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Bizarre dermal armour suggests the first African ankylosaur

Abstract

Ankylosauria is a diverse clade of armoured dinosaurs whose members were important constituents of many Cretaceous faunas. Phylogenetic analyses imply that the clade diverged from its sister taxon, Stegosauria, during the late Early Jurassic, but the fossil records of both clades are sparse until the Late Jurassic (~150 million years ago). Moreover, Ankylosauria is almost entirely restricted to former Laurasian continents, with only a single valid Gondwanan taxon. Spicomellus afer gen. et sp. nov. appears to represent the earliest-known ankylosaur and the first to be named from Africa, from the Middle Jurassic (Bathonian–Callovian) of Morocco, filling an important gap in dinosaur evolution. The specimen consists of a rib with spiked dermal armour fused to its dorsal surface, an unprecedented morphology among extinct and extant vertebrates. The specimen reveals an unrealized morphological diversity of armoured dinosaurs during their early evolution, and implies the presence of an important but undiscovered Gondwanan fossil record.

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Fig. 1: Morphology and histology of Spicomellus afer, NHMUK PV R37412.
Fig. 2: Details of the histology of Spicomellus afer, NHMUK PV R37142.

Data availability

All data associated with this paper are included in Extended Data. The specimen described in this study is reposited in the collections of the Natural History Museum, London, under specimen number NHMUK PV R37412. This published work and the nomenclatural acts it contains are registered with ZooBank (LSID: urn:lsid:zoobank.org:act:D12DDAB4-E164-411D-8406-B7B3DEC52F71LSID: urn:lsid:zoobank.org:act:D12DDAB4-E164-411D-8406-B7B3DEC52F71).

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Acknowledgements

C. Hatch (Natural History Museum) prepared thin sections of the specimen; A. Ball (Natural History Museum) took high-resolution photographs of the slides; B. Creisler (Natural History Museum) advised on etymology. T.M.S. acknowledges support from the Swiss National Science Foundation (grant no. 31003A_179401). We thank the members of the London fossil vertebrates journal club for discussion.

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Contributions

S.C.R.M. and P.M.B. devised the study. D.O. examined the stratigraphy. S.J.S., T.M.S. and E.E.B. carried out histological analysis. V.F. carried out XCT scanning and analysis. S.C.R.M., P.M.B., D.O., S.J.S., T.M.S., E.E.B., V.F., Z.J. and T.J.R. interpreted the data and wrote the manuscript.

Corresponding author

Correspondence to Susannah C. R. Maidment.

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The authors declare no competing interests.

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Peer review information Nature Ecology & Evolution thanks the anonymous reviewers for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Translucent XCT reconstruction of NHMUK PV R37412, Spicomellus afer.

Red shading indicates a grainy cement or fill used to consolidate the specimen. a, lateral and b, dorsal view. Also see Supplementary video.

Extended Data Fig. 2 XCT-scan image of a longitudinal cross-section through NHMUK PV R37412.

White ovals highlight areas where it is possible to see the continuity of cortical and trabecular bone from the spikes to the rod.

Extended Data Fig. 3 The osteoderm and rib parts of the rod were segmented using the following procedure.

a, a section of the specimen was identified for focus; b, longitudinal sections of the specimen were examined in XCT data; c, the boundary between the osteoderm and the rib was identified on longitudinal sections; d, the data were labelled.

Extended Data Fig. 4 Histological thin-section (plane polarized light) showing detail of the spine.

A vascular channel can be observed in the top left of the image. The woven bone matrix of the cortex is dominated by primary osteons. Scattered secondary osteons can be observed in the mid and inner cortex. Large resorption cavities lined with lamellar bone can be observed in the trabecular bone of the core (top right). Red arrows indicate growth (=resting) lines.

Extended Data Fig. 5 Thin section photomicrograph (plane-polarized light) showing detail of the structural fibres in the upper osteodermal part of the rod.

Structural fibre bundles intersect roughly perpendicular to each other. The opaque cast in the top half of the image is probably diagenetic alteration.

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Maidment, S.C.R., Strachan, S.J., Ouarhache, D. et al. Bizarre dermal armour suggests the first African ankylosaur. Nat Ecol Evol (2021). https://doi.org/10.1038/s41559-021-01553-6

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