Yuanyanglong bainian

Yuanyanglong bainian is an early-diverging oviraptorosaur from the Early Cretaceous period, specifically the Aptian-Albian stage (about 113–100.5 million years ago). Found in the Maortu locality of Inner Mongolia, China, this dinosaur is named Yuanyanglong after the Mandarin word for “lovebird,” symbolizing the pair of specimens discovered together, and bainian, meaning “a hundred years,” commemorating the centenary of the first oviraptorosaur description. Its discovery enriches knowledge about the diversity and morphology of early oviraptorosaurs, showing a unique blend of adaptations.

Physical Characteristics

Yuanyanglong bainian was a small-bodied oviraptorosaur, reaching about 2 meters (6.5 feet) in length and weight ranging 8.8-14.8 kg, but using volumetric approach to estimating dinosaur size it was smaller (1.2 m and 7.7 kg). The fossils, which consist of partial pelvises, hind limbs, and vertebrae, reveal a distinctive body structure. The ilium (hip bone) has a unique configuration, with a preacetabular process (front part of the ilium) 40% longer than the postacetabular process (back part), a characteristic unusual among oviraptorosaurs. Additionally, Yuanyanglong exhibits a fused tibiotarsus (shin) and tarsometatarsus (ankle), with elongated legs, which is typical for agile dinosaurs but rare among early-diverging oviraptorosaurs.

The arctometatarsalian condition of its feet, where the third metatarsal (middle foot bone) is pinched between the other two, is similar to adaptations seen in some fast-running dinosaurs, suggesting that Yuanyanglong may have been capable of agile movement. Its body plan combines features of both early and late-diverging oviraptorosaurs, making it an intriguing transitional form.

Diet and Feeding Habits

Gastroliths, or stomach stones, were found in association with Yuanyanglong bainian. These stones likely aided in grinding plant material within the stomach, much like in some modern birds. This feature, seen in only a few other oviraptorosaurs, suggests that Yuanyanglong may have had a gastric mill, allowing it to process tough vegetation or hard-shelled prey.

Its diet remains somewhat speculative, but given the presence of gastroliths, Yuanyanglong may have been omnivorous or herbivorous. The food-processing adaptations align with an early-diverging position in the oviraptorosaur evolutionary tree, indicating it likely had a varied diet.

Habitat and Distribution

Yuanyanglong bainian was discovered in the Miaogou Formation of Inner Mongolia, China, a region that, during the Early Cretaceous, was characterized by a braided river system and wetland environments. The Miaogou Formation preserves diverse dinosaur fauna, including large herbivores and smaller theropods, indicating a well-supported ecosystem. The presence of water bodies and dense vegetation would have provided an ideal environment for an oviraptorosaur adapted to ground foraging and possibly wading.

Behavior and Social Structure

The two specimens of Yuanyanglong bainian were discovered in close proximity, suggesting that it may have been gregarious, or at least tolerant of others of its species. While there is no conclusive evidence of social behavior, the discovery of paired individuals hints that these dinosaurs may have lived in small groups or pairs. The body structure, with features suggesting agility and the presence of gastroliths, implies that Yuanyanglong was an active forager, potentially with a varied diet suited to the seasonal environment.

Discovery and Research

The holotype (PV02476-1) and referred specimen (PV02476-2) were unearthed at the Maortu locality in Inner Mongolia and described as Yuanyanglong bainian by Mingze Hao and colleagues in 2024. The well-preserved pelvis and hindlimbs provide insight into its unique morphology, particularly its pelvic and limb adaptations. Phylogenetic analysis positions Yuanyanglong as a sister taxon to Avimimidae and Caenagnathoidea, indicating it is part of an early-diverging oviraptorosaur lineage with traits suggesting a wading ecology.

Age and Formation of Yuanyanglong bainian

Yuanyanglong bainian, was discovered in the Miaogou Formation at the Maortu locality in western Inner Mongolia, China. Although the Miaogou Formation lacks precise dating, studies of the formation’s dinosaur, testudinal, stratigraphic, sedimentological, and charophyta evidence suggests it dates to the upper Lower Cretaceous period, likely the Aptian-Albian age.

This makes the formation slightly younger than the Jehol fossil-bearing beds.

The Yuanyanglong bainian fossils were found in grey-green, fine-grained sandstone within a larger block of brown matrix. This suggests a river environment with relatively weak hydrodynamic forces.

Significance and Interesting Facts

Yuanyanglong bainian is notable for its transitional anatomy, bridging features of early and advanced oviraptorosaurs. Its unique pelvic and hind limb adaptations suggest that it may have been suited to an agile, wading lifestyle, a hypothesis supported by its elongated lower limbs and fused ankle bones. This dinosaur provides valuable insight into the evolutionary adaptations of early oviraptorosaurs and offers clues about the diversity of ecological niches occupied by this group during the Early Cretaceous.