centrosaurinae – Nix Illustration

Lokiceratops

Lokiceratops rangiformis was a ceratopsian dinosaur that lived during the Late Cretaceous (~78 million years ago) in what is now Montana, USA. Estimated at about 6.7m long (~22ft), it was one of the largest known members of the centrosaurine branch of the ceratopsians.

It had a unique arrangement of ornamentation on its skull, with no nose horn, two long brow horns, and a pair of huge asymmetrical curving blade-like spikes on the top of its square frill – some of the largest known frill spikes of any ceratopsian.

It lived in a swampy environment near the shore of the Western Interior Seaway, in an area that seems to have had an unusually high diversity of ceratopsians – along with Lokiceratops there were three other centrosaurines (Medusaceratops, Albertaceratops, and Wendiceratops), and one chasmosaurine (Judiceratops).

(There’s also a possibility that it might not actually be a unique species. We know some other ceratopsians’ faces changed quite drastically as they aged, so Lokiceratops could instead represent a fully mature individual of Medusaceratops.)

Strange Symmetries #17: Spiky Surprise

Styracosaurus albertensis was a ceratopsid dinosaur living during the late Cretaceous about 75 million years ago, in what is now Alberta, Canada. Around 5m long (~16′), it was one of the most elaborately ornamented horned dinosaurs, with a long nose horn and multiple elongated spikes on its frill.

There was actually quite a lot of variation in the frills of Styracosaurus, with varying numbers of long spikes and extra hook-like projections present on some individuals. But one recently-discovered specimen nicknamed “Hannah” is especially surprising – it had a noticeable amount of asymmetry in its skull. The left and right sides show different numbers and arrangements of spikes, so much so that if the two halves had been discovered separately they might have been identified as belonging to two completely different species.

Frill arrangements are often used to define different ceratopsids, so if this level of individual variation and asymmetry existed in other species, too, then we may need to reevaluate some of them.

Weird Heads Month #14: Horns and Frills

We can’t go through this month without having an appearance from the most famous group of weird-headed dinosaurs: the ceratopsids!

Their distinctive-looking skulls were highly modified from those of their ancestors, with large bony frills extending from the back of their heads, various elaborate horns and spikes, enormous nasal cavities, large hooked beaks at the front of their snouts, and rows of slicing teeth further back.

And while typically depicted as purely herbivorous, ceratopsids’ powerful parrot-like beaks and lack of grinding teeth suggest they may actually have been somewhat more omnivorous – the Cretaceous equivalent of pigs – still feeding mainly on plant matter but also munching on carrion and opportunistically eating smaller animals when they got the chance.

Machairoceratops cronusi here lived during the late Cretaceous of Utah, USA, about 77 million years ago. Only one partial skull has ever been found belonging to an individual about 4.5m long (14’9″), but it wasn’t fully grown and so probably reached slightly larger sizes.

It had two long spikes at the top of its frill, similar to its close relative Diabloceratops but curving dramatically forward and downwards above its face. Whether they were purely for display or used in horn-locking shoving matches is unknown, but either way it was a unique arrangement compared to all other known ceratopsids.

Medusaceratops

Medusaceratops lokii, a ceratopsid from the Late Cretaceous of Montana, USA (~77.5 mya).

About 6m long (19′8″), it had long brow horns and large curved spikes on its frill – an arrangement very similar in appearance to the centrosaur Albertaceratops, and initially its fossils were misidentified as belonging to that particular ceratopsid. But in 2010 it was recognized as a different genus, and based on some partial frill remains it was classified as a very early chasmosaur (a different branch of the ceratopsids which includes Triceratops), related to other early forms like Mercuriceratops.

Its genus name was based on the snake-haired Medusa from Greek mythology, while its species name comes from the Norse trickster god Loki – both in reference to the years of confusion about the identity of Medusaceratops’ fossils, and the distinctive curved horns on the helmet of Marvel’s Loki.

And, true to its name, the confusion wasn’t over yet.

Recently more fossil material and a new study have shown it was still being misclassified. Now it seems like Medusaceratops was actually part of the centrosaur lineage all along, and was indeed a very close relative of Albertaceratops.

It also turns out that what were thought to be numerous Albertaceratops fossils found in the same location were all just even more Medusaceratops. Instead of a mixture of two different ceratopsids there’s a single big bonebed representing some sort of mass-mortality event of only this one animal.

Similar mass bonebeds have been found for other centrosaurs in the same area and around the same age. Perhaps there were frequent flash floods at the time, or they were attempting to migrate across fast-flowing rivers like some modern animals, but we still don’t actually know for certain why they died en masse so frequently.

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.)

Ceratopsian Month #16 – Achelousaurus horneri

Achelousaurus (“Achelous lizard”) seems to have been a transitional form among the Pachyrhinosaurini. While slightly more basal members like Einiosaurus had well-developed nose horns, and the later Pachyrhinosaurus had enormous flattened nasal bosses, Achelousaurus was somewhere in-between.

Living in Montana, USA, about 74 million years ago, it reached sizes of about 6m long (19′8″). Instead of horns, rough patches of bone on its skull supported bosses over its snout and eyes, which in life would have been covered by thick layers of keratinous skin.

Unlike adults, juveniles had small brow horns with bony cores which gradually developed into full bosses as they grew. It’s possible that the bosses of mature individuals were used for headbutting or ramming behaviors.

Ceratopsian Month #15 – Einiosaurus procurvicornis

Einiosaurus (“buffalo lizard”) was part of a branch of the centrosaurs known as the Pachyrhinosaurini, a group with especially elaborate nose ornamentation.

Living about 74 million years ago in Montana, USA, it’s known from hundreds of bones representing over fifteen different individuals of varying ages. It had little-to-no brow horns, and two long spikes at the top of its frill – but also one of the most unusual-looking nose horns of all the ceratopsids, curving strongly forward and downward into a large hooked shape.

The juvenile remains show evidence of very rapid growth during their first few years of life, only starting to slow down around age 3-5, suggesting that was the point they began to reach reproductive maturity. The largest specimens are estimated to have measured about 4.5m long (14′9″), although they appear to have been subadults who still hadn’t quite reached their full size.