deeper face, and a tall forward-pointing nasal horn, while the other has a shorter frill, a narrow face, and a more subdued nasal horn, variable in orientation. The first form may be male, the second female. Styracosaurus is very closely related, and may well be the same genus. 
Coronosaurus brinkmani Ryan, Evans and Shepherd, 2012 (originally Centrosaurus brinkmani Ryan and A. Russell, 2005) (?Centrosaurus) late middle Campanian (LK) of Alberta This taxon was originally described as a second species of Centrosaurus, from older rocks than classic C. apertus (the Oldman Formation, for those of you in the know). It has received its own genus because it has sorted out as more closely related to Styracosaurus. This, of course, also leaves the alternative of including Styracosaurus albertensis as a species of Centrosaurus, if that is where your tastes lie.
Coronosaurus has a few interesting skull features including flattened, laterally-directed orbital horns, prominent bundles of nodes surrounding the projections that arch over the frill from the back, and laterally-projecting spines lateral to the bundle of nodes. Unlike Centrosaurus, it lacks the same sort of prominent inward-curving hooks found at the frill indentation. It has been found in bonebeds.

Pachyrhinosaurini:

Taxon or Taxa: Time/Place: Comments:
Sinoceratops zhuchengensis Xu X., Wang K.-B., Zhao X.-J., and Li D.-J., 2010 ?early middle Maastrichtian (LK) of China Sinoceratops (no points for guessing the country of origin) is the first unequivocal ceratopsid described from Asia (Turanoceratops might be a ceratopsid, but it's hovering in Basal Limbo somewhere near the boundary. Yes, feel free to imagine a hovering Turanoceratops). It is presently known from a partial skull and a braincase, and favored the traditional stout centrosaurine nose horn. The frill has a series of broad flat blunt projections, which also curl forward. Sinoceratops was large for a centrosaurine.
Xenoceratops foremostensis Ryan, Evans, and Shepherd, 2012 early middle Campanian (LK) of Alberta The basal centrosaurine Xenoceratops is known from various skull bones pertaining to at least three individuals, primarily from the frill. This is convenient for classification purposes, but leaves us with an incomplete picture of its "mug" at this time. The frill ornamentation is dominated by a pair of broad diverging parietal spikes, with a pair of prominent knobs decorating the anterior-lateral corners of the parietal. It is among the oldest known centrosaurines at this time, representing the lowest chunk of the Belly River Group, the Foremost Formation (for reference, the Dinosaur Park Formation which has supplied us with so many centrosaurs and styracosaurs, is in the same group of rock units, but is two formations higher; you have to go through the Oldman Formation to get there). The remains were uncovered in 1958.
Einiosaurus procurvicornis Sampson, 1995 early late Campanian (LK) of Montana Einiosaurus has a very unusual nasal horn which bears a striking resemblance to a bottle opener (although possibly only in males) and has two spines sticking out rearward from the frill's margin. For a time before it was described, it was thought to be a species of Styracosaurus.
Achelousaurus horneri Sampson, 1995 middle late Campanian (LK) of Montana Achelousaurus combines the dual frill spines of Einiosaurus with the thick nose and brow pads of Pachyrhinosaurus. Some workers suspect it is actually a species of Pachyrhinosaurus.
Pachyrhinosaurus: Sternberg, 1950 P. canadensis (type) Sternberg, 1950 middle late Campanian (LK) of Alberta Pachyrhinosaurus is known for having thick pads of bone where the nose and brow horns would be in most ceratopsids. It was a fairly common Edmontonian dinosaur; remains from many individuals are known, over a wide geographic range. All appear to have dual side\front pointing spikes at the rear of the frill, but only some have what is described as "unicorn" horns, which project from the midline bar of the frill; these individuals pertain to P. lakustai, from the long-discussed Pipestone Creek bonebed. P. lakustai is also older than the type. The roughly equally-long-discussed Alaskan species has been named P. perotorum, which has forward-projecting tabs about where you'd see the tongue-like projections in Centrosaurus. It currently enjoys the status of latest centrosaurine species. Other species from Alberta may be known, including the "Wapiti River" pachyrhinosaur. There is also something very similar to Pachyrhinosaurus in the Dinosaur Park Formation.
P. lakustai Currie, Langston, and Tanke, 2008 middle late Campanian (LK) of Alberta
P. perotorum Fiorillo and Tykoski, 2011 early late Maastrichtian (LK) of Alaska

 

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