Deep within a crop field in eastern Spain, paleontologists uncovered something they had almost given up hope of ever finding, an intact stegosaur skull.
Paleontologists working in eastern Spain have described what they say is the most complete stegosaur skull ever recovered in Europe, belonging to a species that roamed the continent roughly 150 million years ago.
The specimen was identified as Dacentrurus armatus, a four-legged plant-eating dinosaur of the Late Jurassic, first described in 1875.
A Skull That Seldom SurvivesDinosaur skulls are among the most poorly preserved elements in the fossil record, a problem particularly acute for stegosaurs.
The skull and vertebra described in the new study are held at the Museo Aragonés de Paleontología in Teruel.
Deep within a crop field in eastern Spain, paleontologists uncovered something they had almost given up hope of ever finding, an intact stegosaur skull. The fossil, belonging to a species first described 150 years ago, is so exceptionally preserved that it has forced researchers to rethink the entire evolutionary history of plated dinosaurs.
Paleontologists working in eastern Spain have described what they say is the most complete stegosaur skull ever recovered in Europe, belonging to a species that roamed the continent roughly 150 million years ago. The find, announced in the journal Vertebrate Zoology, comes from a fossil site in the municipality of Riodeva, in the Teruel province of Aragon.
The specimen was identified as Dacentrurus armatus, a four-legged plant-eating dinosaur of the Late Jurassic, first described in 1875. Alongside the anatomical description, the research team has proposed a new classification framework for stegosaurs broadly, introducing a previously unnamed evolutionary group they call Neostegosauria.
A Skull That Seldom Survives
Dinosaur skulls are among the most poorly preserved elements in the fossil record, a problem particularly acute for stegosaurs. According to the study, published by paleontologists Sergio Sánchez-Fenollosa and Alberto Cobos of the Fundación Conjunto Paleontológico de Teruel-Dinópolis, nearly half of all currently valid stegosaur species have yielded no cranial material whatsoever. Only three taxa (Huayangosaurus taibaii, Hesperosaurus mjosi, and Stegosaurus stenops) were previously known from significant portions of their skulls.
Dacentrurus armatus cervical vertebra (MAP-9030), Riodeva, Spain; anterior, lateral, posterior, dorsal and ventral views ©Vertebrate Zoology
The newly described specimen, catalogued as MAP-9029, consists of the posterior half of the skull roof, including portions of the frontal and parietal bones, both postorbitals, both squamosals, the supraoccipital, and a fragment of what appears to be the left paroccipital process. A mid-cervical vertebra was recovered alongside it, and the two elements are considered part of the same individual based on their proximity in the deposit and consistent sizing.
Among the anatomical details the fossil has clarified is the orientation of the supraoccipital bone at the back of the skull, which in this specimen forms an angle greater than 90 degrees with the plane of the skull roof, a feature not previously documented in any other stegosaur. The researchers identify this as a new autapomorphy, meaning a defining characteristic unique to the species. Sánchez-Fenollosa described the skull as key to “understanding how stegosaurian skulls evolved,” noting that the fossil has revealed “previously unknown aspects of the anatomy of Dacentrurus armatus.”
A New Framework for Stegosaur Evolution
Beyond its anatomical significance, the skull prompted the team to undertake a comprehensive phylogenetic analysis (the study of evolutionary relationships) using a new data matrix comprising 115 morphological characters and 30 operational taxonomic units, the most extensive undertaken for the group to date.
The analysis, applying Maximum Parsimony methodology, suggests that Stegosauria divides into two major branches: Huayangosauridae and Stegosauridae. Within Stegosauridae, the researchers define a new clade, Neostegosauria, encompassing the more derived members of the family, including Kentrosaurus from Africa, Stegosaurus from North America, and Dacentrurus from Europe.
Chronogram showing temporal, palaeogeographical, and phylogenetic relationships of stegosaurian dinosaurs.©Vertebrate Zoology
According to the study, neostegosaurs inhabited Africa and Europe during the Middle and Late Jurassic, North America during the Late Jurassic, and Asia through the Late Jurassic and into the Early Cretaceous. The analysis also places the Argentine species Isaberrysaura mollensis (previously classified as an ornithopod) within Huayangosauridae, and for the first time includes Mongolostegus exspectabilis, a fragmentary Asian species, in any stegosaurian phylogeny.
The researchers acknowledge that support values for most stegosaurian groupings remain weak, a recurring limitation across studies of the group. They attribute this to the fragmentary nature of most stegosaur specimens, with the majority represented by single partial skeletons. Alberto Cobos noted that the Riodeva site continues to produce material, including additional bones from the same adult individual and rare juvenile remains, a combination described in the study as particularly uncommon in this type of dinosaur.
The site, known as Están de Colón, was first discovered in 2004 and has yielded roughly 200 fossil elements across two excavation seasons. The skull and vertebra described in the new study are held at the Museo Aragonés de Paleontología in Teruel. Research there, the authors write, is ongoing.
