An analysis of fossils of Troodon formosus, a bird-like dinosaur that lived in North America about 75 to 78 million years ago, allowed tracking the development of the hip bones and legs from the embryonic stage to adulthood. The study, published in the journal PLOS One, could also help resolve longstanding questions about the classification of this species.
Researchers from Montana State University and North Carolina State University analyzed fossils of pelvic bones and hind limbs found in the western part of the U.S. state of Montana. The specimens represent different developmental stages, from embryos to adult individuals, allowing reconstruction of the changes that occurred over the life of these dinosaurs.
The analysis revealed consistent changes in texture, shape and relative proportions of different parts of the bones. Among them, the ratio between the length of the femur and that of the tibia was higher in adult specimens compared to juveniles. The changes appear to have occurred in relatively consistent growth phases, which suggests a limited influence of environmental conditions on the development of these structures.
The researchers also observed considerable variation in the size of adult individuals and, according to previous studies, they consider that foot problems may have been common in this species.
A new reference specimen for the species
The results could have implications for the classification of Troodon formosus. Currently, the “type specimen” of the species — the specimen used as a reference to identify other fossils — is represented by a single tooth, a situation that has contributed to doubts about the validity of the genus Troodon.
The team proposes that a set of pelvic fossils and hind limb fossils, from juvenile and adult individuals, could become the main reference specimen for the species. The eventual change, however, depends on a decision still pending by the International Code of Zoological Nomenclature.
The researchers believe that new studies could help better understand the biology and lifestyle of these dinosaurs, including how they walked or ran.
