Paleontologists have unearthed a new species of bird-like dinosaur in Mexico, notable for its unusually thick, dome-shaped skull. This fossil suggests the creature engaged in head-to-head combat with others of its kind—a behavior previously unseen in closely related dinosaur groups.
A Unique Troodontid: Xenovenator espinosai
The newly identified species, named Xenovenator espinosai, lived roughly 73 million years ago during the Late Cretaceous period. It belongs to the Troodontidae family, known for their agility and relatively large brains. What sets this dinosaur apart is the dramatically thickened roof of its skull, reaching up to 1.2 cm in some areas.
Key anatomical features include:
- Heavily domed frontals and parietals (skull bones)
- Dense bone structure with interlocking sutures
- Rough, striated outer surface
These characteristics closely resemble those found in pachycephalosaurids—dinosaurs famous for their reinforced skulls used in head-butting. However, Xenovenator is only distantly related to these groups, making this adaptation a surprising development.
The Case for Intraspecific Combat
Researchers believe the thickened skull was an adaptation for intraspecific combat, meaning fighting among members of the same species. The team used CT scans to confirm the skull’s dense construction, further supporting this theory.
Why does this matter?
Previously, adaptations for physical combat were largely undocumented in non-avian theropods (meat-eating dinosaurs). The discovery of Xenovenator provides the first known example of such modification in paravians (a group including birds and their closest dinosaur relatives).
The variation in skull thickness among specimens suggests differences in age or sex, with older or male individuals potentially developing more extreme reinforcement.
Implications for Dinosaur Evolution
The discovery highlights the role of sexual selection in shaping dinosaur evolution. Display structures and weapons were common, but Xenovenator suggests that combat may have been more widespread than previously thought, particularly within the Troodontinae subfamily.
The presence of a related species, Xenovenator robustus, in New Mexico suggests a unique clade of thick-skulled troodontids endemic to the southwestern region of North America.
“Sexual selection, including adaptations for display and combat, was a widespread phenomenon in Late Cretaceous dinosaurs.”
The research was published in the journal Diversity. The fossil underscores the remarkable diversity of dinosaurs in the Late Cretaceous and emphasizes how competition for mates or territory drove the evolution of specialized physical traits.
Ultimately, the discovery of Xenovenator espinosai provides valuable insight into the behavior and evolutionary pressures faced by small, lightly built theropods during the age of dinosaurs.
