ceratopsians – Nix Illustration

Ceratopsian Month #31 – Triceratops horridus

Of course we’re ending this month with the most famous of the ceratopsians, the dinosaur superstar Triceratops (“three-horned face”).

Dating to the very end of the Cretaceous, between 68 and 66 million years ago, it was the most common ceratopsid in North America at the time, ranging from Alberta, Canada down to Colorado, USA. Two different species are currently recognized within the genus – T. horridus in the older part of that time range, and T. prorsus in the younger rock layers.

It was one of the very largest ceratopsians, with the biggest individuals reaching sizes of about 7.9-9m (26’-29’6”). Many fossil remains have been found, representing growth stages from juveniles to adults (with Torosaurus speculated to represent the most fully mature individuals), and a lot of variation in exact horn and frill shape is seen between different skulls. One specimen nicknamed “Yoshi’s trike” had some of the longest brow horns of any ceratopsid, with the bony cores alone measuring 1.15m long (3′9″).

Unusually for a chasmosaur, it had a very short and solid frill with no weight-reducing holes, suggesting the structure served a much more defensive role than in other ceratopsids. Damage to the frill bones in some specimens appears to have been caused by other Triceratops, giving support to the popular depiction of these dinosaurs locking horns in fights.

Tooth-marks from the equally-famous Tyrannosaurus have also been found on Triceratops bones. Not all of these predator-prey encounters were fatal, however, with some specimens showing evidence of healing around the damaged areas.

Fossilized skin impressions show that Triceratops was scaly – but with scales unlike those of any other known dinosaur, showing large polygonal scales interspersed with even bigger knobbly scales with odd “nipple-shaped” conical projections in their centers. It’s possible that the “nipples” may have supported larger structures (as I’ve illustrated above), but unfortunately no official scientific description of this skin has been published yet and details about it are vague.

And with this final entry, here’s the chasmosaur evolutionary tree:

Ceratopsian Month #30 – Torosaurus latus

Torosaurus (“perforated lizard”) was a particularly widespread member of the Triceratopsini, found across western North America. Fossils are known from Canada all the way down to New Mexico and Texas in the southern regions of the USA, although the southernmost specimens represent a second species within the genus, T. utahensis.

Living about 68-66 million years ago, it was one of the largest ceratopsids, reaching body lengths of around 7.5m (24’7″). The size and shape of its three horns varied between individuals, from short and straight to much longer and curving forwards.

It had one of the longest skulls of any known land animal, with some specimens’ heads measuring at least 2.5m long (8′2″). Around half of that length consisted solely of its frill, the shape of which was also quite variable – some were very flat while others curved upwards, and the top edge could be either rounded, straight, or have a “heart-shaped” notch.

In 2010 a study was published by John Scannella and Jack Horner, hypothesizing that Torosaurus wasn’t a unique genus and was actually the fully mature form of Triceratops. While poor media reporting briefly sent the internet into a panic about Triceratops “never existing”, further studies by other paleontologists have failed to come up with the same results, and the debate doesn’t seem to have come to any overall consensus yet.

Ceratopsian Month #29 – Regaliceratops peterhewsi

The Triceratopsini branch of the chasmosaurs first split off somewhere around 75 million years ago, with Titanoceratops being the earliest known member. But they don’t seem to have really diversified until several million years later, towards the very end of the Cretaceous 70-68 million years ago, around the time the centrosaurs had already mostly disappeared.

Regaliceratops (“royal horned face”) dates to about 68-67 million years ago, and is estimated to have measured around 5m long (16’4″). Known from a single near-complete skull discovered in Alberta, Canada, the fossil specimen was nicknamed “Hellboy” for both its stubby brow horns and the immense difficulty of removing it from the surrounding rock.

It had highly unusual ornamentation for a chasmosaur – a long nose horn, short brow horns, and large crown-like spikes ringing its relatively short frill – convergently resembling the sort of arrangement seen in many centrosaurs.

Ceratopsian Month #28 – Vagaceratops irvinensis

Vagaceratops (“wandering horned face”) was originally thought to be a species of Chasmosaurus, but was separated out into its own genus in 2010 after new studies suggested it was much more closely related to Kosmoceratops.

Measuring around 5m long (16’4”), it lived about 75 million years ago in Alberta, Canada – much farther north than its Utahn relative, inspiring its “wandering” genus name. It had a short nose horn, and brow horns reduced down to low bosses, along with a distinctive squared-off frill topped with a row of forward-curving spikes.

Ceratopsid forelimb posture has been a long-standing puzzle in paleontology. While the hindlimbs were clearly held straight under the body, the bones of the forelimbs are a lot more ambiguous, and various different arrangements have been proposed over the years from straight to heavily sprawled and lizard-like.

While the fully sprawled position mostly fell out of favor during the dinosaur renaissance, debate continued about whether ceratopsids had a fully straight forelimb posture or some sort of in-between arrangement with the elbows slightly bent out to the sides. In 2007, digital scans of Vagaceratops’ forelimb bones were used to model how it could have walked, suggesting the best fit was in fact the intermediate position.

Ceratopsian Month #27 – Kosmoceratops richardsoni

Kosmoceratops (“ornamented horned face”) was discovered in Utah, USA, and had one of the most ornate skulls of any known dinosaur.

Living about about 75 million years ago, it’s known from a partial skeleton and an almost complete skull and is estimated to have measured around 5m long (16’4”).

Its frill was relatively short and wide for a chasmosaur, topped with a “fringe” of eight long folded-over spikes and a pair of sideways-curving hooks. Its brow horns curved sideways, and its nose horn was thin and flattened into a blade-like shape.

Overall it had a total of fifteen large horns and spikes – ten big frill spikes, two brow horns, a nose horn, and two cheek spikes – along with sixteen additional scallops along the sides of its frill.

Ceratopsian Month #26 – Spiclypeus shipporum

Spiclypeus (“spiked shield”) lived in Montana, USA, about 76-75 million years ago. Known from one partial skull and a few pieces of the rest of the skeleton, representing a mature adult about 10 years old, it’s estimated to have measured between 4.5 and 6m in length (14’9″-19’8″).

Damage to the frill bones on one side of the skull show evidence of an infected injury, possibly inflicted by the horns of another Spiclypeus during a fight. The forelimb bones also showed symptoms of arthritis and abscessed bone infection, suggesting this particular fossilized individual had suffered a lot of pain towards the end of its life.

The first two pairs of Spiclypeus’ frill spikes were fused together, folding forward over the top of the frill, and its brow horns curved out to the sides. Its ornamentation seems to have been transitional between the straighter frill spikes of earlier chasmosaurs and later more elaborately curled forms.

The fossil remains show close similarity to two other ceratopsids known from highly fragmentary material – the dubious Pentaceratops aquilonius, and the poorly-known Ceratops montanus, the type genus of the entire ceratopsian group. All three might even be the same species (in which case Ceratops would take priority as the oldest valid name), but without more and better specimens it’s not possible to tell for certain.

Ceratopsian Month #25 – Pentaceratops sternbergii

Despite its name, Pentaceratops (“five-horned face”) only had three main facial horns just like most other ceratopsids. The extra two “horns” actually refer to the cheek spikes which protruded out sideways from its face – a feature seen in all ceratopsids to some degree, but especially long and sharply pointed in Pentaceratops.

Living about 76-73 million years ago, its fossils are known from New Mexico and Colorado, USA. A possible second species, P. aquilonius, was discovered much farther north in Alberta, Canada, but this identification is somewhat dubious due to the remains being highly fragmentary.

Multiple specimens have been found, with a full body length of around 5-6m (16’4″-19’8”). One especially large specimen previously identified as Pentaceratops was nearly 7m long (23′), but has since been moved into its own separate genus Titanoceratops.

Pentaceratops’ frill was one of the largest of all known ceratopsids, similar in size and shape to that of its close relative Utahceratops, with a U-shaped top edge and a pair of forward-curving spikes.

Ceratopsian Month #24 – Utahceratops gettyi

Utahceratops (“Utah horned face”) lived about 76-75 million years ago in Utah, USA. Partial remains of six different individuals have been found, allowing for about 95% of the skull and 70% of the rest of the skeleton to be accurately reconstructed – giving a full body length of around 4.5m (14’9″), with the skull alone being over 2m long (6′6″).

Its nose horn was positioned quite far back on its snout, and its short blunt brow horns pointed out to the sides. The top of its long frill ended in a U-shaped notch, with the first pair of spikes curving forwards.

Despite how proportionally large the skulls of chasmosaurs like Utahceratops were, they weren’t nearly as heavy as they might look. Instead of being made of solid bone, there were large openings in the frill (known as fenestrae) that helped to significantly reduce its weight.

Ceratopsian Month #23 – Chasmosaurus belli

The basis for the whole chasmosaur grouping of the ceratopsids, Chasmosaurus (“chasm lizard”) lived about 76-75 million years ago in Alberta, Canada. Two different species are currently recognized within the genus, with the smaller C. russeli found in older rock layers and the type species C. belli being slightly younger.

Many different fossils are known, including a juvenile, with C. belli adults reaching a size of around 4.8m (15’8”). Different individuals display a lot of variation in their ornamentation, especially in the size and curve of their brow horns – and some specimens even lost their brow horns completely, with the bony cores being resorbed with age.

It shared its habitat with its distant relative Centrosaurus, but since Chasmosaurus had a longer narrower snout than its centrosaur cousin it probably fed on different types of vegetation.

Skin impressions are also known from around the right hip region on one specimen, showing large scales in spaced-out horizontal rows among much smaller scales.

Ceratopsian Month #22 – Coahuilaceratops magnacuerna

Coahuilaceratops (“Coahuila horned face”) was the first ceratopsid discovered in Mexico, living about 72-71 million years ago. Known from partial skull material and other fragmentary remains, it’s estimated to have measured around 5-6m in length (16′4″-19′8″)

It seems to have been an early member of a branch of the chasmosaur evolutionary tree that included animals more closely related to Chasmosaurus than to Triceratops. (This grouping doesn’t currently have an official name, but similarly to @a-dinosaur-a-day I’ll be referring to them as the “Chasmosaurini”.)

Its brow horns were proportionally huge for its size, each reaching up to 1.2m long (4′) – some of the largest of all known ceratopsids.