Theropods

Theropods are a major group of dinosaurs within the clade Theropoda, a subset of Saurischia. They are primarily bipedal and mostly carnivorous, though some lineages became omnivorous or herbivorous. The theropod lineage originated in the Late Triassic and diversified through the Jurassic and Cretaceous, occupying a wide range of ecological roles. Birds are the only living theropods, having evolved from small, feathered members of the group during the Mesozoic.

Taxonomically, Theropoda includes several major subgroups. Basal theropods such as Ceratosauria led to the more derived Tetanurae, which in turn spawned groups like Megalosauroidea, Allosauroidea, and Tyrannosauroidea. A large and diverse subgroup, Coelurosauria, includes small to medium predators and the feathered theropods that gave rise to birds. Within Coelurosauria, dromaeosaurids and troodontids are close relatives of early birds, culminating in Avialae, the lineage leading to modern birds.

Anatomy and adaptations: Theropods typically have a hollow skeleton and a three-toed hind foot. Forelimbs vary from short and robust to long and flexible. Many theropods bore sharp teeth, though some later lineages lost teeth or became toothless in the avian descendants. Feathers are known in many theropods and are a defining feature of birds. They also show adaptations for running, capturing prey, and in some lineages, flight-related traits.

Ecology and significance: Theropods occupied diverse ecological niches, from small insectivores to giant apex predators. Notable examples include Tyrannosaurus rex, Allosaurus, and spinosaurs, as well as the bird lineage that survives today. The group is central to understanding dinosaur evolution and the origin of birds.