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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.

Ceratopsian Month #21 – Mercuriceratops gemini

The chasmosaurs were the second major branch of the ceratopsids, and ranged throughout most of western North America from Mexico to Canada during the end portion of the Cretaceous (~78-66 mya). They tended to have larger brow horns than their centrosaur cousins, and more elongated frills that lacked elaborate spikes.

Mercuriceratops (“Mercury horned face”) was one of the earliest chasmosaurs, living in Alberta, Canada and Montana, USA about 77 million years ago. Known only from two almost-identical skull fragments found on each side of the Canada-USA border, its full body size is uncertain – but estimates range from 4 to 6m (13′-19′8″).

It had prominent projections on the sides of its frill, forming distinctive “wing” shapes unlike any other known ceratopsid.

The rest of its ornamentation is still unknown, but it was likely similar to other early chasmosaurs like Judiceratops, with moderately-sized brow horns and a small nose horn.

Ceratopsian Month #20 – Styracosaurus albertensis

The last centrosaur for this month is one of the most distinctive and recognizable of all ceratopsians – the elaborate Styracosaurus (“spiked lizard”).

Known from Alberta, Canada, about 75 million years ago, it was part of the Centrosaurini branch of the centrosaur evolutionary tree, closely related to both Centrosaurus and Coronosaurus. Many fossils have been found in several different bonebeds, including some nearly complete skeletons with body lengths of around 5.5m (18′).

There was a lot of variation in the frill ornamentation between different Styracosaurus individuals. They could have either two or three pairs of very long spikes at least 50cm long (19″), along with various smaller hooks, knobs, or tab-shaped projections.

The long nose horn was also very variable between specimens, with some pointing slightly backwards, some being straight, and others pointing forwards. Juveniles are known to have had small pointed brow horns which became even more reduced in adults.

Tomorrow we’re moving on to the chasmosaurs, so here’s the centrosaur evolutionary tree:

Ceratopsian Month #19 – Coronosaurus brinkmani

Coronosaurus (“crowned lizard”) was a very close relative of Centrosaurus – so close, in fact, that it was originally named as a second species of Centrosaurus itself, before being recognized as a separate genus a few years later.

Living around 77 million years ago, it was a medium-sized centrosaur about 5m long (16′4″). Multiple specimens are known from two bone beds in Alberta, Canada, with different ages represented. Juvenile Coronosaurus skulls looked very similar to juvenile Centrosaurus, only developing their own distinct ornamentation as they matured.

It had a slightly backwards-pointing nose horn, brow horns that curved out to the sides, and a pair of downward-curving frill spikes. Uniquely among all known ceratopsians, it also had large irregular masses of short spikelets at the top of its frill forming a distinctive “crown”.

Ceratopsian Month #18 – Centrosaurus apertus

Centrosaurus (“pointy lizard”) lends its name to the entire centrosaur group of ceratopsids – and also to a major branch within the centrosaur evolutionary tree, the Centrosaurini.

Known from Alberta, Cananda, around 76-75 million years ago, it grew up to about 6m long (19′8″) and is known from a huge number of fossils from thousands of individuals in gigantic bonebeds. These seem to represent enormous herds, making Centrosaurus one of of the most common dinosaurs in the region at the time.

It had a single large horn on its nose, which started off pointing backwards as a juvenile and changed shape as it grew, gradually hooking forwards. Two especially long spikes at the top of its frill curved strongly downwards, while its brow horns were reduced to small points.

Skin impressions are also known from one specimen, preserving a region around the right hip and upper leg, showing a pattern of small polygonal scales interspersed with larger rounded scales.

Ceratopsian Month #17 – Pachyrhinosaurus canadensis

Pachyrhinosaurus (“thick-nosed lizard”) has become one of the more recognizable ceratopsian names in the last couple of decades, but its remains have actually been known for over 70 years, first discovered in the mid-1940s.

Three different species have been named within the genus, all living about 74-69 million years ago in Alberta, Canada, and Alaska, USA. The type species P. canadensis dates to roughly the middle of that time span, at an age of around 71 million years.

It was one of the largest of the centrosaurs, with the biggest specimens estimated to have measured up to 8m long (26′). Thousands of fossils have been found in a bone bed that seems to represent a mass mortality event – possibly a herd caught in a flash flood – with ages ranging from juveniles to adults.

Rather than horns, Pachyrhinosaurus had huge flattened bosses on its skull, which nearly grew together into a single large mass in both P. canandensis and the younger species P. perotorum. The older species P. lakustai instead had more separated bosses and a “unicorn horn” on its forehead.

(I’m also hardly the first person to speculate about fluffy pachyrhinosaurs, but since they lived in a chilly Arctic environment it’s certainly an interesting possibility.)