Known enantiornithine fossils include eggs, embryos, and hatchlings. An enantiornithine embryo, still curled in its egg, has been reported from the Yixian Formation. Juvenile specimens can be identified by a combination of factors: rough texture of their bone tips indicating portions which were still made of cartilage at the time of death, relatively small breastbones, large skulls and eyes, and bones which had not yet fused to one another. Some hatchling specimens have been given formal names, including ""Liaoxiornis delicatus""; however, Luis Chiappe and colleagues considered the practice of naming new species based on juveniles detrimental to the study of enantiornithines, because it is nearly impossible to determine which adult species a given juvenile specimen belongs to, making any species with a hatchling holotype a "nomen dubium".