Tyrannosaurus rex, the superstar of the field of paleontology, is having a bit of a resurgence in the public consciousness lately. Just last year, Jurassic World: Dominion earned a billion dollars, making it the third highest grossing film of 2022. In addition to the success of “Jurassic World”, accolades for series like Adult Swim’s animated drama “Primal” and Apple TV’s documentary series “Prehistoric Planet” prove the continued chokehold the T. rex has on our collective imaginations. In lieu of this surge in popularity, you may stumble across a popular publication or science-based social media account expounding on how this school bus-sized predator’s closest living relative is the chicken. Visualize a tyrannosaur running parallel to a barnyard rooster.
For people who grew up with Steven Spielberg’s 1993 blockbuster hit, that bold claim seems almost like libel. However, this widely circulated talking point draws a (hilarious) parallel between the dinosaurs of the distant past and their living heirs. Is this statement an accurate reflection of our modern understanding of the dinosaur family tree? Is Tyrannosaurus rex’s closest living relative our modern chickens? Short answer: Yes! Long answer: Also yes! Our common poultry is the closest thing alive today to the T. rex, but then so are penguins, ostriches, hawks, hummingbirds, parrots and every other bird alive today. The truth is that all birds, as well as a bunch of other bird-like dinosaurs, are equally closely related to T. rex. The distinction may seem like an attempt at splitting hairs, but this delineation over who’s related to who is incredibly important to understanding the processes of evolution.
To help resolve the relationships between T. rex and modern fowl, we have to dive into their evolutionary histories (buckle up). Both Tyrannosaurus and Paraves, the clade of dinosaurs that includes birds and things like Velociraptor, are theropods, meaning two-legged, meat-eating dinosaurs. This group also includes Hollywood stars like Dilophosaurus and Spinosaurus. These reptiles are all united by the anatomy of their hips, features of their skulls, the fact they all had hollow bones and the likelihood of being covered in some form of feathers (yes, you read that right). Traits like hollow bones and plumages adapted overtime to fit entirely different ways of life as each group separated from one another. While giants like T. rex used the hollow air spaces in their bones as scaffolding to allow for bulkier bodies, ancient birds used them to lighten their loads and take flight. Despite how wildly different these features became, those four main characteristics all hail from an ancestral stock of puny carnivores. By comparing the features found in these animals against one another, the long history of their evolution can be charted like a royal pedigree, all leading back to that first population of bipedal meat-eaters.
With this baseline established, it can safely be said that birds are dinosaurs. Cool! So then what’s up with Paraves and tyrannosaurs? They’re both sisters. More accurately, sister clades; two groups of living things with a shared ancestry. It’s kind of like how you and your cousin who won’t shut up about crypto can say you are more closely related to each other than either of you are to some guy on the street. The same principle applies to the populations of dinosaurs that lead to both birds and tyrannosaurs as compared to other giant theropods. Weirdly enough, this means that the family that includes T. rex is more closely related to birds than it is to similar hulking predators like Giganotosaurus.
This level of diversity between 40-foot-long predators and whatever a seagull is supposed to be is only limited to one of three main branches of the dinosaur family tree. There were also the ornithischians, whose members include famous figures like Triceratops and Stegosaurus, and the long-necked sauropods, which were the largest things to ever walk on land. These many different forms of life are all unified under one biological grouping, which is kind of insane to think about. The myriad birds wandering around the Arbor right now are closely related to animals that could grow as large as a Boeing jet. All this goes to show how connected life truly is.