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• Tyrannosaurid is a family of large bipedal carnivorous theropod dinosaurs of the Late Cretaceous.

• The family includes the well-known tyrannosaur.

• They have reduced-size forelegs.

• Tyrannosaurids were the apex predators during their time.

• Their status as dominant carnivores has gathered considerable interest since their discovery.

• They are well studied and a lot of information regarding their anatomy, diversity, growth, and evolution were obtained.

• However, there is lack of information regarding the earliest stages of tyrannosaurid development.

• Tyrannosaurid eggs and embryos remain difficult to find.

• Juvenile specimens are usually rare.

• Researchers discovered baby tyrannosaurid bones and teeth from the Campanian–Maastrichtian of western North America.

• The discovery provides the first window into this critical period of the life of a tyrannosaurid.

• A lower jaw from an embryo of Daspletosaurus measuring 3 centimeters long reveals distinct tyrannosaurine characters like a chin and a deep Meckelian groove.

• The specimen reveals the earliest stages of tooth development.

• Researchers can combine data from other embryonic specimen to estimate the minimum hatchling size of tyrannosaurids.

• Another tooth from an upper jaw may have come from Albertosaurus sarcophagus.

• This tooth shows that the hallmark characters that distinguish tyrannosaurids from other theropods that were present early in life.

• The sites that produced these embryonic bones provide clues to the nesting activity of tyrannosaurids.

Sources:

Gregory F. Funston, Mark J. Powers, S. Amber Whitebone, Stephen L. Brusatte, John B. Scannella, John R. Horner, and Philip J. Currie. Baby tyrannosaurid bones and teeth from the Late Cretaceous of western North America. Canadian Journal of Earth Sciences. 0(0): 1-22. https://doi.org/10.1139/cjes-2020-0169

[1] https://www.merriam-webster.com/dictionary/tyrannosaurid

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