|My life reconstruction of Stellasaurus done in watercolors. Ziggy Stardust-style facial markings and body stripes may have been an adaptation to communicate with members of its own species. (Nature has produced weirder things.)|
Stellasaurus is characterized by having a massive nose horn that curved backwards, towards the tail end of the animal, much like the horn of a modern rhinoceros. Stellasaurus' nose horn was also slightly laterally compressed, like a blade, rather than having a more rounded cross-section, which is unusual for ceratopsians. Finally, this dinosaur sported two long, upwards-facing horns on either side of its frill. The evolutionary purpose of these horns was likely for some sort of intraspecies communication, likely display and/or combat with rivals. Because there is just so much variation in headgear amongst ceratopsian species, it is unlikely they were purely for defense against predators. Stellasaurus was a member of the centrosaurine group of ceratopsians, which are characterized by their deeper snouts and proportionally smaller neck frills.
|Right and left views of Stellasaurus' massive rhinoseros-like nose horn. (image from Wilson's 2020 paper linked below)|
There are a lot of ceratopsian taxa on the fossil record. New members of this wildly successful group of dinosaurs are being published every year. That being said, Stellsasaurus is a particularly important find because it appears to help show an actual evolutionary line in action. We know evolution is an ongoing process of older forms of organisms changing over time into newer forms in response to environmental changes. That being said, it isn't common to be able to say with certainty one taxa was a direct ancestor or descendent of another in the fossil record. However, looking at the frill horns of Stellasaurus, and then comparing them to the frill horns of other ceratopsians that lived in the same place as it from different times, paleontologists were able to see a likely linear transition between at least five different kinds of ceratopsians!
|Left and right sides of Stellasaurus' frill and frill horns. Note how it has two growing from each side. (Image from Wilson's 2020 paper linked below.)|
|Stellasaurus provides a crucial puzzle piece in showing a possible direct transitional line among several different taxa of centrosaurine ceratopsians.|
That is all for this week. As always please leave your thoughts below!
Wilson, John P.; Ryan, Michael J.; Evans, David C. (2020). "A new, transitional centrosaurine ceratopsid from the Upper Cretaceous Two Medicine Formation of Montana and the evolution of the 'Styracosaurus-line' dinosaurs". Royal Society Open Publishing. 7 (4).