| Spicomellus | |
|---|---|
 | |
| Skeletal reconstruction including the holotype (yellow) and referred (white) specimens | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| 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 extinctgenus of unusual earlyankylosaurian dinosaur from theEl Mers III Formation (Bathonian age) of Morocco. The genus contains asingle species,Spicomellus afer, representing the oldest named definitive ankylosaur. The species was initially described in 2021 based on a single rib with fusedosteoderms, 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 ofspines 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, theNatural History Museum in London acquired an unusual Moroccan fossil from a commercial fossil dealer inCambridge.[1] The specimen consists of a single dorsalrib 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 paleontologistSusannah Maidment and Moroccan geologist Driss Ouarhache were able to relocate the locality from which the specimen was collected. It originates from layers of theEl Mers III Formation in theMiddle Atlas mountains near the town ofBoulemane inFès-Meknès region, Morocco. Maidment and Ouarhache visited this location in 2019 and 2020, respectively, to examine itssedimentology andstratigraphy. The specimen was scanned usingX-ray computed tomography (XCT) andhistologically sectioned to confirm its authenticity and ankylosaurian nature.[2]
In 2021, Maidment and colleaguesdescribedSpicomellus afer as a new genus and species of ankylosaurian dinosaurs based on this specimen,accessioned asNHMUK PV R 37412. Thegeneric name,Spicomellus, combines theLatin wordsspica, meaning "spike", andmellum, which refers to a collar. Thespecific name,afer, is a Latin word referring to something inhabiting Africa.[2]
In 2023, an expedition of paleontologists from England, America, and Morocco revisted thetype locality in an attempt to locate additional material ofSpicomellus.[1][3] The team collected a partial skeleton including cranial bones (a leftquadrate and other unidentified fragments), several vertebrae (twocervicals, twodorsals, foursacrals, four free (unfused)caudals, and two 'handle' caudals), six dorsalribs, all of which bear the fused spikes seen in the holotype, bothscapulocoracoids, a partialpelvic girdle (ilia andpubes and the rightischium), twometatarsals, 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 atSidi Mohamed Ben Abdellah University as specimens USMBA 5–84.[4]
SeveralSpicomellus 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 afossil preparation laboratory at Sidi Mohamed Ben Abdellah University, and train Moroccan paleontologists to lead excavations in the area.[3]
Abundant diverseeurypodan dinosaurs have been found in JurassicLaurasian sediments, but their remains are rarer inGondwanan deposits.Spicomellus is the second described eurypodan taxon fromNorth Africa, after the stegosaurAdratiklit, named in 2020.[2][5] A second stegosaur,Thyreosaurus, was named in 2024.[6]
.svg)
The preserved dermal spikes of the holotype rib are fused directly to the bone, a trait unique toSpicomellus and not known from any othervertebrate. Some prehistoric animals, includingProtuberum (acynodont) andEuscolosuchus (apseudosuchian), have superficially similar modified ribs. In all other known ankylosaurs, theosteoderms are embedded into the muscle tissue, rather than fused to the underlying bone.[2][7]
Fused 'handle vertebrae' with associated ossified tendons are known from the tail ofSpicomellus, which likely indicate it had a tail weapon. Since the actual weapon has currently not been found, the morphology of this structure inSpicomellus is unclear. In later-diverging ankylosaurids, the weapon isclub-like in shape, while inparankylosaurs such asStegouros, it is frond-like. Regardless, it represents the oldest known occurrence of a tail weapon within the Ankylosauria.[1] 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 inSpicomellus is unique. Many partial osteoderms have been found, but their arrangement on the body is unknown.[4]
Spicomellus is the oldest definitive ankylosaur currently named. Few other ankylosaurs are known from a similar time.Sarcolestes, known from a partial lower jaw, was found in England'sOxford Clay Formation, which dates to the youngerCallovian age.[2] An unnamedthyreophoran from theBajocian-agedBearreraig Sandstone Formation of theIsle of Skye, Scotland, could be older thanSpicomellus, but it is unclear if these fragmentary remains belonged to astegosaur or anankylosaur.[8]
Preliminary assessments of the holotype led researchers to consider stegosaurian relationships for the species.[7] In their 2021 description ofSpicomellus, Maidment et al. discussed several lines of evidence supporting the placement ofSpicomellus as a basalankylosaurian. They had considered the possibility that the rib was actually part of the jaw of anosteichthyan fish, since some members have teeth fused to their jaws. However, since there is no evidence of orthodentine—an important component of fish teeth—they considered this classification unsupported. Based on the T-shaped cross section of the rib,Spicomellus can reasonably be assigned to theEurypoda (the clade including stegosaurs and ankylosaurs, all of which bear T-shaped ribs). Furthermore, the structural fibers of the osteoderms are interwoven, with aplywood-like arrangement, which is seen in ankylosaurs but not other thyreophorans.[2]
Based on their description of additional remains in 2025, Maidment and colleagues tested thephylogenetic affinities ofSpicomellus in the thyreophoran-focused dataset of Raven et al. (2023).[9] In their strict reduced consensus tree (shown below inTopology A), they recoveredSpicomellus in an early-diverging clade within the Ankylosauria outside of either theAnkylosauridae orNodosauridae. This clade comprises an unresolvedpolytomy featuring—in addition toSpicomellus—Ahshislepelta,Chuanqilong,Gobisaurus, andShamosaurus. Using extended implied weights (shown below inTopology B), they instead recoveredSpicomellus in abasal position within the family Ankylosauridae, as the sister taxon to the clade formed byGobisaurus andShamosaurus. These contrasting results are displayed in thecladograms below, with equivalent taxa indicated in matching colors for clarity:[4]
| Topology A: strict consensus tree | Topology B: extended implied weights
|
Spicomellus is known from the El Mers III Formation (El Mers Group) of Morocco.[2] This would have been part of the supercontinentGondwana during theMiddle Jurassic. The formation is currently represented by continental mixedclastic, evaporitic, andcarbonate sediments.[5] Thesedimentology andstratigraphy of the locality suggest a shallow marinedepositional environment. This setting was marked by episodic marine incursions, suggesting fluctuating sea levels.[10]
The El Mers III formation has also yielded the remains of twostegosaurs,Adratiklit andThyreosaurus.[5][6] The presence of the ankylosaurSpicomellus in addition to these genera indicates that the two major thyreophoran groups (Ankylosauria and Stegosauria) coexisted for more than 20 million years. This implies that the putative extinction of the stegosaurs in theEarly Cretaceous may have happened for reasons other than an increased diversity of ankylosaurs at that time. An unnamedturiasaur (known from teeth)[11] and an unnamedneornithischian (known from a partial femur) are also known from this formation.[12]Theropod dinosaurs andcrocodylomorphs are known from the El Mers Group based on footprints.[13][14]
