Prenoceratops

Although much less famous than their larger horned and frilled relatives, the leptoceratopsids were a widespread and successful group of ceratopsian dinosaurs during the Late Cretaceous, with fossils known from North America, Asia, and Europe (and, dubiously, Australia).

They were fairly small stocky quadrupedal dinosaurs, sort of pig-like, with short deep jaws and powerful beaks adapted for eating fibrous low-level plants like ferns and cycads – and to process such tough food they even evolved a chewing style similar to mammals like rodents.

Prenoceratops pieganensis here is known from the Two Medicine Formation bone beds in Montana, USA, dating to about 74 million years ago. Around 1.5-2m long (~5′-6’6″), it was very similar to its later relative Leptoceratops, but had a slightly lower, more sloping shape to its skull.

Weird Heads Month #18: Boneheaded Dinosaurs

Pachycephalosaurs are highly recognizable dinosaurs with their thick spiky skulls, and it’s not hugely surprising that they were the evolutionary cousins of the equally weird-headed ceratopsians.

Much like their frilled relatives they had beaks at the tips of their snouts and large gut cavities for digesting plant matter, but they also had surprisingly sharp theropod-like teeth in front of their more standard herbivore teeth further back – suggesting they may also have been opportunistic omnivores, occasionally snacking on carrion or small animals similarly to modern pigs or bears.

Their striking-looking dome heads were probably used for combat, headbutting or flank-butting each other, and many fossil skulls show evidence of injuries that would have been caused by that sort of behavior.

The eponymous Pachycephalosaurus wyomingensis lived in North America right at the end of the Cretaceous, about 70-66 million years ago. It was one of the largest of its kind, reaching lengths of around 4.5m (14’9″), and was characterized by a large bony dome-head surrounded by small blunt spikes.

But it turns out that was probably only what it looked like as a fully mature adult.

Recent discoveries of juvenile Pachycephalosaurus skulls confirmed a hypothesis proposed a few years earlier: these dinosaurs changed appearance drastically as they grew up, and younger individuals had been mistaken for separate species. They started off with domeless flat heads, bristling with long spikes (a form previously named Dracorex hogwartsia) then as they matured their domes began to grow (previously Stygimoloch spinifer) and by full maturity they had big domes with the spikes shrunk down to smaller stubbier knobs (the classic Pachycephalosaurus look).

This particular reconstruction depicts a Stygimoloch-like subadult individual, not quite fully mature and still sporting some longer spikes.

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.