This study is led by researchers from Jilin University in China and the University of Toronto in Canada. It focuses on a cluster of 13 well-preserved Psittacosaurus skeletons and articulated gastroliths unearthed from the Lower Cretaceous Yixian Formation near Lujiatun Village, Liaoning Province. The fossil assemblage, housed at Dinosaur Evolution Research Center, Jilin University, offered a rare window into the early life stages of one of the most abundant and well-documented dinosaur genera.
Psittacosaurus lived during the Early Cretaceous. Since the first report of Psittacosaurus discoveries in Mongolia a century ago, at least 12 valid species have been recognized to date. These species have been discovered primarily in East Asia, including China, Mongolia, and Russia, with fossil records also documented in Thailand in Southeast Asia. The unearthed fossils cover a complete developmental sequence from newly hatched juveniles to adult individuals, providing valuable materials for paleontologists to explore dinosaur growth, development, and behavioral habits.
Previous fossil records have widely documented the presence of gastroliths in subadult or adult Psittacosaurus individuals, yet no fossil evidence has indicated that newly hatched juveniles also possessed gastroliths. Some researchers have linked the gastroliths in Psittacosaurus to their diet of hard plant materials, suggesting they functioned to aid digestion. Whether this dinosaur clade developed the habit of ingesting stones for digestive assistance only after reaching adulthood has long been a matter of debate.
To determine the age of these Psittacosaurus, researchers conducted a histological analysis of the femora from four individuals of varying body sizes in these specimens. Through the analysis, the team confirmed that all 13 individuals were less than one year old at the time of death. Key skeletal features—including the absence of growth rings (lines of arrested growth), the presence of rapid-growth woven-fibered bone tissue, and high vascularization—indicated these were hatchlings in a phase of accelerated development. Their femur lengths, ranging from 4.78 to 7.45 cm, suggested a faster growth rate than previously observed in other Psittacosaurus species, hinting at potential taxonomic differences within the Yixian Formation.
The study found that each of the 13 juvenile individuals preserved a large number of pebble-like small stones in the abdominal region of their skeletons, with these stones concentrated below the ribs. All gastroliths from one of the individuals were extracted for lithological identification and analysis. These gastroliths varied in shape from sub-angular to rounded, with rough surfaces; most exhibited a slightly spindle-shaped or angular outline. The average length was 8.85 mm, with the largest reaching 15.13 mm in length, a total mass of 11.14 g, and an occupied area of approximately 9.4 cm² in the specimen.
All the gastroliths in this study meet the following conditions: (1) the pebbles were preserved in situ; (2) the pebbles were firmly embedded in the tuff matrix; (3) a large number of pebbles appeared concentrated in a small area; (4) all pebbles were associated with articulated skeletons; (5) the pebbles were mainly located in the lower part of the thoracic cavity.
Furthermore, researchers calculated the body mass of a single Psittacosaurus individual and compared its gastrolith mass with the modern avian regression. The data point for this individual falls close to the regression line correlating gastrolith mass and body mass in extant birds. This cross-taxon similarity suggests that Psittacosaurus may have exhibited behavior similar to that of birds—ingesting stones to aid digestion. This finding provides new evidence in support of the hypothesis that Psittacosaurus used gastroliths to assist in digestion.
The presence of gastroliths in these specimens indicates that hatchling Psittacosaurus also required these stones to aid digestion, maintaining a dietary habit of feeding on high-fiber hard plant materials similar to that of mature individuals from an early age.
This discovery not only revises the previous understanding that gastroliths were exclusive to adult Psittacosaurus but also reveals that this dinosaur clade maintained a relatively stable dietary strategy throughout their life cycle. This finding provides key evidence for reconstructing the paleoecological evolution of early ceratopsians.
See the article:
Wang L, Li X, Wen Q, Chen J, Reisz R. 2026. Gastroliths in hatchling Psittacosaurus show early dietary habits. Science China Earth Sciences, 69(1): 340–347, https://doi.org/10.1007/s11430-025-1759-4
Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.