Those Complicated North American Chasmosaurs
It has happened before and we are certain that it will happen again. A scientist examining the fossilised remains of dinosaurs within the collection of a museum, finds that on analysis, specimens ascribed to known genera, turn out to be new species. Dr. Nick Longrich from the Biology and Biochemistry department of the University of Bath was studying Ceratopsian (horned dinosaur) specimens at the Canadian Museum of Nature (Ottawa, Canada) and thanks to his research, two horned dinosaur fossils, known from the Dinosaur Provincial Park Formation of Alberta and previously believed to represent Anchiceratops and Chasmosaurus may actually represent animals new to science.
Writing in the scientific journal “Cretaceous Research”, Dr. Longrich proposes that the fossils he studied, although from Canada, resemble dinosaurs known from much further south, from New Mexico and Utah to be precise.
How could this be? Let’s start with by looking at the landmass we now know as North America and what it looked like some seventy-five million years ago in the Late Cretaceous. In the Late Cretaceous, rising sea levels and tectonic forces led to the formation of an immense shallow sea that covered much of the continent. This sea, which effectively linked the Arctic Ocean with the Gulf of Mexico, is known as the Western Interior Seaway. The extent of the seaway changed over millions of years, shaping the landmasses and also influencing the flora and fauna that lived on them. Towards the very end of the Cretaceous further plate movements and a phase of resulting mountain building led to the shrinking of the sea, the seaway retreated shrinking to represent a marine environment less than 10% of its maximum area by the beginning of the Cenozoic.
North America in the Late Cretaceous
Picture Credit: Dr. Ron Blakey of Colorado Plateau Geosystems, Inc
The picture above shows how the shape of the continent is believed to have changed over the last ten million years or so of the Cretaceous Period, now back to Dr. Longrich. The landmass that existed on the western side of this seaway is known as Laramidia. Dinosaurs dominated this part of the world, just as they did in all the other terrestrial environments during the Cretaceous, but the fossil record preserved indicates that there was a tremendous variety of dinosaurs in this part of the world. What is more, there seems to have been distinct faunal provinces, the southern portion of this landmass had different dinosaurs to those found on the northern parts of Laramidia. The fossil record seems to show ethnicity in the fauna that evolved, how and why this occurred (even if it actually occurred at all), has been hotly debated by palaeontologists. Some scientists have suggested that there must have been physical barriers between populations that over tens of thousands of years permitted new, distinct species to evolve.
To read an article related to this: A Surge in Mountain Building May Have Led to Dinosaur Diversification
The horned dinosaur specimens studied by Dr. Longrich had previously been classified as Anchiceratops and Chasmosaurus, species known from Canada, the north of Laramidia. However, after re-analysing these particular fossils, he realised that they more closely resembled dinosaurs from the southern part of the Laramidia landmass. Two frill fragments from the uppermost Dinosaur Park Formation, found near Manyberries, south-east Alberta, that had thought to represent Anchiceratops have been re-classified as Pentaceratops dinosaur material. These Canadian frill bones are sufficiently different in their morphology from Pentaceratops sternbergii, which is known from New Mexico, that they have been ascribed to a new Pentaceratops species – P. aquilonius
An Artist’s Impression of Pentaceratops aquilonius
Picture Credit: University of Bath
Pentaceratops aquilonius may have been very closely related to the southern Pentaceratops (P. sternbergii), but it was smaller and it had differently shaped frill bones and a different arrangement of hornlets (epiparietals). The genus name means “five horned face”, although, just like the much later and more famous Triceratops, this dinosaur only had three horns. The elongated jugal bones on the side of the skull had horny outgrowths, when viewed from the front, this dinosaur had the appearance of having five horns. The species name aquilonius means “northern” – a reference to where this dinosaur roamed.
The second horned dinosaur fossil specimens, studied by Dr. Longrich had been thought to represent Chasmosaurus. However, the British palaeontologist noted that the partial skull in the Canadian Museum of Nature’s collection closely resembled another type of horned dinosaur called Kosmoceratops. Fossils of Kosmoceratops have been found in Utah, (Grand Staircase-Escalante National Monument), this horned dinosaur was named and described back in 2010.
To read more about Kosmoceratops: Those Curious Ceratopsians
Phylogenetic analysis of the skull’s characteristics places this specimen in a sister taxon to Kosmoceratops richardsoni, the name ascribed to the Utah fossil finds. More fossils are required from the Dinosaur Provincial Park Formation before a new species of Kosmoceratops can be erected.
Not So Distinct Northern and Southern Provinces in Laramida
Picture Credit: University of Bath
The diagram above maps the two dinosaurs (coloured red) in situ with other Chasmosaurine dinosaur fossil discoveries. Dinosaurs would spread from one part of the continent to another and then diverge from their “home” ancestors to evolve into a new species. Competition between the different species then would have prevented the dinosaurs from moving between the northern and southern provinces, although changes in climate and flora may too have had an affect. The established populations may have been able to resist migrations as they had specifically evolved to cope with local conditions.
Dr. Longrich stated:
“We thought we had discovered most of the species, but it seems there are many undiscovered dinosaurs left. There are lots of species out there, we’ve really only just scratched the surface.”
But why were there so many species of mega fauna in this part of the world during the Late Cretaceous. This pattern is not seen in many ecosystems today. Dr Longrich has a theory, he thinks:
“In living mammals, there tend to be relatively few large species, and they have large ranges. With Cretaceous dinosaurs, we see a lot of large species in a single habitat. They also tend to be very regional, as you move from one habitat to another, you get a completely different set of species.”
These patterns of distribution might help explain why palaeontologists keep finding more types of dinosaur, when they sample different habitats, they find different species.
Dr. Longrich speculates that the biology of these reptiles could be the reason for these patterns:
“In this sense, dinosaur biology seems quite different from mammal biology. It could be that mammals are more intelligent and so they tend to have more flexible behaviour, they adapt their behaviour to their habitats. On the other hand, dinosaurs may have had to adapt themselves physically to survive in a different habitat and as a result, they evolved into new species. Perhaps that’s the reason why there are so many species.
The Ceratopsian fauna of Laramidia has posed a number of important questions for palaeontologists. For example, in Alberta bone beds of Centrosaurine dinosaurs (one group of Ceratopsians) are relatively common, a number of bone bed deposits have been found, whereas fossils of Chasmosaurines (the other group of Ceratopsians) are much rarer altogether and very little bone bed evidence has been discovered.
Why might this be?
We said at the beginning of this article that there had been previous cases of a new species of dinosaur being discovered when museum collections are re-examined, to read about a similar case, but this time involving the Sauropoda, see the link below.
Where’s the best place to find a new species of dinosaur: Look in a Museum for a New Dinosaur