Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile.

Area of Science:

• Paleontology
• Vertebrate Paleontology
• Mesozoic Reptiles

Background:

• Armored dinosaurs (Ankylosauria) are known for tail weapons like spikes and clubs.
• Southern Gondwanan armored dinosaurs are rare, potentially representing early Ankylosauria branches.

Purpose of the Study:

• To describe a new, mostly complete skeleton of a small armored dinosaur from southern Chile.
• To investigate the phylogenetic position and evolutionary significance of this new dinosaur.

Main Methods:

• Description of a semi-articulated skeleton of Stegouros elengassen gen. et sp. nov.
• Phylogenetic analyses to determine evolutionary relationships.
• Comparative anatomy of cranial and postcranial features.

Main Results:

• Stegouros elengassen possessed a unique tail weapon: a flat, frond-like structure of osteoderms.
• Phylogenetic analyses placed Stegouros within Ankylosauria, closely related to Australian and Antarctic forms.
• A new clade, Parankylosauria, is proposed for the earliest diverging Gondwanan ankylosaurs.

Conclusions:

• Stegouros elengassen represents a basal Gondwanan ankylosaur with a novel tail weapon.
• The discovery highlights the diversity of tail weapon evolution in armored dinosaurs.
• Parankylosauria provides insight into the early diversification of ankylosaurs in the Southern Hemisphere.