Open Paleo

Spicomellus

Maidment et al., 2021 SPY-co-MEL-lus

From Latin 'spica' meaning 'spike' and Latin 'mellum' meaning 'collar', referring to the spiked osteoderms fused to the rib of the holotype specimen

168.2–161.5 million years ago Bathonian–Callovian, Middle Jurassic
Middle Jurassic stages

Spicomellus is an extinct genus of unusual early ankylosaurian dinosaur from the El Mers III Formation (Bathonian age) of Morocco. The genus contains a single species, Spicomellus afer, representing the oldest named definitive ankylosaur. The species was initially described in 2021 based on a single rib with fused osteoderms, rendering its life appearance and relationships uncertain. In 2025, several additional bones, including osteoderms and cranial and postcranial remains, were described, revealing that it bears a unique array of spines over the body, including extremely elongated spikes around the neck and pelvis. It likely had a tail weapon, making it the oldest known ankylosaur with this structure.

Diagnosis

  1. T-shaped dorsal ribs in cross-section with fused rod-like osteoderm on dorsal surface
  2. Series of co-ossified conical dermal spines projecting from osteoderm
  3. Plywood-like arrangement of structural fiber bundles in osteoderm (orthogonal pattern, ~90° crossing)
  4. Spines rounded in cross-section, projecting dorsally from rod

Species

Spicomellus afer Maidment et al., 2021

Type species

From Latin 'afer' meaning 'African' or 'inhabiting Africa', referring to the provenance of the specimen from Morocco.

Holotype
NHMUK PV R 37412 , Natural History Museum
Material
Partial dorsal rib bearing four co-ossified spines, fused osteoderm on dorsal surface
Horizon
El Mers III Formation, Bathonian–Callovian, Middle Jurassic , 168.2–161.5 million years ago
Locality
Boulahfa, Boulemane, Morocco

Notable specimens

  • USMBA 5-84

    Université Sidi Mohamed Ben Abdellah Found 2023 complementary

    Referred partial skeleton collected in 2023 and described in 2025, revealing cranial and postcranial anatomy absent in the single-rib holotype: a cervical half-ring with very long spikes, a sacral shield, and fused 'handle' caudals indicating a tail weapon.

    Maidment et al. (2025)

References

  1. Maidment, S. C. R.; Ouarhache, D.; Ech-charay, K.; Oussou, A.; Boumir, K.; El Khanchoufi, A.; Park, A.; Meade, L. E.; Woodruff, D. C.; Wills, S.; Smith, M.; Barrett, P. M.; Butler, R. J. (2025). Extreme armour in the world's oldest ankylosaur. Nature 1-6. doi:10.1038/s41586-025-09453-6

    Considers it most likely an early-diverging ankylosaurid, inside Ankylosauridae in the implied-weights tree and in a polytomy with Ankylosauridae and Nodosauridae in the reduced consensus tree.

    maidment2025b
  2. Maidment, S. C. R.; Strachan, S. J.; Ouarhache, D.; Scheyer, T. M.; Brown, E. E.; Fernandez, V.; Johanson, Z.; Raven, T. J.; Barrett, P. M. (2021). Bizarre dermal armour suggests the first African ankylosaur. Nature Ecology & Evolution 5(12): 1576-1581. Springer Science and Business Media LLC. doi:10.1038/s41559-021-01553-6 maidment2021a
  3. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Ornithischians. Princeton University Press.

    Source of the body length, mass, and hip height estimates, and the appearance features.

    jones2026a