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A lambeosaurine hadrosaurid (hollow-crested duck-billed dinosaur) from the Late Cretaceous of Montana and Alberta. Hypacrosaurus is well known from nesting sites, eggs, and embryos, which reveal much about its growth and development.
An adult and juvenile Hypacrosaurus to scale. Hypacrosaurus is known from nesting sites, eggs, and embryos, which document its growth from hatchling to adult.
What changes as a young Hypacrosaurus grows up? Much like other terrestrial vertebrates, the head is quite large when young, but decreases in relative size in the adult. The forelimbs also shift proportions, with the humerus (upper arm bone) becoming proportionately shorter compared to the femur (thigh bone), presumably indicating a shift in locomotion.
| Stage | Length m | Skull m | Femur m | Humerus m | Skull ÷ femur | Humerus ÷ femur |
|---|---|---|---|---|---|---|
| Adult | 5m | 0.44m | 0.68m | 0.33m | 0.65 | 0.49 |
| Juvenile | 1m | 0.16m | 0.15m | 0.09m | 1.07 | 0.60 |
Juvenile
Adult and juvenile
