Modern Sciences is no stranger to odd dinosaur finds, like Greenland’s Issi saaneq find from just last month. This wouldn’t even be the first time that we’ve discussed ankylosaurs, or the famous armored dinosaurs and the cousins of the stegosaurs; a rough discussion into the ankylosaurs can be read on our piece about Spicomellus afer, which is a good contender for the oldest ankylosaur ever discovered.
This particular find form Chile, however, is making heads turn because of its distinct body feature. Like most ankylosaurs, Stegouros elengassen carried with it a tail tipped with specially-modified bone, implying it was used for self-defense. What makes S. elengassen stand out, however, was the shape of its tail; it straight-up looks like an Aztec sword. This remarkable find was published in the journal Nature.
Said study co-author and University of Chile vertebrate paleontologist Alexander Vargas to LiveScience: “The tail would have looked like a sword; it’s so flat, […] a bit like an Aztec sword, or the Aztec club called the macuahuitl.”
The peculiar dinosaur was actually found all the way back in 2018, and was nestled within Cretaceous rock; this places S. elengassen within the Cretaceous period, and was dated between 74.9 to 71.7 million years ago. The skeletal fossil was found in pretty good condition all things considered, with the bones from the waist down found in the correct order; the researchers attribute this to the dinosaur possibly dying in an area filled with sediment, like near a river or in quicksand.
The unique beast’s name is a nod to both its tail and the people who live around the area where it was found. “Stegouros” roughly translates to “roof tail” in Greek, referring to the odd shape of its tail; “Elengassen,’ on the other hand, is derived from the language of the local Aónik’enk people, and is based from the name of an armored beast in their mythology.
The uniqueness of S. elengassen’s tail doesn’t stop there, either; it’s also the shortest tail ever found for an ankylosaur. It consists of seven pairs of specific bony deposits called osteoderms, which is a feature that can still be found in living crocodiles and alligators today. Its odd sword shape stands in contrast to the usual fare of other ankylosaurs, which look like either clubs or spikes.
This particular ankylosaur itself was also a sort-of unique case, as ankylosaurs were mostly known for fossils obtained from Laurasia, a supercontinent left over from Pangaea’s split during the earlier Jurassic period. Pangaea actually split into roughly two supercontinents: Laurasia in the north, and Gondwana in the south. The two halves of Pangaea, with only a few exceptions, would later go on and form a majority of the continents north and south of the equator today.
It wasn’t actually known for certain whether ankylosaurs ever managed to exist in Gondwana, as a majority of the ankylosaurs were found in continents that were part of Laurasia. With S. elengassen now making the tally for Gondwana-born ankylosaurs reach three, scientists are now more certain than ever that these dinosaurs survived in the Southern Hemisphere after Pangaea’s split physically split their family tree apart.
“The first completely studied ankylosaur from the Southern Hemisphere […] are lacking many of the specialized traits that the ankylosaurs of the North had, and that they already had in the mid-Jurassic,” said Vargas. “So these must have split off before the mid-Jurassic, which speaks of very ancient roots. […] We all know tail clubs, we all know the tail spine, but this is a new […] Southern Hemisphere lineage that evolved a third kind of tail weapon.”
References
- Geggel, L. (2021, December 1). ‘Very weird’ ankylosaur’s tail looked like an Aztec war club. LiveScience. https://www.livescience.com/new-ankylosaur-dinosaur-chile
- Soto-Acuña, S., Vargas, A. O., Kaluza, J., Leppe, M. A., Botelho, J. F., Palma-Liberona, J., Simon-Gutstein, C., Fernández, R. A., Ortiz, H., Milla, V., Aravena, B., Manríquez, L. M. E., Alarcón-Muñoz, J., Pino, J. P., Trevisan, C., Mansilla, H., Hinojosa, L. F., Muñoz-Walther, V., & Rubilar-Rogers, D. (2021). Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile. Nature, 1–5. https://doi.org/10.1038/s41586-021-04147-1
