A herbivorous dinosaur once thought to be a juvenile has now been identified as a fully grown adult, revealing a small-bodied new species called Foskeia pelendonum.

The discovery reconstructs how small dinosaurs fit together evolutionarily and reveals relationships across the complex branches of the dinosaur family tree.

Fossils discovered in northern Spain preserve several skeletons of the same small herbivore, including at least one already fully grown specimen.

By recording the remains as a distinct adult species, Paul-Emile Dieudonné of the Free University of BrusselsVUB) showed that the animal’s small size reflects evolutionary miniaturization rather than youth.

Prove that dinosaurs came of age

Scientists first needed to determine whether the fossil belonged to a young dinosaur or a fully grown adult.

To answer this question, researchers studied thin sections of limb bones under a microscope using a technique called osteohistology. This technique reveals the growth patterns that are preserved inside the bone.

They discovered deceleration lines near the exterior. This is a sign that the largest specimen was present. Foscare perendonum He was already sexually mature.

This confirms that this dinosaur remained small even as an adult. boy larger seed stage.

Previous discoveries included only limbs and a spine, not enough features to define a new species. A 2016 study described the remains but stopped short of naming the animals.

Subsequent discoveries of the skull finally revealed unique features that allowed scientists to confidently identify this dinosaur.

This delay illustrates how missing body parts, especially the skull, can hinder species recognition, even if the fossil has been sitting in a collection for years.

A skull full of surprises

The skull fragments proved important because they allowed researchers to identify the dinosaur as a separate species, rather than just describing scattered bones.

To study the fragile parts without damaging them, the team used microcomputed tomography. This is a type of X-ray scan that creates detailed 3D images that allow scientists to digitally assemble the skull.

rebuilt skull revealed a rare feature. The front of the upper jaw was fused into a single solid part, and some of the teeth were pointed slightly forward, changing the way the jaws interlocked when the animal bit.

These unexpected features showed that this dinosaur was not just a smaller version of a large herbivore. Instead, it has its own unique anatomy, meaning body size alone cannot explain how it fits into dinosaur evolution.

the rock sets the clock

The river overflowed over its banks in the lowland plains, leaving behind a thick layer of red mud that later turned into rock. Geologists place these formations on official nautical charts used around the world at approximately 126 million to 113 million years ago.

Red soil from the floodplain buried the ruins, but then erosion And when the waterway moved, the skeletons were scattered before collectors could find them.

Because the skull is thin and fragile, its setting made it the most difficult part of the skull to recognize and preserve.

Identify dinosaur lineages

where to understand Foscare perendonum The researchers compared the bones to those of many other dinosaurs using phylogenetic analysis, a method of grouping species based on common physical characteristics.

The results showed that the small dinosaurs of Spain were close to the plant-eating dinosaurs of Australia. MuttaburasaurusThis suggests that some distant plant-eating dinosaurs were more closely related than previously thought.

The analysis also further expanded the European subfamily of plant-eating dinosaurs, Rhabdodontia, and added a much older member to the group, helping to fill a gap of about 70 million years in its fossil record.

At the same time, the study revived the long-debated idea that several major plant-eating dinosaur lineages may belong to a larger group called plant dinosaurs. Characteristics of the new species’ skull line up with those found in other herbivores that were once thought to be unrelated.

“This hypothesis should be further tested with more data,” Dieudonné said, stressing that as new fossils are discovered, the proposed link needs to be confirmed.

If broader groupings can be maintained, it could simplify the way scientists understand the evolutionary relationships among plant-eating dinosaurs.

Living in a dense forest

The proportions of teeth and limbs suggest Foscare perendonum They feed close to the ground and rely on quick dashes to avoid danger. Special tooth wear suggests a hardy plant, and the hips and legs show a changed posture as it grows.

Researchers say this provides explosive speed. jungleIn tight spaces, you get high speed rotation for long distance runs.

The fossils include several growth stages, suggesting that the animals may have changed their behavior and movements to suit their bodies.

Miniaturization reshapes evolution

The reduction in body size may mask a major evolutionary jump, a process known as dwarfism, the evolution toward smaller adult body sizes.

In this case, the small skull still had complex characteristics, forcing researchers to rethink how quickly certain traits appear.

“These fossils prove that evolution “We experimented as thoroughly with small body sizes as with large body sizes,” Dieudonné said.

Based on that insight, the VUB team used this small fossil as a more powerful test of the relationship between age, anatomy, and evolution in plant-eating dinosaurs.

Future discoveries from similar rock formations will help determine whether the proposed new family relationships remain stable as scientists add more species and features to the picture.

The research will be published in a journal paleontology papers.

Image credit: Martina Charnel

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