The Earliest Armoured Ankylosaur: Spicomellus afer

During the Middle Jurassic, an unusual armoured dinosaur roamed the floodplains of what is now Morocco in North Africa. This dinosaur, Spicomellus afer, possessed an extraordinary body covered with elaborate armour. Its discovery represents the earliest known fossil record of ankylosaurs and pushes the evolutionary history of this group back by at least thirty million years. The find has dramatically reshaped palaeontologists' understanding of how ankylosaur body armour and tail weapons evolved, and it also encourages a reconsideration of the function of the complex structures seen on these dinosaurs.

Life reconstruction of Spicomellus afer（Image source：Connor Ashbridge， CC BY 4.0 ）

Ankylosaurs are a well-known group of ornithischian dinosaurs. They were quadrupedal herbivores with broad bodies and relatively short limbs, typically protected by thick bony plates and spines embedded in the skin. One of the most famous representatives is Ankylosaurus magniventris, a Late Cretaceous dinosaur from North America that carried a massive tail club. Members of this group were covered in extensive dermal armour, with osteoderms and spikes spread across the back and limbs. However, fossils documenting the early stages of ankylosaur evolution are extremely scarce. For the Early and Middle Jurassic, the fossil record has long been fragmentary and poorly understood. Only a few scattered remains were previously known, such as isolated teeth and osteoderms from the Oxford Clay Formation in England and teeth from the Bathonian White Limestone Formation, suggesting that ankylosaurs might already have existed at that time.

Life reconstruction of Ankylosaurus magniventris（Image source：UnexpectedDinoLesson， CC BY 4.0 ）

In 2021, a single rib fragment bearing fused spikes was discovered in Morocco and named Spicomellus afer. Because the geological layer in which it was found was older than any previously known ankylosaur fossil, researchers proposed that it might represent the oldest ankylosaur yet discovered. However, the evidence at that time was limited to that single rib, making the identification uncertain. New excavations have now produced a much more complete partial skeleton, confirming that Spicomellus truly belongs to Ankylosauria. Yet the armour of this dinosaur is unlike that of any other vertebrate, living or extinct.

The newly discovered specimen also comes from Morocco, specifically from the El Mers III Formation in the Middle Atlas Mountains. This formation dates to the Bathonian stage of the Middle Jurassic, approximately 167 million years ago. Geological evidence indicates that the area was a floodplain environment containing rivers and wetlands, suggesting that Spicomellus inhabited a landscape rich in water and vegetation. The fossil remains appear to represent a single individual rather than a mixture of bones from multiple animals. Because illegal fossil collecting is widespread in the region and some Spicomellus material may already have entered European black markets, the researchers deliberately withheld the precise locality to prevent further damage to the site.

The skeleton includes numerous bones such as cervical vertebrae, dorsal vertebrae, sacral vertebrae, caudal vertebrae, parts of the scapulocoracoid and pelvis, and a remarkable array of osteoderms and spikes of many shapes and sizes. Among the most striking features is the armour surrounding the neck. This region formed a cervical half-ring composed of multiple fused elements. Five long spikes extended from this structure, and the longest of the lateral spikes could reach about 87 centimetres in length. The dorsal ribs themselves also bore spikes fused directly to their upper surfaces. Six dorsal ribs are preserved in the fossil, and while the first rib carries two spikes, the third through fifth ribs each bear six spikes. Over the pelvis lay a fused sacral shield covered with numerous small and large spikes arranged in a grid-like pattern. In addition to these structures, the armour included a wide variety of osteoderms with diverse shapes, including slender spikes, blade-like forms, conical elements and compound osteoderms in which multiple spikes were fused to a single base plate.（For fossil-related images, please visit the following website due to copyright restrictions: https://www.nature.com/articles/s41586-025-09453-6）

The tail of Spicomellus reveals an unexpected feature. Two of the distal caudal vertebrae are fused and show elongate prezygapophyses and associated ossified tendons, features characteristic of the “handle” vertebrae that support a tail club in later ankylosaurs. This discovery indicates that tail-weapon structures appeared far earlier than previously thought. Earlier hypotheses suggested that the specialized vertebrae forming the base of ankylosaur tail clubs evolved only in the Early Cretaceous. The presence of these structures in a Middle Jurassic ankylosaur therefore pushes the origin of tail weaponry back by roughly thirty million years. It also implies that tail weapons may have been present early in ankylosaur evolution, with some later lineages subsequently simplifying or losing them.

Before this discovery, most ankylosaur fossils were known from the Northern Hemisphere landmass known as Laurasia. Only a small number had been found in the southern supercontinent Gondwana. Because of this, some researchers proposed the existence of a separate group of southern ankylosaurs called Parankylosauria, which were thought to possess unusual tail weapons. Examples include Stegouros from Chile, which had a flattened, fan-shaped tail weapon, and Antarctopelta from Antarctica, which may have possessed a similar structure. However, the phylogenetic analysis performed in the new study indicates that Spicomellus is not especially closely related to these Gondwanan forms. Instead, it appears to be more closely related to early Asian ankylosaurs such as Gobisaurus and Shamosaurus. This result suggests that the evolutionary relationships among ankylosaurs in the Northern and Southern Hemispheres are more complex than previously assumed and that a distinct southern lineage may not have existed.

Life reconstruction of Stegouros elengassen（Image source：Mauricio david alvarez abel， CC BY-SA 4.0 ）

Life reconstruction of Gobisaurus domoculus（Image source：Foolp， CC BY-SA 4.0 ）

The extravagant armour of Spicomellus raises important questions about its function. Although armour is often interpreted as a defensive adaptation, the researchers argue that the enormous neck spikes would not have been particularly effective for defence. In fact, such long projections might even have hindered movement or provided predators with something to grasp. If defence were the sole function, ankylosaurs could simply have developed the thick, regular armour plates seen in many Cretaceous species. The unusually ornate armour of Spicomellus therefore may have served additional purposes.

One plausible explanation is display associated with sexual selection. In many living animals, energetically costly structures such as deer antlers, peacock tails or the horns of certain beetles evolve through sexual selection rather than direct survival advantages. These features function as signals used in mate attraction or competition between individuals of the same species. The long cervical spikes of Spicomellus may have played a similar role. Over time, ankylosaur armour appears to have become simpler and heavier, especially by the Cretaceous period. This trend suggests that the function of armour gradually shifted toward stronger defensive protection. Some researchers propose that this shift may have been linked to the appearance of larger and more diverse predators during the Late Cretaceous.

Spicomellus afer is currently the only Jurassic ankylosaur known from Africa and the oldest ankylosaur discovered so far. Its discovery fundamentally alters our understanding of ankylosaur evolution. The complex and elaborate armour of this dinosaur suggests that early ankylosaurs may have been strongly influenced by sexual selection, with display structures playing a major role in their early evolutionary history. Comparable processes may also have occurred in other dinosaur groups. In theropod dinosaurs, for example, evolutionary changes eventually led from structures used in physical combat to those used for visual display as feathers evolved. The case of Spicomellus illustrates that the evolution of animal form is shaped not only by predator–prey interactions but also by display, aesthetics and reproductive strategies.

Author: Shui-Ye You

Reference:

Maidment SCR et al. (2025). Extreme armour in the world's oldest ankylosaur. Nature.

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