This strange little dinosaur is forcing a rethink of evolution

"From the very first moment anybody sees this animal one is staggered by its extreme smallness," says Dieudonné. "And yet it preserves a highly derived cranium with unexpected anatomical innovations."

Fossils That Challenged Longstanding Assumptions

The fossils come from at least five individuals and were first discovered by Fidel Torcida Fernández-Baldor of the Dinosaur Museum of Salas de los Infantes. Their tiny proportions stood out immediately.

"From the beginning, we knew these bones were exceptional because of their minute size. It is equally impressive how the study of this animal overturns global ideas on ornithopod dinosaur evolution," he says.

What the Name Foskeia pelendonum Means

The name Foskeia comes from ancient Greek. The prefix fos means 'light', reflecting the extremely small and lightweight bodies of adult individuals (Dieudonné et al. 2023). The element 'skei' is derived from boskein, meaning foraging. The species name pelendonum honors the Pelendones, a Celtiberian tribe that once lived in the Fuentes del Duero region (north of the province of Soria, southeast of Burgos and perhaps the southeast of La Rioja).

Why This Dinosaur Matters to Evolutionary Science

Researchers say Foskeia plays a critical role in understanding dinosaur evolution. Marcos Becerra (Universidad Nacional de Córdoba) emphasizes that small size did not mean simplicity: "Miniaturization did not imply evolutionary simplicity -- this skull is weird and hyper-derived."

Thierry Tortosa (Sainte Victoire Natural Reserve) highlights its broader importance: "Foskeia helps fill a 70-million-year gap, a small key that unlocks a vast missing chapter."

Tábata Zanesco Ferreira (Universidade Federal do Rio de Janeiro) adds: "This is not a 'mini Iguanodon', it is something fundamentally different."

According to Penélope Cruzado-Caballero (Universidad de La Laguna), "Its anatomy is weird in precisely the kind of way that rewrites evolutionary trees."

Bone Structure Reveals Adult Size and Fast Metabolism

Microscopic analysis of the bones, overseen by Dr. Koen Stein (Vrije Universiteit Brussel), shows that the largest fossil belonged to a fully mature adult. The internal structure of the bones reveals important clues about growth and metabolism.

"Bone microstructure tells us that at least one individual was an adult… with a metabolic regime approaching that of small mammals or birds. Knowledge of growth and development is essential if we want to compare the anatomy of Foskeia with other species. Young individuals are prone to changes in anatomical features as they grow." Stein explains.

A New Spot on the Dinosaur Family Tree

Using updated evolutionary modeling, the team found that Foskeia is most closely related to the Australian dinosaur Muttaburrasaurus, placing it within the group Rhabdodontomorpha. This also expands the known diversity of the European clade Rhabdodontia.

The analysis further supports the revival of a long-debated grouping known as Phytodinosauria. "In our results, the plant-eating dinosaurs… form a natural group called Phytodinosauria," says Dieudonné. "This hypothesis should be further tested with more data."

Small Body, Specialized Lifestyle

Even with its tiny build, Foskeia was well adapted to its environment. The dinosaur had specialized teeth and appears to have changed posture as it grew, relying on short bursts of speed to move through dense forest habitats.

"These fossils prove that evolution experimented just as radically at small body sizes as at large ones," Dieudonné says. "The future of dinosaur research will depend on paying attention to the humble, the fragmentary, the small."