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Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile

2021; Nature Portfolio; Volume: 600; Issue: 7888 Linguagem: Inglês

10.1038/s41586-021-04147-1

1476-4687

Sergio Soto‐Acuña, Alexander O. Vargas, Jonatan Kaluza, Marcelo Leppe, João Francisco Botelho, José Palma-Liberona, Carolina S. Gutstein, Roy A. Fernández, Héctor Ortíz, Verónica Milla, Bárbara Aravena, Leslie M.E. Manríquez, Jhonatan Alarcón-Muñoz, Juan Pablo Pino, Cristine Trevisan, Héctor D. Mansilla, Luis Felipe Hinojosa, Vicente Muñoz-Walther, David Rubilar-Rogers,

Ichthyology and Marine Biology

Armoured dinosaurs are well known for their evolution of specialized tail weapons-paired tail spikes in stegosaurs and heavy tail clubs in advanced ankylosaurs1. Armoured dinosaurs from southern Gondwana are rare and enigmatic, but probably include the earliest branches of Ankylosauria2-4. Here we describe a mostly complete, semi-articulated skeleton of a small (approximately 2 m) armoured dinosaur from the late Cretaceous period of Magallanes in southernmost Chile, a region that is biogeographically related to West Antarctica5. Stegouros elengassen gen. et sp. nov. evolved a large tail weapon unlike any dinosaur: a flat, frond-like structure formed by seven pairs of laterally projecting osteoderms encasing the distal half of the tail. Stegouros shows ankylosaurian cranial characters, but a largely ancestral postcranial skeleton, with some stegosaur-like characters. Phylogenetic analyses placed Stegouros in Ankylosauria; specifically, it is related to Kunbarrasaurus from Australia6 and Antarctopelta from Antarctica7, forming a clade of Gondwanan ankylosaurs that split earliest from all other ankylosaurs. The large osteoderms and specialized tail vertebrae in Antarctopelta suggest that it had a tail weapon similar to Stegouros. We propose a new clade, the Parankylosauria, to include the first ancestor of Stegouros-but not Ankylosaurus-and all descendants of that ancestor.