Tyrannosaurus

Tyrannosaurus was long considered a monospecific genus containing only T. rex. In 2022, a controversial study by Paul, Persons, and Van Raalte proposed dividing it into three species—T. rex, T. regina, and T. imperator—based on differences in tooth morphology and the robustness of the femur. However, this split has not gained wide acceptance in the scientific community.

The genus is characterized by its massive, reinforced skull, which could reach 1.5 m in length. Its banana-shaped teeth measured up to 30 cm including the root. Key anatomical features included fused nasal bones and a rear-skull structure specialized for transmitting immense bite forces. Like other tyrannosaurids, it had short, two-fingered arms. While its hindlimbs were long, biomechanical models suggest that adults were fast walkers rather than true sprinters. Estimates for their top speed range between 17 and 28 km/h.

Its bite force was the highest recorded for any terrestrial animal, estimated between 35,000 and 60,000 N at the rear of the jaw. This allowed the dinosaur to crush bone, a capability confirmed by bite marks found on the vertebrae and pelvises of Triceratops and Edmontosaurus. Evidence from fossil stomach contents and shed teeth shows that large herbivores like hadrosaurs and ceratopsians were its primary food source.

We have a detailed understanding of the life history of T. rex thanks to bone histology. Hatchlings were about 1 m long and grew slowly for their first ten years. During their teens, they entered a period of rapid growth, gaining around 1,800 kg per year. They reached skeletal maturity at approximately 18–20 years and lived for up to three decades. The specimen known as Sue is one of the oldest recorded, having lived about 28 years. Face-biting wounds on several fossils suggest these animals engaged in aggressive interactions with each other. Whether they hunted in groups is still a topic of discussion, though fossil associations like the "Wyrex" find suggest they may have formed social groups.

• Sue (FMNH PR 2081) — most complete T. rex known (~90% by volume), Field Museum, Chicago.
• Stan (BHI 3033) — Black Hills Institute, sold at auction 2020 for $31.8M, future display in Abu Dhabi Natural History Museum.
• Scotty (RSM P2523.8) — possibly heaviest known specimen, Royal Saskatchewan Museum.
• Trix (Naturalis RGM 792.000) — third most complete, Naturalis Biodiversity Center, Leiden.
• Tristan-Otto (MB R.91216) — Museum für Naturkunde, Berlin.

The active questions: Nanotyrannus validity (juvenile T. rex vs separate genus, see Tyrannosauridae); the three-species hypothesis (Paul et al. 2022 vs Carr et al. 2022 rebuttal); the extent of feathering (current consensus: mostly scaly with limited possible filaments); the scavenger vs predator debate (long settled in favour of opportunistic apex predator); top running speed (biomechanically capped well below the 70 km/h Jurassic Park number).

Tyrannosaurus rex is the most-depicted extinct animal in Western culture. From Charles R. Knight's 1906 paintings, through King Kong (1933), the AMNH mount, Jurassic Park (1993), to Prehistoric Planet (2022), every era has its T. rex. The species is one of very few extinct animals known by name to nearly every literate person on Earth.

• tyrannosaurus-rex
• tyrannosauridae
• theropoda

• Brusatte, S. L. (2018). The Rise and Fall of the Dinosaurs. William Morrow.
• Carr, T. D. (2020). A high-resolution growth series of Tyrannosaurus rex. PeerJ, 8, e9192.
• Persons, W. S., Currie, P. J., & Erickson, G. M. (2020). An older and exceptionally large adult specimen of Tyrannosaurus rex. Anatomical Record, 303, 656–672.
• Paul, G. S., Persons, W. S., & Van Raalte, J. (2022). The Tyrant Lizard King, Queen and Emperor. Evolutionary Biology, 49, 156–179.
• Carr, T. D., et al. (2022). Insufficient evidence for multiple species of Tyrannosaurus. Evolutionary Biology, 49, 327–341.