Spicomellus

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Spicomellus
Temporal range:
Ma
↓
Illustration of the holotype.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Thyreophora
Clade: †Ankylosauria
Genus: †Spicomellus
Maidment et al., 2021
Species:
†S. afer
Binomial name
†Spicomellus afer
Maidment et al., 2021

Spicomellus is an extinct genus of early

El Mers III Formation (Bathonian-Callovian) of Morocco. The genus contains a single species, S. afer, known from a single rib with fused osteoderms
. Spicomellus represents the oldest named ankylosaur.

Discovery and naming

The Spicomellus

El Mers III Formation near Boulahfa in Boulemane, Fès-Meknès region, Morocco. It was later acquired by London's Natural History Museum from a commercial fossil dealer. The specimen consists of a single rib with four co-ossified spines. The holotype was CT scanned and histologically sectioned to confirm that it was an ankylosaurian.[1]

In 2021, Maidment et al. described Spicomellus afer as a new genus and species of ankylosaurian thyreophoran based on these fossil remains. The generic name, Spicomellus, combines the Latin words "spicus", meaning "spike" and "mellus", which refers to a collar of spikes. The specific name, afer, is a Latin word referring to something inhabiting Africa.[1]

Abundant diverse

eurypodan dinosaurs have been found in Jurassic Laurasian sediments, but their remains are rarer in Gondwanan deposits. Spicomellus is the second described eurypodan taxon from North Africa, after Adratiklit.[1][2]

Description

The preserved dermal spikes of the holotype were fused directly to the bone, a trait unique to Spicomellus and not known from any other vertebrate. Some prehistoric animals, including Protuberum (a cynodont) and Euscolosuchus (a pseudosuchian), have superficially similar modified ribs. In all other known ankylosaurs, the osteoderms are embedded into the muscle tissue, rather than fused to underlying bone.[1][3]

Classification

Preliminary assessments of the holotype led researchers to consider stegosaurian relationships for the species.

Eurypoda. Furthermore, the structural fibers of the osteoderms are interwoven, with a plywood-like arrangement, which is seen in ankylosaurs but not other thyreophorans.[1]

Spicomellus is the oldest known ankylosaur that has currently been named from anywhere in the world. Few other ankylosaurs are known from a similar time.

ankylosaur.[4]

Paleoecology

Spicomellus is known from the El Mers III Formation (

stegosaurs Adratiklit and Thyreosaurus.[2][5] Predators of the ecosystem consisted of indeterminate theropods (possible megalosaurids).[6] The sauropod Atlasaurus is also known from the contemporaneous terrestrial Guettioua Formation.[7]

The discovery of Spicomellus also shows that the two major thyreophoran groups (Ankylosauria and Stegosauria) coexisted for over 20 million years, and implies that the putative extinction of the stegosaurs in the Early Cretaceous may have happened for reasons other than an increased diversity of anyklosaurs at that time.[1]

Studies by the describing authors of the

locality suggested a shallow marine depositional environment with continental mixed clastic, evaporitic and carbonate sediments.[2]

References

  1. ^
    S2CID 237616095
    .
  2. ^
    ISSN 1342-937X
    .
  3. ^ a b Davis, Josh (September 23, 2021). "New species of dinosaur had armour unlike anything seen before". Natural History Museum. Retrieved September 23, 2021.
  4. doi:10.1144/sjg37010019
    .
  5. doi:10.1016/j.gr.2024.03.009
    .
  6. ^ J. Jenny, A. Le Marrec, and M. Monbaron. (1981). Les empreintes de pas de dinosauriens dans le Jurassique moyen du Haut Atlas central (Maroc): nouveaux gisements et precisions stratigraphiques. Geobos. 14(3):427-431
  7. ^ M. Monbaron, D. A. Russell, and P. Taquet. (1999). Atlasaurus imelakei n.g., n.sp., a brachiosaurid-like sauropod from the Middle Jurassic of Morocco. Comptes Rendus de l'Académie des Sciences à Paris, Sciences de la Terre et des Planètes 329:519-526.
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