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.

Ceratopsian Month #04 – Auroraceratops rugosus

Auroraceratops (“dawn horned face”) lived during the Early Cretaceous of China (~130-100 mya). Around 2m long (6′6″), it had a shorter and wider snout than other early ceratopsians, with a more flattened broader head shape.

It was closely related to other small Asian species like Koreaceratops, and was probably primarily bipedal due to its proportionally short arms. But, since it falls at a transitional point in ceratopsian evolution between bipedal ancestors and quadrupedal later forms, it may have adopted a four-legged posture while feeding or moving at slow speeds.

Its skull had several patches of thickened bone, found directly in front of its eyes and on its lower jaw. These could have had some visible tough keratinous coverings in life – although I’ve not depicted any here – and could potentially have been used for pushing and butting during fights.

The back of its small frill shows evidence of attachment sites for its jaw muscles, suggesting that ceratopsian frills may have originally evolved to support large powerful chewing muscles before being secondarily modified into elaborate display structures.

Ceratopsian Month #03 – Aquilops americanus

Although most early ceratopsians are known from Asia, during the Early-to-Mid Cretaceous a few dispersed across to North America via a land connection in Beringia.

These migration events happened at least three times, and Aquilops (“eagle face”) was part of the first wave of immigrants, dating to 109-100 mya and representing one of the earliest ceratopsians discovered in North America. Known from a single tiny skull found in Montana, USA, its full size would have been only around 60cm long (2′) – about the size of a large rabbit.

The narrow triangular shape of its snout suggests it was probably a selective browser, feeding on leaves and soft shoots in low-level foliage. Its hooked beak also had a raised bump on the front, which may have supported a larger display structure such as a horn.

Ceratopsian Month #02 – Psittacosaurus sp.

Living during the Early Cretaceous (~126-101 mya) in Mongolia, Siberia, and China, Psittacosaurus (meaning “parrot lizard”) represents an early specialized offshoot of the ceratopsians – it wasn’t directly ancestral to any of the later forms, instead being more of an evolutionary cousin.

It’s one of the most well-studied of all non-avian dinosaurs, represented by hundreds of fossils at all ages from hatchlings to adults. A large number of species have been named within the genus, although there’s disagreement about how many are actually valid, and even some of the best-preserved specimens still haven’t been given an official species classification.

Growing up to about 2m long (6′6″), it had sideways-flaring cheek horns and little-to-no frill, and only four fingers on its hands instead of the five seen in all other ceratopsians. One fossil preserves an amazing level of soft-tissue detail, showing the outline of the body, a row of long bristles, skin membranes running from its ankles to the base of its tail, and even evidence of the countershaded color pattern the animal had in life.

While adults were fully bipedal, hatchlings and juveniles seem to have moved around on all fours – suggesting that some of their direct ancestors may have evolved to be quadrupedal before secondarily re-acquiring two-legged locomotion.

Ceratopsian Month #01 – Yinlong downsi

It’s time for another month of themed blog posts, and this August features one of the most iconic groups of dinosaurs: the “horn-faced” ceratopsians!

Existing for almost 100 million years, from the Late Jurassic all the way up to the K-Pg mass extinction, ceratopsians originated in Asia and were part of a group called marginocephalians, sharing a common ancestor with the closely related pachycephalosaurs. The earliest members barely resembled their more famous descendants, lacking showy headgear and looking more like fairly generic basal neornithischians – but by the time of the Late Cretaceous their descendants had migrated across to North America and evolved into large quadrupeds, with some forms like Triceratops being so incredibly common that they must have been the dominant herbivores in their environments.

So let’s start right at the beginning of the group with…

Continue reading “Ceratopsian Month #01 – Yinlong downsi”

Ampelomeryx

Ampelomeryx ginsburgi, a palaeomerycid ungulate from the Early Miocene of France (~17 mya). About the size of a deer, around 1m tall at the shoulder (3′3″), it was a distant relative of modern giraffids.

Males sported three distinctive ossicone-like ‘horns’ – two over their eyes and a third forked one at the back of the skull – and protruding tusks like some modern deer, which probably served a similar purpose in fights against each other.

Titanoboa

Titanoboa cerrejonensis, a boine snake from the Mid-to-Late Paleocene of Colombia, South America (~60-58 mya). Estimated to have reached lengths of up to 12-14m (39-46′) it was one of the largest known snakes of all time, about twice the length of the biggest modern anacondas and pythons. It was probably able to reach such a huge size due to a combination of factors – mainly a very warm climate and the absence of large terrestrial predators immediately following the K-Pg extinction a few million years earlier.

Despite frequently being depicted eating dyrosaurid crocodiles, the anatomy of Titanoboa’s skull suggests it primarily fed on fish. Considering that some of the fish in its tropical riverine habitat were some of the largest available prey in the area, reaching around 3m in length (10′), a piscivorous diet would actually make a lot of sense for a such a big snake.

Dinomischus

Dinomischus isolatus, an enigmatic animal from the mid-Cambrian Burgess Shale Formation in British Columbia, Canada (~505 mya). Only about 2cm (0.8″) in total length, it had a soft cup-shaped body topped with a whorl of about 20 solid plate-like “petals”, and lived attached to the seafloor by a thin stalk.

Impressions of its internal anatomy show the presence of a U-shaped gut, with its mouth and anus positioned next to each other in the center of the “petals”. It probably fed in a similar manner to crinoids, filtering small particles of food from the surrounding sea water.

But what type of creature it actually was is still unknown. Although comparisons have been made with several different groups – particularly the tiny entoprocts – Dinomischus doesn’t seem to quite fit in anywhere.

Despite this ongoing mystery, a few other similar fossils have been found that seem to be its relatives. Specimens of another species of Dinomischus from slightly older deposits in China show different “petal” shapes, and have been named as D. venustum. Another Burgess Shale animal called Siphusauctum gregarium may also be closely related.

Balbaroo fangaroo

An early relative of kangaroos, Balbaroo fangaroo. Known from a couple of partial skulls discovered at the Riversleigh World Heritage Area in Queensland, Australia, it lived during the Early Miocene (~23-16 mya) and was probably about the size of a cat, around 45-60cm long (18-24″) not including the tail.

It had unusually enlarged canine teeth forming prominent “fangs” – hence its species name – which may have been used for display and fighting in a similar manner to some ungulates such as water deer and camelids.

Based on the skeletons of other closely related species, it probably wasn’t able to hop. Instead it would have moved around quadrupedally, and the shape of its feet suggest it was also capable of climbing like a modern tree kangaroo.