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.

In 2019, the Natural History Museum in London acquired an unusual Moroccan fossil from a commercial fossil dealer in Cambridge. The specimen consists of a single dorsal rib fragment fused to a flat osteoderm bearing four spines on the external surface. After discussions with the English seller and the Moroccan fossil dealer from whom the specimen was obtained, English paleontologist Susannah Maidment and Moroccan geologist Driss Ouarhache were able to relocate the locality from which the specimen was collected. It originates from layers of the El Mers III Formation in the Middle Atlas mountains near the town of Boulemane in Fès-Meknès region, Morocco. Maidment and Ouarhache visited this location in 2019 and 2020, respectively, to examine its sedimentology and stratigraphy. The specimen was scanned using X-ray computed tomography (XCT) and histologically sectioned to confirm its authenticity and ankylosaurian nature.

In 2021, Maidment and colleagues described Spicomellus afer as a new genus and species of ankylosaurian dinosaurs based on this specimen, accessioned as NHMUK PV R 37412. The generic name, Spicomellus, combines the Latin words spica, meaning "spike", and mellum, which refers to a collar. The specific name, afer, is a Latin word referring to something inhabiting Africa.

In 2023, an expedition of paleontologists from England, America, and Morocco revisted the type locality in an attempt to locate additional material of Spicomellus. The team collected a partial skeleton including cranial bones (a left quadrate and other unidentified fragments), several vertebrae (two cervicals, two dorsals, four sacrals, four free (unfused) caudals, and two 'handle' caudals), six dorsal ribs, all of which bear the fused spikes seen in the holotype, both scapulocoracoids, a partial pelvic girdle (ilia and pubes and the right ischium), two metatarsals, an cervical half ring with very long spikes, and a sacral shield with both large and small spikes. Several plates, spikes of various shapes and sizes, and 'compound' osteoderms that combine small and large spikes fused to a base, were also found. In 2025, Maidment and colleagues described this second specimen, accessioned at Sidi Mohamed Ben Abdellah University as specimens USMBA 5–84.

Several Spicomellus bones have been illegally excavated and exported from Morocco, and then sold online. As such, efforts are being made to establish a protected area in the fossiliferous regions, as well as educate the local people, start a fossil preparation laboratory at Sidi Mohamed Ben Abdellah University, and train Moroccan paleontologists to lead excavations in the area.

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 the stegosaur Adratiklit, named in 2020. A second stegosaur, Thyreosaurus, was named in 2024.

The preserved dermal spikes of the holotype rib are 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 the underlying bone.

Fused 'handle vertebrae' with associated ossified tendons are known from the tail of Spicomellus, which likely indicate it had a tail weapon. Since the actual weapon has currently not been found, the morphology of this structure in Spicomellus is unclear. In later-diverging ankylosaurids, the weapon is club-like in shape, while in parankylosaurs such as Stegouros, it is frond-like. Regardless, it represents the oldest known occurrence of a tail weapon within the Ankylosauria. The abundant and extremely long spines, known from the neck and pelvic region, may have evolved for both defense and display. Smaller spikes were dispersed over the rest of the body, including some fused to a sacral shield over the hips. The cervical half-ring (bony 'collar' around the neck) bears two fused plates and five fused spikes radiating outward. The largest and most complete spike is 87 centimetres (34 in) long. While cervical half-rings are common in ankylosaurs, the morphology seen in Spicomellus is unique. Many partial osteoderms have been found, but their arrangement on the body is unknown.