Ceratosaurus is one of the more common large, predatory dinosaurs. Fifty years ago, when all large theropods looked like each other, Ceratosaurus was the one with the horn on its nose, alongside Allosaurus, which was the large theropod with three fingers, and Tyrannosaurus, which was the largest theropod with two fingers.
Today, the large theropods are much more nuanced. For one thing, Tyrannosaurus, Allosaurus, and Ceratosaurus all belong to very different groups. Allosaurus is a carnosaur, alongside other large theropods such as Sinraptor, Acrocanthosaurus, and Giganotosaurus. Tyrannosaurus is now part of Tyrannosauroidea, a large group that contains not only large theropods, such as Tarbosaurus, Daspletosaurus, and Yutyrannus, but also smaller creatures such as Eotyrannus, Guanlong, and Protoceratosaurus. As for Ceratosaurus, it has been put in the group Ceratosauria. This is a unique group that includes Abelisauridae, which includes Carnotaurus, and Noasauridae, which includes Masiakasaurus and Limusaurus. However, while Ceratosaurus belonged in the same larger group as abelisaurs and noasaurs, for a long time, Ceratosaurus had no known close relative. That has changed in recent years.
First of all, there is Genyodectes. This theropod is from Argentina and it is only known from the front tips of the jaws. Interestingly, Genyodectes has been known since 1901, but its remains are so fragmentary that its identification was uncertain. It has been classified as a tyrannosaur and as an abelisaur in the past. It was not until 2004 that it was convincingly argued that Genyodectes was a close relative of Ceratosaurus, probably belonging with it in the same family, Ceratosauridae. Much more recently, a partial skeleton found in Italy and was named Saltriovenator in 2018. While it was not placed in the family Ceratosauridae, it was suggested that Saltriovenator could be in the family, and definitely bore some similarities to it. Thus, as it now stands, Ceratosaurus is no longer alone. It definitely was in the same family as Genyodectes and it is possible that Saltriovenator also belonged to the same family.
The story of Ceratosaurus and its relatives, though briefly presented here, is interesting. It shows how much our understanding of dinosaurs have changed over time. Initially, it seemed like Ceratosaurus was unique, one of a kind. However, newer discoveries and analyses have shown that there is at least one, possible two other dinosaurs that were very similar to Ceratosaurus. One of these, Genyodectes has been known for over a hundred years, but it has only been recently that it has been compared to Ceratosaurus. Saltriovenator is simply a more recent discovery.
Both Genyodectes and Saltriovenator show how much our understanding of paleontology can change. This is something that should always be kept in mind when reading about fossils and their interpretations. Things can easily change when new discoveries are made or even just as new analyses are made. This is not to say that we should doubt what paleontologists tell us, just that we should always be aware that our interpretation of fossils is strongly influenced by biases and presumptions made by paleontologists.
-Written by Steven King