The Ceratopsid family is divided in two subfamilies: the three-horned/long-frilled one and the single-horned/short-frilled one. note Among three-horned/long-frilled ceratopsids you'll see Chasmosaurus, Pentaceratops & Torosaurus more often; less-frequently, Arrhinoceratops & Anchiceratops. About the single-horned kinds, other than the stock Styracosaurus the chances are to meet Monoclonius or Centrosaurus (which could actually be the same animal). Since the 1990s the no-horned Pachyrhinosaurus has also become a frequent sight. Some of them have even made occasional apparitions in fictional media other than in documentaries.
I'm the real Bullsaur... or am I just too old?: Torosaurus
Despite its size and popularity Triceratops is not the most striking-looking horned dinosaur: it is larger than almost every other ceratopsid and had long frontal horns, all right, but its nasal horn is very short (in some individuals looks like a simple bump) and its bony shield is kinda uncospicuous, being quite smooth, short, and with no promiment spikes (Styracosaurus or Centrosaurus have much longer nasal horn and spiked shields). Not counting the fact that some close Trike's relatives show much more impressively extended frills, sometimes with an amazingly angular edge: ex. Chasmosaurus, Pentaceratops, and the most impressive of all, Torosaurus. Although relatively simple in shape, the frill of the torosaur is so vast that make its skull reaching 2.5 m in length, more than a fully-grown human: until the late 1990s it was the biggest known head of any land-animal ever. Unlike Chasmosaurus and Pentaceratops which had relatively short frontal horns, those of Torosaurus were as long as those of Triceratops (or even a bit more) — making the adult "toro" an astounding view even for a hungry Tyrannosaurus rex.
All ceratopsids lived in Late Cretaceous, always in North America (except one or two); but only Torosaurus lived alongside Triceratops. Commonly thought to mean “bull lizard” (toro = bull in Spanish): a very apt name, only… Torosaurus actually means "perforated lizard". This because it has holes in its bony frill, unlike Triceratops. The same size of Triceratops or even bigger (up to 9 tons extimated), Torosaurus is also considered one of the closest Triceratops relatives. In fact they are so similar, it has been proposed at the end of the 2000s that Torosaurus was just a grown-stage of Triceratops; since the name Triceratops has been created before Torosaurus, the latter could get the same fate of “Brontosaurus”.
Whatever the case, the torosaur is recognizable thanks to its huge but smooth shield (many triceratopses had small bumps all around the edge of it): while the Triceratops frill covered only the neck of the animal, the Torosaurus one covered even its shoulders when put horizontally; when its head was lowered, the frill automatically raised in an upright position, making the animal looking bigger if seen from the front, possibly scaring predators or rivals. Apart from the frill Torosaurus and Triceratops had very similar heads, with two long bull-like frontal horns and one much shorter on the nose. If the two animals were one and the same, however, the longer horns and frill might just be old-age-related traits.
Torosaurus and Triceratops were portrayed as two different animals in the last episode of Walking with Dinosaurs (justified though, since was made in year 1999). Interestingly, is Torosaurus which has the main role in the story - Triceratops appears only in the form of one carcass. Considering the more-striking look of the “Toro”, this choice was wittily made to avert Stock Dinosaurs while playing straight Rule of Cool at the same time.
I've got fishhooks, but drowned in the river: Centrosaurus
If you think Triceratops was the ultimate rhino-dino, is only because you have never heard about Centrosaurus. The latter had a look that literally resembled a rhinoceros. Its nasal horn was much longer compared to Triceratops, and maybe was used in the same way of a modern black rhino - for obvious reasons, this cannot be verified. While the usual frontal horns were mere hints on Centrosaurus, renforcing even more the rhino-resemblance. About the frill, it was rather short, undulating-edged, with that pair of bony openings (covered with skin in the living animal), present in every ceratopsian outside Triceratops. The most unexpected thing is a pair of bony “hooks” curving downwards from the top of the shield; for some reason, they are often taken out in Centrosaurus models or drawings.
Named in the beginning of the XX century, most of its remains were then attributed to another relative, “Monoclonius” (see below), which has long been the archetypical “unicorn-dinosaur” in books and documentaries. Then, a spectacular find was made in Alberta in year 1980: a whole graveyard of about 500 Centrosauruses died together, probably killed while trying to cross a river in flood. This discover was one of the first concrete evidence of migrating behaviour in dinosaurs, a bit like modern caribous and wildebeest (which also sometimes die in group during their river-crossings). Since then, Centrosaurus has replaced “Monoclonius” in books/docus as “the one-horned ceratopsid”. Curiously, the centrosaur was unnecessarily renamed "Eucentrosaurus" in year 1988, but returned Centrosaurus again soon after.
I'm the real Rhinosaur... or am I just too young?: “Monoclonius”,
“Monoclonius” has been a very early discover, made in the XIX century during the Bone-Wars, but now is regarged by many as the juvenile-stage of Centrosaurus and its relatives. If so, then “Centrosaurus” would become invalid, because "Monoclonius" was the first name created. Two of the most familiar ceratopsid names, Torosaurus and Centrosaurus, risk now to get the same fate of “Brontosaurus”.
"Monoclonius" (which doesn't mean "one horn" but "one sprout") was slightly smaller than Centrosaurus but with the same rhinoceros-like appearence (long nose-horn and no real front-horns), and its frill had not the famous downwarding "hooks" of Centrosaurus (or it had them much shorter). It was discovered during the Bone Wars: while Triceratops was officially described by Marsh, "Monoclonius" was one of the few prominent bone-war dinosaurs first-described by Cope. Another less-known “unicorn” is “Brachyceratops”; found in the early XX century, it is known only from juveniles, and like “Monoclonius”, could just be a young stage of another ceratopsid.
I'm Thick Nose, not Thick Head: Pachyrhinosaurus
Ceratopsids are classically known as “horned dinosaurs”: but this one seems not to have liked our definition. Pachyrhinosaurus (“thick-nosed lizard”), at a first glance, resembles more an oversized Protoceratops than a Triceratops: it has no true horns on its skull, it had a thickened boss upon its nose, sometimes described as similar to a lunar crater. To compensate, its short frill has an elaborate shape, with two horn-like spikes protruding from its rear-corners, other minor undulations elsewhere, and a small prominence pointing upwards from the center of the shield.
It’s worth noting, however, that juvenile pachyrhinosaurs did have a typical ceratopsid nose horn that was absorbed into the skull as they grew. This detail, along with its great size, massive limbs and other elements, firmly demonstrates that it is a true ceratopsid, more precisely a Centrosaurine - that is, a relative of Centrosaurus and Styracosaurus. As a matter of fact, Pachyrhinosaurus was the last surviving Centrosaurine, living at the same time as T. rex and Triceratops (though much farther north).
Before the nineties Pachyrhinosaurus was one of the rarest ceratopsids: then, in the 1990s, a whole herd was discovered in Alaska. Since other Pachyrhinosaurus remains have been found much souther, this might be another proof of migrating behavior among horned dinosaurs. Pachyrhinosaurus should never get confounded with Pachycephalosaurus: both had something “thick” in their skull, but in the latter’s case was the head. Another thick-nosed, horn-lacking ceratopsid was discovered in the 1990s, Achelousaurus, which shows a longer couple of frill-spikes but a less-complex frill than Pachyrhinosaurus.
I love geometry: Chasmosaurus
Maths are not always a exclusively-nerd thing. It can also be amusing, expecially when you can apply it to dinosaurs. Chasmosaurus can just be recognized by the geometry of its frill: strikingly angular in shape, if seen frontally almost seemed a reversed Isosceles Triangle with the base on the top and the apex attached to the skull. Its edge was also complex: smooth and V-shaped at the “hypothenusa”, spiky on the two upper corners, and half-smooth / half-undulating on the two “cathetes”. Moreover, this frill was also extremely elongated, almost like the Torosaurus one, and was arguably used for the same purpose.
The remaining head was far less spectacular: the horns were three likeTriceratops, but were rather short in comparison – some individuals had mere hints of the frontal ones; we’re not sure if they’re from females or distinct species. One fragmentary ceratopsid which was often confused with Chasmosaurus is "Eoceratops"("dawn horned face"), which was one of the first true ceratopsians living before Chasmosaurus proper.
Known since the 1910s, Chasmosaurus is one of the most common ceratopsids in fossil record, and is often considered the prototype of the (usually) long-shielded subgroup: the Chasmosaurines (or Ceratopsines), which includes also Triceratops. However, the genus Chasmosaurus has been recently split in several new genera (year 2010). In Fictionland, the chasmosaur was portrayed in one old movie, and some modern-cartoon "Triceratops" have a suspiciously Chasmosaurus-like triangular frill.
I've got five horns: Pentaceratops
Despite many of the aforementioned ceratopsians had the usual “saurus” ending, most described genuses have the same suffix of the Great-Stock member. -ceratopses do abund here: after Triceratops (“three horned face”) and Protoceratops (“first horned face”), the most well-known is Pentaceratops (“five-horned face”). But did it really had five horns? Well… no. They were only three. The other two “horns” actually were simple protrusions arising from each cheekbone - a common ceratopsian trait, but particularly evident in Pentaceratops.
One of the classic long-frilled ceratopsids, Pentaceratops was pratically the intermediate form between Torosaurus and Chasmosaurus: smaller than Torosaurus but bigger than Chasmosaurus, lived before the former but after the latter. Its horns were shorter than Torosaurus but more developed than many Chasmosauruses. Its frill was neither elliptical / smooth like the Toro’s one, nor triangular / complex like the Chasmo’s: it was rectangular and lightly serrated around its whole perimeter.
Known since the first half of the XX century from remains discovered in Texas, Pentaceratops gained more attention in the 1990s after the discover of a gigantic skull which was attributed to its genus. Before that, Torosaurus, with its 2.5 m long skull, used to bear the record for “the biggest-headed land animal ever”; this putative pentaceratops’ skull was 3 m long. Science Has Marched On however, and this specimen has been deemed a separate animal in January 2011, Titanoceratops.
The Ceratops Family: Anchiceratops & Arrhinoceratops
As a whole, Centrosaurs Styracosaurs Pachyrhinosaurs Chasmosaurs might be considered the “predecessors” of Triceratops. The latter was elephant-sized, lived 70-65 million years ago just before the mass-extinction and shared its world with the mythical Tyrannosaurus rex; the former were only rhino-sized, lived 80-70 million years ago, and had to be pleased with its “humbler” relatives (Albertosaurus, Gorgosaurus, and Daspletosaurus).
If you see a battle between a tyrannosaurid and a ceratopsid in some CGI documentary, expect to see Triceratops instead of the less-gigantic CentroStyracoPachyrhinoChasmosaurs. Good luck if you find other less-known contemporaries, like Anchiceratops and Arrhinoceratops. The first one was very Chasmosaurus-like with a similar angular frill but entirely smooth laterally and entirely tubercled at its top. The second has a similar ornamentation but a much shorter frill. Anchiceratops is nonetheless abundant in fossil record, while Arrhinoceratops is a rarer find; when discovered was initially thought to lack the nasal horn, hence its prefix “arrhino” which means “no horns on the nose”.
And then, there's Avaceratops, a small ceratopsian of uncertain affinites whose name means “Ava’s horned face” (its discoverer named it from his wife’s name in 1988). Even though resembles a miniature Centrosaurus it actually could be one of the closest Triceratops relatives, and like the latter, has a round frill with no openings in it. Described in the 2000s, Albertaceratops ("Alberta horned face") could make the perfectly-opposite case: it has long frontal horns like those of a chasmosaurine, but is actually more related with centrosaurine ceratopsids.
Horned Hairdos: Einiosaurus & recently-found ceratopsids
Well, it’s true: ceratopsids have really bizarre hairdos. The most astonishing is, needless to say, that of Styracosaurus, with its multiple “horns” protruding from the frill. But some relatives made even their frontal horn a very odd-looking thing: for example Einiosaurus. Only discovered in the 1990s, it was initially believed a new styracosaurian species, but with only two terminal spikes on its shield. The strange thing here is the nasal horn: strongly curved, thickened and pointing forwards, as the animal could signal its target like a pointer dog… more realistically, its shape could have been for ornamental purpose.
As recently as years 2010/2011, many new ceratopsid species have been discovered, with various frill-shapes. Rubeosaurus, for example, was very similar to Styracosaurus (and originally considered a species of the latter just like Einiosaurus), but with shorter frill-spikes and longer nasal horn. Diabloceratops uniquely coupled the pair of long frontal horns with two long frill-spikes. The most spectacular is perhaps Kosmoceratops: similar to Chasmosaurus, it shows an entire set of curved hooks protruding from the frill-top like a fanciful fringe. Slightly before that was described a more normal-looking ceratopsid, Eotriceratops ("dawn Triceratops", not to be confused with "Eoceratops"): extimated 11 meters long, it is one of the biggest ceratopsid known so far, as large as the largest Triceratopses. Last example, Sinoceratops ("Chinese horned face"); even though incomplete, it's the only confirmed ceratopsid found in Asia to date.
Illustrious unknowns: Ceratops & Agathaumas
Who knows which is the official prototype of the Ceratopsid family? Well… just Ceratops. Found by Marsh during the Bone Wars, it was its first horned dino, but has left only a fragmentary skull. It could be Chasmosaurus or something else, and has been largely ignored by everyone. Not the same about "Agathaumas".
This animal was also found during the “wars”, this time by Cope; only some pieces of skeleton are known but not skulls, and since non-cranial remains are not diagnostic enough, Agathaumas is impossible to describe. Many suspect it’s only a Triceratops individual. And yet, it has had a famous appearance in the 1925 movie version of "The Lost World" (one of the first apparition of dinosaurs in cinema), in which it was portrayed with a Triceratops look. That apparition made it rather popular at the time, but now has obvioulsy get forgotten.