#chasmosaurine

Ceratopsids were geographically limited to only Laramidia but becoming locally abundant there. A single centrosaurine is known from beyond that continent, Sinoceratops zhuchengensis, which had managed to cross Beringia and settle within China. A single chasmosaurine managed to cross into Asia as well, though it came by another route. Bathyceratops vitulus is a marine animal found in the algal forests around Japan. At 4 meters long and 2000kg they are of average size for a ceratopsid. Their proportions however are anything but average: their limbs are short and stocky, while the body and neck have elongated. The tail and frill are exceptionally short and the eyes and antorbital buttress have been elevated. The narial window has become rostrocaudally shortened and dorsally heightened. Unlike most other tetrapods their nostrils have migrated away from the front of the narial window and instead are located at the dorsal peak of it. All are adaptations to their life of bottom walking and punting to the surface. They feed upon the kelp-like algae that grows near the shore and occasionally snack upon mollusks or echinoderms. While their legs are short they are still quite capable of walking ashore, though this primarily only done to sleep and nest. They are social creatures and are rarely seen alone, usually foraging in pods of 2 to 20. Pods belong to larger colonies of hundreds of individuals that will gather upon communal beaches or rocks to sleep and socialize. The ancestor of B. vitulus likely became aquatic in Western Laramidia and from there followed the coast until it reached its current range. The majority of the species is found around Japan with a discontinuous second population around what will become the Kamchatka peninsula. A second species, B. vagrans, is found in the red algae forests around the Meiji and Detroit volcanic islands, though how they crossed so much open ocean to get there remains a mystery.

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Dinosaur Eotriceratops xerinsularis, of Late Cretaceous, Canada!

While Triceratops is often held as the largest ceratopsian, there are few that are even bigger. One of, if not the largest, of these is Eotriceratops xerinsularis, with a skull length alone of around 3 m (9.8 ft) and an estimated body length of 8.5–9 metres (28–30 ft) and weight of 11 metric tons (12 short tons). It was a close relative of Triceratops, Nedoceratops, and Torosaurus, and looked similar, aside from several anatomical differences in its skull morphology, and of course its massive size. It was also older than the three, and was in fact basal to them, their possible ancestor. The fossil of Eotriceratops was actually first noted by paleontologist Barum Brown in 1910, during an expedition on Dry Island Provincial Park, but it was neglected because he was more interested in finding the Albertosaurus specimens in the area (everybody always seems to care more about the theropods). The fossil sat there and eroded and chipped away until a Royal Tyrrell Museum exhibition in 2001, when it was rediscovered by the group’s cook, Glen Guthrie, by accident.

Eotriceratops xerinsularis is known from the Horseshoe Canyon Formation of Alberta, Canada. It would have lived alongside other ceratopsians like Anchiceratops, Montanoceratops, and Pachyrhinosaurus canadensis, hadrosaurs like Edmontosaurus regalis and Saurolophus osborni, ankylosaurs like Anodontosaurus lambei, pachycephalosaurs like Sphaerotholus edmontonense, alvarezsaurids like Albertonykus, dromaeosaurs like Atrociraptor, and ornithomimids like Dromiceiomimus, Ornithomimus, and Struthiomimus. The apex predator of this formation was the aforementioned Albertosaurus, but it was highly unlikely it could have taken on a healthy adult Eotriceratops, and possibly only sick, injured, and young Eotriceratops would have had to fear the tyrannosaurid. Possible additional Eotriceratops specimens, which have been variously included in the species Ojoceratops fowleri and Torosaurus (as T. utahensis), are also known from the same time period, in New Mexico’s Ojo Alamo Formation and Utah’s North Horn Formation (respectively) and may actually belong to Eotriceratops.

Coahuilaceratops, a genus of chasmosaurine ceratopsian dinosaur, is thought to have possessed among the largest horns of any known dinosaur, even though it is based on incomplete remains. Its horns may have rivaled the size of those of larger chasmosaurines such as Triceratops and Torosaurus, at 1.2 m (4 ft) long.

Styracosaurus, anthon500 (deviantart)

Speciation, Cladogenesis and Anagenesis

Speciation is a term used by scientists to describe the process by which a population of organisms give rise to a new species. The idea of a species is wholly man-made, and its true definition varies, but for the purpose of this article:

A species is the largest grouping of individuals which can produce fertile offspring from a mating pair. A species can also be defined as having a specific karyotype (a unique arrangement of DNA chromosomes), or in the case where we don't have genetic data, by having enough unique changes to be significantly different from others in their genetic family.

Cladogenesis in Bears, Source

When we discuss speciation, usually it is Cladogenesis that comes to mind. Cladogenesis occurs when a portion of the population splits off and develops adaptations separately. Think for example, Brown Bears and Polar Bears, which we suspect originated from the same ancestor species.

Anagenesis is a different process, where the separation of species is not a difference in space and/or compatibility, but a difference in time. Think for example Homo sapiens and it's ancestors. I could probably trace an uninterrupted line of ancestors back 10s of millions of years ago, but if you dug up that ancestor's bones, palaeontologists wouldn't call it Homo sapiens.

Anagenesis in Hominids, Source

A population separated by nothing but time alone would still be referred to as different species, because they would have different physical traits and genetic make-up.

Both cladogenesis and anagenesis occurs in populations over time. One group may develop without any splintering for millions of years, and then a group splits off later to become a separate species.

Cladogenesis and Anagenesis, Source

Anagenesis in Ceratopsians

So with that explanation out of the way, let's get to the part that's actually interesting: dinosaurs. Like all organisms, speciation in dinosaurs would've occurred by populations splitting up and specialising, or dying out. But recently, the idea of speciation by anagenesis has been proposed in a certain group of dinosaurs.

Ceratopsians are a group mostly identifiable by their large imposing neck frills and face horns. New species are proposed when they differ enough in the shape and length of their eyebrow horns and their nose horns, the height and width of their neck frills, and the arrangements of parietal horns on and around their frill. There's lots of room for variety in ceratopsian face arrangements.

Styracosaurus, Victor Sales (Deviantart)

Styracosaurus is a fairly mainstream dinosaur, but what's probably not as well known are its close relatives. Ceratopsians such as Stellasaurus and Einiosaurus have been found in fossil beds nearby Styracosaurus. And although there may have been some niche partitioning or sexual selection allowing these dinosaurs to coexist in the same place, new research suggests they were the same group separated by time.

Top: Stellasaurus, HodariNundu (deviantart)

Bottom: Einiosaurus, Calisius (deviantart)

Sexual pressures can drive animals to rapidly develop extreme physical traits for no other reason other than to look attractive. Modern dinosaur species (birds) can have a variety of physically exaggerated traits that serve no purpose beyond attracting mates. In Cockatoos, it's erect feather head crests. In Peacocks, it's massive colourful tail plumes. So perhaps in Ceratopsians, it was face and frill ornamentation.

When Stellasaurus was first described as a species separate from Styracosaurus, some Palaeontologists decided that it represented a transitional species. The relatively straight nasal horn of Styracosaurus had developed into a thicker, more curved structure later in the lineage. The neck frill became sturdier and more robust, the frill horns curving in strange directions. The supposed endpoint in the lineage is Pachyrhinosaurus, who's nasal horn is now a solid plate of bone, and the neck frill is decorated with a variety of horns pointing in every which-way. It may be a less pointy dinosaur, but it was very heavily decorated. And sex sells.

Top: Styracosaurus Anagenesis, Christopher DiPiazza

Bottom: Pachyrhinosaurus, Raph Lomotan (deviantart)

The Centrosaurine Styracosaurus lineage is not the only subject of Ceratopsian Anagenesis. The Chasmosaurine line has also been suspected of transitional forms, with the recent discovery of Navajoceratops. But in that lineage, speciation pushed towards longer brow horns and taller neck frills in the younger species.

New discoveries Navajoceratops and Terminocavus, Ville Sinkkonen

It is important to note at the time of writing, these theories are not accepted by all of the Palaeontological community. And that also my explanation is not as detailed or accurate as someone with all the right background knowledge could give. So if you are intrigued as to how this theory could be better explained, here's some further reading:

Chris DiPiazza (2020) Stellasaurus: Beast of the Week

John Wilson et al (2020) A new, transitional centrosaurine ceratopsid from the Upper Cretaceous Two Medicine Formation of Montana and the evolution of the ' Styracosaurus-line' dinosaurs

Stephen Belletini (2020) Was "Rubeosaurus" Styracosaurus After All? YDAW Synapisode #6 (Youtube)

Mercuriceratops!

Today’s Doodle: Chasmosaurus belli at the North American Museum of Ancient Life

Spiclypeus shipporum was a large chasmosaurine ceratopsian from Late Cretaceous Montana, USA. It is only known from one specimen (a partial skull, vertebrae, ribs, a left humerus, a left ilium and the left hindlimb) nicknamed “Judith” after the Judith River Formation. But this specimen is very unique, with brow horns that swept out to the side and two epiparietals (frill horns) fused and curling down over its frill. Judith appeared to also have sustained an infection in their frill, hypothesised to have come from an injury inflicted by a rival Spiclypeus, where the rival’s brow horns pierced into the bone of Judith’s frill. They also had a more serious infection in their humerus, with a large abscess, as well as evidence of arthritis. Judith was an adult, at least 10 years old, and it’s suspected that they had reach an advanced age before dying, despite their injuries. They were a testament to the rough life of combat and survival ceratopsians faced, and their resilience in spite of it all.

Spiclypeus lived in the Judith River Formation during the Late Campanian. It would have lived on a coastal floodplain criss-crossed by rivers and oxbow lakes. It may have lived alongside other ceratopsians, but there is a hypothesis that Spiclypeus, Ceratops montanus, and Pentaceratops aquilonius may all be the same species, however, so far their remains are too fragmentary to form a conclusion. It would have also shared space with the hadrosaur Corythosaurus, the ankylosaurs Edmontonia and Zuul, and the pachycephalosaur Hanssuesia. Theropods included the dromaeosaurs Dromaeosaurus and Saurornitholestes, the avialan Hesperornis altus, and the tyrannosaurid apex predators Daspletosaurus and Gorgosaurus. Other reptiles included lizards, turtles, the choristodere Champsosaurus, and the alligatoroids Leidyosuchus and Deinosuchus.