Tyrannosaurus rex, an iconic symbol of the age of dinosaurs, was a powerful two-legged carnivore known for its immense size and fearsome predatory nature. Its deep evolutionary connections to the present day might surprise many.
The Unexpected Answer: Birds
The closest living relatives of Tyrannosaurus rex are birds, such as chickens and ostriches. This connection may seem counterintuitive given the stark differences in size and appearance between a colossal extinct predator and modern-day avian species. However, scientific evidence overwhelmingly supports birds as modern dinosaurs. Birds are the only surviving lineage of dinosaurs, having successfully navigated the mass extinction event that ended the Mesozoic Era.
Unraveling the Evidence
The scientific community has gathered compelling evidence linking T. rex and other non-avian theropod dinosaurs to birds.
Skeletal Similarities
Shared anatomical features of their skeletons provide significant evidence. Both birds and many theropod dinosaurs possessed hollow bones, a trait found in dinosaurs like Allosaurus. Another distinguishing skeletal feature is the furcula, or wishbone, present in most birds and discovered in various theropod dinosaurs, including tyrannosaurids.
Fossil Discoveries
Fossil discoveries further solidify this link, particularly with feathered dinosaurs. While direct fossilized feather impressions for T. rex are limited, many close relatives like Yutyrannus possessed feather-like structures or full feathers. These discoveries suggest feathers were a widespread trait among theropods, implying T. rex ancestors likely had some form of feathering.
Molecular Evidence
Molecular evidence provides another layer of support. Researchers extracted collagen proteins from a 68-million-year-old T. rex femur. Analysis revealed striking similarities to collagen in modern-day chickens and ostriches. This molecular data offered the first direct biochemical evidence affirming the evolutionary connection between non-avian dinosaurs and birds.
Beyond Birds: The Archosaur Family Tree
To fully grasp T. rex’s place in the tree of life, it helps to understand the broader group known as Archosauria. This diverse clade includes all dinosaurs, birds, and crocodilians. Archosaurs originated approximately 250 million years ago, in the late Permian Period, and their descendants would come to dominate terrestrial vertebrate life during the Mesozoic Era.
Despite their ancient appearance and reptilian characteristics, crocodilians are not the closest living relatives to T. rex. While both birds and crocodilians are living representatives of the Archosauria, their evolutionary paths diverged significantly. The lineage leading to birds (Avemetatarsalia) and the lineage leading to crocodilians (Pseudosuchia) split early in archosaur history. Crocodilians represent a distinct branch that separated much earlier. Thus, crocodilians are ancient cousins, while birds are direct relatives.