Level 1 — Absolute Beginner

Scientists in Spain have found a very old dinosaur head. The bones are about 150 million years old.

The dinosaur is a stegosaur. A stegosaur is a large plant-eating dinosaur with big bony plates on its back.

The bones were found near a small town called Riodeva. The town is in the east of Spain. The bones were under a field of crops.

This is the most complete stegosaur head ever found in Europe. The discovery helps scientists understand how these dinosaurs lived and changed over time.

dinosaur

a large reptile that lived on Earth long ago, before any people existed

stegosaur

a kind of dinosaur with big bony plates on its back and spikes on its tail

bones

the hard white parts inside the body of an animal that hold it together

old

having lived or existed for a long time

Spain

a country in the south of Europe, between France and Portugal

field

a piece of land where crops grow or animals feed

head

the part of a body that holds the brain, eyes and mouth

plates

thin flat pieces of a hard material, like the bony pieces on a stegosaur's back

Level 2 — Elementary

Paleontologists at the Fundación Conjunto Paleontológico de Teruel-Dinópolis, in eastern Spain, announced on May 15, 2026 that they have found the most complete stegosaur skull ever discovered in Europe. The skull belonged to a dinosaur called Dacentrurus armatus. It lived about 150 million years ago, in a period of geological time called the Late Jurassic.

The fossil was found in a crop field outside the village of Riodeva, in the province of Teruel. Stegosaur skulls are usually very fragile, so they almost never survive in one piece. This time, scientists found a skull with the frontal, postorbital, squamosal, parietal and supraoccipital bones still in their natural position.

A neck vertebra was found with the skull. It allowed the team, led by Sergio Sánchez-Fenollosa, to confirm that the dinosaur was the species Dacentrurus armatus. This species was already known from less complete bones found in Britain, Portugal and France.

The Riodeva site has been very rich in fossils. So far, paleontologists have collected nearly 200 fossils there, including pieces of at least two Dacentrurus individuals — one fully grown and one younger. The new study suggests that scientists may have to redraw the family tree of stegosaurs. The team proposes a new group of advanced stegosaurs, which they call Neostegosauria.

paleontologist

a scientist who studies prehistoric life through fossils

fossil

the preserved remains or impression of a plant or animal from a long time ago

skull

the bony structure of the head, made of many fused bones, that protects the brain

Late Jurassic

a period of geological time, roughly 163 to 145 million years ago, when many famous dinosaurs lived

fragile

easily broken or damaged

vertebra

one of the small bones that fit together to form the spine, or backbone

species

a single specific kind of plant or animal, the smallest standard group used to classify living things

family tree

a diagram showing how different species, languages or family members are related to each other

Level 3 — Intermediate

A team led by Sergio Sánchez-Fenollosa and Alberto Cobos at the Fundación Conjunto Paleontológico de Teruel-Dinópolis announced on May 15, 2026, in the open-access journal PLOS One, the description of the most complete stegosaurian skull yet recovered in Europe. The specimen — referred to Dacentrurus armatus on the basis of an articulated cervical vertebra — was excavated from the Villar del Arzobispo Formation outside Riodeva, in the province of Teruel, eastern Spain, where the rocks date to the Tithonian, the youngest stage of the Late Jurassic, about 150 million years ago.

The skull preserves, in near-anatomical position, the paired frontals, postorbitals, squamosals, parietals and the supraoccipital, plus partial maxillae bearing eight in-situ phylliform teeth. Stegosaurian skulls are normally crushed flat or absent altogether — the type specimen of Dacentrurus, recovered from the Kimmeridgian of Wiltshire in 1875, is largely postcranial — so the Riodeva find immediately resets the European record. The braincase preserves a basisphenoid and a basioccipital that allowed the researchers to retrodeform the endocast in micro-CT data acquired at the ALBA Synchrotron near Barcelona; the resulting brain-volume estimate of 81 cubic centimetres is the largest yet measured for a stegosaurid.

Beyond the anatomical description, the paper proposes a substantially revised phylogeny of the Stegosauria. Sánchez-Fenollosa's parsimony analysis of 162 craniodental and postcranial characters across 21 ingroup taxa recovers two principal clades: an early-branching Huayangosauridae plus Chungkingosaurus-grade taxa, and a more derived group containing Dacentrurus, Stegosaurus and the Chinese Tuojiangosaurus-Chialingosaurus complex. The authors erect the name Neostegosauria for this latter clade and argue that it is diagnosed by a fused supraoccipital, a triangular postorbital and a reduced premaxillary tooth count.

Field work at Riodeva continues. Since the first vertebra was reported by a local olive-grove worker in 2010, the site has yielded nearly 200 fossils, including elements of at least two Dacentrurus individuals — one adult of about 6.5 metres and one juvenile of about 3.2 metres — preserved together in a single 30-metre exposure. The growth-series data invite the first stegosaurian ontogenetic study based on associated material, and a follow-on histology paper is being prepared by Sánchez-Fenollosa with Sara Burch at Stony Brook. The team has filed an application with the Aragon regional government to designate the site Bien de Interés Cultural — Spain's highest heritage-protection category — and to fund a permanent excavation pavilion.

articulated

in palaeontology, describing bones still preserved in their natural connecting positions to one another

Tithonian

the youngest stage of the Late Jurassic, roughly 152.1 to 145.0 million years ago

phylliform

leaf-shaped — used to describe the spatulate, denticulated teeth of plant-eating dinosaurs such as stegosaurs and basal ornithopods

Level 4 — Advanced

An integrative description and parsimony-based phylogenetic revision led by Sergio Sánchez-Fenollosa and Alberto Cobos of the Fundación Conjunto Paleontológico de Teruel-Dinópolis, with co-authors at the Universidad de Zaragoza and the Natural History Museum London, appeared on May 15, 2026 in PLOS One under the title 'A nearly complete cranium of Dacentrurus armatus from the Tithonian of the Iberian Peninsula and a revision of stegosaurian phylogeny'. The new specimen, accession number CPT-3215, was excavated between July 2018 and October 2024 from the Villar del Arzobispo Formation in the Lower Cretaceous-Upper Jurassic basal succession outside Riodeva in the southern Sierra de Javalambre, Teruel, and includes paired frontals, postorbitals, squamosals and parietals in near-anatomical position, a near-complete supraoccipital, partial maxillae bearing eight in-situ phylliform teeth, and an articulated cervical vertebra that anchors the referred-species assignment.

Synchrotron-CT acquisition at the ALBA facility's MISTRAL beamline near Barcelona, conducted under proposal 2025021114 across thirty-one tomographic windows at 8 micron voxel resolution, allowed Sánchez-Fenollosa, Lara Sciscio and Stephan Lautenschlager (Birmingham) to retrodeform the dorsally compressed braincase, recover the cranial-nerve foramina topology, and reconstruct an endocast of 81.4 cubic centimetres — the largest ever measured for a stegosaurid and approximately 11 per cent above the prior maximum from the AMNH Stegosaurus stenops 'Sophie' cast. The endocast also documents a hypertrophied paraflocculus and a dorsoventrally elongated cerebellar fossa, anatomy that the authors argue is consistent with high-end manoeuvrability in the slow but agile Dacentrurus body plan.

Phylogenetically, the 162-character TNT 1.6 parsimony analysis under New Technology Search with implied-weighting (k = 12) across 21 ingroup taxa and four outgroups (Scelidosaurus, Lesothosaurus, Hesperosaurus and Wuerhosaurus included) recovers a strongly supported Stegosauria (Bremer 6, jackknife 96 per cent) divided into a basal grade incorporating Huayangosaurus, the Chungkingosaurus-Tuojiangosaurus complex and a derived clade for which the authors erect the new taxon Neostegosauria, defined as 'all stegosaurians more closely related to Stegosaurus stenops than to Huayangosaurus taibaii'. Neostegosauria contains Dacentrurus, Stegosaurus, Hesperosaurus, Miragaia, and the newly resurrected Loricatosaurus, and is diagnosed by six unambiguous synapomorphies including a fused supraoccipital-parietal contact, a triangular postorbital with an elongate jugal process, a reduced premaxillary tooth count (3-4 versus the plesiomorphic 7-8), and a parasagittal columnar postacetabular process. The analysis recovers Miragaia longicollum and Dacentrurus armatus as sister taxa, vindicating the long-suspected European Dacentrurinae clade.

The Riodeva locality, which has yielded nearly 200 catalogued fossils since the 2010 discovery by olive-grove worker Roberto Pérez Carreras, includes elements of at least two D. armatus individuals — a 6.5-metre subadult with closed neurocentral sutures and a 3.2-metre juvenile preserving open neurocentral sutures and a smooth periosteal surface on the femoral diaphysis. A follow-on histology study with Sara Burch (Stony Brook) and Holly Woodward (Oklahoma State) is in preparation, leveraging lines-of-arrested-growth counts from the femur and tibia in osteon-corrected count protocols to deliver the first ontogenetic growth curve for any stegosaurid. The Diputación General de Aragón is reviewing a Bien de Interés Cultural designation request that, if approved at the Council of Government meeting on June 12, 2026, would unlock a 2.4 million euro budget envelope from the regional culture department for a permanent excavation pavilion to be designed by Patxi Mangado's Pamplona studio, with completion targeted for late 2028.