By Ashley Strickland, CNN — Paleontologists say new research may bring scientists closer to distinguishing male and female hadrosaurs, the duck-billed dinosaurs that were widespread during the Late Cretaceous Period.
Determining sex from fossilized bones has long been a challenge for paleontologists because the soft tissues and behaviors that often distinguish males from females in living animals are rarely preserved in the fossil record. Hadrosaurs, or duck-billed dinosaurs, were abundant herbivores from roughly 100.5 million to 66 million years ago, and their remains have been recovered from multiple continents, giving researchers a large sample of skeletal material to study. The latest work aims to use that abundance to tease apart anatomical patterns that could signal sex differences in this particular group.
Historically, scientists have relied on several indirect approaches to infer sex in extinct animals. In some rare instances, reproductive tissue preserved within bone — known as medullary bone, a temporary tissue formed by egg-laying females in modern birds — has been used to identify individual dinosaurs as female. Elsewhere, investigators have examined consistent size differences, distinct ornamentation such as crests or horns, and bone histology to propose male-versus-female assignments, though findings can be controversial because variation between juveniles and adults, and between individuals of the same sex, can mimic patterns expected from sexual dimorphism. Those complications have made confident sex identification difficult except in well-preserved, exceptional cases.
Hadrosaurs present both opportunities and challenges for this problem. Their fossils are commonly found and often include well-preserved skulls that in some species bear elaborate crests or other structures. These features have prompted questions about whether such structures were sexually selected, used for species recognition, or related to other functions like sound production. The wide geographic and temporal distribution of hadrosaur fossils provides a broad dataset that researchers can analyze statistically, but distinguishing features that reflect sex rather than age, species differences, or individual variation requires careful comparative work.
The recently reported research, described by the investigators as bringing scientists closer to identifying the sex of hadrosaurs, builds on the broader effort to develop reliable criteria for sexing dinosaurs. While specific methodologies were not detailed here, the work follows a longstanding scientific trajectory: using patterns in large samples, bone microstructure, and known analogues among living animals to infer which traits are most likely tied to sex. Applying multiple lines of evidence can help reduce ambiguity, but the interpretation of such evidence remains subject to further testing and debate in the field.
If the techniques being developed prove robust, they could allow paleontologists to reconstruct more accurate pictures of hadrosaur social behavior, mating systems and population structure. Knowing the sex ratio of fossil assemblages, for example, would inform hypotheses about herd composition, parental care, and life history strategies. It could also clarify whether certain cranial ornaments and other skeletal traits were sexually dimorphic or served other biological roles.
Researchers working on this problem are likely to test proposed criteria by examining large museum collections and newly collected specimens, comparing patterns across different hadrosaur species and growth stages. Additional validation may come from finding more examples of reproductive tissue preserved in bone or from other rare preservation windows that can independently indicate sex. As with many paleontological questions, further discoveries and the accumulation of data will be central to refining conclusions.
The new research signals progress in a longstanding paleontological puzzle, but it does not yet represent a definitive solution for identifying sex across all dinosaur groups. Continued study of hadrosaurs, using the group's abundant fossil record and multiple analytical approaches, will determine how broadly applicable the emerging criteria prove to be and what they reveal about the lives of these Late Cretaceous herbivores.