Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile

Abstract

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 Ankylosauria2,3,4. 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.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Skeletal anatomy of the S. elengassen holotype (CPAP-3165).
Fig. 2: Caudal weapon of S. elengassen holotype (CPAP-3165).
Fig. 3: Evolution of armoured dinosaurs and their tail weaponry.

Similar content being viewed by others

Data availability

All data supporting the findings of this study are available in the paper and its Supplementary Information. Raw data from all CT scans are available online (https://www.morphosource.org/concern/biological_specimens/000382748). The LSID for this publication is urn:lsid:zoobank.org:pub:4D3ABFEE-5F21-4632-96F9-FE8C1542ACF7. The LSID ZooBank code for the new genus (Stegouros) is: urn:lsid:zoobank.org:act:5306DD47-2130-4866-8DB4-09092C632A4A. The LSID ZooBank code for the new species (Stegouros elengassen) is: urn:lsid:zoobank.org:act:992A259B-75EE-4206-89FB-6666FBCBDFA6. TNT files for phylogenetic analysis are provided on Zenodo (https://zenodo.org/record/5706422#.YZQ7Kr3Q8-R).

References

  1. Arbour, V. M. & Zanno, L. E. The evolution of tail weaponization in amniotes. Proc. R. Soc. B 285, 20172299 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  2. Thompson, R. S., Parish, J. C., Maidment, S. C. & Barrett, P. M. Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora). J. Syst. Palaeontol. 10, 301–312 (2012).

    Google Scholar 

  3. Arbour, V. M. & Currie, P. J. Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs. J. Syst. Palaeontol. 14, 385–444 (2016).

    Google Scholar 

  4. Wiersma, J. P. & Irmis, R. B. A new southern Laramidian ankylosaurid, Akainacephalus johnsoni gen. et sp. nov., from the upper Campanian Kaiparowits Formation of southern Utah, USA. PeerJ 6, e5016 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  5. Reguero, M. A. & Goin, F. J. Paleogeography and biogeography of the Gondwanan final breakup and its terrestrial vertebrates: new insights from southern South America and the “double Noah’s Ark” Antarctic Peninsula. J. South Am. Earth Sci. 108, 103358 (2021).

    Article  Google Scholar 

  6. Leahey, L. G., Molnar, R. E., Carpenter, K., Witmer, L. M. & Salisbury, S. W. Cranial osteology of the ankylosaurian dinosaur formerly known as Minmi sp. (Ornithischia: Thyreophora) from the Lower Cretaceous Allaru Mudstone of Richmond, Queensland, Australia. PeerJ 3, e1475 (2015).

    PubMed Central  PubMed  Google Scholar 

  7. Salgado, L. & Gasparini, Z. Reappraisal of an ankylosaurian dinosaur from the Upper Cretaceous of James Ross Island (Antarctica). Geodiversitas 28, 119–135 (2006).

    Google Scholar 

  8. Claraz, J. Diario de Viaje de Exploración al Chubut, 1865-1866 (Ediciones Marymar, 1988).

  9. Hone, D. W. E., Farke, A. A. & Wedel, M. J. Ontogeny and the fossil record: what, if anything, is an adult dinosaur? Biol. Lett. 12, 20150947 (2016).

    Article  PubMed  PubMed Central  Google Scholar 

  10. Gutiérrez, N. M. et al. Tectonic events reflected by palaeocurrents, zircon geochronology, and palaeobotany in the Sierra Baguales of Chilean Patagonia. Tectonophysics 695, 76–99 (2017).

    Article  ADS  Google Scholar 

  11. Manríquez, L. M., Lavina, E. L., Fernández, R. A., Trevisan, C. & Leppe, M. A. Campanian-Maastrichtian and Eocene stratigraphic architecture, facies analysis, and paleoenvironmental evolution of the northern Magallanes Basin (Chilean Patagonia). J. South Am. Earth Sci. 93, 102–118 (2019).

    Article  ADS  Google Scholar 

  12. Raven, T. J. & Maidment, S. C. The systematic position of the enigmatic thyreophoran dinosaur Paranthodon africanus, and the use of basal exemplifiers in phylogenetic analysis. PeerJ 6, e4529 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  13. Vickaryous, M. V., Maryańska, T. & Weishampel, D. B. in The Dinosauria (eds Weishampel, D. B. et al.) 464–477 (Univ. California Press, 2004).

  14. Coombs Jr W. P. in Dinosaur Systematics: Approaches and Perspectives (eds Carpenter, K. & Currie, P. J.) 269–279 (Cambridge Univ. Press, 1990).

  15. Pereda-Suberbiola, X., Galton, P. M., Mallison, H. & Novas, F. A plated dinosaur (Ornithischia, Stegosauria) from the Early Cretaceous of Argentina, South America: an evaluation. Alcheringa 37, 65–78 (2013).

    Article  Google Scholar 

  16. Norman, D. B. Scelidosaurus harrisonii from the Early Jurassic of Dorset, England: postcranial skeleton. Zool. J. 189, 47–157 (2020).

    Google Scholar 

  17. Sereno, P. C. The evolution of dinosaurs. Science 284, 2137–2147 (1999).

    Article  CAS  PubMed  Google Scholar 

  18. Maidment, S. C., Norman, D. B., Barrett, P. M. & Upchurch, P. Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). J. Syst. Palaeontol. 6, 367–407 (2008).

    Article  Google Scholar 

  19. Carpenter, K., DiCroce, T., Kinneer, B. & Simon, R. Pelvis of Gargoyleosaurus (Dinosauria: Ankylosauria) and the origin and evolution of the ankylosaur pelvis. PLoS ONE 8, e79887 (2013).

    Article  ADS  PubMed  PubMed Central  Google Scholar 

  20. Norman, D. B. Scelidosaurus harrisonii from the Early Jurassic of Dorset, England: the dermal skeleton. Zool. J. 190, 1–53 (2020).

    Google Scholar 

  21. Burns, M. E. & Currie, P. J. External and internal structure of ankylosaur (Dinosauria, Ornithischia) osteoderms and their systematic relevance. J. Vertebr. Paleontol. 34, 835–851 (2014).

    Article  Google Scholar 

  22. Han, F., Forster, C. A., Xu, X. & Clark, J. M. Postcranial anatomy of Yinlong downsi (Dinosauria: Ceratopsia) from the Upper Jurassic Shishugou Formation of China and the phylogeny of basal ornithischians. J. Syst. Palaeontol. 16, 1159–1187 (2018).

    Article  Google Scholar 

  23. Norman, D. B. Scelidosaurus harrisonii (Dinosauria: Ornithischia) from the Early Jurassic of Dorset, England: biology and phylogenetic relationships. Zool. J. 191, 1–86 (2021).

    Google Scholar 

  24. Raven, T. J. & Maidment, S. C. A new phylogeny of Stegosauria (Dinosauria, Ornithischia). Palaeontology 60, 401–408 (2017).

    Article  Google Scholar 

  25. Loewen, M. A. & Kirkland, J. I. The evolution and biogeographic distribution of Ankylosauria: new insights from a comprehensive phylogenetic analysis. J. Vertebr. Paleontol (Program and Abstracts). 2013, 163-164A (2013).

    Google Scholar 

  26. Molnar, R. E. Preliminary report a new ankylosaur from the Early Cretaceous of Queensland, Australia. Mem. Queensland Mus. 39, 653–668 (1996).

    Google Scholar 

  27. Molnar, R. E. in The Armored Dinosaurs (ed. Carpenter, K.) 341–362 (Indiana Univ. Press, 2001).

  28. Arbour, V. M., Burns, M. E. & Currie, P. J. A review of pelvic shield morphology in ankylosaurs (Dinosauria: Ornithischia). J. Paleontol. 85, 298–302 (2011).

    Article  Google Scholar 

  29. Lamanna, M. C. et al. Late Cretaceous non-avian dinosaurs from the James Ross Basin, Antarctica: description of new material, updated synthesis, biostratigraphy, and paleobiogeography. Adv. Polar Sci. 30, 228–250 (2019).

    Google Scholar 

  30. de Ricqlès, A., Suberbiola, X. P., Gasparini, Z. & Olivero, E. Histology of dermal ossifications in an ankylosaurian dinosaur from the Late Cretaceous of Antarctica. Asoc. Paleontol. Argent. 7, 171–174 (2001).

    Google Scholar 

  31. Arbour, V. M. & Currie, P. J. Ankylosaurid dinosaur tail clubs evolved through stepwise acquisition of key features. J. Anat. 227, 514–523 (2015).

    Article  PubMed  PubMed Central  Google Scholar 

  32. Arbour, V. M. & Zanno, L. E. Tail weaponry in ankylosaurs and glyptodonts: an example of a rare but strongly convergent phenotype. Anat. Rec. 303, 988–998 (2020).

    Article  Google Scholar 

  33. Maidment, S. C., Raven, T. J., Ouarhache, D. & Barrett, P. M. North Africa’s first stegosaur: implications for Gondwanan thyreophoran dinosaur diversity. Gondwana Res. 77, 82–97 (2020).

    Article  ADS  Google Scholar 

  34. Goloboff, P. A. & Catalano, S. A. TNT version 1.5, including a full implementation of phylogenetic morphometrics. Cladistics 32, 221–238 (2016).

    Article  PubMed  Google Scholar 

  35. Arbour, V. M., Zanno, L. E. & Gates, T. Ankylosaurian dinosaur palaeoenvironmental associations were influenced by extirpation, sea-level fluctuation, and geodispersal. Palaeogeogr. Palaeoclimatol. Palaeoecol. 449, 289–299 (2016).

    Article  Google Scholar 

  36. Goloboff, P. A., Farris, J. S. & Nixon, K. C. TNT, a free program for phylogenetic analysis. Cladistics 24, 774–786 (2008).

    Article  Google Scholar 

  37. Siddall, M. E. Stratigraphic fit to phylogenies: a proposed solution. Cladistics 14, 201–208 (1998).

    PubMed  Google Scholar 

  38. Wills, M. A. Congruence between phylogeny and stratigraphy: randomization tests and the gap excess ratio. Syst. Biol. 48, 559–580 (1999).

    Article  Google Scholar 

  39. Pol, D. & Norell, M. A. Comments on the Manhattan stratigraphic measure. Cladistics 17, 285–289 (2001).

    Article  PubMed  Google Scholar 

  40. Pol, D., Norell, M. A. & Siddall, M. E. Measures of stratigraphic fit to phylogeny and their sensitivity to tree size, tree shape, and scale. Cladistics 20, 64–75 (2004).

    Article  PubMed  Google Scholar 

  41. Pol, D. & Norell, M. A. Uncertainty in the age of fossils and the stratigraphic fit to phylogenies. Syst. Biol. 55, 512–521 (2006).

    Article  PubMed  Google Scholar 

Download references

Acknowledgements

We thank F. Suazo, E. Nuñez, D. Bajor, J. P. Guevara, D. Flores, S. Jiménez, I. Meyer-Navia, S. Davis and members of the J. Clark team for help in the field and/or fossil preparation; Estancia Cerro Guido and especially the Matetic, Simunovic and Reyes families for granting access and important logistical support in the field; the Consejo de Monumentos Nacionales (National Monuments Council) of the Chilean Ministry of Culture, Arts and Heritage for fieldwork permits; M. Reguero for access and help with the Antarctopelta holotype; J. Vidal for technical support in the acquisition of CT images; and staff at the Willi Hennig society for free distribution of TNT software. This research was supported by the Agencia Nacional de Investigación y Desarrollo ANID (National Agency for Research and Development) of the Chilean Ministry of Science, Technology, Knowledge and Innovation through grants PIA Anillo ACT172099 (to A.O.V.), FONDECYT 1190891 (to A.O.V.), FONDECYT 1151389 (to M.A.L.), and PhD scholarships for S.S.-A., J.A.-M., J.P.-L. and J.P.P.

Author information

Authors and Affiliations

Authors

Contributions

J.K., S.S.-A., H.O., B.A., J.A.-M., J.P.P. and V.M. extracted the fossil. J.K., S.S.-A., B.A. and J.A.-M. carried out laboratory preparation. J.P.-L., J.F.B., S.S.-A. and V.M.-W. processed and sampled CT and μCT data. S.S.-A. and A.O.V. described the material. S.S.-A. and A.O.V. scored phylogenetic matrices. S.S.-A. conducted the maximum-parsimony analyses. C.S.-G. and V.M. carried out taphonomic studies. M.A.L., L.M.E.M., R.A.F., J.P.P., H.M., C.T., D.R. and L.F.H. carried out geological and palaeoenvironmental studies. A.O.V. and S.S.-A. wrote the bulk of the manuscript; S.S.-A., C.S.-G., V.M. and J.P.P. made figures. All of the authors collected data and contributed to the writing, discussion and conclusions.

Corresponding authors

Correspondence to Sergio Soto-Acuña or Alexander O. Vargas.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks James Kirkland and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Cranial bones of S. elengassen holotype (CPAP-3165).

a, skull in lateral view (with left? supraorbital reversed). b, posterior skull in dorsal view. c, premaxilla in ventral view. d, left maxilla lateral view. e, f, both maxillae in ventral view. g, left? supraorbital dorsal view. h, i, predentary in occlusal and ventral views. j, basisphenoid in palatal view. k, right dentary in lingual view. Scale bars, 10 cm.

Extended Data Fig. 2 Postcranial axial skeleton of S. elengassen holotype (CPAP-3165).

a-c axis in anterior and right lateral views. d-f, anterior cervical vertebra in anterior, right lateral and ventral views. g-i, posterior cervical vertebra in anterior, right lateral and dorsal views. j-l, anterior dorsal vertebra in anterior, right lateral and dorsal views. m, n, posterior dorsal vertebra in anterior and right lateral views. o, synsacral vertebrae in right lateral view. p, anterior caudal vertebrae in right lateral view. q, posterior caudal vertebrae in right lateral view. Scale bar 10 cm.

Extended Data Fig. 3 Sternal, pectoral girdle and forelimb bones of S. elengassen holotype (CPAP-3165).

a, b, sternal plates in ventral view. c-e, right coracoid in lateral, medial and glenoideal views. f-i left humerus in anterior, posterior, proximal and distal views. j, left radius in lateral view. k, left ulna in anterior view. l, m, left hand in proximal and dorsal views. n, originally semiarticulated right hand in dorsal view. o, fully prepared right hand in dorsal view. Scale bars, 10 cm.

Extended Data Fig. 4 Pelvic girdle, hindlimbs and dermal armour of S. elengassen holotype (CPAP-3165).

a, right ilium in lateral view. b, pelvis in ventral view. c, d, left pubis in lateral and medial views. eh, left femur in proximal, distal and posterior views. i, right femur in lateral view. j, left foot in dorsal view. k, right foot in lateral view. l, m, isolated mid-sized ovalate keeled osteoderm in dorsal and lateral views. n, o, sacral covering in dorsal and ventral views. p, keeled osteoderm with deeply excavated inner surface associated with right ulna in ventrolateral view. q, flat osteoderm associated with right radius in dorsal view. Scale bars, 10 cm (a–k, n, o) 2 cm (l, m, p, q).

Extended Data Fig. 5 Paired comparisons of the axial skeleton between S. elengassen holotype CPAP-3165 (left) and A. oliveroi holotype MLP 86-X-28-1 (right).

Synsacral complex in a, b, anterior, c, d, posterior and e, f, ventral views; anterior caudal vertebrae (6th in Stegouros elengassen) in h, i, posterior and j, k, right lateral views; posterior caudal vertebrae (17th in Stegouros elengassen) in l, m, dorsal and n, o, posterior views. Scale bars, 2 cm (a, c, e, h, j, l, n), 5 cm (b, d, f, g, i, k, m, o).

Extended Data Fig. 6 Anatomy of caudal weapon osteoderms in S. elengassen holotype (CPAP-3165) and A. oliveroi holotype (MLP 86-X-28-1).

a, digital reconstruction and b, photograph of Stegouros elengassen caudal weapon cross section (at level of first osteoderm pair and 14th caudal vertebra) in anterior and left lateral views. c, d, Antarctopelta oliveroi dorsal osteoderm of the first pair in left lateral and anterior views. e, Stegouros elengassen, 3D reconstruction of the left second osteoderm in dorsal and internal views. f, Antarctopelta oliveroi left second osteoderm fragment in dorsal and internal views. g, h, Stegouros elengassen, digital reconstruction of the caudal weapon cross section (at level of second pair and 17th caudal vertebra) in anterior and posterior views. i, j, proposed configuration of the caudal weapon of Antarctopelta oliveroi in anterior and posterior views. Scale bars 10 cm.

Extended Data Fig. 7 Comparison of cervical and pedal bones between S. elengassen holotype (CPAP-3165) and A. oliveroi holotype (MLP 86-X-28-1).

ad, Stegouros elengassen posterior cervical vertebra in anterior, right lateral, posterior, and dorsal views. eh. Antarctopelta oliveroi posterior cervical vertebra in anterior, right lateral, posterior, and dorsal views. i, j Stegouros elengassen right foot in dorsal and ventral views. k, l, Antarctopelta oliveroi right metatarsal in dorsal and ventral views. m, Antarctopelta oliveroi isolated pedal phalanx in dorsal, proximal and ventral views. Scale bars 5 cm.

Extended Data Fig. 8 Comparison of dermal skeleton between S. elengassen holotype (CPAP-3165) and A. oliveroi holotype (MLP 86-X-28-1).

a, Stegouros elengassen dermal ossicles in internal view. b, Antarctopelta oliveroi disarticulated dermal ossicles. c, Antarctopelta oliveroi dermal ossicle close-up exposed in internal view. df, sacral covering fragments of Antarctopelta oliveroi. Scale bars, 5 mm (1, b), 1 mm (c), 10 cm (d-f).

Extended Data Fig. 9 Comparison of teeth and dentary of S. elengassen holotype (CPAP-3165) and A. oliveroi holotype (MLP 86-X-28-1).

ad, Stegouros elengassen digital reconstruction of cheek tooth in labial, mesial, lingual, and distal views. eh, Antarctopelta oliveroi tooth (reversed) in labial, mesial, lingual, and distal views. ik, Stegouros elengassen right dentary (mirrored for better comparison) in labial, lingual and occlusal views. ln Antarctopelta oliveroi right dentary fragment in labial, lingual and occlusal views. Scale bars 5 mm (a-d), 10 mm (e-h), 10 cm (i-n).

Extended Data Table 1 Results of phylogenetic analysis

Supplementary information

Supplementary Information

(1) Taphonomical aspects of the holotype. (2) Geological and Palaeoenvironmental context. (3) Additional comparisons to Antarctopelta oliveroi. (4) Results of the phylogenetic analyses. (5) References.

Reporting Summary

Peer Review File

Supplementary Video 1

3D reconstruction of the tail weapon of Stegouros based on the digital segmentation of a CT scan volume.

Supplementary Video 2

Transversal view of the segmented volume for the tail weapon of Stegouros.

Supplementary Video 3

Digital endocast of the tail weapon of Stegouros.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Soto-Acuña, S., Vargas, A.O., Kaluza, J. et al. Bizarre tail weaponry in a transitional ankylosaur from subantarctic Chile. Nature 600, 259–263 (2021). https://doi.org/10.1038/s41586-021-04147-1

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41586-021-04147-1

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing