Ceratopsian Month #14 – Wendiceratops pinhornensis

Wendiceratops (“Wendy’s horned face”) was one of the older known centrosaurs, living about 79 million years ago in Alberta, Canada – but it had a slightly higher position in the evolutionary tree than more basal forms like Xenoceratops, indicating just how incredibly quickly the early ceratopsids diversified.

Partial remains of several individuals have been found, representing both adults and juveniles, with an estimated full size of around 6m long (19′8″).

It had forward-curving frill spikes, similar to those of its close relative Sinoceratops, and a large nose horn. The size of its brow horns are unknown, so the ones seen in this reconstruction are based on the fairly well-developed horns of other similarly-aged centrosaurs.

Ceratopsian Month #13 – Sinoceratops zhuchengensis

Sinoceratops (“Chinese horned face”) was the first and only ceratopsid known from China, and possibly also the only one known from the entirety of Asia – depending on whether Turanoceratops counts as a true ceratopsid or not.

Discovered in the Shandong province, it dates to about 73 million years ago and was one of the larger centrosaurs at an estimated length of at least 6m (19′8″).

It had a well-developed nose horn and highly reduced brow horns, and forward-curving spikes around the edge of its frill that gave it a crown-like appearance. Uniquely for a ceratopsid, it also had some protruding bumps just below the spikes, creating a second row of ornamentation.

The presence of Sinoceratops in China shows that at least one lineage of centrosaurs dispersed across to Asia in the Late Cretaceous, but they seem to have been quite rare animals on that side of Beringia. While other dinosaur groups such as hadrosaurs and tyrannosaurs seemed to do just fine on both continents, something prevented the ceratopsids from being nearly as prolific as their North American relatives.

Ceratopsian Month #12 – Albertaceratops nesmoi

As its name suggests, Albertaceratops (“Alberta horned face”) was discovered in Alberta, Canada. Living around 77 million years ago, it’s known from an almost complete skull and would have had an estimated full body length of about 5.8m (19′).

It had fairly long brow horns and a boss-like nasal horn, similar to the arrangement in Xenoceratops, with a pair of large curving hook-shaped spikes at the top of its frill.

Some similar fossil remains found in Montana, USA, were attributed to Albertaceratops, but later studies showed that they actually belonged to a completely different ceratopsid – a chasmosaur eventually named as Medusaceratops.

[2018 update: Medusaceratops wasn’t actually a chasmosaur, but a centrosaur closely related to Albertaceratops!]

Ceratopsian Month #11 – Xenoceratops foremostensis

Xenoceratops (“alien horned face”) was one of the earliest centrosaurs known from Canada, discovered in Alberta and dating to about 80-78 million years ago – very similar in age to the more southern Diabloceratops.

It’s estimated to have been around 6m long (19′8″), and although the known fragmentary fossil material doesn’t include much of its face, there’s evidence of it having fairly long brown horns and a long low boss-like nasal horn.

It a had a pair of forward-pointing knobs and a pair of large spikes at the top of its frill, but the exact number and arrangement of the rest of its ornamentation isn’t clear. This particular image is based on Scott Hartman’s “best guess” Xenoceratops skeletal, but other reconstructions vary.

Ceratopsian Month #10 – Nasutoceratops titusi

The second centrosaur discovered in the southern portion of Laramidia, Nasutoceratops (“large-nosed horned face”) lived 75 million years ago in Utah, USA. It would have measured around 4.8m long (15′8″), and had very long horns, curving out to the sides and then twisting forwards into a shape that convergently resembles those of modern cattle.

It appears to have been part of a unique side branch of the early centrosaurs known as the Nasutoceratopsini, which had long brow horns, small nose horns, and only modestly decorated frills compared to their other relatives. This group also includes representatives from further north such as Avaceratops and several other still-unnamed specimens.

Its snout was short and deep, with an unusually huge nasal cavity – even for a ceratopsid – and shows evidence of pneumatic air sacs. Skin impressions were also found around its left shoulder, showing a pattern of 1cm (0.4″) hexagonal scales surrounded by smaller triangular scales.

Ceratopsian Month #09 – Diabloceratops eatoni

At this point in ceratopsian evolution we’ve reached the ceratopsids – the big, elaborately horned and frilled group that includes famous names like Triceratops and Styracosaurus. First evolving from their smaller North American ancestors around 90-80 million years ago, these dinosaurs rapidly diversified and developed a huge variety of different head ornamentations during the last 20 million years or so of the Cretaceous.

Here the family tree gets a little more complicated, with two major subdivisions of the ceratopsids splitting off from a common ancestor: the centrosaurs and the chasmosaurs. We’ll be focusing on the centrosaurs to start off, and moving on to chasmosaurs later in the month.

Continue reading “Ceratopsian Month #09 – Diabloceratops eatoni”

Ceratopsian Month #08 – Turanoceratops tardabilis

Turanoceratops (“Turan horned face”) was very slightly younger than Zuniceratops, living about 90 million years ago in the Late Cretaceous. At around 2m long (6′6″) it was another small transitional form very very closely related to the true ceratopsids, but there’s still disagreement about whether it was actually a proper member of that group or not.

Its fossil remains were discovered in Uzbekistan, making it the earliest ceratopsid-like ceratopsian known from Asia rather than North America – and showing that there were still populations of ceratopsians dispersing back and forth between the two continents.

Only fragmentary fossils have been found, so while we know it had large brow horns we don’t know whether it had a nose horn or what the shape of its frill was. So most of the rest of its appearance here is rather speculative.

Ceratopsian Month #07 – Zuniceratops christopheri

Zuniceratops (“Zuni horned face”) was discovered in New Mexico, USA, and dates to the Late Cretaceous (~91 mya). Estimated to have been about 3.5m long (11′5″), it was one of the earliest ceratopsians with well-developed horns over its eyes.

It had a transitional mix of features between basal ceratopsians and the later larger forms – having brow horns and a long narrow snout, but a frill lacking decorative scalloped edges – suggesting that the horned ceratopsids evolved from more “primitive” ancestors already within North America rather than migrating in later from Asia.

Bones from several different individuals have been found, showing that their teeth became more firmly rooted with age, going from single-rooted in juveniles to double-rooted in adults. The brow horns also appear to have grown continuously throughout Zuniceratops’ life, with those of older specimens being much larger.

Ceratopsian Month #06 – Protoceratops andrewsi

The protoceratopsids were a mainly Asian branch of the ceratopsians (with one species also known from Europe), splitting off shortly after the leptoceratopsids. Although still fairly small, they looked a lot more like a typical ceratopsian than their ancestors, with relatively big heads for their body size and large neck frills.

The best-known member of this group was the 1.8m long (6′) Protoceratops (“first horned face”), which lived in Mongolia during the Late Cretaceous (~75-71 mya). It was a very common animal, with hundreds of fossils representing all different stages of growth, and large numbers found together suggest it may have lived in herds.

The size and shape of its frill differed a lot between individuals, with some being short and compact and others being much longer or wider. Some paleontologists have considered this to be evidence of sexual dimorphism, but further studies show no clear distinctions between the proposed “male” and “female” morphs – it was probably just natural genetic variation among the population.

For many years a fossilized clutch of eggs was believed to belong to Protoceratops, with a nearby Oviraptor with a crushed skull thought to be an egg-eating thief killed while trying to raid the nest. The later discovery of an identical egg containing an Oviraptor embryo revealed that the story was the wrong way around – the Oviraptor was the one brooding and protecting its nest all along. 

Another famous fossil preserves a fight between a Protoceratops and a Velociraptor, the pair dying together before being buried in sand. The predator’s sickle claw was lodged into the Protoceratops’ neck, while the ceratopsian was crushing the Velociraptor’s arm in its beak.

(Oh, and Protoceratops fossils also probably didn’t actually inspire legends about griffins.)

Ceratopsian Month #05 – Leptoceratops gracilis

During the mid Cretaceous, around 100-80 million years ago, the leptoceratopsids split off from the main ceratopsian lineage. Fairly small with low frills, they were a successful group lasting throughout the rest of the Mesozoic. Seeming to originate in western North America, a few species have been found in Asia that may represent a dispersal event back across Beringia, and partial remains are also known from Europe and Appalachia. There’s even a dubious identification from Australia.

Leptoceratops (“small horned face”) was one of the last of this branch of the ceratopsians, living during the very end of the Cretaceous (~66 mya). About 2m long (6′6″), its fossils have been found in Alberta, Canada, and Wyoming, USA, and it would have lived alongside some of its larger distant cousins like the much more famous Triceratops.

Its skeleton shows it was a stocky quadrupedal sort of pig-like animal. Short deep jaws with strong teeth gave it a powerful bite, adapted for slicing and crushing, and it was probably specialized for a diet of very tough plant matter.