From Fragmentary Bones to a Defined Species: Foskeia pelendonum from the Iberian Peninsula

The red floodplain deposits around Salas de los Infantes, in the Province of Burgos, Spain, date to the late Barremian to early Aptian of the Lower Cretaceous. During this time, the Iberian Peninsula lay within the final stages of rift-related geological activity, where fluvial systems and floodplains intertwined to produce a highly variable depositional environment. These conditions contributed to a rich and diverse record of continental vertebrate fossils. Within this geological context, a previously unnamed ornithopod dinosaur has now been identified and formally described as Foskeia pelendonum. The generic name Foskeia derives from the Greek fos (φῶς), meaning "light," used here metaphorically to refer to a lightweight body, while -keia stems from boskein (βόσκειν), meaning "to forage." The specific name pelendonum refers to the Pelendones, a Celtiberian population of the region.

Foskeia pelendonum（Courtesy of Martina Charnell）

The material attributed to this new taxon is highly fragmentary, consisting of disarticulated remains from multiple individuals and lacking a complete skeleton. These fossils were first collected in 1998 from a small site known as Vegagete, covering an area of less than one square metre. Initially, the material was tentatively assigned to a hypsilophodontid-grade ornithischian, comparable to Hypsilophodon. However, subsequent studies demonstrated that this early interpretation was unsupported. The preserved anatomical features were largely non-diagnostic and lacked the derived characters necessary for precise taxonomic placement.

Hypsilophodon foxii（Courtesy of Roman Ilyin）

For many years, the absence of cranial material limited further progress, leaving the classification unresolved. This changed when cranial elements were later identified among the existing material. These specimens were subjected to micro-computed tomography (micro-CT), allowing digital segmentation and three-dimensional reconstruction. Through this process, the fragmented remains could be reassembled in virtual space, revealing the overall morphology of the skull. A suite of distinctive anatomical features emerged, providing the basis for the formal diagnosis of the species.

Among its defining characteristics, Foskeia pelendonum possesses fused premaxillae and anteriorly inclined premaxillary teeth, a configuration rarely observed among ornithopods. In addition, the anteriormost dentary tooth is filiform in shape, representing an extreme and unusual dental morphology. This, together with the ventrolateral extension of the insertion of the musculus adductor mandibulae externus superficialis, suggests a distinctive pattern of jaw mechanics during feeding. The craniomandibular joint is positioned relatively high above the occlusal plane, a feature that would have influenced the angle of bite and the transmission of masticatory forces. Taken together, these traits indicate that Foskeia may not have functioned as a typical small-bodied herbivorous ornithopod, but rather belonged to a lineage characterized by a specialized feeding strategy.

Anteriormost filiform dentary tooth (1d)（Image source：Dieudonné PE et al. (2026)， CC BY 4.0 ）

The available fossil material indicates that Foskeia pelendonum was a diminutive dinosaur. Histological analysis of the femora reveals a growth series ranging from probable neonates to late subadults, with no fully mature individuals identified. Based on the largest known specimens, the estimated total body length does not exceed approximately 1.5 metres. This suggests that Foskeia may represent one of the smallest known ornithopods.

Bone histology also provides insight into its ontogenetic development. In late juvenile stages, the femora display increasingly pronounced cortical textures associated with muscle attachment sites, indicating strengthening musculature. This pattern implies that early juveniles possessed relatively weak and underdeveloped hindlimb musculature, possibly relying more heavily on quadrupedal locomotion. Only later in development did individuals acquire a fully bipedal posture, indicating that locomotor behaviour shifted significantly through ontogeny.

Phylogenetically, Foskeia pelendonum is placed within Rhabdodontomorpha, a clade of ornithopods, and further contributes to the definition of a more restricted European clade, Rhabdodontia. This placement refines our understanding of early ornithopod evolution and clarifies relationships within this group.

Phylogenetic position of Foskeia pelendonum（Image source：Dieudonné PE et al. (2026)， CC BY 4.0 ）

Beyond taxonomy, this discovery also bears on broader palaeobiogeographical questions. Phylogenetic analyses suggest a close relationship between Foskeia and the Australian genus Muttaburrasaurus. This supports the hypothesis of an "Apulian route," proposing that land connections existed between Europe and Gondwana during the Early Cretaceous, allowing faunal exchange across these regions.

Hypothesized Apulian route（Paleogeography from the PALEOMAP Project (Christopher R. Scotese)）

From scattered fragments to a formally recognized species, the identification of Foskeia pelendonum illustrates how technological advances and detailed anatomical study can transform fragmentary material into a coherent evolutionary narrative. What once appeared as isolated and ambiguous remains now contributes to a clearer understanding of ornithopod diversity and evolution during the Early Cretaceous.

Author: Shui-Ye You

Reference:

Dieudonné PE et al. (2026). Foskeia pelendonum, a new rhabdodontomorph from the Lower Cretaceous of Salas de los Infantes (Burgos Province, Spain), and a new phylogeny of ornithischian dinosaurs. Papers in Palaeontology.