An artistic reconstruction of Spicomellus afer. One cervical half-ring with elongate spikes, small spikes covering the dorsum of the body and large spikes and a sacral shield over the hips are in their known positions on the body; the location of all other armour, and the presence of spikes at the end of the tail, is conjectural. Credit: Matthew Dempsey (CC BY-NC-ND)
New fossil evidence reveals the world’s oldest ankylosaur boasted extravagant, spiked armour – including spikes fused onto and projecting from its ribs – unlike any other living or extinct animal.
The partial skeleton also indicates the species, Spicomellus afer, likely sported a clubbed tail weapon more than 30 million years before any other ankylosaur.
Project co-lead Susannah Maidment from the University of Birmingham and Natural History Museum in the UK, says finding such elaborate armour in an early ankylosaur changes understandings of how these dinosaurs evolved.
“Spicomellus had a diversity of plates and spikes extending from all over its body, including metre-long neck spikes, huge upwards-projecting spikes over the hips, and a whole range of long, blade-like spikes, pieces of armour made up of 2 long spikes, and plates down the shoulder,” says Maidment.
“We’ve never seen anything like this in any animal before.
“It’s particularly strange as this is the oldest known ankylosaur, so we might expect that a later species might have inherited similar features, but they haven’t.”
Ankylosaurs roamed the Earth from the middle of the Jurassic period – about 165 million years ago (mya) – until the catastrophic extinction event which wiped out the dinosaurs at the end of the Cretaceous period 66 mya.
The clade of quadrupedal, short-limbed and wide-bodied herbivorous dinosaurs are best known for the plates, spines and other osteoderms (skin bones) which covered their skulls and backs.
Osteoderms still occur in living animals today, including turtles, armadillos, turtles, crocodilians, and other reptiles.
But the evolution of Ankylosauria’s unusual body plan remains largely undocumented due to a lack of fossils from its earliest members.
In 2021, the first Spicomellus specimen – a rib fragment with fused spikes uncovered in Morocco – was tentatively put forward as the oldest known ankylosaur.
According to the authors of the most recent study published in Nature, the new, more complete skeleton “demonstrates unequivocally its ankylosaurian identity”.
Selected postcranial elements and dermal armour of S. afer. Credit: Maidment et al., Nature (2025)
The finding suggests that ankylosaur armour started out much more elaborate and subsequently became more simple.
“The ornate, complex and baroque armour of Spicomellus suggests that, early in their history, ankylosaur armour was under strong sexual selection and that it evolved initially primarily for display, rather than defence,” they write.
The authors believe that later ankylosaurs may have co-opted and simplified the armour to be more defensive as multitonne therapod predators, larger mammals, and crocodilians evolved in the Cretaceous.
“Alternatively, this simplification of armour could point to a switch from visual to combative display during courtship.”
One feature that may have survived is Spicomellus’ tail weaponry.
Some of its surviving tail vertebrae are fused together to form a structure known as a handle, which likely formed part of a tail club. Before now, these structures were thought to have evolved only in the Early Cretaceous.
Project co-lead Richard Butler, also from the University of Birmingham, says seeing and studying the Spicomellus fossils for the first time was spine-tingling.
“We just couldn’t believe how weird it was and how unlike any other dinosaur, or indeed any other animal we know of alive or extinct. It turns much of what we thought we knew about ankylosaurs and their evolution on its head and demonstrates just how much there still is to learn about dinosaurs.”