Tyrannosaurus rex

Tyrannosaurus rex is the type and only universally accepted species of Tyrannosaurus. Adults reached 12–13 m long, stood roughly 3.5 m at the hip, and weighed 6.5 to 9.5 tonnes. The skull alone could exceed 1.5 m. Its teeth were oval in cross-section, thick-rooted, banana-shaped, and serrated; some exceeded 30 cm with root included, and were replaced continuously through life. The forelimb famously reduces to two fingers and about a metre of arm, but it is heavily muscled. A T. rex could probably curl around 200 kg.

The hind limbs were long, and the elongated lower-leg-to-thigh ratio hints at cursorial ancestry even in adults. Recent biomechanical modelling caps an adult T. rex at 17–28 km/h: fast enough to outrun any human, slower than the Jurassic Park jeep. Sub-adults were proportionally lighter and faster.

Skin impressions from multiple individuals (Wyrex, Trix, and others) show small pebbly polygonal scales over the body. Whether sparse filamentous feathers persisted into adulthood is unsettled, though they are well attested in the related Yutyrannus. Cullen et al. (2023) argues for fully lipped jaws rather than the bare-tooth grin of older reconstructions, consistent with all living non-crocodilian saurians and with the enamel-wear patterns on T. rex teeth.

T. rex was the apex predator of the Hell Creek ecosystem. Primary prey were Triceratops, Edmontosaurus, juvenile Ankylosaurus, and other large Maastrichtian herbivores. Tooth-marked vertebrae, healed bite wounds in Triceratops frills, and a shed T. rex tooth lodged in an Edmontosaurus tail all confirm active predation. The bite force of an adult (~35,000–60,000 N at the back teeth) is the highest ever measured for a terrestrial vertebrate, and bone-crushing damage is preserved on dozens of specimens.

Growth was extraordinary. From hatchlings of about a metre, T. rex packed on roughly 1,800 kg per year through its teen years, reaching skeletal maturity at 18–20 and living to around 28–30. Juveniles and sub-adults were lithe, long-legged, and proportionally smaller-headed; they may have occupied a different ecological niche than adults, which is part of why the "Nanotyrannus" question keeps coming back.

• Sue (FMNH PR 2081) — Field Museum, Chicago. Most complete (~90% by volume).
• Stan (BHI 3033) — most-replicated specimen, sold for $31.8M at auction 2020.
• Scotty (RSM P2523.8) — possibly heaviest known, Royal Saskatchewan Museum.
• Trix (Naturalis RGM 792.000) — Naturalis, Leiden.
• Wyrex (BHI 6230) — Houston Museum of Natural Science; preserves skin impressions.

Lipped vs lipless jaws: Cullen et al. (2023) presented strong evidence, based on enamel hydration patterns and foramen distribution, that T. rex had fully lipped jaws like a Komodo dragon rather than bared teeth. Three-species split: Paul, Persons & Van Raalte (2022) proposed splitting T. rex into three species; Carr et al. (2022) rebutted. Nanotyrannus: see Tyrannosauridae. Feathering extent: probably sparse and limited in adults. Pack hunting: debated; loose social grouping is plausible but unproven.

T. rex is the platonic dinosaur. Charles Knight painted it in 1906; it was on screen by The Lost World (1925) and King Kong (1933); Jurassic Park (1993), Walking with Dinosaurs (1999), and Prehistoric Planet (2022) all gave it top billing. Its name recognition rivals any extinct organism on the planet.

• tyrannosaurus
• tyrannosauridae
• theropoda
• triceratops
• edmontosaurus

• Brusatte, S. L. (2018). The Rise and Fall of the Dinosaurs. William Morrow.
• Cullen, T. M., et al. (2023). Theropod dinosaur facial reconstruction and the importance of soft tissues in paleobiology. Science, 379, 1348–1352.
• 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.
• Erickson, G. M., et al. (2004). Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs. Nature, 430, 772–775.